A site investigation in one form or another is always required for any engineering or bulding estructure. The investigation may range in scope from a simpleexamination of surface soils with or without a few shallow trial pits, to a detailed study of the soil and ground water conditions to a considerable depth below the surface by means of boreholes andin-situ anda laboratory test on the materials encountered.
The extent of the work depends on the importance and foundation arrangement of the structure, the complexity of the soil conditions, andthe information which may be available on the behaviour of existing foundations on similar soils. Thus it is not normal practice to sink borcholes anda carry out soil test for single- or two- storydwelling houses or similar structures since there is usually adequate knowledge of the required foundation depths and bearing pressures in any particular locality.
Sufficient information to check thepresumed soil conditions can usually be obtained by examing open sewer trenches or shallow excavations for roadworks, or from a few shallow trial pits or hand auger borings. Only if troublesomefoundation conditions such as layers of peat or loose fill material were encountered would it be necessary to sink deep boreholes, possibly supplemented by soil tests.
More extensive investigations forlight structures are needed where there are problems of deep-scated swelling and shrinkage of clays or when builiding in ground conditions where there is no information on foundation behaviour, forexample in undeveloped territories overseas where there may be climatic or other factors which have an important effect on foundation design.
A detailed site investigation involving deep boreholes andlaboratory testing of soils is always a necessity for heavy structures such as bridges, multi-storey buildings, or industrial plants. Even if rock is know to be present at a shallow depth ir is...