Geology Reference
In-Depth Information
Figure 7.7
Fault in
valley at Kornhill,
Hong Kong. Poor-
quality rock in fault
zone resulted in
foundations being
taken tens of metres
deeper than in
better rock away
from the fault zone.
Hong Kong
Figure 7.7
shows foundations for high-rise structures under con-
struction at Kornhill, Hong Kong. The presence of a major fault
(weathered zone in line with the valley) meant that foundations
had to be taken locally tens of metres deeper than adjacent foun-
dations. Clearly, the valley was indicative of the potential for poor
ground conditions. That said, all valleys are not associated with
faults and all major faults are not associated with valleys. At
Kornhill, some faults that had been anticipated caused no dif
cul-
ties whilst other unpredicted faults were discovered during con-
struction (Muir
et al
., 1986).
A tunnel was to be constructed in northern England through
Carboniferous mudstones, and a tunnel boring machine (TBM) was
selected for the construction. The disc cutters of the machine are seen in
Figure 7.8.
Normally, you should not be able to photograph this view
of the machine until the tunnel has been completed and the TBM has
entered a reception excavation. Unfortunately, in this case the tunnel
had collapsed during construction when the TBM encountered a fault
(Figure 7.9)
. The TBM came to a halt as material collapsed around it.
The only way of advancing the tunnel was to sink a shaft in advance of
the TBM and excavate a larger tunnel by hand, back to the collapse,
and freeing the machine
(Figure 7.10)
. This of course was expensive
and led to some dispute. The contractor (constructing the tunnel and
whose TBM had got buried) claimed that he did not expect such poor
ground. An expert for the client said that he should have done so
