Geology Reference
In-Depth Information
(Wallis, 1999). This description is somewhat at odds with the observa-
tions of Skempton et al . (1969) and others of joints and
fissures in
London Clay, including numerous polished and slickensided ones. The
contractor
Some unforeseeable and completely
unpredictable behaviour or geotechnical mechanism in the clay body is
the only explanation for the collapse
'
s expert argued that:
'
(Wallis, 1999) linked to the
opinions of other experts that the excavated tunnels should have stood
up for up to 80 days. It is noted that in subsequent years several authors
have highlighted the importance of low shear strength
…'
flexural shears in
the London Clay (Chandler, 2000; Hutchinson, 2001), which have led
to landsliding, including near to Heathrow, but no such surfaces were
apparently observed in the post-collapse investigations at HEX
(Norbury, personal communication; HSE, 2000).
7.8.2 Planning for a major tunnelling system under
the sea: SSDS Hong Kong
The Stategic Sewerage Disposal Scheme (SSDS) Stage 1 was an ambi-
tious project to construct a series of shafts and deep tunnels at typical
depths of 120
145m, leading from a number of catchments around
Victoria Harbour in Hong Kong to a central treatment works con-
structed at Stonecutters Island. The layout of the scheme is set out in
Figure 7.22 and details are given by McLearie et al . (2001).
-
Figure 7.22 Layout
of SSDS Stage
1 tunnels A to
G, Hong Kong
harbour. Darker
shades are granitic
rock: gt
m
gt
gt
gd
G
¼
granite,
gd
granodiorite,
¼
Kai Tak Airport
m
monzonite.
Most of the other
rocks are mainly of
volcanic origin.
Base map is from
Fletcher (2004).
¼
F
E
D
Tsing Yi Island
Lantau Island
Stonecutters Island
B
A
gt
m
Hong Kong Island
m
0
5
10 km
 
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