Geology Reference
In-Depth Information
elastically (without permanent damage) for a 1 in 1,000 year event but
for a, very unlikely, maximum credible event, some degree of damage
would be accepted.
The factors to review at this stage include natural hazards such as
earthquake loading, strong winds, heavy rain and high groundwater
pressures or
flooding. Anthropogenic factors to consider include
industrial contamination and proximity of other structures and any
constraints that they may impose.
The third verbal equation of Knill & Price (Knill, 2002) addresses the
interaction between the geological and environmental conditions at a
site and the construction and operation constraints (Hencher &
Daughton, 2000). Excavation will always give rise to changes in stresses,
and the ground may need to be supported. Excavations may also result
in changes in groundwater, and the consequences need to be addressed
and mitigated if potentially harmful. Similarly, loading from struc-
tures has to be thought through, not only because of deformations but
also because of potentially raising water pressures, albeit temporarily.
There will also be hazards associated speci
cally with the way the
project is to be carried out. For example, a drill and blast tunnel is very
different to one excavated by a tunnel boring machine and will have
speci
c ground hazards associated with its construction (
Chapter 6).
Similarly, the construction constraints are very different for bored
piling compared to driven piles (
Table 4.5).
The systematic review
and investigation of site geology and environmental factors, discussed
earlier, needs to be conducted with speci
c reference to the project at
hand. This will hopefully allow the key hazards to be identi
ed and
design to be robust yet cost-effective. Nevertheless, models are always
simpli
cations, and the engineer must adopt a cautious and robust
approach when designing, especially where the geological conditions
are potentially variable and where that variability might cause diffi-
-
culties, as illustrated by the case of a tunnel failure reported in
Chapter 7
(Grose & Benton, 2005).
Table 4.5 Examples of the in
uence of engineering works
FACTOR
CONSIDERATIONS
loading/unloading
-
settlement, failure, opening of joints, increased permeability in cut slopes,
blast vibrations
static/dynamic
change in water table
increased or decreased pressure head, change in effective stress, drawdown
leading to settlement, induced seismicity from reservoir loading
denudation or land
clearance
increased in
ltration, erosion, landsliding
