The Ingenieur Vol 57 January-March 2014 The Ingenieur Vol 57 January-March 2014 | Page 17

Figure 14(b) – Rock Burst at TBM 1

Figure 14(a)- Rock Burst at TBM 2

Figure 15–Tunnel Surface with Fibre Mortar

Several mitigation steps were taken to
overcome the rock burst along the tunnel route,
including the installion of netting and spraying the
fibre mortar at the location of rock bursts. Figure
15 shows mitigation steps to overcome rock burst.

friable clay or sandy material at the tunnel crown.
Permeability tests were carried out using two
methods:
a. Lugeon Test, and
b. Johnson Formation Test (JFT)
In order to figure out the permeability of
fractured granite rock under the river, a series
of Lugeon tests (Pressurized water permeability
tests) were carried out by utilising additionallybored vertical boreholes. The test results showed

Drill and Blast Under Sg. Kerau
One of the greatest challenges faced during the
tunnel construction was tunnelling across Sg.
Kerau in Pahang. The cover between the river bed
and tunnel crown is 10m and it was considered
possible that the river bed might collapse into the
tunnel due to the high water ingress.
Of the 10m overburden at the river crossing
area, the rock portion was assumed to be about
5m thick with weathered condition right above the
tunnel crown, and above this 5m thick rock section
was alluvial material, which was assumed to
consist of silt, sand and gravel. Therefore, counter
measures had to be considered from two aspects;
how to tackle the assumed ingress water and how
to stabilize the tunnel face during excavation.
Additional boreholes were carried out at the
locations. The result of this series of investigations
showed that there was only 3-4m of rock coverage
above the tunnel crown and, furthermore, the
rock was found to be significantly fractured and
weathered, indicating that there might be some

Figure 16 Lugeon Test Map Around Kerau River
15