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The stability of the foundation of a building, a bridge, an embankment or any other structure built
on soil depends on the strength and compressibility characteristics of the subsoil. The field and
laboratory investigations required to obtain the essential information on the subsoil is called Soil
Exploration or Soil Investigation. Soil exploration happens to be one of the most important parts of
Foundation Engineering and at the same time the most neglected part of it. Terzaghi in 1951
(Bjerrum, et al., 1960) had rightly remarked, that “Building foundations have always been treated
as step children”. His remarks are relevant even today. The success or failure of a foundation
depends essentially on the reliability of the various soil parameters obtained from the field
investigation and laboratory testing, and used as an input into the design of foundations.
Sophisticated theories alone will not give a safe and sound design.
Soil exploration is a must in the present age for the design of foundations of any project. The
extent of the exploration depends upon the magnitude and importance of the project. Projects such
as buildings, power plants, fertilizer plants, bridges etc., are localized in areal extent. The area
occupied by such projects may vary from a few square meters to many square kilometers.
Transmission lines, railway lines, roads and other such projects extend along a narrow path. The
length of such projects may be several kilometers. Each project has to be treated as per its
requirements. The principle of soil exploration remains the same for all the projects but the
program and methodology may vary from project to project.
The elements of soil exploration depend mostly on the importance and magnitude of the
project, but generally should provide the following:

  1. Information to determine the type of foundation required such as a shallow or deep foundation.
  2. Necessary information with regards to the strength and compressibility characteristics of
    the subsoil to allow the Design Consultant to make recommendations on the safe bearing
    pressure or pile load capacity.

Soil exploration involves broadly the following:

  1. Planning of a program for soil exploration.
  2. Collection of disturbed and undisturbed soil or rock samples from the holes drilled in the
    field. The number and depths of holes depend upon the project.
  3. Conducting all the necessary in-situ tests for obtaining the strength and compressibility
    characteristics of the soil or rock directly or indirectly.
  4. Study of ground-water conditions and collection of water samples for chemical analysis.
  5. Geophysical exploration, if required.
  6. Conducting all the necessary tests on the samples of soil /rock and water collected.
  7. Preparation of drawings, charts, etc.
  8. Analysis of the data collected.
  9. Preparation of report.

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