Civil Engineering Reference
In-Depth Information
and this situation should be adequately investigated. Industrial waste may also give
rise to corrosive ground conditions and in built-up areas, the previous use of the
ground should be established. Chemical tests on soil samples may be carried out to
give additional information with respect to the leachability of contaminants.
2.4 Sampling, in-situ testing and laboratory testing
In certain respects, decisions regarding the optimum programme of sampling and test-
ing may only be made after some knowledge of the ground conditions at the site has
been gained, and some conclusions regarding the possible piling alternatives have been
reached. This situation emphasizes the need for a flexible approach and the value of
preliminary studies to facilitate the initial assessment. In many cases, the selection of
a suitable pile type is controlled by external factors such as access conditions, cost,
vibration or noise level, so that there is in general no simple way to relate a pile type
to the prevailing soil and groundwater conditions.
Guidelines are given in B5930, section 4.3, for sample spacing, the size of bulk
samples, types of sampling equipment and the intervals between in-situ tests, and
these are applicable to the recommendations given in the following notes.
Some situations may arise where special tests may be required or the intensity of
sampling or testing may have to be increased to provide sufficient data on particular
aspects. An example would be the estimation of rock modulus in a weak fissured or
blocky rock, where, for instance, plate-bearing tests combined with intensive large-
diameter rotary diamond coring and possibly other in-situ tests may be necessary.
Such an approach would be very dependent on the costs involved in the additional
exploration compared with the costs of deeper, or larger (possibly over-conservative)
pile foundations.
The usual forms of cable tool boring equipment and rotary drilling equipment are
appropriate, but in view of the additional depth of boring likely to be necessary, larger
than usual starting diameters for boreholes and drillholes may be prudent. This permits
'stepping down' at an intermediate depth in order to maintain a reasonable rate of
progress. Normal sampling and testing methods suffice, but there is a bias towards in-
situ static and dynamic penetration tests, especially the standard penetration tests (SPT)
and (static) cone penetration test (CPT), since pile design by empirical methods can be
based directly on the results. Provided the ground does not contain cemented material
or large boulders, cone penetration testing may be preferred to the SPT, particularly
as many pile design methods are linked increasingly to the cone resistance. Table 2.1
summarizes typical in-situ tests that may be carried out, and their application to pile
design.
2.5 Methods of exploration for various soil types
In the following sections, specific soil types are described with appropriate methods
of exploration. Whilst the ground conditions may well closely approximate those
described, intermediate or mixed conditions are quite likely, and a combination of
methods would then be employed. Pile design is related to the soil conditions, and if
established methods of design are to be employed, the investigation should provide
appropriate parameters.
