Civil Engineering Reference
In-Depth Information
* In accordance with the UK National Annex to EN 1997-2:2007, in the UK, BS 1377:1990 remains the
standard for all laboratory testing of soils, with the exception of the fall cone test, which is covered instead
by EN ISO 17892-6:2004
The practices adopted in site investigations have been around for many years and whilst EN 1997-2
does offer a different strategy for the carrying out of ground investigation and testing work, the estab-
lished equipment and procedures in use will not change significantly. The rest of this chapter is arranged
to align with the structure of EN 1997-2.
6.2 Planning of ground investigations
The most significant (and the most expensive) part of a site investigation is the ground investigation (i.e.
that stage where the ground profile and groundwater levels are established and where samples of soil
and rock are taken for identification and testing). In order to maximise the value and relevance of the
information and data gleaned during the ground investigation, it is critical that the investigation is well
planned. Careful planning ensures that a cost-efficient investigation is achieved and that all the informa-
tion required for the geotechnical design is obtained. This careful planning is achieved by performing
several pre- ground investigation information searches, assessments and analyses.
6.2.1 Desk study
The desk study is generally the first stage in a site investigation. The size and extent of the study will vary
according to the nature of the project and the anticipated ground conditions. It involves collecting and
collating published information about the site under investigation and pulling it all together to build a
conceptual model of the site. This model can then be used to guide the rest of the investigation, especially
the ground investigation. Much of the information gathered at the desk study stage is contained in maps,
published reports, aerial photographs and personal recollection.
Sources of information
The sources of information available to the engineer include geological maps, topographical maps (Ord-
nance Survey maps), soil survey maps, aerial photographs, mining records, groundwater information,
existing site investigation reports, local history literature, meteorological records and river and coastal
information. Details of a few of these are provided below but a thorough description of the sources of
desk study information is given by Clayton
et al
. (
1995
).
Geological maps
Geological maps provide information on the extent of rock and soil deposits at a particular site. The signifi-
cance of the geological information must be correctly interpreted by the engineer to assist in the further
planning of the site investigation. Geological maps are produced by the British Geological Survey (BGS).
Topographical maps
Ordnance Survey maps provide information on, for example, the relief of the land, site accessibility, and the
land forms present. A study of the sequence of maps for the same location produced at different periods
in time, can reveal features which are now concealed and identify features which are experiencing change.
Soil survey maps
A pedological soil survey involves the classification, mapping and description of the surface soils in the
area and is generally of main interest to agriculturists. The soil studied is the top 1-1.5 m, which is the
