building codes have provisions that set out the extent of a site investigation. It is mandatory
that a visit be made to the proposed site.
In the early stages of a project, the available information is often inadequate to allow a
detailed plan to be made. A site investigation must be developed in phases.
1.5 Phases of a Soils Investigation
The soil investigation is conducted in phases. Each preceding phase affects the extent of
the next phase. The various phases of a soil investigation are given below:
Phase I. Collection of available information such as a site plan, type, size, and importance of
the structure, loading conditions, previous geotechnical reports, topographic maps, air
photographs, geologic maps, hydrological information and newspaper clippings.
Phase II. Preliminary reconnaissance or a site visit to provide a general picture of the
topography and geology of the site. It is necessary that you take with you on the site visit all
the information gathered in Phase I to compare with the current conditions of the site. Here
visual inspection is done to gather information on topography, soil stratification, vegetation,
water marks, ground water level, and type of construction nearby.
Phase II. Detailed soils exploration. Here we make a detailed planning for soil exploration
in the form trial pits or borings, their spacing and depth. Accordingly, the soil exploration is
carried out. The details of the soils encountered, the type of field tests adopted and the type
of sampling done, presence of water table if met with are recorded in the form of bore log.
The soil samples are properly labeled and sent to laboratory for evaluation of their physical
and engineering properties.
Phase IV. Write a report. The report must contain a clear description of the soils at the site,
methods of exploration, soil profile, test methods and results, and the location of the
groundwater. This should include information and/or explanations of any unusual soil, waterbearing stratum, and soil and groundwater condition that may be troublesome during