Geology Reference
In-Depth Information
Chapter 6.
Another requirement of the model is to allow the support
requirements to be predicted along the tunnel. For example, in a long
drill and blast/hand-excavated tunnel, some sections of the ground, in
good rock, may need little support, others will need local reinforce-
ment to prevent rock blocks falling. In other sections, through weak
ground or where there are high water pressures, the tunnel might need
a thick reinforced concrete liner. A ground model needs to be prepared
that includes predictions of rock quality along the route. These predic-
tions are needed so that the team constructing the tunnel knowwhat to
expect and where to take special precautions. The predictions are also
necessary so that the contractor can prepare a realistic tender price for
the construction and as a reference so that all parties can judge whether
conditions were more dif
cult than might have been anticipated, so
that additional payment can be made to the contractor, if appropriate,
as discussed in
Chapter 2.
The model also needs to allow the in
uence
of the works on other structures to be assessed. In
Figure 3.63,
each
end of the tunnel terminates in urban areas. The problems of noise,
vibrations, dewatering and physical interaction with existing founda-
tions and slopes need to be considered and these are all aspects where a
comprehensive ground model is essential. Where the tunnel passes
underneath the hill, there may be unusually high lateral stresses caus-
ing squeezing on the tunnel. The possible faults identi
ed along the
route may be associated with particularly poor ground and possibly
high in
ow of groundwater.
