Geology Reference
In-Depth Information
can have consequences for others along the coast, as suspected for the
damage to the village of Hallsands in Devon, which had to be largely
abandoned (Tanner & Walsh, 1984).
An excellent review on ground subsidence
natural and due to mining,
is given by Waltham (2002). Ground subsidence occurs naturally due
to lowering of the water table from water extraction, oil and gas
extraction, shrinkage of clay, and dissolution of salt deposits, lime-
stone and other soluble rocks (e.g. Cooper & Waltham, 1999). Sub-
surface piping can occur associated with landslides in any rocks,
including granite (Hencher et al., 2008). The results can be dramatic,
with sudden collapses of roads or even loss of buildings. Care must
therefore be taken to consider these possible hazards during site
investigation.
Underground mining dates back thousands of years in some areas
(e.g.
-
flints from chalk) and on a major scale for hundreds of years.
Consequently, there are very incomplete records. In desk study, the
first approach will always be to consult existing records and docu-
ments, but wherever there is some resource, such as coal, that might
have been mined, the engineering geologist needs to consider that
possibility. Investigations can be put down on a pattern, speci
cally
targeted at the suspected way that mining might have been carried out
(pillar and stall or bell pit, for example). Air photograph interpretation
will often be useful and geochemical analysis of soil can give some
indication of past mining activities.
Many sites around the world are severely contaminated, often
because of man
is activities. This means that if the site is to be
used for some new purpose, it may need to be cleaned up to be
made habitable. Similarly, when constructing near or through
possibly contaminated land, this needs to be investigated and the
contamination mitigated, possibly by removing the contaminated
soil to a treatment area. Barla & Jarre (1993) describe precautions
for tunnelling beneath a land
'
ll site. Guidance on investigation is
given in BSI (2001), CIRIA (1995) and many other sources of
information are given by the AGS (Appendix A). Sometimes the
contamination is dealt with at site. Desk study can often identify
projects where there are severe risks because of previous or cur-
rent land use. Industrial sites such as old gas works, tanneries,
chemical works and many mines are particularly problematical.
Severeprecautionsneedtobetakenwhendealingwithsuchsites
and works will probably be controlled by legislation.
