Civil Engineering Reference
In-Depth Information
drilled at chainage 2250 m on the section in Fig. 17.1. (How many more boreholes
would you need to drill before you could draw the section in Fig. 17.1, given some
idea of the basic geology of the site?)
(b) Interpretive reports
An interpretive report will contain all the information in a factual report or it may refer
to a separate factual report, but it will contain geological and engineering interpreta-
tions of the results of the investigations. An interpretive report should contain detailed
engineering geological maps and sections giving a comprehensive three-dimensional
picture of the engineering geology and hydrogeology of the site. For each of the prin-
cipal soil and rock strata identified the interpretive report should give values for the
parameters for strength, stiffness and permeability that will be used in the design.
(These should relate to the requirements for the design of the individual structures in
the scheme and the methods of analysis proposed.)
17.8 Summary
1. In any geotechnical engineering activity investigations are required to determine
the ground conditions. The objectives are to locate and identify all the principal
soil and rock strata, estimate design values for their strengths and stiffnesses and
determine the groundwater conditions.
2. Ground investigations should, ideally, be carried out in stages, involving desk
studies, preliminary investigations and detailed investigations. Detailed investiga-
tions consist of test pitting, drilling and sampling, laboratory testing and
in situ
testing.
3. Often reasonable estimates can be made of the state and the undrained strength
of soil in the ground from the geological history of deposition, erosion and
groundwater changes (see Chapter 18). These estimates are, however, likely to
be substantially modified by structure and ageing (see Chapter 16).
4. The results of a ground investigation may be contained either in a factual report
or in an interpretive report. The principal component of a factual report is the
borehole logs which record all the details of each borehole: it will also record the
procedures and results of the laboratory and
in situ
tests. An interpretive report
should contain, in addition, cross-sections of the site showing all the principal soil
and rock strata, recommended values for all the required design parameters, and,
possibly, outline designs.
5. On completion of an investigation you should be able to provide, at least, the
following information:
(a) Cross-sections and plans showing the location of each of the principal strata
and the groundwater conditions.
(b) A list of the principal strata. This should include, for each stratum: descrip-
tions of the nature and state of the soil or rock based on classification tests;
the geological name a description of the depositional environments and the
subsequent geological events.
(c) A full description of the groundwater conditions.
