DHARMSOIL EXPLORATION 725
topography. The nature and extent of vegetative cover will determine costs relating to site
clearance. Availability of water and electrical power, proximity to major transporation routes,
environmental protection regulations of various agencies and availability of sufficient area for
post-construction use may be the other factors which could affect construction procedures.
Information on subsurface conditions existing at a site is also an important requirement.
The possible need for dewatering will be revealed by the subsurface investigation. Necessity
for bracing of excavations for foundations can be established.
The importance of adequate site investigation and soil exploration cannot be overem-
phasised because the lack of it could lead to increased costs due to unforeseen difficulties and
the consequent modifications in the design and execution of the project. Usually, the cost of a
thorough investigation and exploration programme will be less than 1% of the total cost of the
entire project.
Site investigations may involve one or more of the following preliminary steps:
- Reconnaissance
- Study of maps
- Aerial photography
18.2.1 Reconnaissance
Reconnaissance involves an inspection of the site and study of the topographical features. This
will yield useful information about the soil and ground-water conditions and also help the
engineer plan the programme of exploration. The topography, drainge pattern, vegetation and
land use provide valuable information. Ground-water conditions are often reflected in the
presence of springs and the type of vegetation. The water levels in wells and ponds may indi-
cate ground-water but these can be influenced by intensive use or by irrigation in the proxim-
ity of the area.
Valuable information about the presence of fills and knowledge of any difficulties en-
countered during the building of other nearby structures may be obtained by inquiry. Aerial
reconnaissance is also undertaken if the area is large and the project is a major one.
Reconnaissance investigation gives a preliminary idea of the soils and other conditions
involved at the site and its value should not be underestimated. Further study may be avoided
if reconnaissance reveals the inadequacy or unsuitability of the site for the proposed work for
any glaring reasons.
18.2.2Study of Maps
Information on surface and subsurface conditions in an area is frequently available in the
form of maps. Such sources in India are the Survey of India and Geological Survey of India,
which provide topographical maps, often called ‘toposheets’. Soil conservation maps may also
be available.
A geological study is essential. The primary purpose of such a study is to establish the
nature of the deposits underlying the site. The types of soil and rock likely to be encountered
can be determined, and the method of exploration most suited to the situation may be selected.
Faults, folds, cracks, fissures, dikes, sills and caves, and such other defects in rock and soil
strata may be indicated. Data on the availability of natural resources such as oil, gas and
minerals will have to be considered carefully during the evaluation of a site. Legal and