In general there are two types of subsurface investigation that new construction may require; the first being a conceptual subsurface investigation, or route selection study, where the geotechnical engineer is asked by the designers to identify the best of several possible routes or locations for the proposed structures, or to evaluate foundation alternatives. This type of project generally does not require a detailed subsurface investigation. It is normally limited to geologic reconnaissance and some sampling, field identification of subsurface conditions to achieve generalized site characterization, and general observations such as the depth to rock or competent soils, presence of sinkholes and/or solution cavities, organic deposits in low lying
swampy areas, and/or evidence of old fill, debris, or contamination.
The second and more common type of subsurface investigation is the detailed investigation to be performed for the purpose of detailed site characterization to be used for design. Frequently, the design phase investigation is performed in two or more stages. The initial, or preliminary design, stage investigation is typically performed early in the design process prior to defining the proposed structure elements or the specific locations of foundations, embankments or earth retaining structures. Accordingly, the preliminary design investigation typically includes a limited number of boring and testing sufficient for defining the general stratigraphy, soil and rock characteristics, groundwater conditions, and other existing features of importance to foundation design. Site investigation studies can be done for any of the following purposes:
- Determine the location of the project
- Foundation design and soil improvement
- Project impacts on the environment
- Existing structure evaluation
- Stability control