Civil Engineering Project Management (4th Edition)
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132 <strong>Civil</strong> <strong>Engineering</strong> <strong>Project</strong> <strong>Management</strong><br />
should always be warned when greater accuracy than this must be obtained<br />
with concrete. Usually discrepancies of 5 mm can be taken up in the floor screed<br />
of granolithic or terrazzo ground down to the desired smooth finish. To get<br />
tiling accurately laid, small pieces of tile are mortared onto the floor base at<br />
intervals across it, their level being fixed precisely to the correct finished level<br />
by use of the instrument level. A straight edge is then used to keep the finished<br />
tiling at the right level between tile pieces, which are cut off as the work proceeds.<br />
There are, however, some experienced tradesmen who exhibit astonishing<br />
skill in tiling an area perfectly level given only one level point.<br />
12.6 Site investigations<br />
Site investigations taken at an early, feasibility stage of a project will seldom<br />
be adequate for construction. More site tests will be necessary for individual<br />
foundations, etc. British Standard BS 5930: 1999, Code of practice for site investigations,<br />
acts as a general guide for further site tests, but this needs to be supplemented<br />
by information contained in other publications as suggested at the<br />
end of this chapter. The resident engineer will be expected to have an understanding<br />
of the major principles and techniques of soil mechanics so that he<br />
can direct work intelligently. But for specifying tests and interpreting their<br />
results, an experienced geotechnical engineer is essential, otherwise misleading<br />
assumptions can be made which later lead to serious trouble on a job.<br />
There is an ‘art’ as well as a science in deciding what additional site investigations<br />
should take place when construction is started. Advice from a geotechnical<br />
engineer or engineering geologist should always be sought, but when<br />
choosing where to site extra boreholes or trial pits ‘hunch’ and ‘suspicion’ can<br />
play a part. A hunch should not be dismissed as unscientific; it can arise from<br />
studying the known facts and an apprehension that more needs to be known<br />
about some aspect of a situation than is currently known at the time. An experienced<br />
engineer will always worry more about what he does not know about<br />
below-ground conditions, than what he does know. Thus investigating some<br />
suspicion there might be a possible unconformity in conditions below ground<br />
can sometimes prove more revealing than gridding an area with boreholes<br />
at regular intervals – but not always!<br />
12.7 Trial pits<br />
Hand-dug trial pits are expensive, take time to excavate and are not always<br />
as informative as expected. They do, however, expose a formation so that it<br />
can be examined in detail. This may be important if thin layers of weak clay<br />
or pre-existing shear zones are suspected below ground. The starting size for<br />
a pit depends on the depth it is to be sunk. If required to a depth of 5 m for
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