Geology Reference
In-Depth Information
Figure 3.55
Limestone
pavement with
protojoints etched
out by dissolution
Malham, West
Yorkshire.
3.6 Water
3.6.1 Introduction
Water is critically important to many geotechnical projects. Surface
water causes erosion and
flooding; groundwater controls effective
stress and, therefore, frictional strength, and can be a major problem
for tunnelling. Water problems for most civil engineering design and
construction is dealt with by measurement and monitoring using piezo-
meters, backed up by numerical modelling and analysis
(Chapters 4
and
6)
. Groundwater levels do not generally
fluctuate too much in
response to individual rainstorms, other than close to the surface,
which is signi
cant for shallow landslides, as discussed below, but not
for most other engineering works. More signi
cant are groundwater
changes brought about by engineering works, either deliberately
(e.g. dewatering to carry out excavations in the dry) or as an unintended
consequence, for example, where tunnelling below a site. Lowering of
the water table inevitably causes water migration and potentially inter-
nal erosion, a loss of buoyancy, increase in effective stress and self-
weight compaction of soil and rock. This may result in settlement and
