Chapter 3Site Investigation

3.1 General

Site investigation is essential in determining the physical, chemical and engineering properties of subsoil to arrive at the required foundation system. However, in areas which have already been developed, information may be obtained regarding the existing local knowledge, records of trial pits, boreholes, etc, in the vicinity, and the behaviour of the existing structures, particularly those of a similar nature to those proposed. This information may be made use of for design of foundation of lightly loaded structures of not more than two storeys and also for deciding the scope of further investigation for other structures.

3.1.1 If the existing information is not sufficient or is inconclusive, the proposed site should be explored in detail as per good practice $[6-2(1)]$ , so as to obtain a knowledge of the type, uniformity, consistency, thickness, sequence and dip of the strata, hydrology of the area and also the engineering properties. In the case of lightly loaded structures of not more than two storeys the tests required to obtain the above information are optional, mainly depending on site conditions.

3.1.1.1 Site reconnaissance would help in deciding future programme of field investigations, that is, to assess the need for preliminary or detailed investigations. Information on some of these may be obtained from topographical maps, geological maps, pedological and soil survey maps, seismic maps and aerial photographs.

Geological maps of the area give valuable information of the site conditions. The general topography will often give some indications of the soil conditions and their variations. In certain cases the earlier uses of the land (like quarries, agricultural land, buried canals, etc) may have a very important bearing on the proposed new structures.

PART 6 STRUCTURAL DESIGN — SECTION 2 SOILS AND FOUNDATIONS

The presence of harmful chemicals in the subsoil can be easily identified by geology or by reconnaissance.

Data regarding removal of overburden by excavation, erosion or landslides should be obtained. This gives an idea of the amount of preconsolidation the soil strata has undergone. Similarly, data regarding recent fills is also important to study the consolidation characteristics of the fill as well as the original strata. Data regarding swelling or expansive soils will be useful information.