In areas likely to have expansive soil, the building official shall require soil tests to determine where such soils do exist.
- Plasticity index (PI) of 15 or greater, determined in accordance with ASTM D 4318.
- More than 10 percent of the soil particles pass a No. 200 sieve (75 µm), determined in accordance with ASTM D 422.
- More than 10 percent of the soil particles are less than 5 micrometers in size, determined in accordance with ASTM D 422.
- Expansion index greater than 20, determined in accordance with ASTM D 4829.
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.
Where deep foundations will be used, a geotechnical investigation shall be conducted and shall include all of the following, unless sufficient data upon 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.
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:
2.1 A site-specific study in accordance with Section 21.5 of ASCE 7; or
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:
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; and
3.7. Flotation of buried structures.
4. Discussion of mitigation measures such as, but not limited to:
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; or
4.4. Any combination of these measures and how they shall be considered in the design of the structure.