Civil Engineering Reference
In-Depth Information
Ground investigations
17.1 Introduction
Engineers designing structures and machines normally choose materials and specify
their strength and stiffness and they often combine materials to make composites
(e.g. steel and concrete in reinforced concrete). Similarly, highway engineers can
specify the soils and rocks to be used in the construction of roads. Geotechnical engi-
neers, on the other hand, cannot choose and must work with the materials in the
ground. They must therefore determine what there is in the ground and the engineering
properties of the ground, and this is the purpose of ground investigations.
The basic techniques of ground investigation are drilling, sampling and testing,
in situ
and in the laboratory, but these must be complemented by geological information and
a sound appreciation of the relevant soil mechanics principles. Consequently, it is in
the area of ground investigation that geology and engineering combine and where
engineering geologists and geotechnical engineers cooperate.
Ground investigation is, of course, far too big a topic to be covered in one short
chapter and all I will do here is outline the basic issues as a starting point for fur-
ther study. The detailed techniques vary from country to country, and from region
to region, and depend both on the local ground conditions, on historical precedents,
on contractural procedures and on the available equipment and expertise. As with
laboratory testing, procedures for ground investigations are covered by national stan-
dards and codes of practice; in the United Kingdom this is BS 5930:l999. You should
look up the standards covering the region where you work in to see what they con-
tain. Detailed descriptions of the current practices in the United Kingdom are given by
Clayton, Simons and Matthews (1995).
17.2 Objectives of ground investigations
When you look at the face of a cliff or an excavation you see a section of the ground
and when you look at a site you have to imagine what an excavation would reveal.
A major part of a ground investigation is to construct a three-dimensional picture
of the positions of all the important soil and rock layers within the site that may be
influenced by, or may influence, the proposed construction. Of equal importance is
the necessity to sort out and identify the groundwater conditions. In distinguishing the
important soil and rock layers engineering classifications based on the nature and state
