Site conditions. Examination of the site includes history, geology, visual inspection of the site and adjacent area, and local design and construction experience. Maps may provide data on wooded areas, ponds, streams, depressions, and evidence of earlier construction that can influence soil moisture and groundwater level. Existence of former solid waste disposal sites within the construction area should be checked. Some forms of solid waste, i.e., old car bodies and boulders, make installation of deep foundations difficult or result in unacceptable lateral deviation of driven piles. Guidance on determining potential problems of deep foundations in expansive clay is given in TM 5-818-7, “Foundations in Expansive Soils.” Special attention should be payed to the following aspects of site investigation:
(1) Visual study. A visual reconnaissance should check for desiccation cracks and nature of the surface soil. Structural damage in nearby structures which may have resulted from excessive settlement of compressible soil or heave of expansive soil should be recorded. The visual study should also determine ways to provide proper drainage of the site and allow the performance of earthwork that may be required for construction.
(2) Accessibility. Accessibility to the site and equipment mobility also influence selection of construction methods. Some of these restrictions are on access, location of utility lines and paved roads, location of obstructing structures and trees, and topographic and trafficability features of the site.
(3) Local experience. The use of local design and construction experience can avoid potential problems with certain types of foundations and can provide data on successfully constructed foundations. Prior experience with and applications of deep foundations in the same general area should be determined. Local building codes should be consulted, and successful experience with recent innovations should be investigated.
(4) Potential problems with driven piles. The site investigation should consider sensitivity of existing structures and utilities to ground movement caused by ground vibration and surface heave of driven piles.
The condition of existing structures mprior to construction should be documented with sketches and photographs.