Geology Reference
In-Depth Information
site and other construction factors that caused the problems. Very often
mismanagement is fundamental to why critical factors are missed, over-
looked for not dealt with properly, as discussed for tunnels byMuirWood
(2000). For the followingdiscussion, case examples aregroupedaccording
to the predominant cause following the geology plus environment plus
construction approach introduced in
Chapter 4
(
Table 4.1).
This is not
always easy to do because it is often a combination of factors that led to
failure or to the extent of the failure. A fourth category introduced here is
systematic failure
where fundamental decisions or concepts seemtohave
played a major role in what occurred.
-
Geotechnical hazards occur at a full range of scales frommicro (miner-
alogy, friction) to macro (plate tectonics, typhoons). Material factors
are at the scale of hand-held samples or pieces of core. It is the scale of
most laboratory and
in situ
tests. Hazards at this scale are associated
with the physical and chemical nature and properties of the various
geological materials making up the site and used in construction,
including their durability.
Carsington Dam failed in July 1984, during construction, when it had
almost reached full design height (see Section 7.4.1 for full discussion).
One of the lesser-known problems with the Carsington Dam project,
however, concerned chemistry of the materials making up the dam,
which should have been anticipated. The damwas constructed of locally
derived rock
fill with a clay core. The rock included black shale with
CARSINGTON DAM (1984)
limestone riprap
clay core
'yellow
clay'
Coal Measures mudstone rock fill
(with pyrites)
H
2
O
+
Ca CO
3
+
F
e
S
→
CO
2
[killed workers]
in situ
mudstone
+
H
2
SO
4
[polluted streams]
