Section 1803 Geotechnical Investigations
Exception: The building official shall be permitted to waive the requirement for a geotechnical investigation where satisfactory data from adjacent areas is available that demonstrates an investigation is not necessary for any of the conditions in Sections 1803.5.1 through 1803.5.6 and Sections 1803.5.10 and 1803.5.11.
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:
- Plasticity index (PI) of 15 or greater, determined in accordance with ASTM D4318.
- More than 10 percent of the soil particles pass a No. 200 sieve (75 µm), determined in accordance with ASTM D422.
- More than 10 percent of the soil particles are less than 5 micrometers in size, determined in accordance with ASTM D422.
- Expansion index greater than 20, determined in accordance with ASTM D4829.
A subsurface soil investigation shall be performed to determine whether the existing ground water table 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.
Exception: A subsurface soil investigation to determine the location of the ground water table shall not be required where waterproofing is provided in accordance with Section 1805.
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:
- Recommended deep foundation types and installed capacities.
- Recommended center-to-center spacing of deep foundation elements.
- Driving criteria.
- Installation procedures.
- Field inspection and reporting procedures (to include procedures for verification of the installed bearing capacity where required).
- Load test requirements.
- Suitability of deep foundation materials for the intended environment.
- Designation of bearing stratum or strata.
- Reductions for group action, where necessary.
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:
- Specifications for the preparation of the site prior to placement of compacted fill material.
- Specifications for material to be used as compacted fill.
- Test methods to be used to determine the maximum dry density and optimum moisture content of the material to be used as compacted fill.
- Maximum allowable thickness of each lift of compacted fill material.
- Field test method for determining the in-place dry density of the compacted fill.
- Minimum acceptable in-place dry density expressed as a percentage of the maximum dry density determined in accordance with Item 3.
- Number and frequency of field tests required to determine compliance with Item 6.
- Specifications for the preparation of the site prior to placement of the CLSM.
- Specifications for the CLSM.
- Laboratory or field test method(s) to be used to determine the compressive strength or bearing capacity of the CLSM.
- Test methods for determining the acceptance of the CLSM in the field.
- Number and frequency of field tests required to determine compliance with Item 4.
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:
- Slope instability.
- Total and differential settlement.
- Surface displacement due to faulting or seismically induced lateral spreading or lateral flow.
- 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.
- 2.1. A site-specific study in accordance with Chapter 21 of ASCE 7.
- 2.2. In accordance with Section 11.8.3 of ASCE 7.
- 3.1. 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.
- 4.1. 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.
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. This geotechnical report shall include, but need not be limited to, the following information:
- A plot showing the location of the soil investigations.
- A complete record of the soil boring and penetration test logs and soil samples.
- A record of the soil profile.
- Elevation of the water table, if encountered.
- 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.
- Expected total and differential settlement.
- Deep foundation information in accordance with Section 1803.5.5.
- Special design and construction provisions for foundations of structures founded on expansive soils, as necessary.
- Compacted fill material properties and testing in accordance with Section 1803.5.8.
- Controlled low-strength material properties and testing in accordance with Section 1803.5.9.