Page 158 - Civil Engineering Project Management, Fourth Edition

Site surveys, investigations and layout
143
The drainage of clay or clay and silt can present difficulty. The problem is not
so much that it cannot be done, but that it can take a long time, perhaps many
weeks. Sand drains (i.e. bored holes filled with fine sand), can be satisfactory as
part of the permanent design of the works, but they usually operate too slowly
to be of use during construction. If ground is too soft, any attempt to start excav-
ating it by machine may make matters considerably worse, and end with the
machine having to be hauled out. The act of removing overburden may make a
soft area even softer as springs and streams, otherwise restrained by the over-
burden material, break out and change the area to a semi-liquid state. If the resi-
dent engineer sees the contractor moving towards these difficulties he should
advise him of the possible consequences, and endeavour to give assistance in
devising a better approach. A paramount need may be to call in an experienced
geotechnical engineer to investigate the problem and give advice as to the best
policy to handle the situation.

References

Schofield W. Engineering surveying. Butterworth-Heinemann, 2001.
ICE Site Investigation in Construction, 1993. (Part 1 Without site investigation
ground is a hazard; Part 2 Planning, procurement and quality
management; Part 3 Specification for ground investigations; Part 4
Guidelines for the safe investigation by drilling of landfills and
contaminated land.)
Clayton C.R.I., Simons N.E., Matthews M.C. Site investigation. Blackwell, 1995.
Transport and Road Research Laboratory, Road Note No. 17, Protection of
Subgrades and Granular Bases by Surface Dressing. (An early publication but
useful for construction of site roads.)
BS 1377:1990: Methods of test for soil for civil engineering purposes, Parts 1–9.
(Part 1 General requirements and sample preparation; Part 4 Compaction
tests; Part 9 In-situ tests.)
BS 5606:1990: Guide to accuracy in building.
BS 5930:1981: Site investigations code of practice.
BS 5964:1980: Methods for setting out and measurement of buildings.
BS 8004:1986: Foundations code of practice.