Geology Reference
In-Depth Information
Figure 7.23
View along
Tunnel F (1995).
Note
flow weir in
invert.
The original contractor halted work in June 1996 and took
advice on the likely time to complete the tunnels from specialist con-
sultants brought in to assess the situation. Following negotiations
between the contractor and the government, the contractor was
removed from the SSDS project in December 1996 and this was
followed by arbitration.
In 1997, the project was re-let as three separate contracts, which
were completed by November 2000. The contractual arrangements are
unknown in terms of acceptance of ground risks but what is known is
that considerable dif
culties were encountered, including tunnelling
through major fault zones (as had been predicted by the specialists
advising the original contractor at the time that he stopped work). In
Tunnel F, the Tolo Channel Fault Zone comprised 268m of mostly
poor-quality rock, which required up to 20 grout holes of typically 54m
length around the full perimeter, with grout quantities averaging
5,000kg/m of tunnel through most of the fault zone (McLearie,
et al ., 2001). Some details of the additional works and additional
costs resulting are given in the Legislative Council Panel on
Environmental Affairs report (2000).
Other problems associated with the re-let tunnelling contracts
included settlement in an area of recent reclamation about 1km
away from Tunnel C.
ows into Tunnel C from a discrete
highly fractured fault zone peaked at 10,400 l/min (compared to a
permitted limit of about 1,000l/min for the full length of the 5.3km
Tunnel C) and this led to considerable drawdown, settlement and
damage to several housing developments (Maunsell, 2000; Kwong,
2005).
The
In
final breakthrough of the tunnels was four years late and US
$200 million over budget (Wallis, 2000).
 
 
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