Section 1803A — GEOTECHNICAL INVESTIGATIONS

1803 A .1 General. Geotechnical investigations shall be conducted in accordance with Section 1803 A .2 and reported in accordance with Section 1803A.7. The classification and investigation of the soil shall be made under the responsible charge of a California regis- tered geotechnical engineer. All recommendations contained in geotechnical and geohazard reports shall be subject to the approval of the enforcement agency. All reports shall be prepared and signed by a registered geotechnical engineer, a certified engineering geolo- gist and a registered geophysicist, where applicable.

1803 A .2 Investigations required. Geotechnical investigations shall be conducted in accordance with Sections 1803 A .3 through

Exception s : 1. Geotechnical reports are not required for one-story, wood-frame and light-steel-frame buildings of Type II or Type V construction and 4,000 square feet (371 m [2] ) or less in floor area, not located within Earthquake Fault Zones or Seismic Hazard Zones as shown in the most recently published maps from the California Geological Survey (CGS) or in seismic hazard zones as defined in the Safety Element of the local General Plan. Allowable foundation and lateral soil pressure values may be determined from Table 1806A.2.

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2. A previous report for a specific site may be resubmitted, provided that a reevaluation is made and the report is found to be currently appropriate.

1803 A .3 Basis of investigation. Soil classification shall be based on observation and any necessary tests of the materials disclosed by borings, test pits or other subsurface exploration made in appropriate locations. Additional studies shall be made as necessary to evaluate slope stability, soil strength, position and adequacy of load-bearing soils, the effect of moisture variation on soil-bearing capacity, compressibility, liquefaction and expansiveness.

1803 A .3.1 Scope of investigation. The scope of the geotechnical investigation including the number and types of borings or soundings, the equipment used to drill or sample, the in-situ testing equipment and the laboratory testing program shall be determined by a registered design professional. There shall not be less than one boring or exploration shaft for each 5,000 square feet (465 m [2] ) of building area at the foundation level with a minimum of two provided for any one building. A boring may be considered to reflect subsurface conditions relevant to more than one building, subject to the approval of the enforcement agency.

Borings shall be of sufficient size to permit visual examination of the soil in place or, in lieu thereof, cores shall be taken.

Borings shall be of sufficient depth and size to adequately characterize sub-surface conditions.

1803 A .4 Qualified representative. The investigation procedure and apparatus shall be in accordance with generally accepted engineering practice. The registered design professional shall have a fully qualified representative on site during all boring or sampling operations.

1803 A .5 Investigated conditions. Geotechnical investigations shall be conducted as indicated in Sections 1803 A .5.1 through 1803 A .5.12.

1803 A .5.1 Classification. Soil materials shall be classified in accordance with ASTM D2487. Rock shall be classified in accordance

with ASTM D5878.

1803 A .5.2 Questionable soil and rock. Where the classification, strength, moisture sensitivity or compressibility of the soil or rock is in doubt or where a load-bearing value superior to that specified in this code is claimed, the building official shall be permitted to require that a geotechnical investigation be conducted.

1803 A .5.3 Expansive soil. In areas likely to have expansive soil, the building official shall require soil tests to determine where such soils do exist.

Soils meeting all four of the following provisions shall be considered to be expansive, except that tests to show compliance with Items 1, 2 and 3 shall not be required if the test prescribed in Item 4 is conducted:

1. Plasticity index (PI) of 15 or greater, determined in accordance with ASTM D4318.

2. More than 10 percent of the soil particles pass a No.200 sieve (75 µm), determined in accordance with ASTM D6913.

3. More than 10 percent of the soil particles are less than 5 micrometers in size, determined in accordance with ASTM D6913.

4. Expansion index greater than 20, determined in accordance with ASTM D4829.

1803 A .5.4 Groundwater. A geotechnical investigation shall be performed to determine if:

1. Groundwater is above or within 5 feet (1524 mm) below the elevation of the lowest floor level where such floor is located below the finished ground level adjacent to the foundation.
2. The groundwater depth will affect the design and construction of buildings and structures.

1803 A .5.5 Deep foundations. Where deep foundations will be used, a geotechnical investigation shall be conducted and shall include all of the following, unless sufficient data on which to base the design and installation is otherwise available:

1. Recommended deep foundation types and installed capacities.
2. Recommended center-to-center spacing of deep foundation elements.
3. Driving criteria.
4. Installation procedures.
5. Field inspection and reporting procedures (to include procedures for verification of the installed bearing capacity where required).
6. Load test requirements.
7. Suitability of deep foundation materials for the intended environment.
8. Designation of bearing stratum or strata.
9. Reductions for group action, where necessary.

1803 A .5.6 Rock strata. Where foundations are to be constructed on or in rock, the geotechnical investigation shall assess variations in rock strata depth, competency and load-bearing capacity.

1803 A .5.7 Excavation near foundations. Where excavation will reduce support from any foundation, a registered design professional shall prepare an assessment of the structure as determined from examination of the structure, available design documents, available subsurface data, and, if necessary, excavation of test pits. The registered design professional shall determine the requirements for support and protection of any existing foundation and prepare site-specific plans, details and sequence of work

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for submission. Such support shall be provided by under-pinning, bracing, excavation retention systems or by other means acceptable to the building official.

1803 A .5.8 Compacted fill material. Where shallow foundations will bear on compacted fill material more than 12 inches (305 mm) in depth, a geotechnical investigation shall be conducted and shall include all of the following:

1. Specifications for the preparation of the site prior to placement of compacted fill material.

2. Specifications for material to be used as compacted fill.

3. Test methods to be used to determine the maximum dry density and optimum moisture content of the material to be used as compacted fill.

4. Maximum allowable thickness of each lift of compacted fill material.

5. Field test method for determining the in-place dry density of the compacted fill.

6. Minimum acceptable in-place dry density expressed as a percentage of the maximum dry density determined in accordance with Item 3.

7. Number and frequency of field tests required to determine compliance with Item 6.

1803 A .5.9 Controlled low-strength material (CLSM). Where shallow foundations will bear on controlled low-strength material (CLSM), a geotechnical investigation shall be conducted and shall include all of the following:

1. Specifications for the preparation of the site prior to placement of the CLSM.
2. Specifications for the CLSM.
3. Laboratory or field test method(s) to be used to determine the compressive strength or bearing capacity of the CLSM.
4. Test methods for determining the acceptance of the CLSM in the field.
5. Number and frequency of field tests required to determine compliance with Item 4.

1803 A .5.10 Alternate setback and clearance. Where setbacks or clearances other than those required in Section 1808 A .7 are desired, the building official shall be permitted to require a geotechnical investigation by a registered design professional to demonstrate that the intent of Section 1808 A .7 would be satisfied. Such an investigation shall include consideration of material, height of slope, slope gradient, load intensity and erosion characteristics of slope material.

1803 A .5.11 Seismic Design Categories C through F. For structures assigned to Seismic Design Category C, D, E or F, a geotechnical investigation shall be conducted, and shall include an evaluation of all of the following potential geologic and seismic hazards:

1. Slope instability.

2. Liquefaction.

3. Total and differential settlement.

4. Surface displacement due to faulting or seismically induced lateral spreading or lateral flow.

1803 A .5.12 Seismic Design Categories D through F. For structures assigned to Seismic Design Category D, E or F, the geotechnical investigation required by Section 1803 A .5.11 shall include all of the following as applicable:

1. The determination of dynamic seismic lateral earth pressures on foundation walls and retaining walls supporting more than 6 feet (1.83 m) of backfill height due to design earthquake ground motions.
2. The potential for liquefaction and soil strength loss evaluated for site peak ground acceleration, earthquake magnitude and source characteristics consistent with the maximum considered earthquake ground motions. Peak ground acceleration shall be determined based on one of the following: 2.1. A site-specific study in accordance with Chapter 21 of ASCE 7.

2.2. In accordance with Section 11.8.3 of ASCE 7.

3. An assessment of potential consequences of liquefaction and soil strength loss including, but not limited to, the following:

3.1. Estimation of total and differential settlement.

3.2. Lateral soil movement.

3.3. Lateral soil loads on foundations.

3.4. Reduction in foundation soil-bearing capacity and lateral soil reaction. 3.5. Soil downdrag and reduction in axial and lateral soil reaction for pile foundations. 3.6. Increases in soil lateral pressures on retaining walls.

3.7. Flotation of buried structures.

4. Discussion of mitigation measures such as, but not limited to, the following: 4.1. Selection of appropriate foundation type and depths. 4.2. Selection of appropriate structural systems to accommodate anticipated displacements and forces.

4.3. Ground stabilization.

4.4. Any combination of these measures and how they shall be considered in the design of the structure.

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Geohazard reports shall be required for all proposed construction.

Exceptions: 1. Reports are not required for one-story, wood-frame and light-steel-frame buildings of Type II or Type V construction and 4,000 square feet (371 m [2] ) or less in floor area, not located within Earthquake Fault Zones or Seismic Hazard Zones as shown in the most recently published maps from the California Geological Survey (CGS) or in seismic hazard zones as defined in the Safety Element of the local General Plan. 2. Reports are not required for the following scopes of work in existing buildings: nonstructural alterations, voluntary struc- tural alterations without foundation work, or structural repairs for damage not caused by an earthquake. [OSHPD 1 & 4] Incidental structural additions or alterations.

3. A previous report for a specific site may be resubmitted, provided that a reevaluation is made and the report is found to be currently appropriate.

The purpose of the geohazard report shall be to identify geologic and seismic conditions that may require project mitigations. The reports shall contain data which provide an assessment of the nature of the site and potential for earthquake damage based on appro- priate investigations of the regional and site geology, project foundation conditions and the potential seismic shaking at the site. The report shall be prepared by a California-certified engineering geologist in consultation with a California-registered geotechnical engineer.

The preparation of the geohazard report shall consider the most recent CGS Note 48; Checklist for the Review of Engineering Geology and Seismology Reports for California Public School, Hospitals and Essential Services Buildings. In addition, the most recent version of CGS Special Publication 42: Earthquake Fault Zones, A Guide for Government Agencies, Property Owners / Developers, and Geoscience Practitioners for Assessing Fault Rupture Hazards in California, shall be considered for project sites proposed within an Alquist-Priolo Earthquake Fault Zone. The most recent version of CGS Special Publication 117, Guidelines for Evaluating and Mitigating Seismic Hazards in California, shall be considered for project sites proposed within a Seismic Hazard Zone. All conclusions shall be fully supported by satisfactory data and analysis.

In addition to requirements in Sections 1803A.5.11 and 1803A.5.12, the report shall include, but need not be limited to, the following: 1. Site geology. 2. Evaluation of the known active and potentially active faults, both regional and local. 3. Ground-motion parameters, as required by Sections 1613A and 1617A, and ASCE 7.

Where geotechnical investigations are required, a written report of the investigations shall be submitted to the building official by the permit applicant at the time of permit application. The geotechnical report shall provide completed evaluations of the foundation conditions of the site and the potential geologic/seismic hazards affecting the site. The geotechnical report shall include, but shall not be limited to, site-specific evaluations of design criteria related to the nature and extent of foundation materials, groundwater conditions, liquefaction potential, settlement potential and slope stability. The report shall contain the results of the analyses of problem areas identified in the geohazard report. The geotechnical report shall incorporate esti- mates of the characteristics of site ground motion provided in the geohazard report. This geotechnical report shall include, but need not be limited to, the following information:

1. A plot showing the location of the soil investigations.
2. A complete record of the soil boring and penetration test logs and soil samples.
3. A record of the soil profile.
4. Elevation of the water table, if encountered. Historic high ground water elevations shall be addressed in the report to adequately evaluate liquefaction and settlement potential.
5. Recommendations for foundation type and design criteria, including but not limited to: bearing capacity of natural or compacted soil; provisions to mitigate the effects of expansive soils; mitigation of the effects of liquefaction, differential settlement and varying soil strength; and the effects of adjacent loads.
6. Expected total and differential settlement.
7. Deep foundation information in accordance with Section 1803 A .5.5.
8. Special design and construction provisions for foundations of structures founded on expansive soils, as necessary.
9. Compacted fill material properties and testing in accordance with Section 1803 A .5.8.
10. Controlled low-strength material properties and testing in accordance with Section 1803 A .5.9. 11. The report shall consider the effects of stepped footings addressed in Section 1809A.3. 12. The report shall consider the effects of seismic hazards in accordance with Section 1803A.6 and shall incorporate the associ- ated geohazard report.

1803A.8 Geotechnical peer review. [DSA-SS and DSA-SS/CC] When alternate foundations designs or ground improvements are employed or where slope stabilization is required, a qualified peer review by a California-licensed geotechnical engineer, in accordance with Section 322 of Part 10, Title 24, CCR, may be required by the enforcement agency. In Section 322 of Part 10, Title 24, CCR, where reference is made to structural or seismic-resisting system, it shall be replaced with geotechnical, foundation or ground improvement, as appropriate.

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