Chapter 12
SENSITIVE AREA DISTRICT (SA) AND GEOLOGIC HAZARDSlinklink

http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308
10-12-1: PURPOSE:
10-12-2: DEFINITIONS:
10-12-3: APPLICABILITY:
10-12-4: RESPONSIBILITY FOR GEOLOGIC HAZARD STUDIES:
10-12-5: MINIMUM QUALIFICATIONS OF THE GEOLOGIST:
10-12-6: MINIMUM QUALIFICATIONS OF THE ENGINEER:
10-12-7: PRELIMINARY ACTIVITIES:
10-12-8: GEOLOGIC HAZARD INVESTIGATION PERMIT:
10-12-9: GEOLOGIC HAZARD STUDIES AND REPORTS REQUIRED:
10-12-10: GEOLOGIC HAZARD REPORTS:
10-12-11: REVIEW OF GEOLOGIC HAZARD REPORTS:
10-12-12: LAND DISTURBANCE PERMIT REGULATIONS:
10-12-13: COMPLIANCE WITH PERMIT:
10-12-14: PROTECTIVE DEVICES:
10-12-15: MAINTENANCE OF SITE:
10-12-16: ACCESS AND HAUL ROUTES:
10-12-17: CONSENT OF ADJACENT PROPERTY OWNERS:
10-12-18: CUTS AND FILLS:
10-12-19: EROSION CONTROL AND DRAINAGE DEVICES:
10-12-20: AREAS SUBJECT TO SLIDES AND UNSTABLE SOIL:
10-12-21: PLANTING AND IRRIGATION OF CUT AND FILL SLOPES:
10-12-22: LOT STANDARDS AND IDENTIFICATION OF BUILDING ENVELOPE:
10-12-23: PROPERTY LINE AND CORNER MARKERS:
10-12-24: SLOPE PROTECTION EASEMENTS:
10-12-25: MASTER DRAINAGE PLAN REQUIRED:
10-12-26: LANDSCAPING OF CERTAIN LOTS FOR EROSION CONTROL:
10-12-27: EROSION CONTROL AND REVEGETATION:
10-12-28: WET WEATHER PLAN:
10-12-29: DISCLOSURE WHEN A GEOLOGIC HAZARD REPORT IS REQUIRED:
10-12-30: WARNING AND DISCLAIMER:
10-12-31: CHANGE OF USE:
10-12-32: CONFLICTING REGULATIONS:
10-12-33: APPENDICES:
10-12-33-1: APPENDIX A, MINIMUM STANDARDS FOR SURFACE FAULT RUPTURE HAZARD STUDIES:
10-12-33-2: APPENDIX B, MINIMUM STANDARDS FOR SLOPE STABILITY ANALYSIS:
10-12-33-3: APPENDIX C, MINIMUM STANDARDS FOR LIQUEFACTION INVESTIGATIONS AND EVALUATIONS:

10-12-1: PURPOSE:linklink


A. The purpose of the SA district is to designate and describe those areas within the city that possess environmental characteristics which require special public consideration of use applications which might affect the structure of the land. These "sensitive land development regulations" provide standards, guidelines and criteria, having the effect of minimizing flooding, fire, erosion, and other natural and manmade hazards, and protect people and property while protecting the natural scenic character of the sensitive land areas not suitable for development, or suitable for development only after mitigation of hazards and ensuring the efficient expenditure of public funds.


B. The standards, guidelines and criteria to be achieved by the SA district overlay zone shall include, but not be limited to, the following:

1. The protection of the public from natural and manmade hazards;

2. The minimizing of the threat and consequential damages of fire in foothill areas by establishing fire protection measures;

3. The preservation of natural features, wildlife habitat and open space;

4. The preservation of public access to mountain areas and natural drainage channels;

5. The preservation and enhancement of visual and environmental quality by use of natural vegetation and the prohibition of excessive excavation and terracing;

6. The establishment of traffic circulation facilities that ensure ingress and egress for vehicles, including emergency vehicles, into all developed areas at any time of the year with minimal cuts, fills or visible scars;

7. The encouragement of variety of development designs and concepts that are compatible with the natural terrain of the foothill areas, that will preserve open space and natural landscape;

8. The establishment of land use management criteria that will encourage protection of natural elements while allowing a harmonious and satisfying residential environment;

9. Encouragement of regard for the view of the foothills, and from the foothills;

10. Determine areas in the city that, due to geologic hazards, may not be suitable for development, and may require engineering measures to reduce the hazards to an acceptable level.


C. The intent of geologic hazards regulations is to protect the health, safety, and welfare of the citizens of the city of North Salt Lake, protect the city's infrastructure and financial health, and minimize adverse effects of geologic hazards to public health, safety, and property by encouraging wise land use.


D. This chapter and its appendices address surface fault rupture, slope stability, and liquefaction hazards and present minimum standards and methods for evaluating geologic hazards.


E. Results of geologic hazard studies shall comply with this chapter and its appendices. The standards set forth in the appendices are minimum requirements. More complex projects may require more detailed and in depth evaluations than outlined herein. In addition, the appendices shall not supersede other more stringent requirements that may be required by other regulatory agents.


F. Site specific geologic hazard assessments performed by qualified engineering geologists shall be required prior to developing projects located within a sensitive area district or otherwise required areas of potential geologic hazard. The developer shall submit the applicable study and complete the report process as provided in this chapter. (Ord. 2015-16, 10-20-2015)

http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318789
10-12-2: DEFINITIONS:linklink

As used in this chapter:

ACCEPTABLE AND REASONABLE RISK: No loss or significant injury to occupants, no release of hazardous or toxic substances, and minimal structural damage.

ACCESSORY BUILDING: Any structure not designed for human occupancy, which may include tool or storage sheds, gazebos, and swimming pools.

ACTIVE FAULT: A fault displaying evidence of displacement along one or more of its traces during Holocene time, which is approximately ten thousand (10,000) years ago to the present.

AVALANCHE: A large mass of snow, ice, soil or rock, or a mixture of these materials, falling, sliding, or flowing rapidly under the force of gravity.

BEST MANAGEMENT PRACTICES (BMP): Activities, facilities, measures, planning or procedures used to minimize erosion and sedimentation and manage stormwater before, during, and after earth disturbance activities.

BUILDABLE AREA: Based on an accepted engineering geology report, the portion of a site not impacted by geologic hazards, or the portion of a site where it is concluded the identified geologic hazards can be mitigated to a level where risk to human life, property and city infrastructure are reduced to an acceptable and reasonable level and where structures may be safely sited.

CITY: The public works director, city engineer, community development director, planning manager, building official or other city employee.

CITY COUNCIL: The city council of the city of North Salt Lake.

CRITICAL FACILITIES: Essential, hazardous, special occupancy facilities, and occupancy categories III and IV as defined in the currently adopted international building code, and lifelines such as major utility, transportation, and communication facilities and their connections to critical facilities.

DEBRIS FLOW: A slurry of rock, soil, organic material, and water transported in an extremely fast and destructive flow that flows down channels and onto and across alluvial fans; including a continuum of sedimentation events and processes including debris flows, debris floods, mudflows, clear water floods, or alluvial fan flooding.

DEVELOPMENT: All critical facilities, subdivisions, single- and multi-family dwellings, commercial and industrial buildings; also additions to or intensification of existing buildings, storage facilities, pipelines and utility conveyances, and other land uses.

ENGINEERING GEOLOGIST: A Utah licensed geologist, who, through education, training, and experience, is competent in applying geologic data, geologic techniques, and geologic principles, which includes conducting field investigations, so that geologic conditions and geologic factors affecting engineered works, groundwater resources, and land use planning are recognized, adequately interpreted, and clearly presented for use in engineering practice, land use planning, and for the protection of the public, and who utilizes specialized geologic training and experience to provide quantitative geologic information and recommendations and also works with and for land use planners, environmental specialists, architects, public policy makers, and property owners to provide geologic information on which decisions can be made.

ENGINEERING GEOLOGY: Geologic work that is relevant to engineering and environmental concerns, and the public health, safety, and welfare. Engineering geology is the application of geological data, principles, and interpretation so that geological factors affecting planning, design, construction, and maintenance of engineered works, land use planning, and groundwater resources are adequately recognized and properly interpreted for use in engineering, land use planning, and related practice.

ESSENTIAL FACILITY: Any buildings or other structures intended to remain operational in the event of an adverse geologic event, including all structures defined in section 10-12-33-1, table A2 of this chapter.

FAULT: A fracture in the earth's crust forming a boundary between rock or soil masses that has moved relative to each other.

FAULT SCARP: A steep slope or cliff formed by movement along a fault.

FAULT SETBACK: An area on either side of a fault within which structures for human occupancy or critical facilities or their structural supports are not permitted.

FAULT TRACE: The intersection of a fault plane with the ground surface, often present as a fault scarp, or detected as a lineament on aerial photographs.

FAULT ZONE: A corridor of variable width along one or more fault traces within which deformation has occurred.

GEOLOGIC HAZARD: A surface fault rupture, liquefaction, slope stability, landslide, debris flow, or rockfall that may present a risk to life or property.

GEOLOGIC HAZARD STUDY AREA: A potentially hazardous area as shown on the geologic hazard study area maps within which hazard investigations are required prior to development.

GEOTECHNICAL ENGINEER: A professional, Utah licensed engineer who, through education, training and experience, is competent in the field of geotechnical engineering.

GEOTECHNICAL ENGINEERING: The investigation and engineering evaluation of earth materials including soil, rock, and manmade materials and their interaction with earth retention systems, foundations, and other civil engineering works. The practice involves the fields of soil mechanics, rock mechanics, and earth sciences and requires knowledge of engineering laws, formulas, construction techniques, and performance evaluation of engineering.

GOVERNING BODY: The city council of the city of North Salt Lake.

LANDSLIDE: The downslope movement of a mass of soil, surficial deposits or bedrock, including a continuum of processes between landslides, and earth flows.

LIQUEFACTION: A process by which certain water saturated soils lose bearing strength because of earthquake related ground shaking and subsequent increase of groundwater pore pressure.

NONBUILDABLE AREA: That portion of a site which a geologic hazards report has concluded may be impacted by geologic hazards that cannot be reasonably mitigated to an acceptable level, and where the siting of habitable structures, structures requiring a building permit, or critical facilities, is not permitted.

ROCKFALL: A rock or mass of rock, newly detached from a cliff or other steep slope which moves downslope by falling, rolling, toppling, or bouncing; includes rockslides, rockfall avalanches, and talus.

SETBACK: An area within which support of habitable structures or critical facilities is not permitted.

SLOPE STABILITY: The resistance of a natural or artificial slope or other inclined surface to failure by slope movement, usually assessed under both static and dynamic (earthquake induced) conditions.

STRUCTURE DESIGNED FOR HUMAN OCCUPANCY: Any residential dwelling or any other structure used or intended to support or shelter any use or occupancy, which is expected to have an occupancy rate of at least two thousand (2,000) person hours per year, but does not include an accessory building. (Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318790
10-12-3: APPLICABILITY:linklink


A. Provisions: The provisions of this chapter shall apply to any zoning district in the city and shown as within the sensitive lands overlay area on the sensitive lands map or any other areas as required by subsection D of this section.


B. Additional Provisions: This chapter makes additional provisions to those otherwise set forth in the land use and subdivision ordinances, and other chapters of the act. Additional requirements not covered in this chapter may be required by the city engineer if determined that it reasonably appears that there are additional hazards associated with the site. In the event of conflict between such foregoing designated chapters of this title, the more restrictive provisions shall apply.


C. Expired Approvals: Subdivisions, planned unit developments, or other construction projects, whose preliminary or final plat approvals have expired or are proposed to be redeveloped, further subdivided or amended, shall be subject to the provisions of this chapter.


D. Additional Property Outside Overlay Zone: Properties located outside the boundaries of the sensitive lands overlay map will be subject to the regulations and standards of this chapter in the event that the city engineer determines the property to have any of the following: an average slope of fifteen percent (15%) or greater; known, suspect, or probable geologic hazards; critical wildlife habitat or natural features; critical drainage channels; or other vital infrastructure. (Ord. 2015-16, 10-20-2015)

http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318791
10-12-4: RESPONSIBILITY FOR GEOLOGIC HAZARD STUDIES:linklink


A. Geologic hazard studies often involve both engineering geology and geotechnical engineering. Engineering geologic studies shall be performed under the direct supervision of a qualified engineering geologist. Geotechnical engineering studies shall be performed under the direct supervision of a qualified geotechnical engineer.


B. Project developers and their consultants shall present the results of any geologic hazard study in compliance with this chapter, its appendices and the latest guidelines adopted by the Utah geological survey. The standards set forth in the appendices to this chapter are the city's minimum requirements, but may be made more restrictive (in specific, fact sensitive circumstances) by the DRC based on recommendations of the city engineer or city geologic consultant, or designee, if evidence becomes available that suggests more stringent requirements are appropriate. In addition, the appendices shall not supersede other more stringent requirements that may be required by other regulatory agencies or governmental entities that have jurisdiction.


C. Building permits on single lots:

1. Any lot, whether or not in platted subdivisions, which is in the sensitive lands overlay area, or otherwise meets the criteria defined herein, shall be submitted with a site specific geotechnical report in accordance with chapter 18 of the international building code (IBC) and any engineered construction plan which has been designed in compliance with the recommendations made within the geotechnical report for site excavation, grading, slope stability, structural components, landscaping, or any other geologic hazard mitigation specified.

2. The building permit may be issued administratively after it is determined that the lot may be developed in accordance with the intent of this chapter.

3. The building official shall require the geotechnical firm to observe the excavation of the site and submit verification of soil conditions and suitability of the site for construction.

4. If the only hazard associated with the site is high liquefaction, then the applicant must submit a soils report with recommendations for control of subsurface water as well as footing and foundation design. (Ord. 2015-16, 10-20-2015)

http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318792
10-12-5: MINIMUM QUALIFICATIONS OF THE GEOLOGIST:linklink

Engineering geology and the evaluation of geologic hazards is a specialized discipline within the practice of geology requiring technical expertise and knowledge of techniques not commonly used in other geologic investigations. Therefore, geologic hazard investigations involving engineering geologic studies shall only be accepted by the city of North Salt Lake when conducted and signed by a qualified engineering geologist. The minimum qualifications of the engineering geologist who performs geologic hazard investigations are:


A. An undergraduate or graduate degree in geology, engineering geology, or geological engineering, or closely related field, from an accredited college or university;


B. At least five (5) full years of experience in a responsible position in the field of engineering geology in Utah, or in a state with similar geologic hazards and regulatory environment. This experience must demonstrate the engineering geologist's knowledge and application of appropriate techniques in performing geologic hazard studies; and


C. A Utah state professional geologist's license. (Ord. 2015-16, 10-20-2015)

http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318793
10-12-6: MINIMUM QUALIFICATIONS OF THE ENGINEER:linklink

Evaluation and mitigation of geologic hazards often require contributions from a qualified geotechnical engineer, particularly in the design of mitigation measures. Geotechnical engineering is a specialized discipline within the practice of civil engineering requiring technical expertise and knowledge of techniques not commonly used in civil engineering investigations. Therefore, geologic hazard investigations requiring contributions from a qualified geotechnical engineer will only be accepted by the city of North Salt Lake when also signed and sealed by a qualified geotechnical engineer. Minimum qualifications of the geotechnical engineer who participates in geologic hazard investigations are:


A. A graduate degree in civil engineering, with an emphasis in geotechnical engineering; or a BS degree in civil engineering with twelve (12) semester hours of post BS credit in geotechnical engineering or course content related to evaluation of geologic hazards from an accredited college or university;


B. At least five (5) full years of experience in a responsible position in the field of geotechnical engineering in Utah, or in a state with similar geologic hazards and regulatory environment, and experience demonstrating the engineer's knowledge and application of appropriate techniques in participating in geologic hazard studies; and


C. A Utah state professional engineer's license. (Ord. 2015-16, 10-20-2015)

http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318794
10-12-7: PRELIMINARY ACTIVITIES:linklink


A. Geologic Hazard Investigation: This section shall apply to any geologic hazard investigation for the purpose of determining the feasibility of development or for the purpose of exploring, evaluating or establishing locations for permanent improvements.


B. Scoping Meeting: The developer or consultant shall schedule a scoping meeting with the city to evaluate the engineering geologist/geotechnical engineer's investigative approach. At this meeting, the consultant shall present a work plan that includes locations of anticipated geologic hazards and locations of proposed exploratory excavations, such as trenches, borings, and CPT soundings, which meet the minimum standard of practice. The investigation approach should allow for flexibility due to unexpected site conditions. Field findings may require modifications to the work plan. Upon completion of a successful scoping meeting, a geologic hazard investigation permit application may be submitted to the city of North Salt Lake.


C. Geologic Hazard Investigation Permit: As required by this chapter and except as otherwise noted therein, no person shall commence or perform any land disturbance, grading, relocation of earth, or any other land disturbance activity, without first obtaining a geologic hazard investigation permit. Application for the permit shall be filed with the city engineer on forms furnished by the city for such purposes only after a scoping meeting has been completed.


D. Contact Information: The applicant shall specify a primary contact responsible for coordination with the city during the land disturbance activity. (Ord. 2015-16, 10-20-2015)

http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318795
10-12-8: GEOLOGIC HAZARD INVESTIGATION PERMIT:linklink


A. Application For Permit: Application for a geologic hazard investigation permit shall be filed with the city engineer on forms furnished by the city for such purpose. Applications shall include all the plans, specifications, reports, documentation and information required herein. Three (3) sets of all required plans, specifications and reports shall be submitted with each application. All such plans, specifications and reports shall be prepared and signed by a civil engineer, or other professionally qualified individual, where applicable. Additional experts in applicable fields shall be utilized for preparation of such documents and reports as appropriate. No application shall be processed until all required plans, specifications, reports, documentation and information have been received by the city in accordance with the provisions and requirements of this title.


B. Plans And Specifications: Each application shall include a detailed site plan including the following:

1. A vicinity map;

2. The property lines and dimensions and bearings;

3. The location of any existing buildings or structures on the property or within fifty feet (50') of the property boundary;

4. Existing vegetation;

5. Accurate topography, including a minimum of one hundred feet (100') outside project boundary;

6. The elevations, dimensions, locations, extent, and slopes of all proposed land disturbance activities shown by contours or other means;

7. Locations of proposed test pits, bores, trenches, or other excavations;

8. Known or probable locations of geologic hazards;

9. The estimated start and completion dates for the proposed land disturbance activities and proposed land disturbance activities schedule and permit term;

10. Temporary construction entrance and exit plans;

11. Signed, written authorization from the property owner giving the applicant permission to access the property and perform the proposed land disturbance;

12. Any additional plans, drawings, or calculations required by the city engineer;

13. Grading plan for the proposed land disturbance activity and site;

14. Drainage plan for the proposed land disturbance activity and site;

15. Erosion and sediment control plan for the proposed land disturbance activity and site; and

16. Revegetation plan for the proposed land disturbance activity and site.


C. Fees: All applicable fees shall be paid by applicant with the filing of an application for a permit in accordance with the consolidated fee schedule. An application shall not be deemed complete until the required fees have been received by the city.


D. Conditions Of Approval: In granting any permit pursuant to the provisions of this chapter, the city engineer or the city engineer's authorized representative may attach such conditions as may be reasonably necessary to protect public health and safety. Such conditions may include, but will not be limited to:

1. The improvement of any existing site condition to bring it up to the standards of this title;

2. Requirements for fencing excavations or fills which would otherwise be hazardous;

3. Duration of permit; and

4. Posting of a performance bond for the completion of the work proposed in the geologic hazards investigation application, including, but not limited to, the proposed remediation and restoration of the site.


E. Denial Of Geologic Hazard Investigation Permits:

1. A geologic hazard investigation permit shall not be issued in any case where it is found that the work proposed by the applicant is hazardous, or is likely to endanger any private property, result in the deposit of debris on any public way, or interfere with any existing drainage course; as determined by the city engineer,

2. A geologic hazard investigation permit shall not be issued if the proposed land disturbance activity would not comply with the requirements of an applicable site plan, subdivision plat, or any provisions of law, including the provisions of this title.


F. Approved Plans: The applicant shall retain the approved set of plans and specifications at the site covered by the geologic hazard investigation permit at all times during which the work authorized thereby is in progress. No approved plans or specifications shall be changed, modified, altered or amended, without approval of the city engineer.


G. Emergencies: The provisions of this title shall not apply to any land disturbance activity which is conducted during a period of emergency or disaster, as declared and defined by the city, and which is directly connected with or related to the relief of conditions caused by such emergency or disaster. (Ord. 2015-16, 10-20-2015)

http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318796
10-12-9: GEOLOGIC HAZARD STUDIES AND REPORTS REQUIRED:linklink

Any applicant requesting development approval on a parcel of land within a geologic hazard study area or where there are known or readily apparent geologic hazards and the area is not depicted on the geologic hazards study area maps, shall submit to the city five (5) paper copies and one electronic copy of a site specific geologic hazard study report. (Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318797
10-12-10: GEOLOGIC HAZARD REPORTS:linklink


A. Each geologic hazards report shall be site specific and shall identify all known or suspected potential geologic hazards, originating on site or off site, whether previously identified or previously unrecognized, that may affect the subject property. All geologic hazards reports shall include the original or wet signature and professional seal, both in blue ink, of the qualified professional. Geologic hazards reports coprepared by professional geologists and engineers shall include both professionals' original signature and seal in blue ink.


B. Surface fault rupture reports shall contain all requirements as described in section 10-12-33-1, "Appendix A, Minimum Standards For Surface Fault Rupture Hazard Studies", of this chapter. Surface fault rupture studies shall be prepared by a qualified engineering geologist.


C. Slope stability and landslide reports shall contain all requirements as described in section 10-12-33-2, "Appendix B, Minimum Standards For Slope Stability Analysis", of this chapter. Slope stability and landslide studies shall be prepared by a qualified engineering geologist and a qualified geotechnical engineer.


D. Liquefaction reports shall contain all requirements as described in section 10-12-33-3, "Appendix C, Minimum Standards For Liquefaction Investigations And Evaluations", of this chapter. Liquefaction analyses shall be prepared by a qualified geotechnical engineer. Liquefaction investigations are not required for residential construction classified in the international residential code as R-3.


E. The preparation of geologic hazard reports shall follow the most recent guidelines published by the Utah geological survey, a division of the Utah department of natural resources.


F. All geologic hazards reports shall include, at a minimum:

1. A one to twenty four thousand (1:24,000) scale geologic map, with references, showing the general surface geology (landslides, alluvial fans, etc.), bedrock geology where exposed, bedding attitudes, faults, and other geologic structural features;

2. A detailed site map of the subject area, at a scale equal to or more detailed than one inch equals two hundred feet (1" = 200'), showing the locations of subsurface investigations and site specific geologic mapping performed as part of the geologic investigation, including boundaries and features related to any geologic hazards, topography, and drainage. The site map must show the location and boundaries of the property, geologic hazards, delineation of any recommended setback distances from hazards, and recommended locations for structures. Buildable and nonbuildable areas shall be clearly identified;

3. Trench logs, when applicable, prepared in the field and presented in the geologic hazard report at a scale equal to, or more detailed than, one inch equals five feet (1" = 5');

4. Boring logs when applicable, prepared with standard geologic nomenclature;

5. Listing of aerial photographs used and other supporting information, as applicable;

6. Conclusions, clearly supported by adequate data included in the report, that summarize the characteristics of the geologic hazards, and that address the potential effects of the geologic conditions and geologic hazards on the proposed development and occupants thereof, particularly in terms of risk and potential damage;

7. Specific recommendations for additional or more detailed studies, as may be required to understand or quantify a geologic hazard;

8. An evaluation of whether or not mitigation measures are required, including an evaluation of multiple mitigation options;

9. Specific recommendations for avoidance or mitigation of the effects of the hazards, consistent with the purposes set forth in section 10-12-1 of this chapter, including design or performance criteria for engineered mitigation measures and all supporting calculations, analyses, modeling or other methods, and assumptions. Final design plans and specifications for engineered mitigation must be signed and stamped by a qualified geotechnical, civil and/or structural engineer, as appropriate;

10. Data upon which recommendations and conclusions are based, shall be clearly stated in the report; and

11. A statement shall be provided regarding the suitability of the proposed development from a geologic hazard perspective.


G. When a submitted report does not contain adequate data to support its findings, additional or more detailed studies shall be required to explain or quantify a particular geologic hazard or to describe how mitigation measures recommended in the report are appropriate and adequate. (Ord. 2015-16, 10-20-2015)

http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318798
10-12-11: REVIEW OF GEOLOGIC HAZARD REPORTS:linklink


A. The city shall review any proposed land use which requires preparation of a geologic hazards report under this chapter to determine the possible risks to the safety of persons, property and city infrastructure from geologic hazards.


B. Prior to consideration of any request for preliminary plat approval or site plan approval, the geologic hazards report, if required, shall be submitted to the city for review.


C. All direct costs associated with the review of geologic hazard studies shall be paid by the applicant.


D. The city shall determine whether the report complies with all of the following standards:

1. A suitable geologic hazard report has been prepared by qualified professionals.

2. The proposed land use does not present an unreasonable risk to the health, safety, and welfare of persons or property, including buildings, storm drains, public streets, culinary water facilities, utilities or critical facilities, whether off site or on site, or to the aesthetics and natural functions of the landscape, such as slopes, streams or other waterways, drainage, or wildlife habitat, whether off site or on site, because of the presence of geologic hazards or because of modifications to the site due to the proposed land use.

3. The proposed land use demonstrates that, consistent with the state of the practice, the identified geologic hazards can be mitigated to a level where the risk to human life and damage to property are reduced to an acceptable and reasonable level in a manner which will not violate applicable federal, state, or local statutes, ordinances or regulations. Mitigation measures shall consider, in their design, the intended aesthetic functions of other governing ordinances such as the sensitive lands overlay zone. The applicant shall include with the geologic hazards report a mitigation plan that defines how the identified hazards or limitations will be addressed without impacting or adversely affecting off site areas. Mitigation measures shall be reasonable and practical to implement especially if such measures require ongoing maintenance by property owners.


E. The city may set other requirements as are necessary to overcome any geologic hazards and to ensure that the purposes of this chapter are met. These requirements may include, but are not limited to:

1. Additional or more detailed studies to understand or quantify the hazard or determine whether mitigation measures recommended in the report are adequate;

2. Specific mitigation requirements, establishing buildable and nonbuildable areas, limitations on slope grading, and controls on grading or revegetation;

3. Grading plans, when required, shall be prepared, signed and sealed by a licensed professional engineer. As built grading plans, when required, shall be signed and sealed by the project geotechnical engineer as well as the professional engineer that prepared the grading plans. Grading plans, when required, shall include, at a minimum, the following:

a. Maps of existing and proposed contours;

b. Present and proposed slopes for each graded area;

c. Existing and proposed drainage patterns;

d. Location and depth of all proposed cuts and fills;

e. Description of methods to be employed to achieve stabilization and compaction;

f. Location and capacities of proposed drainage, structures, and erosion control measures based on maximum runoff for a 100-year storm;

g. Location of existing buildings or structures on or within one hundred feet (100') of the site, or which may be affected by proposed grading and construction; and

h. Plans for monitoring and documentation of testing, field inspections during grading, and reporting to the city;

4. Installation of monitoring equipment and seasonal monitoring of surface and subsurface geologic conditions, including groundwater levels; and

5. Other requirements such as time schedules for completion of the mitigation and phasing of development.


F. The city of North Salt Lake may also establish additional requirements necessary to protect the health, safety, and welfare of the citizens, protect city infrastructure and financial health, and minimize potential adverse effects of geologic hazards to public health, safety, and property as a condition of approval of any development which requires a geologic hazards report.


G. The city of North Salt Lake may require qualified professionals to be on site, at the cost of the developer, during certain phases of construction, particularly during grading phases and the construction of retaining walls. For any real property where development has proceeded on the basis of a geologic or geotechnical report which has been accepted by the city, no final inspection shall be completed, performance bond released, or building permit issued until the geotechnical engineer or engineering geologist who signed and approved the report certifies, in writing, that the completed improvements conform to the descriptions and requirements contained in the geologic or geotechnical report.


H. An applicant may appeal any decision made under the provisions of this chapter only after the city has issued a written review of a report. The appeal shall be submitted in writing to the city recorder within ten (10) days of the issuance of the written review or other decision and shall set forth the specific grounds or issues upon which the appeal is based. The city shall assemble a professional panel of three (3) qualified experts to serve as the appeal authority for any technical dispute. The panel shall consist of an expert designated by the city, an expert designated by the applicant, and an expert chosen by the city's and the applicant's designated experts. If the city's and the applicant's designated experts cannot reach a consensus of the third expert within thirty (30) days, the city shall select the third expert. Decisions of the panel will be binding and will be based on the majority decision of the panel. The costs of the appeal process shall be paid by the applicant. (Ord. 2015-16, 10-20-2015)

http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318799
10-12-12: LAND DISTURBANCE PERMIT REGULATIONS:linklink

As part of the final plat approval and in addition to other subdivision regulations, final construction plans shall be designed according to the following land disturbance regulations in sections 10-12-14 to 10-12-33 of this chapter. After a final plat has been approved, the approved final construction plans along with any associated documents and bonding shall constitute a land disturbance permit. (Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318800
10-12-13: COMPLIANCE WITH PERMIT:linklink

The land disturbance permit holder and contractor and their agents shall carry out the proposed land disturbance activities in accordance with the approved plans and specifications, the conditions of the land disturbance permit, and the requirements of this title and all other applicable ordinances, rules, regulations and standards of the city. (Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318801
10-12-14: PROTECTIVE DEVICES:linklink

The land disturbance permit holder and contractor and their agents shall maintain all required protective devices and temporary drainage during the progress of the land disturbance activities and shall be responsible for the observance of the hours of work, dust control, methods of hauling, and other applicable regulations. (Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318802
10-12-15: MAINTENANCE OF SITE:linklink

The land disturbance permit holder and contractor and their agents shall be responsible for the maintenance of the site and the removal of all debris during the term of the permit. (Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318803
10-12-16: ACCESS AND HAUL ROUTES:linklink

Temporary construction entrance and exit routes shall be provided by the permit holder in accordance with the approved plans and permit at key access points to the site or project to eliminate the problem of tracking mud and debris from the construction site onto private or public streets. The city engineer may impose conditions to the land disturbance permit with respect to access or haul routes to and from land disturbance activity sites, the hours of work, methods of controlling dust, and safety precautions involving pedestrian or vehicular traffic as determined required in the interest of the public health, safety and welfare. (Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318804
10-12-17: CONSENT OF ADJACENT PROPERTY OWNERS:linklink

If any land disturbance activity requires entry onto adjacent property for any reason, the land disturbance permit applicant shall obtain the written consent of the adjacent property owner or their authorized representative and shall file a copy of such consent with the city engineer before a land disturbance permit may be issued. (Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318805
10-12-18: CUTS AND FILLS:linklink


A. Height: Except as otherwise provided herein, no finished fill slope shall exceed a vertical height of twenty five feet (25'). The city engineer may approve, in writing, a fill slope in excess of twenty five feet (25') as deemed appropriate in his or her sole discretion based upon the circumstances and conditions of the proposed site and fill. Any fill slope proposed in excess of twenty five feet (25') shall be supported by documentation and a report prepared and signed by a professional engineering geologist and geotechnical engineer attesting to the appropriateness, safety and stability of the proposed fill slope. Such documentation and report shall be prepared at the applicant's expense and shall address the need for and design of intervening terraces or other necessary measures to provide for the safety and stability of the proposed slope.


B. Slope: Except as otherwise provided herein, no cut or fill shall exceed a slope of two horizontal to one vertical (2:1). The city engineer may approve, in writing, a cut or fill slope in excess of two horizontal to one vertical (2:1) as deemed appropriate in his or her sole discretion based upon the circumstances and conditions of the proposed site and the cut or fill. Any cut or fill slope proposed in excess of two horizontal to one vertical (2:1) shall be supported by documentation and a report prepared and signed by a professional engineering geologist and geotechnical engineer attesting to the appropriateness, safety and stability of the proposed cut or fill slope. Such documentation and report shall be prepared at the applicant's expense and shall address the need for and design of necessary measures to provide for the safety and stability of the proposed cut or fill slope.


C. Unstable Material: The city engineer may require, in writing any cut or fill to be constructed with an exposed surface flatter than two horizontal to one vertical (2:1) when, in the city engineer's opinion, under the particular conditions, such flatter surface is deemed necessary for stability or safety.


D. Intervening Terraces: When intervening terraces are used on slopes two horizontal to one vertical (2:1), terraces shall be finished using materials as approved by the city and shall have a minimum width of six feet (6'). Terraces shall be extensively landscaped in accordance with an approved landscaping plan. Terraces shall be spaced at vertical intervals of twenty five feet (25'); provided, however, for slopes less than forty feet (40') in vertical height, terraces shall be approximately at mid height. For slopes flatter than two horizontal to one vertical (2:1), where soil conditions require, intervening terraces may also be required.


E. Compaction: All fills shall be placed, compacted, inspected, and tested in accordance with the provisions of this title and any other city construction standards. If the strict enforcement of the compaction provisions of this section is determined by the city engineer to be unnecessary because of the proposed or probable use of the land, the city engineer may waive the requirements. The requirements of this section shall not be waived when structures are to be supported by the fill, the fills are being placed in areas to be designated as hillside, or where the fills are necessary as a safety measure to aid in preventing the saturation, settling, slipping, or erosion of the fill.


F. Fills Toeing Out On Natural Slopes: Except as otherwise provided herein, no fills toeing out on natural slopes which are steeper than two horizontal to one vertical (2:1) shall be permitted. The city engineer may approve such fills toeing out on natural slopes which are steeper than two horizontal to one vertical (2:1) as deemed appropriate in his or her sole discretion based upon the circumstances and conditions of the proposed site and fill. Any fill slope proposed to toe out on natural slopes which are steeper than two horizontal to one vertical (2:1) shall be supported by documentation and a report prepared and signed by a professional engineering geologist and geotechnical engineer attesting to the appropriateness, safety and stability of the proposed fill. Such documentation and report shall be prepared at the applicant's expense and shall address the need for and design of necessary measures to provide for the safety and stability of the proposed fill.


G. Combined Cut And Fill Slopes: Combined cut and fill slopes shall meet the requirements of this section insofar as steepness, height, and benching are concerned except that, where the slope exceeds twenty five feet (25') in height, the required drainage bench shall be placed at the top of the cut slope.


H. Setback: Fill placed on or above the top of an existing or proposed cut or natural slope steeper than three horizontal to one vertical (3:1) shall be set back from the top of the slope a minimum distance as required by the international building code, as adopted by the city, or as approved by the city engineer based upon submitted reports and documentation for the project.


I. Existing Fills: All existing manmade fills on any and all sites shall be properly evaluated by a soils engineer. If deficiencies exist, recommendations and design criteria for corrective measures shall be included within the soils engineering report.


J. Measure Of Settlement: The city engineer or the building official may require, in writing, the determination of the settlement characteristics of any fills to establish that any movements have substantially ceased. In such cases, a system of bench marks shall be installed by a civil engineer or land surveyor at critical points on the fill, and accurate measurements of both horizontal and vertical movements shall be taken and evaluated by the geotechnical engineer for a period of time sufficient to define the settlement behavior. The evaluation period shall be monitored in accordance with the approved geotechnical report for the project.


K. Buttress Fills: All buttress fills shall be designed in accordance with the city's construction standards and the recommendations and design criteria, including the subdrain system, submitted by the geotechnical engineer or engineering geologist with the approval of the city engineer.


L. Limitations: For all lots created after the adoption of this chapter, the following limitations shall apply: Toes of fill slopes shall not be made nearer to a rear property boundary line than seven feet (7'). (Ord. 2015-16, 10-20-2015)

http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318806
10-12-19: EROSION CONTROL AND DRAINAGE DEVICES:linklink

Best Management Practices, such as, but not limited to, intervening terraces, diverter terraces, vee channels, runoff computations, drainage dispersal walls, subdrains and site drainage, shall be provided and designed in accordance with this chapter and any other applicable City ordinances. (Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318807
10-12-20: AREAS SUBJECT TO SLIDES AND UNSTABLE SOIL:linklink

A detailed evaluation shall be completed for all areas subject to slides or unstable soils by a geotechnical engineer or engineering geologist including design criteria for corrective measures. Exploratory work or reports are required for such conditions in accordance with geologic hazard investigation permit requirements set forth in section 10-12-8 of this chapter. (Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318808
10-12-21: PLANTING AND IRRIGATION OF CUT AND FILL SLOPES:linklink

All manufactured cut and fill slopes shall be planted and maintained until established. Temporary irrigation may be required in accordance with the provisions of this chapter and any other applicable City ordinances. The developer is responsible for operating and maintaining the irrigation system until such time as the planted material is well established as determined, in writing, by the City Engineer. (Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318809
10-12-22: LOT STANDARDS AND IDENTIFICATION OF BUILDING ENVELOPE:linklink

In order to facilitate the preservation of slopes, natural terrain and vegetation, or avoidance of geologic hazards, the minimum depth of a lot in feet, as regulated in this title may be modified by the City Council upon recommendation by the Planning Commission. The resulting area must contain a "buildable area" as defined by section 10-1-46 of this title.

The developer shall indicate on the site plan and subdivision plat for the site or project, the maximum building envelope, or area of ultimate land/vegetation disturbance, including designation of the building envelope's distance from the lot or site boundary lines, which will be caused by the proposed structure and its appurtenances. Prior to the beginning of any type of land disturbance or construction on a given lot, the contractor performing the work is responsible for identifying the building envelope in the field by marking of the building envelope perimeter. The building official may require markers to be surveyed when deemed necessary or appropriate. Marking of the building envelope shall be inspected by the City's building division prior to commencement of any land disturbance activity on the lot. (Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318810
10-12-23: PROPERTY LINE AND CORNER MARKERS:linklink

The developer shall ensure that property lines and corner survey markers are installed for the site or project. These markers are to include rebar placed at the back corners of each lot and markers placed on the curb for locating the side property lines. If curb and gutter do not exist, the front markers are to be placed in the road pavement. Additional survey markers may be required on property lines as deemed necessary by the building official. (Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318811
10-12-24: SLOPE PROTECTION EASEMENTS:linklink

The developer shall provide slope protection easements for all critical slopes (native or constructed) as part of the project. Critical slopes shall include slopes which average thirty percent (30%) or higher for an elevation change five feet (5') or greater. The City Engineer may declare in writing other slopes less than thirty percent (30%) as critical slopes due to geologic hazard, soil stability, drainage flows, vegetation conditions or designated open space. Slope protection easements shall be provided by both indicating them on the final plat and by separate recordable easement for each individual lot where the easements are located. Such individual easements shall be accompanied by a map indicating areas where land disturbance is prohibited. Easements for individual lots shall be recorded simultaneously with the recordation of the final subdivision plat. (Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318812
10-12-25: MASTER DRAINAGE PLAN REQUIRED:linklink

A master drainage plan shall be designed for all proposed development. At a minimum the plan shall address the following items:


A. Master Drainage Plan Design:

1. Drainage Plan: Applications for development shall include a plan indicating how proposed lots will be graded and drained. This plan shall be of sufficient detail to demonstrate how surface runoff will typically be managed on all lots within the proposed project, including possible locations of swales and detention or retention facilities that will be utilized to control runoff.

2. Notice Of Drainage Easements: A notice of drainage easements shall be recorded on the subdivision plat for the project. The easement shall specify that nothing may be placed within a swale easement that would diminish or reduce functionality of the swale.

3. Swales: Any swale located in rear or side yards shall be designed with materials approved by the city that will prevent erosion, and shall become a permanent feature of the lot. The swale systems shall be shown in a drainage easement on the site plan and final plat for the project.

4. Underground Facilities: The developer may select the option of designing underground drainage facilities to replace aboveground drainage swales if these facilities meet certain city requirements. These requirements include the design being approved in writing by the city engineer, inclusion of these facilities within city approved drainage easements, maintenance of the system by a homeowners' association, and other requirements as may be deemed necessary by the city.

5. Lots Graded Toward Street For Drainage: Except as otherwise provided herein, stormwater runoff from individual lots shall be directed toward the streets at a minimum slope of two percent (2%) for the first twenty five feet (25') from the structure. For homes that are set back more than twenty five feet (25') from the front property line, property may be reduced to a one percent (1%) slope for all areas at least twenty five feet (25') from the structure. Exceptions may be granted by the city engineer in writing, when deemed appropriate and necessary, in accordance with the provisions of this section. Aesthetic reasons such as the creation of view lots shall not constitute sufficient reason for granting an exception.

6. Lots Which Cannot Be Graded Toward The Street; Approval Required: Lots that cannot be drained toward the street may be allowed to drain a portion of their stormwater runoff toward the rear of the yard after review and approval in writing by the city engineer. Prior to obtaining this approval, the developer shall prepare a drainage plan, which indicates how the stormwater will be disposed of from the lot, to either a city owned storm drain, a natural stream or channel, a manmade channel, a lower elevation lot or other city approved facility or retained on site. Such disposal is to be protected by a drainage easement, as described in section 10-12-27 of this chapter, dedicated for this purpose and the facilities are to be bonded for. Drainage easements shall be maintained by the homeowners' association, where applicable, or by individual lot owners.

In the case where stormwater flow is allowed to flow from a higher lot to a lower lot, in elevation, sufficient energy dissipation shall be designed and constructed to reduce the water velocity to an acceptable level to prevent erosion. The design and construction of these energy dissipation structures shall be approved by the engineering department in conjunction with the review and approval of the drainage plan for the project.


B. Conformance To Master Drainage Plan:

1. Applications: Individual applications for building permits shall include lot specific drainage plans which indicate how surface runoff will be managed in conformance with the master drainage plan. Modifications to the design specified in the master drainage plan shall require approval by the city engineer.

2. Installation: Installation of required lot drainage improvements shall be completed and approved prior to issuance of a certificate of occupancy.

3. Maintenance: Individual lot owners shall be responsible for the maintenance of all lot drainage improvements. Nothing may be placed within drainage easements that would diminish or reduce functionality of the drainage system.

4. Notice: The developer shall notify the homebuilders and homeowners of the required lot drainage improvements and the homeowner's obligation to maintain such improvements in perpetuity. The method of notice shall be approved by the city. (Ord. 2015-16, 10-20-2015)

http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318813
10-12-26: LANDSCAPING OF CERTAIN LOTS FOR EROSION CONTROL:linklink

The city reserves the right to require that the lots be revegetated or stabilized upon completion of subdivision improvements or that lots be fully landscaped prior to the issuance of a certificate of occupancy as part of the requirements of the project. The purpose of this requirement is to ensure that for certain areas in the city which have soils susceptible to severe erosion, the erosion is controlled. The criteria to be used by the city are the size of the lot and sizes of adjacent lots, elevation differences between lots, level of disturbance to native soils and vegetation, the type of soils in the project, and any other relevant factors. (Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318814
10-12-27: EROSION CONTROL AND REVEGETATION:linklink

The developer is to indicate erosion control and revegetation best management practice (BMP) to be used for the project on the project drawings and as part of the project descriptions included with the application. Erosion and sedimentation control measures will be inspected prior to commencement of construction, during construction of the subdivision, and once the subdivision construction is complete. The engineering department will be responsible for these inspections. Once the subdivision level construction is complete and improvement work begins on individual lots, erosion and sedimentation control BMP will be the responsibility of the lot owner and will be inspected prior to any lot disturbance, during construction and once lot level construction is complete. (Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318815
10-12-28: WET WEATHER PLAN:linklink

The city engineer may require that land disturbance activities and erosion control or revegetation plans be modified, if unforeseen delays occur due to weather generated problems not considered at the time the land disturbance permit was issued, including submission and approval of a wet weather plan. (Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318816
10-12-29: DISCLOSURE WHEN A GEOLOGIC HAZARD REPORT IS REQUIRED:linklink


A. Whenever a geologic hazards report is required under this chapter, the owner of the parcel shall record a notice running with the land in a form satisfactory to the city of North Salt Lake prior to the approval of any development or subdivision of such parcel. Disclosure shall include signing a disclosure and acknowledgment form provided by the city, which includes:

1. Notice that the parcel is located within a geologic hazards study area as shown on the geologic hazards study area map or as otherwise defined in this chapter; and

2. Notice that a geologic hazards report was prepared and is available for public inspection in the city's files.


B. Where geologic hazards and related setbacks are delineated in a subdivision, the owner shall also place additional notification on the plat stating the above information prior to final approval of the plat. (Ord. 2015-16, 10-20-2015)

http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318817
10-12-30: WARNING AND DISCLAIMER:linklink

The geologic hazards ordinance and sensitive lands overlay area map may be amended as new information becomes available pursuant to procedures set forth in this title. The provisions of this chapter do not in any way assure or imply that areas outside the sensitive lands overlay maps boundary are free from the possible adverse effects of geologic hazards. It is the responsibility of the applicant's geotechnical consultants to employ outside research and data to discover and establish the locations and boundaries of any known and potential geologic hazards. This chapter shall not create any liability on the part of the city of North Salt Lake, or any officer, reviewer, or employee thereof for any damages from geologic hazards that result from reliance on this chapter or any administrative requirement or decision lawfully made hereunder. (Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318818
10-12-31: CHANGE OF USE:linklink

No change in use which results in the conversion of a building or structure from one not used for human occupancy to one that is so used shall be permitted unless the building or structure complies with the provisions of this chapter. (Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318819
10-12-32: CONFLICTING REGULATIONS:linklink

In cases of conflict between the provisions of existing zoning classifications, building code, subdivision ordinance, or any other ordinance of the city of North Salt Lake and the sensitive area and geologic hazards ordinance codified in this chapter, the most restrictive provision shall apply. (Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318820
10-12-33: APPENDICES:linklink
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318821
10-12-33-1: APPENDIX A, MINIMUM STANDARDS FOR SURFACE FAULT RUPTURE HAZARD STUDIES:linklink

1.0 Introduction.

The Wasatch Fault zone (WFZ) is a major tectonic feature in the western United States, extending for about 230 miles from near Fayette, Utah at the south to near Malad, Idaho at the north. Surface faulting has occurred along the WFZ in northern Utah throughout late Pleistocene and Holocene time (Lund, 1990; Black and others, 2003). "Surface faulting" is fault-related offset or displacement of the ground surface that may occur in an earthquake.

The WFZ consists of a series of normal-slip fault segments with relative movement down to the west and up to the east. Ten major fault segments are recognized along the WFZ (Machette and others, 1992), which are believed to be independent in regard to their potential for surface faulting. These segments have distinct geomorphic expression and are clearly visible on aerial photographs.

If a fault were to break the ground surface beneath a building, significant damage could occur, perhaps resulting in injuries or loss of life. To ensure that buildings are not sited across Holocene-age (active) faults, the city of North Salt Lake municipal code, title 10, chapter 12: sensitive area & geologic hazards ordinance requires a site-specific geologic investigation of property situated within the sensitive lands overlay zone and any other areas that may be subject to the presence of fault lines. The primary purposes of the geologic investigation are to assess the surface fault rupture potential of the property and to assess the suitability of the property for the proposed development from the standpoint of surface fault rupture. If a fault is discovered and determined (or presumed) to have moved during the Holocene-age ("active"), appropriate building setbacks from the fault are required such that structures are not located astride the fault trace. Building setbacks must be established prior to development of sites located within the surface-fault-rupture special study area.

A site-specific surface-fault-rupture-hazard study includes a field investigation (usually involving the excavation and geologic documentation of a trench) and report. This appendix describes the minimum standards required by the city for surface-fault-rupture-hazard studies.

The purpose of establishing minimum standards for surface fault rupture hazard studies is to:

(a) Protect the health, safety, welfare, and property of the public by minimizing the potentially adverse effects of surface fault rupture and related hazards;

(b) Assist property owners and land developers in conducting reasonable and adequate studies;

(c) Provide consulting engineering geologists with a common basis for preparing proposals, conducting investigations, and recommending building setbacks; and,

(d) Provide an objective framework for review of fault study reports.

The procedures outlined herein are intended to provide the developer, consulting engineers, geologists and geotechnical engineers with an outline of appropriate exploration methods, standardized report information, and expectations for the report.

These standards constitute the minimum level of effort required in conducting surface-fault-rupture-hazard studies in the city. Considering the complexity of evaluating surface and near-surface faults, additional effort beyond the minimum standards may be required at some sites to adequately address the fault hazard. The information presented herein does not relieve the engineering geologist from his/her duty to perform additional geologic or engineering services he/she believes are necessary to assess the fault rupture potential at a site.

1.2 Properties Requiring A Fault Investigation.

A fault study is required, prior to approval of any land use for properties identified in 10-12-3 of the city of North Salt Lake municipal code. Submittal and review of a site-specific fault study prior to receiving a land use or building permit from the city is required for said areas. It is the responsibility of the applicant to retain a qualified professionals to perform the fault study and to use the latest available data in preparing the required study.

In addition, a fault investigation may be required if on site or nearby fault-related features are identified during the course of other geologic or geotechnical studies performed on or near the site or during construction.

2.0 Minimum Standards For Fault Studies.

Following are the minimum standards for a comprehensive fault investigation. Fault investigations may be reported in conjunction with other geological and geotechnical investigations, or may be submitted separately. In addition to these standards, all fault investigations, reports and recommendations shall follow the latest adopted guidelines published by the Utah geological survey.

2.1 Scoping Meeting.

The developer's consultant must schedule a scoping meeting with the city to evaluate the investigation approach. At this meeting, the consultant should present a site plan that includes: proposed building locations (if known); fault location(s) and orientation; and the proposed trench locations, orientation, length, and depth (see section 2.3, fault investigation method). The investigative approach should allow for flexibility due to unexpected site conditions; field findings may require modifications to the work plan.

2.2 Fault Investigation Method.

Inherent in fault study methods is the assumption that future faulting will recur along pre-existing faults and in a manner consistent with past displacement. The focus of fault investigations is therefore to accurately locate existing faults. If faults are documented, the investigation shall also 1) evaluate the age(s) of movement along the fault trace(s), and 2) estimate amounts of past displacement(s), which is required in order to derive building setbacks.

2.2.1 Previous Studies And Aerial Photograph Review.

A fault investigation shall include, at a minimum, a review of available literature pertinent to the site and vicinity, including previous published and unpublished geologic/soils reports, and interpretation of available stereo-paired aerial photographs. The photographs reviewed should include more than one set and should include pre-urbanization aerial photographs, if available. Efforts must be made to accurately plot the locations of mapped or inferred fault traces on the property as shown by previous studies in the area.

2.2.2 Exploration Methods.

Subsurface exploration consisting of trenching is required. The engineering geologist shall clean and document ("log") trench exposures as described in section 2.3.5. Existing faults may also be identified and mapped in the field by direct observation of young, fault-related geomorphic features, and by examination of aerial photographs. When trenching is not feasible (i.e., the presence of shallow ground water, excessive thickness of fill, etc.), supplemental methods such as closely spaced cone penetration test (CPT) soundings may be employed. Such supplemental methods must be discussed with the city prior to implementation and should be clearly described in the report.

In lieu of conventional trenching or the CPT method, an alternative subsurface exploration program may be acceptable, depending upon site conditions. Such a program may consist of a sufficient number of closely spaced downhole-logged bucket-auger borings, geophysical exploration techniques, or a combination of techniques.

When an alternative exploration program is proposed, a written description of the proposed exploration program along with an exploration plan should be submitted to the city for review, prior to the exploration. The plan must include, at a minimum, a map of suitable scale showing the site limits, surface geologic conditions within several thousand feet of the site boundary, the location and type of the proposed alternative subsurface exploration, and the anticipated earth materials present at depth on the site.

The actual subsurface exploration program to be used on any specific parcel will be determined on an individual basis using the current state of technical knowledge about the fault zone and information gained from previous exploration on adjacent or nearby parcels. At all times, consideration must be given to safety, and trenching should comply with all applicable safety regulations.

2.2.3 Trench Siting.

Exploratory trenches must be oriented approximately perpendicular to the anticipated trend of known fault traces. The trenches shall provide the minimum footage of trenching necessary to explore the portion of the property situated in the surface-fault-rupture hazard study area, such that the potential for surface fault rupture may be adequately assessed. When trenching to determine if faults might affect a proposed building site, the trench should extend beyond the building footprint at least the minimum setback distance for the building type (see table A-1).

Test pits or potholes alone are neither adequate nor acceptable. In some instances more than one trench may be required to cover the entire building area, particularly if the proposed development involves more than one building. Where feasible, trenches shall be located outside the proposed building footprint, as the trench is generally backfilled without compaction, which could lead to differential settlement beneath the footings. Supplemental trenching may be required in order to: 1) further refine fault locations (or the absence thereof); 2) accurately define building restriction areas, and/or; 3) provide additional exposures for evaluating the age of movement along the faults.

2.2.4 Location Determination.

All trenches and fault locations must be surveyed by a registered professional land surveyor. Fault locations should be surveyed with an accuracy of about 0.1 foot or better, so that structural setbacks can be developed.

2.2.5 Depth Of Excavation.

The depth of the trenches will ultimately depend on the trench location, occurrence of ground water, stability of subsurface deposits, and the geologic age of the subsurface geologic units. As a minimum, however, trenches shall extend substantially below the A and B soil horizons and well into distinctly bedded Pleistocene-age materials, if possible. Where possible, the trenches should extend below Holocene deposits and should expose contacts between Holocene materials and the underlying older materials.

Appropriate safety measures pertaining to trench safety for ingress, egress, and working in or in the vicinity of the trench must be implemented and maintained. It is the responsibility of the person in the field directing trench excavation to ensure that fault trenches are excavated in compliance with current occupational safety and health administration excavation safety regulations.

Trench backfilling methods and procedures should be documented in order to establish whether additional corrective excavation, backfilling, and compaction should be performed at the time of site grading.

In cases where Holocene (i.e., active) faults may be present, but pre-Holocene deposits are below the practical limit of excavation, the trenches must extend at least through sediments that are clearly older than several fault recurrence intervals. The practical limitations of the trenching must be acknowledged in the report and recommendations must reflect resulting uncertainties.

2.2.6 Documenting Trench Exposures.

Trench walls shall be cleaned of debris and backhoe smear prior to documentation. Trench logs shall be carefully drawn in the field at a minimum scale of 1-inch equals 5-feet (1:60) following standard and accepted fault trench investigation practices. Vertical and horizontal control must be used and shown on trench logs. Trench logs must document all significant geologic information from the trench and should graphically represent the geologic units observed; see section 2.6.3(e). The strike, dip, and net vertical displacement(s) (or minimum displacement(s)) of faults must be noted. Photographs with appropriate scale information must be included in the trench documentation.

2.2.7 Age Dating.

The geologist shall interpret the ages of geologic units exposed in the trench. When necessary, radiocarbon or other age determinations methods shall be used. If evidence of faulting is documented, efforts shall be made to date the time of latest movement (to determine whether recent (Holocene) displacement has occurred) using appropriate geologic and/or soil stratigraphic dating techniques. If soil stratigraphic dating techniques are used, a geologist experienced in using the techniques and soil-development rates in the area shall perform them.

Many of the surficial deposits within Salt Lake Valley area were deposited during the last pluvial lake cycle, referred to as the Bonneville lake cycle. Although late-stage Bonneville lake cycle sediments do not correspond to the Pleistocene-Holocene boundary (i.e., Bonneville lake cycle deposits are older than 10,000 years old), for purposes of evaluating fault activity, these deposits provide a useful regional datum (particularly so when the entire Holocene sequence of sediments is not present).

For practical purposes, and due to documented Holocene displacement along the Salt Lake segment of the Wasatch fault, any fault which displaces late-stage Bonneville lake cycle deposits should be considered active unless the Bonneville deposits are overlain by clearly unfaulted early Holocene-age deposits. Conversely, the presence of demonstrably unbroken, undeformed, and stratigraphically continuous Bonneville sediments constitutes reasonable geologic evidence for the absence of active faulting.

2.3 Field Review.

A field review by the city is required during exploratory trenching. The applicant must provide a minimum of 48-hours notice to schedule the field review with the city. The trenches should be open, safe, cleaned, and a preliminary log completed at the time of the review. The field review allows the city to evaluate the subsurface data (i.e., age, type of sediments; presence/absence of faulting, etc.) with the consultant. Discussions about questionable features or an appropriate setback distance are encouraged, but the city will not help log the trench, explain the stratigraphy, or give verbal approval of the proposed development during the field review.

2.4 Recommendations For Fault Setbacks.

To address wide discrepancies in fault setback recommendations, the city has adopted the fault setback calculation methodology for normal faults of Christenson and others (2003). The consultant should use this method to establish the recommended fault setback for critical facilities and structures designed for human occupancy. If another fault setback method is used, the consultant must provide justification in the report for the method used. Faults and fault setbacks must be clearly identified on site plans and maps.

Minimum setbacks are based on the type and occupancy of the proposed structures (see table A-1). A setback should be calculated using the formulas presented below, and then compared to the minimum setback established in table A-1. The greater of the two shall be used as the setback. Minimum setbacks apply to both the hanging wall and footwall blocks.

Top of slope and/or toe of slope setbacks required by the local building code must also be considered; again, the greater setback must be used.

Downthrown Fault Block (Hanging Wall)

The fault setback for the downthrown block will be calculated using the following formula: S = U (2D + F/tan.) where:

S   =   Setback within which structures for human occupancy are not permitted  
U   =   Criticality factor, based on the proposed occupancy of the structure (see table A-1)  
D   =   Expected fault displacement per event (assumed to be equal to the net vertical displacement measured for each past event)  
F   =   Maximum depth of footing or subgrade portion of the building  
tan.   =   Dip of the fault (degrees)  

Upthrown Fault Block (Footwall)

The dip of the fault and depth of the subgrade portion of the structure are irrelevant in calculating the setback on the upthrown fault block. Therefore, the setback for the upthrown side of the fault will be calculated as:

S = U x 2D

The setback is measured from the portion of the building closest to the fault, whether subgrade or above grade. Minimum setbacks apply as discussed above.

2.5 Small Displacement Faults.

Small-displacement faults are not categorically exempt from setback requirements. Some faults having less than 4 inches (100 mm) of displacement ("small displacement faults") may be exempt from setback requirements.

Specific structural risk-reduction options such as foundation reinforcement may be acceptable for some small-displacement faults in lieu of setbacks. Structural options must minimize structural damage.

Fault studies must still identify faults and fault displacements (both net vertical displacements and horizontal extension across the fault or fault zone), and consider the possibility that future displacement amounts may exceed past amounts. If structural risk-reduction measures are proposed for small displacement faults, the following criteria must be addressed:

(a) Reasonable geologic data indicating that future surface displacement along the particular fault will not exceed 4 inches.

(b) Specific structural mitigation to minimize structural damage.

(c) A structural engineer must provide appropriate designs and the city shall review the designs.

2.6 Required Outline For Surface Fault Rupture Hazard Studies.

The information described herein may be presented as a separate surface-fault-rupture-potential report or it may be incorporated within other geology or engineering reports that may be required for the property.

The report shall contain a conclusion regarding the potential risk of surface fault rupture on the subject property and a statement addressing the suitability of the proposed development from a surface-fault-rupture-hazard perspective. If exploration determines that there is a potential for surface rupture due to faulting, or if gradational contacts or other uncertainties associated with the exploration methods preclude the determination of absence of small fault offsets, the report should provide estimates of the amplitude of fault offsets that might affect habitable structures.

Surface-fault-rupture-hazard reports submitted to the city are expected to follow the outline and address the subjects presented below. However, variations in site conditions may require that additional items be addressed, or permit some of the subjects to be omitted (except as noted).

2.6.1 Report.

(a) Purpose And Scope Of Work: The report shall contain a clear and concise statement of the purpose of the investigation and the scope of work performed for the investigation.

(b) Geologic And Tectonic Setting: The report shall contain a clear and concise statement of the general geologic and tectonic setting of the site vicinity. The section should include a discussion of active faults in the area, paleoseismicity of the relevant fault system(s), and should reference relevant published and unpublished geologic literature.

(c) Site Description And Conditions: The report shall include information on geologic units, graded and filled areas, vegetation, existing structures, and other factors that may affect site development, choice of investigative methods, and the interpretation of data.

(d) Methods Of Investigation:

(1) Review of published and unpublished maps, literature and records concerning geologic units, faults, surface and ground water, and other factors.

(2) Stereoscopic interpretation of aerial photographs to detect fault-related topography, vegetation or soil contrasts, and other lineaments of possible fault origin. Reference the photograph source, date, flightline numbers, roll, frame numbers and scale.

(3) Observations of surface features, both on-site and off site, including mapping of geologic and soil units; geomorphic features such as scarps, springs, and seeps (aligned or not); faceted spurs, offset ridges or drainages; and geologic structures. Locations and relative ages of other possible earthquake-induced features such as sand blows, lateral spreads, liquefaction, and ground settlement should be mapped and described. Slope failures, although they may not be conclusively tied to earthquake causes, should also be noted.

(4) Subsurface investigations: The report shall include a description of the program of subsurface exploration, including trench logs, purpose of trench locations, and a summary of trenching or other detailed, direct observation of continuously exposed geologic units, soils, and geologic structures. All trench logs shall be at a scale of at least 1-inch equals five-feet.

The report must describe the criteria used to evaluate the ages of the deposits encountered in the trench, and clearly evaluate the presence or absence of active (Holocene) faulting.

(e) Conclusions: Conclusions must be supported by adequate data and shall contain, at a minimum:

(1) Summary of data upon which conclusions are based.

(2) Location of active faults, including orientation and geometry of faults, amount of net slip along faults, anticipated future offset, and delineation of setback areas.

(3) Degree of confidence in and limitations of data and conclusions.

(f) Recommendations: Recommendations must be supported by adequate geologic data and appropriate reasoning behind each statement. Minimum recommendations shall include:

(1) Recommended setback distances per section 2.5. Supporting calculations must be included. Faults and setbacks must be shown on site maps and final recorded plat maps.

(2) Other recommended building restrictions or use limitations (i.e., placement of detached garages, swimming pools, or other non-habitable structures).

(3) Need for additional or future studies to confirm buildings are not sited across active faults, such as inspection of building footing or foundation excavations.

(4) An inspection of the foundation excavation shall be performed to confirm the lack of faulting at the building site.

2.6.2 Report References.

Reports must include citations of literature and records used in the study, referenced aerial photographs or images interpreted (air-photo source, date and flight number, scale), and any other sources of data and information, including well logs, personal communications, etc.

2.6.3 Illustrations.

At a minimum, reports must include the following illustrations:

(a) Location Map: A site location map depicting topographic and geographic features and other pertinent data. Generally a 1:24,000-scale USGS topographic base map will suffice.

(b) Geologic Map: A regional-scale map (1:24,000 to 1:50,000 scale) is generally adequate. Depending on site complexity, a site-scale geologic map (1 inch = 200 ft or more detailed) may also be necessary. The map should show Quaternary and bedrock geologic units, faults, seeps or springs, soil or bedrock slumps, and other geologic and soil features existing on and adjacent to the project site. Geologic cross-sections may be included as needed to illustrate 3-dimensional relationships.

(c) Site Plan: A detailed site plan is required. The site plan should be at a scale of at least 1 inch = 200 feet (or more detailed) and should clearly show site boundaries, proposed building footprints, existing structures, streets, slopes, drainages, exploratory trenches, boreholes, test pits, geophysical traverses, and any other pertinent data.

(d) Site Specific Fault Map: If faulting is documented at a parcel, the report shall include a site-specific fault map. The fault map should be at a scale of at least 1 inch = 200 feet and should clearly show the surveyed locations of trenches (and any other exploratory techniques), surveyed location(s) of faults documented in the trenches, inferred location of the faults between trenches, recommended fault setback distance on each side of the faults, topographic contours, and proposed building locations, if known.

(e) Exploratory Trench Logs: Trench logs are required for each trench excavated as part of the study. Trench logs shall accurately depict all observed geologic features and conditions. Trench logs shall not be generalized or diagrammatic. The minimum scale is 1 inch = 5 feet (1:60) with no vertical exaggeration. Trench logs must accurately reflect the features observed in the trench (see section 2.3.6).

Trench logs shall include: trench orientation and indication of which trench wall was logged; trench top and bottom; stratigraphic contacts; stratigraphic unit descriptions including lithology, USGS soil classification, genesis (geologic origin), age, and contact descriptions; soil (pedogenic) horizons; marker beds; and deformation or offset of sediments, faults, and fissures. Other features of tectonic significance such as buried scarp free-faces, colluvial wedges, in-filled soil cracks, drag folds, rotated clasts, lineations, and liquefaction features including dikes, sand blows, etc. should also be shown. Interpretations of the age and origin of the deposits and any faulting or deformation must be included, based on depositional sequence. Fault orientation and geometry (strike and dip), and amount of net displacement must be measured and noted.

(f) Exploratory Boreholes And CPT Soundings: Should boreholes or CPT soundings be utilized as part of the investigation, reports shall include the logs of the borings/soundings. Borehole logs must include lithology descriptions, interpretations of geologic origin, USGS soil classification or other standardized engineering soil classification (include an explanation of the classification scheme), sample intervals, penetrative resistance values, static ground-water depths and dates measured, total depth of borehole, and identity of the person logging the borehole. Electronic copies of CPT data files should be provided to the city's reviewer, upon request.

(g) Geophysical Data: All geophysical data, showing stratigraphic interpretations and fault locations, must be included in the report, along with correlations to trench or borehole logs to confirm interpretations.

(h) Photographs: Photographs of scarps, trench walls, or other features that enhance understanding of site conditions and fault-related conditions shall be included. Composited, rectified digital photographs of trench walls may be used as background for trench logs, but features as outlined in section (e) above must still be delineated.

TABLE A-1
SETBACK RECOMMENDATIONS AND CRITICALITY
FACTORS (U) FOR IBC OCCUPANCY CLASSES
(International Code Council, 2003)

Class (IBC)   Occupancy Group   Criticality   U   Minimum Setback  
A   Assembly   2   2.0   25 feet  
B   Business   2   2.0   20 feet  
E   Educational   1   3.0   50 feet  
F   Factory/industrial   2   2.0   20 feet  
H   High hazard   1   3.0   50 feet  
I   Institutional   1   3.0   50 feet  
M   Mercantile   2   2.0   20 feet  
R   Residential (R-1, R-2, R-4)   2   2.0   20 feet  
R-3   Residential (R-3, includes single family homes)   3   1.5   15 feet  
S   Storage   -   1   0  
U   Utility and misc.   -   1   0  
  Table A-2   1   3.0   50 feet  


TABLE A-2
ADDITIONAL STRUCTURES REQUIRING GEOLOGIC INVESTIGATION

Buildings and other structures that represent a substantial hazard to human life in the event of failure, but not limited to:

1. Buildings and other structures where more than 300 people congregate in one area.

2. Buildings and other structures with elementary school, secondary school or day care facilities with occupancy greater than 250.

3. Buildings and other structures with occupancy greater than 500 for colleges or adult education facilities.

4. Health care facilities with occupancy greater than 50 or more resident patients but not having surgery or emergency treatment facilities.

5. Jails and detention facilities.

6. Any other occupancy with occupancy greater than 1000.

7. Power generating stations, water treatment or storage for potable water, waste water treatment facilities and other public utility facilities.

8. Buildings and other structures containing sufficient quantities of toxic or explosive substances to be dangerous to the public if released.

Buildings and other structures designed as essential facilities including, but not limited to:

1. Hospitals and other care facilities having surgery or emergency treatment facilities.

2. Fire, rescue and police stations and emergency vehicle garages and fueling facilities.

3. Designated emergency shelters.

4. Designated emergency preparedness, communications, and operation centers and other facilities required for emergency response.

5. Power-generating stations and other public utility facilities required as emergency backup facilities for facilities and structures included in this table.

6. Structures containing highly toxic materials as defined by the most recently adopted version of the IBC where the quantity of the material exceeds the maximum allowable quantities defined by the most recently adopted version of the IBC.

7. Aviation control towers, air traffic centers and emergency aircraft hangars.

8. Buildings and other structures having critical national defense functions.

9. Water treatment and storage facilities required to maintain water pressure for fire suppression.

(Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318822
10-12-33-2: APPENDIX B, MINIMUM STANDARDS FOR SLOPE STABILITY ANALYSIS:linklink

1.0 Introduction.

The procedures outlined herein are intended to provide consultants with a general outline for performing quantitative slope stability analyses and to clarify the expectations of the city of North Salt Lake. These standards constitute the minimum level of effort required in conducting quantitative slope stability analyses in the city of North Salt Lake. Considering the complexity inherent in performing slope stability analyses, additional effort beyond the minimum standards presented herein may be required at some sites to adequately address slope stability. The information presented herein does not relieve consultants of their duty to perform additional geologic or engineering analyses they believe are necessary to assess the stability of slopes at a site.

The evaluation of landslides generally requires quantitative slope stability analyses. Therefore, the standards presented herein are directly applicable to landslide investigations, and also constitute the minimum level of effort when performing landslide investigations.

The purposes for establishing minimum standards for slope stability analyses are to:

(a) Protect the health, safety, welfare, and property of the public by minimizing the potentially adverse effects of unstable slopes and related hazards;

(b) Assist property owners and land developers in conducting reasonable and adequate studies;

(c) Provide consulting geologists and geotechnical engineers with a common basis for preparing proposals, conducting investigations, and mitigation; and,

(d) Provide an objective framework for regulatory review of slope stability reports.

1.2 Areas Requiring Slope Stability Analyses.

Slope stability analyses shall be performed for all sites located within the sensitive lands overlay zone and for all slopes that may be affected by the proposed development which meet the following criteria:

(a) Cut and/or fill slopes steeper than about 2 horizontal (h) to 1 vertical (v).

(b) Natural slopes steeper than or equal to 3 horizontal (h) to 1 vertical (v).

(c) Natural and cut slopes with potentially adverse geologic conditions (e.g., bedding, foliation, or other structural features that are potentially adverse to the stability of the slope).

(d) Natural and cut slopes which include a geologic hazard such as a landslide, irrespective of the slope height or slope gradient.

(e) Buttresses and stability fills.

(f) Cut, fill, or natural slopes of water-retention basins or flood-control channels.

(g) In hillside areas, investigations shall address the potential for surficial instability, debris/mudflows, rock falls, and soil creep on all slopes that may affect the proposed development or be affected by the proposed development.

(h) When evaluating site conditions to determine the need for slope stability analyses, off-property conditions shall be considered (both up-slope to the top(s) of adjacent ascending slopes and down-slope to and beyond the toe(s) of adjacent descending slopes). Also, the consultant shall demonstrate that the proposed hillside development will not affect adjacent sites or limit adjacent property owners' ability to develop their sites.

1.3 Roles Of Geologist And Engineering Consultant.

The investigation of the static and seismic stability of slopes is an interdisciplinary practice. To provide greater assurance that the hazards are properly identified, assessed, and mitigated, involvement of both a geologist and geotechnical engineer is required. Analyses shall be performed only by or under the direct supervision of licensed professionals, qualified and competent in their respective area of practice. A geologist shall provide appropriate input to the geotechnical engineer with respect to the potential impact of the geology, stratigraphy, and hydrologic conditions on the stability of the slope. The shear strength and other geotechnical earth material properties shall be evaluated by the geotechnical engineer. Qualified geologists, geological engineers and geotechnical engineers may assess and quantitatively evaluate slope stability. However, the geotechnical engineer shall perform all design stability calculations. Ground motion parameters for use in seismic stability analysis may be provided by either an engineering geologist or geotechnical engineer.

1.4 Minimum Qualifications Of The Licensed Professional.

Slope stability analyses must be performed by qualified geologists and qualified geotechnical engineers (see sections 10-12-5 and 10-12-6 of the city of North Salt Lake municipal code).

2.0 General Requirements.

Except for the derivation of the input ground motion for pseudostatic and seismic deformation analyses (see section 12), slope stability analyses and evaluations should be performed in general accordance with the latest version of Recommended Procedures For Implementation Of DMG Special Publication 117, Guidelines For Analyzing And Mitigating Landslide Hazards In California (Blake et al., 2002). In addition to these standards, all slope stability analyses, reports and recommendations shall follow the latest adopted guidelines published by the Utah geological survey. Procedures for developing input ground motions to be used in the city of North Salt Lake are described in section 12.1. See title 10, chapter 12 of the city of North Salt Lake municipal code, sensitive area district & geologic hazards ordinance, for supplemental requirements.

3.0 Submittals.

Submittals for review shall include boring logs; geologic cross sections; trench and test pit logs; laboratory data (particularly shear strength test results, including individual stress-deformation plots from direct shear tests); discussions pertaining to how idealized subsurface conditions and shear strength parameters used for analyses were developed; analytical results, including computer output files (if requested); and summaries of the slope stability analyses and conclusions regarding slope stability.

Subsurface geologic and groundwater conditions must be illustrated on geologic cross sections and must be utilized by the geotechnical engineer for the slope stability analyses. If on-site sewage or storm water disposal exists or is proposed, the slope stability analyses shall include the effects of the effluent plume on slope stability.

The results of any slope stability analyses must be submitted with pertinent backup documentation (i.e., calculations, computer output, etc.). Printouts of input data, output data (if requested), and graphical plots must be submitted for each computer-aided slope stability analysis. In addition, data files, recorded on diskettes, CDs, or other electronic media may be requested to facilitate the city's review.

4.0 Factors Of Safety.

The minimum acceptable static factor of safety is 1.5 for both gross and surficial slope stability. The minimum acceptable factor of safety for a calibrated pseudostatic analysis is 1.0 using the method of Stewart and others (2003) (see section 12.2).

5.0 Landslides.

The evaluation of landslides generally requires quantitative slope stability analyses. Therefore, the standards presented herein are directly applicable to landslide investigation, and also constitute the minimum level of effort when performing landslide investigations. Evaluation of landslides shall be performed in the preliminary phase of hillside developments. Where landslides are present or suspected, sufficient subsurface exploration will be required to determine the basic geometry and stability of the landslide mass and the required stabilization measures. The depth of geologic exploration shall consider the regional geologic structure, the likely failure mode of the suspected failure, and past geomorphic conditions.

6.0 Site Investigation And Geologic Studies.

Adequate evaluation of slope stability for a given site requires thorough and comprehensive geologic and geotechnical engineering studies. These studies are a crucial component in the evaluation of slope stability. Geologic mapping and subsurface exploration are normal parts of field investigation. Samples of earth materials are routinely obtained during subsurface exploration for geotechnical testing in the laboratory to determine the shear strength parameters and other pertinent engineering properties.

In general, geologic studies for slope stability consist of the following fundamental phases:

(a) Study and review of published and unpublished geologic information (both regional and site specific).

(b) Review and interpretation of available stereoscopic and oblique aerial photographs, DEMs, and LiDAR.

(c) Geologic field mapping, including, but not necessarily limited to, measurement of bedding, foliation, fracture, and fault attitudes and other parameters.

(d) Documentation and evaluation of subsurface groundwater conditions (including effects of seasonal and longer-term natural fluctuations as well as landscape irrigation), surface water, on-site sewage disposal, and/or storm water disposal.

(e) Subsurface exploration.

(f) Analysis of the geologic failure mechanisms that could occur at the site (e.g., mode of failure and construction of the critical geologic cross sections).

(g) Presentation and analysis of the data, including an evaluation of the potential impact of geologic conditions on the project.

(h) Installation of piezometers in all borings to define the depth to groundwater. The groundwater regime shall be defined geologically.

Geologic/geotechnical reports shall demonstrate that each of these phases has been adequately performed and that the information obtained has been considered and logically evaluated for quality and applicability to the study. Minimum criteria for the performance of each phase are described and discussed in Blake and others (2002).

7.0 Subsurface Exploration.

The purpose of subsurface exploration is to identify potentially significant geologic materials, structures and hydrologic conditions at a site and to provide samples for detailed laboratory characterization of materials from potentially critical zones. Subsurface exploration is almost always required and may be performed by a number of widely known techniques such as bucket-auger borings, conventional small-diameter borings, cone penetration testing (CPT), test pits, trenches, and/or geophysical techniques (see section 4.2 of Blake et al., 2002). A discussion of the applicability of some subsurface exploration techniques follows.

7.1 Trenching.

Subsurface exploration consisting of trenching has proven, in some cases, to be necessary when uncertainty exists regarding whether or not a particular landform is a landslide. Care must be exercised with this exploration method because landslides characteristically contain relatively large blocks of intact geologic units, which in a trench exposure could give the false impression that the geologic unit is "in-place." Although limited to a depth of about 15 feet below existing grades, trenching has also proven to be a useful technique for verifying margins of landslides, although the geometry of a landslide can generally be readily determined from evaluation of stereoscopic aerial photographs. Once a landslide is identified, conventional subsurface exploration drilling techniques will be required (see section 7.2 and 7.3). Slope stability analyses based solely on data obtained from trenches will not be accepted.

7.2 Methods For Bedded Formations.

Conventional subsurface exploration techniques involving continuous core drilling with an oriented core barrel, test pits, and deep bucket-auger borings may be used to assess the subsurface soil and geologic conditions, particularly for geologic units with inclined bedding that includes weak layers.

Particular attention must be paid to the presence or absence of weak layers (e.g., clay, claystone, silt, shale, or siltstone units) during the exploration. Unless adequately demonstrated (through comprehensive and detailed subsurface exploration) that weak (clay, claystone, silt, shale, or siltstone) layers (even as thin as 1/16-inch or less) are not present, a weak layer shall be assumed to possibly occur anywhere in the stratigraphic profile (i.e., ubiquitous weak clay beds).

The depth of the subsurface exploration must be sufficient to assess the conditions at or below the level of the deepest potential failure surface possessing a factor of 1.5 or less. A preliminary slope stability analysis may need to be performed to assist in the planning of the subsurface exploration program.

7.3 Other Geologic Units.

For alluvium, fill materials, or other soil units that do not contain weak interbeds, other exploration methods such as small-diameter borings (e.g., rotary wash or hollow-stem-auger) or cone penetration testing may be suitable.

8.0 Soil Parameters.

Soil properties, including unit weight and shear strength parameters (cohesion and friction angle), may be based on conventional field and laboratory tests as well as on field performance. Where appropriate (i.e., for landslide slip surfaces, along bedding planes, for surficial stability analyses, etc.), laboratory tests for saturated, residual shear strengths must be performed. Estimation of the shear resistance along bedding (or landslide) planes normally requires an evaluation of saturated residual along-bedding-strength values of the weakest interbedded (or slide-plane) material encountered during the subsurface exploration, or in the absence of sufficient exploration, the weakest material that may be present, consistent with site geologic conditions. Strength parameters derived solely from CPT data may not be appropriate for slope-stability analysis in some cases, particularly for strengths along existing slip surfaces where residual strengths have developed. Additional guidance on the selection of strength parameters for slope stability analyses is contained in Blake et al. (2002).

8.1 Residual Shear Strength Parameters.

Residual strength parameters may be determined using the direct shear or ring shear testing apparatus; however ring shear tests are preferred. If performed properly, direct shear test results may approach ring-shear test results. The soil specimen must be subjected to a sufficient amount of deformation (e.g., a significant number of shearing cycles in the direct shear test or a significant amount of rotation in the ring shear test) to assure that residual strength has been developed. In the direct-shear and ring-shear tests, stress-deformation curves can be used to determine when a sufficient number of cycles of shearing have been performed by showing that no further significant drop in shear strength results with the addition of more cycles or more rotation. The stress-deformation curves obtained during the shear tests must be submitted with the other laboratory test results. It shall be recognized that for most clayey soils, the residual shear strength envelope is curved and passes through the origin (i.e., at zero normal stress there is zero shear strength). Any "apparent shear strength" increases resulting from a non-horizontal shear surface (i.e., ramping) or "bulldozing" in residual direct shear tests shall be discounted in the interpretation of the strength parameters.

8.2 Interpretation.

The consultant will need to use considerable judgment in the selection of appropriate shear test methods and in the interpretation of the results to develop shear strength parameters commensurate with slope stability conditions to be evaluated. Scatter plots of shear strength data may need to be presented to allow for assessment of idealized parameters. The report shall summarize shear strength parameters used for slope stability analyses and describe the methodology used to interpret test results and estimate those parameters.

Peak shear strengths may be used to represent across-bedding failure surfaces or compacted fill, in situations where strength degradations are not expected to occur (see guidelines in Blake et al., 2002). Where peak strengths cannot be relied upon, fully softened (or lower) strengths shall be used.

Ultimate shear strength parameters shall be used in static slope stability analyses when there has not been past deformation. Residual shear strength parameters shall be used in static slope stability analyses when there has been past deformation.

Averaged strength parameters may be appropriate for some across-bedding conditions, if sufficient representative samples have been carefully tested. Analyses for along-bedding or along-existing-landslide slip surfaces shall be based on lower-bound interpretations of residual shear strength parameters and comparison of those results to correlations, such as those of Stark and others (2005).

8.3 Default Soil Parameters.

Failure surfaces for known landslides commonly occur within Tertiary volcanics. Those failure surfaces typically are along clay layers formed by the in situ alteration of volcanic tuff deposits. In cases when the failure surface has been sampled and tested, relatively low residual-shear-strength values have been obtained; these values are cohesion equal to 0 psf and a friction angles equal to 11 to 12 degrees.

To assist in understanding shear strengths of these materials, the following shear strength parameters for landslide failure surfaces and along weak layers within the Tertiary volcanics shall be used; cohesion equal to 0 psf and a friction angle equal to 11 degrees, unless otherwise demonstrated. Similar values have been reported from the Springhill landslide in North Salt Lake that is in a similar tuffaceous volcanic formation of Tertiary age. If site-specific testing produces lower residual shear strength than these values, the site-specific test results should be used. If site-specific testing produces higher values, documentation must be provided to demonstrate that the weakest materials were retrieved and tested and that the materials retrieved truly represent the basal landslide slip surface.

9.0 Soil Creep.

The potential effects of soil creep shall be addressed where any proposed structure is planned in close proximity to an existing fill slope or natural slope. The potential effects on the proposed development shall be evaluated and mitigation measures proposed, including appropriate setback recommendations. Setback recommendations shall consider the potential effects of creep forces.

All reports in hillside areas shall address the potential for surficial instability, and soil creep on all slopes that may affect the proposed development or be affected by the proposed development. Stability of slopes along planned or existing access roads shall be addressed.

10.0 Gross Static Stability.

Gross stability includes rotational and translational deep-seated failures of slopes or portions of slopes existing within or outside of but potentially affecting the proposed development. The following guidelines, in addition to those in the Blake and others (2002) document, shall be followed when evaluating slope stability:

(a) Stability shall be analyzed along cross sections depicting the most adverse conditions (e.g., highest slope, most adverse bedding planes, shallowest likely ground water table, and steepest slope). Often analyses are required for different conditions and for more than one cross section to demonstrate which condition is most adverse. When evaluating the stability of an existing landslide, analyses must also address the potential for partial reactivation. Inclinometers may be used to help determine critical failure surfaces and, along with high-resolution GPS, the state of activity of existing landslides. The critical failure surfaces on each cross-section shall be identified, evaluated, and plotted on the large-scale cross section.

(b) If the long-term, static factor of safety is less than 1.5, mitigation measures will be required to bring the factor of safety up to the required level or the project may be redesigned to achieve a minimum factor of safety of 1.5.

(c) The temporary stability of excavations shall be evaluated and mitigation measures shall be recommended as necessary to obtain a minimum factor of safety of 1.3.

(d) Long-term stability shall be analyzed using the highest known or anticipated groundwater level based upon a groundwater assessment performed under the requirements of section 6.0.

(e) Where back-calculation is appropriate, shear strengths utilized for design shall be no higher than the lowest strength computed using back calculation. If a consultant proposes to use shear strengths higher than the lowest back-calculated value, justification shall be required. Assumptions used in back-calculations regarding pre-sliding topography and groundwater conditions at failure must be discussed and justified.

(f) Reports shall describe how the shear strength testing methods used are appropriate in modeling field conditions and long-term performance of the subject slope. The utilized design shear strength values shall be justified with laboratory test data and geologic descriptions and history, along with past performance history, if available, of similar materials.

(g) Reports shall include shear strength test plots consisting of normal stress versus shear resistance (failure envelope). Plots of shear resistance versus displacement shall be provided for all residual and fully softened (ultimate) shear tests.

(h) The degree of saturation for all test specimens shall be reported. Direct shear tests on partially saturated samples may grossly overestimate the cohesion that can be mobilized when the material becomes saturated in the field. This potential shall be considered when selecting shear strength parameters. If the rate of shear displacement exceeds 0.005 inches per minute, the consultant shall provide data to demonstrate that the rate is sufficiently slow for drained conditions.

(i) Shear strength values higher than those obtained through site-specific laboratory tests generally will not be accepted.

(j) If direct shear or triaxial shear testing is not appropriate to model the strength of highly jointed and fractured rock masses, the design strengths shall be evaluated in a manner that considers overall rock mass quality and be consistent with rock mechanics practice.

(k) Shear strengths used in slope stability analyses shall be evaluated considering the natural variability of engineering characteristics inherent in earth materials. Multiple shear tests on each site material are likely to be required.

(l) Direct shear tests do not always provide realistic strength values (Watry and Lade, 2000). Correlations between liquid limit, percent clay fraction, and strength (fully softened and residual) with published data (e.g., Stark and McCone, 2002) shall be performed to verify tested shear strength parameters. Strength values used in analyses that exceed those obtained by the correlation must be appropriately justified.

(m) Shear strengths for proposed fill slopes shall be evaluated using samples mixed and remolded to represent anticipated field conditions. Confirming strength testing may be required during grading.

(n) Where bedding planes are laterally unsupported on slopes, potential failures along the unsupported bedding planes shall be analyzed. Similarly, stability analyses shall be performed where bedding planes form a dip-slope or near-dip-slope using composite potential failure surfaces that consist of potential slip surfaces along bedding planes in the upper portions of the slope in combination with slip surfaces across bedding planes in the lower portions of the slope.

(o) The stability analysis shall include the effect of expected maximum moisture conditions on soil unit weight.

(p) For effective stress analyses, measured groundwater conditions must be adjusted to consider likely unfavorable conditions with respect to anticipated future groundwater levels, seepage, or pore pressure and included in the slope stability analyses.

(q) Tension crack development shall be considered in the analyses of potential failure surfaces. The height and location of the tension crack shall be determined by searching.

(r) Anticipated surcharge loads as well as external boundary pressures from water shall be included in the slope stability evaluations, as deemed appropriate.

(s) Analytical chart solutions may be used provided they were developed for conditions similar to those being analyzed. Generally though, computer-aided searching techniques shall be used, so that the potential failure surface with the lowest factor of safety can be located. Examples of typical searching techniques are illustrated on figures 9.1a through 9.1f in Blake and others (2002). However, verification of the reasonableness of the analytical results is the responsibility of the geotechnical engineer and/or engineering geologist.

(t) The critical potential failure surface used in the analysis may be composed of circles, wedges, planes, or other shapes considered to yield the minimum factor of safety most appropriate for the geologic site conditions. The critical potential failure surface having the lowest factor of safety with respect to shearing resistance must be sought. Both the lowest factor of safety and the critical failure surface shall be documented.

11.0 Surficial Stability Of Slopes.

Surficial slope stability refers to slumping and sliding of near-surface sediments and is most critical during the snowmelt and rainy season or when excessive landscape water is applied. The assessment of surficial slope stability shall be based on analysis procedures for stability of an infinite slope with seepage parallel to the slope surface or an alternate failure mode that would produce the minimum factor of safety. The minimum acceptable depth of saturation for surficial stability evaluation shall be four feet.

11.1 Applicability And Procedures.

Conclusions shall be substantiated with appropriate data and analyses. Residual shear strengths comparable to actual field conditions shall be used in completing surficial stability analyses. Surficial stability analyses shall be performed under rapid draw-down conditions where appropriate (e.g., for debris and detention basins).

Where 2:1 or steeper slopes have soil conditions that can result in the development of an infinite slope with parallel seepage, calculations shall be performed to demonstrate that the slope has a minimum static factor of safety of 1.5, assuming a fully saturated 4-foot thickness. If conditions will not allow the development of a slope with parallel seepage, surficial slope stability analyses may not be required (provided the geologic/geotechnical reviewer concurs).

Surficial slope stability analyses shall be performed for fill, cut, and natural slopes assuming an infinite slope with seepage parallel to the slope surface or other failure mode that would yield the minimum factor of safety against failure. A suggested procedure for evaluating surficial slope stability is presented in Blake et al. (2002).

11.2 Soil Properties.

Soil properties used in surficial stability analyses shall be determined as noted in section 8.1. Residual shear strength parameters for surficial slope stability analyses shall be developed for a stress range that is consistent with the near-surface conditions being modeled. As indicated in section 8.1, it shall be recognized that for most clayey soils, the residual shear strength envelope is curved and passes through the origin (i.e., at zero normal stress there is zero shear strength). For sites with deep slip surfaces, the guidelines given by Blake and others (2002) should be followed.

11.3 Seepage Conditions.

The minimum acceptable vertical depth for which seepage parallel to the slope shall be applied is four feet for cut or fill slopes. Greater depths may be necessary when analyzing natural slopes that have significant thicknesses of loose surficial material.

12.0 Seismic Slope Stability.

In addition to static slope stability analyses, slopes shall be evaluated for seismic slope stability as well. Acceptable methods for evaluating seismic slope stability using calibrated pseudo-static limit-equilibrium procedures and simplified methods (e.g., those based on Newmark, 1965) to estimate permanent seismic slope movements are summarized in Blake and others (2002) also Bray, J.D. and Travasarou, T. (2007) "Simplified Procedure For Estimating Earthquake Induced Deviatoric Slope Displacements" Journal Of Geotechnical And Geoenvironmental Engineering, April 2007, vol. 133, no. 4, pp. 381-392.

Nonlinear, dynamic finite element/finite difference numerical methods also may be used to evaluate slope movements resulting from seismic events as long as the procedures, input data, and results are thoroughly documented, and deemed acceptable by the city.

12.1 Ground Motion For Pseudostatic And Seismic Deformation Analyses.

In regards to defining ground accelerations for seismic slope-stability analyses, the city of North Salt Lake prefers a probabilistic approach to determining the likelihood that different levels of ground motion will be exceeded at a particular site within a given time period. In order to more closely represent the seismic characteristics of the WFZ and better capture this possible high likelihood of a surface-faulting earthquake, design ground motion parameters for seismic slope stability analyses shall be based on the peak accelerations with a 3.5 percent probability in 50 years (1,400-year recurrence interval). Peak bedrock ground motions can be readily obtained via the internet from the United States geological survey (USGS) national seismic hazard maps, data and documentation web page (USGS, 2002), which is based on Frankel and others (2002). PGAs obtained from the USGS (2002) web page should be adjusted for effects of soil/rock (site-class) conditions in accordance with Seed and others (2001). Site specific response analysis may also be used to develop PGA values as long as the procedures, input data, and results are thoroughly documented, and deemed acceptable by the city.

12.2 Pseudo-Static Evaluations.

Pseudo-static methods for evaluating seismic slope stability are acceptable as long as minimum factors of safety are satisfied, and due consideration is given in the selection of the seismic coefficient, kh, reduction in material shear strengths, and the factor of safety for pseudo-static conditions.

Pseudo-static seismic slope stability analyses can be performed using the "screening analysis" procedure described in Blake et al. (2002). For that procedure a kh-value is selected from seismic source characteristics (modal magnitude, modal distance, and firm rock peak ground acceleration) and an acceptable level of deformation (5 cm) is specified. For that procedure, a factor of safety of 1.0 or greater is considered acceptable; otherwise, an analysis of permanent seismic slope deformation shall be performed.

12.3 Permanent Seismic Slope Deformation.

For seismic slope stability analyses, estimates of permanent seismic displacement are preferred and may be performed using the procedures outlined in Blake and others (2002). It should be noted that Bray and Rathje (1998), referenced in Blake and others (2002), has been updated and superseded by Bray and Travasarou (2007), which is the city's currently preferred method. For those analyses, calculated seismic displacements shall be 5 cm or less, or mitigation measures shall be proposed to limit calculated displacements to 5 cm or less.

For specific projects, different levels of tolerable displacement may be possible, but site-specific conditions, which shall include the following, must be considered:

(a) The extent to which the displacements are localized or broadly distributed - broadly distributed shear deformations would generally be less damaging and more displacement could be allowed.

(b) The displacement tolerance of the foundation system - stiff, well-reinforced foundations with lateral continuity of vertical support elements would be more resistant to damage (and hence could potentially tolerate larger displacements) than typical slabs-on-grade or foundation systems with individual spread footings.

(c) The potential of the foundation soils to experience strain softening - slopes composed of soils likely to experience strain softening should be designed for relatively low displacements if peak strengths are used in the evaluation of ky due to the potential for progressive failure, which could involve very large displacements following strain softening.

In order to consider a threshold larger than 5 cm, the project consultant shall provide prior, acceptable justification to the city and obtain the city's approval. Such justification shall demonstrate, to the satisfaction of the city, that the proposed project will achieve acceptable performance.

13.0 Water Retention Basins And Flood Control Channels.

For cut, fill, or natural slopes containing or proposed to contain water-retention basins or flood-control channels, slope stability analyses shall be performed. In addition to analyzing typical static and seismic slope stability, those analyses shall consider the effects of rapid drawdown, if such a condition could develop.

14.0 Mitigation.

When slope stability hazards are determined to exist on a project, measures to mitigate impacts from those hazards shall be implemented. Some guidance regarding mitigation measures is provided in Blake et al. (2002). Slope stability mitigation methods include 1) hazard avoidance, 2) grading to improve slope stability, 3) reinforcement of the slope or improvement of the soil within the slope, and 4) reinforcement of the structure built on the slope to tolerate anticipated slope displacements.

Where mitigation measures that are intended to add stabilizing forces to the slope are to be implemented, consideration may need to be given to strain compatibility. For example, if a compacted fill buttress is proposed to stabilize laterally unsupported bedding or a landslide, the amount of deformation needed to mobilize the recommended shear strength in the buttress shall be considered to confirm that it will not result in adverse movements of the upslope bedding or landslide deposits. Similarly, if a series of drilled soldier piers is to be used to support a potentially unstable slope and a residential structure will be built on the piers, pier deformations resulting from movements needed to mobilize the soil's shear strength shall be compared to tolerable deflections in the supported structure.

14.1 Full Mitigation.

Full mitigation of slope stability hazards shall be performed for developments in the city, except as defined in section 14.2. Remedial measures that produce static factors of safety in excess of 1.5 and acceptable seismic displacement estimates shall be implemented as needed.

14.2 Partial Mitigation For Seismic Displacement Hazards.

On some projects or portions thereof (such as small structural additions, residential "infill projects", non-habitable structures, and non-structural natural-slope areas), full mitigation of seismic slope displacements may not be possible, due to physical or economic constraints. In those cases, partial mitigation, to the extent that it prevents structural collapse, injury, and loss of life, may be possible if it can be provided consistent with IBC philosophies, and if it is approved by the city of North Salt Lake. The applicability of partial mitigations to specific projects will be evaluated on a case-by-case basis.

15.0 Notice Of Geologic Hazard And Waiver Of Liability.

For developments where full mitigation of seismic slope displacements is not implemented, a notice of geologic hazard shall be recorded with the proposed development describing the displacement hazard at issue and the partial mitigation employed. The notice shall clearly state that the seismic displacement hazard at the site has been reduced by the partial mitigation, but not totally eliminated.

In addition, the owner shall assume all risks, waive all claims against the city and its consultants, and indemnify and hold the city and its consultants harmless from any and all claims arising from the partial mitigation of the seismic displacement hazard.
(Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318823
10-12-33-3: APPENDIX C, MINIMUM STANDARDS FOR LIQUEFACTION INVESTIGATIONS AND EVALUATIONS:linklink

1.0 Introduction.

The procedures and standards outlined herein are intended to provide consultants with a general outline for performing liquefaction investigations and to specify the expectations of the city of North Salt Lake. The standards constitute the minimum level of effort required in conducting liquefaction investigations in the city. Considering the complexity inherent in performing liquefaction investigations, additional effort beyond the minimum standards presented herein may be required at some sites to adequately address liquefaction potential at the site. The information presented herein does not relieve consultants of their duty to perform additional geologic or geotechnical engineering analyses they believe are necessary to adequately assess the liquefaction potential at a site.

The purpose of establishing minimum standards for liquefaction investigations is to:

(a) Protect the health, safety, welfare, and property of the public by minimizing the potentially adverse effects of liquefaction and related hazards;

(b) Assist property owners and land developers in conducting reasonable and adequate studies;

(c) Provide consulting geologists and geotechnical engineers with a common basis for preparing proposals, conducting investigations, and mitigation; and,

(d) Provide an objective framework for regulatory review of liquefaction investigation reports.

1.1 Properties Requiring Liquefaction Analyses.

(Figure 1.1)

































Figure 1.1 depicts generalized liquefaction susceptibility for the city, and shall be used to determine whether or not a site-specific liquefaction assessment is required for a particular project.

The liquefaction-potential map is based on a regional-scale investigation of Davis County. These maps may not identify all areas that have potential for liquefaction; a site located outside of a zone of required investigation is not necessarily free from liquefaction hazard. The zone does not always include lateral spread run-out areas. The liquefaction-potential map for Davis County, UT complete technical report is available from the Davis County community development department.

Title 10, chapter 12 of the city of North Salt Lake municipal code, sensitive area district & geologic hazards ordinance requires a site-specific liquefaction investigation to be performed prior to approval of a project based on the land-use/liquefaction potential matrix shown in the following table.

Type Of Facility   High Potential
Liquefaction
Area  
Acceptable
Factor
Of Safety  
Critical facilities (essential facilities, hazardous facilities, and special occupancy structures) as defined in section 10-12-2 of the city of North Salt Lake municipal code   Yes   1.3  
Category III and IV in table 1604.58 of the most recently adopted edition of the IBC   Yes   1.3  
Industrial and commercial buildings   Yes   1.25  
Residential structures and subdivisions   No    

1.2 Roles Of Engineering Geology And Geotechnical Engineering.

The investigation of liquefaction hazard is an interdisciplinary practice. The site investigation report must be prepared by a qualified geologist or geotechnical engineer, who must have competence in the field of seismic hazard evaluation and mitigation, and be reviewed by a qualified geologist and geotechnical engineer, also competent in the field of seismic hazard evaluation and mitigation.

Because of the differing expertise and abilities of qualified geologists and geotechnical engineers, the scope of the site investigation report for the project may require that both types of professionals prepare and review the report, each practicing in the area of their expertise. Involvement of both a qualified geologist and geotechnical engineer will generally provide greater assurance that the hazard is properly identified, assessed, and mitigated.

Liquefaction analyses are the responsibility of the geotechnical engineer, although the geologist should be involved in the application of screening criteria (section 3.0, steps 1 and 2) and general geologic site evaluation (section 4.1) to map the likely extent of liquefiable deposits and shallow groundwater. Engineering properties of earth material shall be evaluated by the geotechnical engineer. The performance of the quantitative liquefaction analysis resulting in a numerical factor of safety and quantitative assessment of settlement and liquefaction-induced permanent ground displacement shall be performed by geotechnical engineers.

The geotechnical and civil engineers shall develop all mitigation and design recommendations. Ground motion parameters for use in quantitative liquefaction analyses may be provided by either the geologist or geotechnical engineer.

1.3 Minimum Qualifications Of The Licensed Professional.

Liquefaction analyses must be performed by qualified geologists and qualified geotechnical engineers (see sections 10-12-5 and 10-12-6 of the city of North Salt Lake municipal code).

2.0 General Requirements.

Except for the derivation of input ground motion (see section 5.0), liquefaction investigations should be performed in general accordance with the latest version of Recommended Procedures For Implementation Of DMG Special Publication 117, Guidelines For Analyzing And Mitigating Liquefaction In California (Martin and Lew, 1999). Additional protocol for liquefaction investigations is provided in Youd and Idriss (1997). In addition to these standards, all liquefaction analyses, reports and recommendations shall follow the latest adopted guidelines published by the Utah geological survey. See title 10, chapter 12 of the city of North Salt Lake municipal code, sensitive area district & geologic hazards ordinance for supplemental requirements. Acceptable factors of safety are shown on the table in section 1.2.

3.0 Preliminary Screening For Liquefaction.

The liquefaction study area map is based on broad regional studies and does not replace site-specific studies. The fact that a site is located within a liquefaction study area does not mean that there is a significant liquefaction potential at the site, only that a study shall be performed to determine if there is.

Soil liquefaction is caused by strong seismic ground shaking where saturated, cohesionless, granular soil undergoes a significant loss in shear strength that can result in settlement and permanent ground displacement. Surface effects of liquefaction include: settlement, bearing capacity failure, ground oscillations, lateral spread and flow failure. It has been well documented that soil liquefaction may occur in clean sands, silty sands, and sandy silt, non-plastic silts and gravelly soils. The following conditions must be present for liquefaction to occur:

(a) Soils must be submerged below the water table;

(b) Soils must be loose to moderately dense;

(c) Ground shaking must be relatively intense; and

(d) The duration of ground shaking must be sufficient for the soils to generate seismically-induced excess pore water pressure and lose their shearing resistance.

The following screening criteria may be applied to determine if further quantitative evaluation of liquefaction hazard is required:

(a) If the estimated maximum past-, current-, and maximum-future-groundwater-levels (i.e., the highest groundwater level applicable for liquefaction analyses) are determined to be deeper than 50 feet below the existing ground surface or proposed finished grade (whichever is deeper), liquefaction assessments are not required. For soil materials that are located above the level of the groundwater, a quantitative assessment of seismically induced settlement is required.

(b) If "bedrock" or similar lithified formational material underlies the site, those materials need not be considered liquefiable and no analysis of their liquefaction potential is necessary.

(c) If the corrected standard penetration blow count, (N1)60, is greater than or equal to 33 in all samples with a sufficient number of tests, liquefaction assessments are not required. If cone penetration test soundings are made, the corrected cone penetration test tip resistance, qc1N, should be greater than or equal to 180 in all soundings in sand materials, otherwise liquefaction assessments are needed. All SPT measurements shall be made with calibrated hammers, where the hammer efficiency is known, and values can be adjusted to (N1)60 for calculations, as needed.

If plastic soil (PI . 20) materials are encountered during site exploration, those materials may be considered non-liquefiable. Additional acceptable screening criteria regarding the effects of plasticity on liquefaction susceptibility are presented in Boulanger and Idriss (2004), Bray and Sancio (2006), and Seed and others (2003).

If the screening investigation clearly demonstrates the absence of liquefaction hazards at a project site and the city concurs, the screening investigation will satisfy the site investigation report requirement for liquefaction hazards. If not, a quantitative evaluation is required to assess the liquefaction hazards.

4.0 Field Investigations.

Geotechnical field investigations are routinely performed for new projects as part of the normal development and design process. Geologic reconnaissance and subsurface explorations are normally performed as part of the field exploration program even when liquefaction does not need to be investigated.

4.1 Geologic Reconnaissance.

Geologic research and reconnaissance are important to provide information to define the extent of unconsolidated deposits that may be prone to liquefaction. Such information should be presented on geologic maps and cross sections and provide a description of the formations present at the site that includes the nature, thickness, and origin of Quaternary deposits with liquefaction potential. There also should be an analysis of groundwater conditions at the site that includes the highest recorded water level and the highest water level likely to occur under the most adverse foreseeable conditions in the future. Shallow groundwater may exist for a variety of reasons, some of which are of natural and or manmade origin. Landscape irrigation, on-site sewage disposal, and unlined manmade lakes reservoirs, and storm-water detention basins may create a shallow groundwater table in sediments that were previously unsaturated.

During the field investigation, the geologist should map the limits of unconsolidated deposits with liquefaction potential. Liquefaction typically occurs in cohesionless silt, sand, and fine-grained gravel deposits of Holocene to late Pleistocene age in areas where groundwater is shallower than about 50 feet.

4.2 Subsurface Explorations.

Subsurface explorations shall consist of drilled-borings and/or cone penetration tests (CPTs). The exploration program shall be planned to determine the soil stratigraphy, groundwater level, and indices that could be used to evaluate the potential for liquefaction by either in situ testing or by laboratory testing of soil samples. Borings and CPT soundings must penetrate a minimum of 50 feet below final ground surface. If a standard penetration test (SPT) is used, sampling intervals shall not exceed 2.5 feet.

For saturated cohesionless soils where the SPT (N1)60 values are less than 15, or where CPT tip resistances are below 60 tsf, grain-size analyses, hydrometer tests, and Atterberg Limits tests shall be performed on these soils to further evaluate their potential for permanent ground displacement (Youd et al., 2002) and other forms of liquefaction-induced ground failure and settlement.

Where a structure may have subterranean construction or deep foundations (e.g., caissons or piles), the depth of investigation should extend to a depth that is a minimum of 20 feet (6 m) below the lowest expected foundation level (e.g., caisson bottom or pile tip) or 50 feet (15 m) below the existing ground surface or lowest proposed finished grade, whichever is deeper. If, during the investigation, the indices to evaluate liquefaction indicate that the liquefaction potential may extend below that depth, the exploration should be continued until a significant thickness (at least 10 feet or 3 m, to the extent possible) of nonliquefiable soils are encountered.

5.0 Ground Motion For Liquefaction Susceptibility And Ground Deformation Analyses.

In regards to design ground accelerations for liquefaction analyses, the city of North Salt Lake prefers a probabilistic approach to determining the likelihood that different levels of ground motion will be exceeded at a particular site within a given time period. In order to more closely represent the seismic characteristics of the WFZ and better capture this possible high likelihood of a surface-faulting earthquake on the Salt Lake City segment, design ground motion parameters for liquefaction analyses shall be based on the peak accelerations with a 3.5 percent probability in 50 years (1,400-year recurrence interval). Peak bedrock ground motions can be readily obtained via the internet from the United States geological survey (USGS) national seismic hazard maps, data and documentation web page (USGS, 2002), which is based on Frankel and others (2002). PGAs obtained from the USGS (2002) web page should be adjusted for effects of soil/rock (site-class) conditions in accordance with Seed and others (2001) or other appropriate methods that consider the site-specific soil conditions and their potential for amplification/deamplification of the high frequency strong motion.

6.0 Remedial Design.

Sites, facilities, buildings, structures and utilities that are founded on or traverse liquefiable soils may require further remedial design and/or relocation to avoid liquefaction-induced damage. These should be investigated and evaluated on a site-specific basis with sufficient geologic and geotechnical evaluations to support the remedial design or mitigative plan. This design or plan may include: changes/modifications to the soil, foundation system, structural frame or support of the building, etc. and shall be reviewed and approved by the city.

7.0 Submittals.

Submittals for review shall include: boring logs; geologic cross-sections; laboratory data; discussions pertaining to how idealized subsurface conditions and parameters used for analyses were developed; analytical results, including computer output files (on request); and summaries of the liquefaction analyses and conclusions regarding liquefaction potential and likely types and amounts of ground failure.

Subsurface geologic and groundwater conditions must be illustrated on geologic cross-sections and must be utilized by the geotechnical engineer for the liquefaction analyses. If on-site sewage or storm-water disposal exists or is proposed, the liquefaction analyses shall include the effects of the effluent plume on liquefaction potential.

The results of any liquefaction analyses must be submitted with pertinent backup documentation (i.e., calculations, computer output, etc.). Printouts of input data, output data (on request), and graphical plots must be submitted for each computer-aided liquefaction analysis. In addition, data files, recorded on diskettes, CDs, or other electronic media, may be requested to facilitate the city's review.
(Ord. 2015-16, 10-20-2015)
http://sterlingcodifiers.com/codebook/index.php?book_id=&chapter_id=75308#s1318824