Geology Reference
In-Depth Information
Complex geology: basalt
intrusions and quartz
monzonite: deep weathering;
extensive natural pipe system;
fault encountered in nearby
tunnel
Fault and
brecciated granite
identified at tunnel
depth in borehole;
rock joints mainly
chlorite coated and
calcite infilled
Approximate line of
sea-bed depression
shown in Admiralty
chart of 1893
-
maybe
line of fault
shown in Admiralty
chart of 1893 - maybe
line of fault
fault encountered in nearby
tunnel
rock joints mainly
chlorite coated and
calcite infilled
Passing underneath
subway tunnels;
possible fault
sing underneath
bway tunnels;
ossible fault
Area of
reclamation
Area of
reclamation
Tunnel in Grade IV/V rock
below newly reclaimed areas
with high water pressure
Valleys with shallow rock
cover and comparatively thick
soil mantle
Complex geology: 3 inferred
faults, rock joints locally infilled
with kaolin and calcite and
chlorite coated
Delay, water inflow and
settlement; difficult
formation of shaft and
launching TBM
Instability, water inflow,
delay and may affect
existing subway tunnels
Further GI required
Ground pre-treatment
Instrumentation and close
monitoring
Instability, water inflow &
delay; difficult formation of
shaft and retrieving TBM
Further GI required
Pretreatment and local
pressure relief
Slurry mode excavation
assessment of possible conditions under the Eastern Tower of
Stonecutters Bridge in Hong Kong at tender stage, based on desk
study together with a proposed borehole investigation targeted at
likely faults and zones of deep weathering. Some broad details of
what was actually found are given in Fletcher (2004) and consequences
by Tapley et al. (2006).
Requirements and practice for GI vary around the world. In
Hong Kong, for example, it is normal practice to put down a borehole
at the location of every bored pile (called a pre-drill). Elsewhere, a
pattern of perhaps three, four or
five boreholes might be adopted
below each pile cap for a major structure. For example, for the
2
nd
Incheon Bridge in South Korea, opened in 2009, for each of the
main cable stay bridge towers there were four boreholes per pile cap,
each of which was about 70 by 25m in plan and supported by 24
large-diameter bored piles. For the Busan-Geoje
fixed link crossing,
completed in 2010, also in South Korea, there were two cable-stay
bridge sections, one with two towers andmain span of 475m, the other
with three towers. The towers were founded on gravity caissons sitting
