The Ingenieur Vol 57 January-March 2014 The Ingenieur Vol 57 January-March 2014 | страница 14

INGENIEUR

Figure 3 – Cross
Section and Progress
of Raw Water Tunnel
Some of the challenges faced during the
PSRWT tunnel excavation:• Cavity (Lepoh Fault)
• High Temperature
• High Water Ingress
• Rock Spalling/Rock Burst (associated
with High Overburden)
• Drill and Blast Under Sg. Kerau
Cavity Encountered at Lepoh Fault
Lepoh Fault is one of the six fault zones along
the tunnel route. It is situated at about 28,590
metres from the tunnel outlet. The rock formation
surrounding this fault was found to be Class B
which is good rock, hard and fresh but affected
by weathering. During the excavation, TBM 2
encountered cavities with loose rocks falling into
the tunnel. It is unusual for cavities to occur in
granite rock as compared to limestone formations
where it is a common phenomenon. During this
incident, all TBM excavation had to stop. Remedial
work had to be carried out in order to ensure
worker safety and to ensure that the TBM would
not be damaged. Mitigation steps were taken to
inject grouting into the cavities and by changing the
tunnel support at the location. Figure 5 and Figure
6 shows the remedial works and face collapse at
the Lepoh Fault.
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VOL 57 JANUARY-MARCH 2014
VOL 55 JUNE 2013

High Temperature
at TBM 2
High
rock
temperatures
were experienced
between 19.5km
to 26km from the
tunnel inlet basin.
The
maximum
rock temperature
recorded
was
about 55.5°C at
the
overburden
of 1250m. The
reason for the
high temperature Figure 4 – Geological and
was not known. Fault Zones
The temperature
at other locations was less than 30°C even without
the use of air conditioning. Several assumptions
were made including, it may associated with the
movement of Bukit Tinggi fault, occurrence of hot
springs and also with high overburden along the
tunnel route. A study was carried out but at the
moment the results seem to be inconclusive. Figure
7 and Figure 8 show the rock and ingress water
temperatures. The maximum working temperature
specified in NIOSH guidelines 35°C.