The Texas Board of Professional Engineers interpretation of the International Residential Code section on foundations (specifically IRC 2012 Sec. R401.4 Soils Tests) is that soil testing should be included on all residential foundations. Besides being required by building codes such as in the IRC and by design manuals such as the Post-Tensioning Institute’s 3rd edition design manual, a quality geotechnical evaluation of a project site can save considerable time and expense and provides the design team with subsurface information and soil properties during the design and planning stages. The data obtained from a laboratory analysis of the soil samples establishes critical design parameters used by the design Engineer. All geotechnical reports should contain certain basic essential information, including:
- Summary of all subsurface exploration data, including a soil profile, exploration logs, laboratory or test results, and ground water information;
- Interpretation and analysis of the subsurface data;
- Specific soil parameters for use by the Design Engineer;
- Discussion of site conditions and possible solutions of anticipated problems;
- Recommended geotechnical special provisions.
Site Specific Soils Testing
A site specific soils report is generally required for all commercial projects. It is also required when building a residential structure on an isolated site where no supporting data is available from Soil Reports taken in the immediate vicinity. Typically two test holes are bored on each lot with several soil samples taken from each hole.
Multi-site / Subdivision Soil Testing
A multi-site report is a relatively low-cost/low-impact approach to reducing potential liability associated with unidentified or unfavorable site conditions. Soil samples are taken from a number of lots within a development then tested in a laboratory to determine the soil properties within that development. The geotechnical report should contain the same basic essential information referenced above that will apply to all lots within a subdivision.