Construction of Twin Bore Pipe Arch Tunnel at Bukit Berapit, Perak, Malaysia by D. Hall, V. Chow, K.C. Lin & Y.Y. Low

1. Construction of Bukit Berapit Twin-Bore Pipe Arch Railway Tunnel
D. Hall, V. Chow, K.C. Lin, Y.Y. Low
Gamuda Engineering Sdn Bhd, Petaling Jaya, Selangor, Malaysia.
don@2t.com.my, wschow@2t.com.my, kclin@2t.com.my, yylow@2t.com.my
Abstract: The Electrified Double Tracking Project (EDTP) between Ipoh-Padang Besar comprises design and construction of infra-
structure and system works for a 329km double track railway line. Bukit Berapit Tunnel is one of two rail tunnels that form part of the
EDTP Ipoh-Padang Besar, the other being Larut Tunnel. Dubbed to be the longest rail tunnel in South-East Asia, Bukit Berapit Tunnel
is twin-bore, 2.9km in length and horse-shoe shape in cross section. Its alignment necessitates multiple river diversions, a road diver-
sion and microtunneling crossings under the North-South Expressway. For construction of Bukit Berapit Tunnel underneath the ex-
pressway, two microtunnelling crossings are required. The first crossing is a 3m diameter triple cell drainage culvert to divert a local
river. The second is a twin-bore tunnel excavated with pipe arch primary support. Both crossings require detailed planning and execu-
tion due to the mixed face embankment, proximity and shallow overburden of the expressway.
1 INTRODUCTION
Triple 3m diameter
1.1 Alignment of Bukit Berapit Tunnel drainage culvert
Bukit Berapit Tunnel spans 2.9km from Changkat Jering in the
north to Padang Rengas in the south in the state of Perak. Its
alignment criss-crosses with a Federal Route, two rivers, and the
North-South Expressway twice, one of them with shallow over-
burden requiring two microtunnelling crossings. (Fig. 1)
Existing twin 3mx3m
Twin-bore railway drainage culvert to be
tunnel with pipe arch demolished & replaced
Fig. 2. Three-dimesional plan view of Bukit Berapit microtunnel-
ling crossings at North-South Expressway
2 CONSTRUCTION OF TRIPLE CELL 3M DIAMETER
Fig. 1. Alignment of Bukit Berapit Tunnel DRAINAGE CULVERT
The tunnel alignment with shallow overburden at the North-
2.1 The New Drainage Crossing under North-South Expressway
South Expressway clashes with an existing twin 3m by 3m in
cross section box culvert underneath the expressway with serves
for drainage flow of a local river and several streams. Soil investigation studies have ascertained that the triple cell 3m
In order to construct the twin-bore railway tunnel, the existing diameter drainage culvert, a new drainage crossing under the
box culvert needs to be demolished and replaced. Drainage and North-South Expressway, is to traverse only in alluvial soil and
hydrology design has indicated that the box culvert is to be re- engineered fill of the expressway embankment. Boreholes have
placed by a triple cell of each 3m diameter pipe, which also shown no indication of granite formation in the path of the cul-
needed to be constructed underneath the expressway. vert. The new culvert has only 4m overburden from top of the
The twin-bore railway tunnel on the other hand, can only be expressway embankment. (Fig. 3)
excavated after installation of 780mm diameter steel pipes or A 3.5m diamater soft ground cutterhead slurry shield micro-
pipe arch as primary support underneath the expressway. (Fig. 2) tunnelling machine is therefore chosen to carry out the the con-
Due to the shallow expressway overburden which is approx- struction. Bentonite slurry is provided as face pressure support
imately 4.0m with varying ground conditions, construction of during mining, as well as, to transport out mined materials. There
both drainage and railway tunnel crossings underneath the ex- is also an annulus grouting mechanism to fill up the space around
pressway embankment require special method and expertise. the pipe after the concrete pipe is jacked through, as a consolida-

2. tion measure. (Fig. 4 and 5)
A temporary sheet pile cofferdam has had to be constructed on
each side of the expressway embankment, in order to act as thrust
and receiving shafts, as well as allow just enough room to lift out
the microtunnelling machine to continue mining each concrete
pipe. The total jacking length of each 3m diameter concrete pipe
averages about 45.5m.
Continuous monitoring by optical targets installed on the ex-
pressway embankment is carried out in order to monitor any sur-
face settlement on the embankment during mining.
The construction of the triple cell 3m diameter concrete pipes
has been successfully completed. The pipes now act as a drainage
Fig. 6. Completed triple cell 3m diameter drainage pipes
culvert to divert the local river and streams that have been flow-
ing through the existing twin box 3m by 3m in the alignment of
the Bukit Berapit Tunnel. (Fig. 6)
3 DEMOLITION OF EXISTING TWIN BOX CULVERT
3.1 The Old Drainage Crossing under North-South Expressway
With the triple cell 3m diameter drainage culvert now all ready to
replace the 3m by 3m twin-box, old drainage crossing, demoli-
tion is ahead to make way for the Bukit Berapit Tunnel.
However, as an existing structure underneath the highway em-
bankment, its demolition is to be carried out step-by-step and
mainly to be rid of the steel bar reinforcement at the side walls
and base slab where it will clash with the tunnel. Demolition se-
quence also calls for pressurized cementatious injections in order
to solidify the embankment surrounding the box culvert. (Fig. 7)
After the step-by-step demolition, the twin box culvert is
eventually sealed off with lean concrete filling for the construc-
Fig. 3. Longitudinal profile (top) and cross section (bottom) of tion of the twin-bore pipe arch tunnel. (Fig. 8 and 9)
the triple cell drainage culvert
Fig. 4. One of the 3m diameter concrete pipes in microtunnelling Fig. 7. Plan (top) and cross section (bottom) of the demolition
action sequence
Fig. 8. Demolition by coring & hacking to rid of reinforcement
Fig. 5. Breakthrough of one of the 3m diameter drainage pipes
for twin-bore pipe arch tunnel construction

3. 4.2 Pipe Arch Microtunnelling Machine Explained
The microtunnelling machine of 800mm outer diameter is of slur-
ry shield type. This means it has bentonite slurry being pumped
to the front of the machine from behind the cutterhead for face
stabilization and to transport out mined materials. Laser guidance
serves to lead the machine’s steering and advance. The machine
and the 780mm outer diameter steel pipes of 10mm thick are
jacked horizontally by two-stage hydraulic jack cylinders.
The microtunneling machine also comes with a retraction
mechanism when rock or obstacles are encountered. Normally,
reaching the receiving shaft allows machine maintenance and
changing of worn out cutterdiscs. When encountering obstacles
Fig. 9. Sealing by lean concrete filling of the 3m by 3m existing
however, there is a risk of the machine being jammed and be-
twin box culvert
come completely damaged even before reaching the receiving
shaft. This mechanism is extremely useful at the right bore where
bedrock profile is high.
4 CONSTRUCTION OF TWIN-BORE PIPE ARCH
Every advance behind the machine is a string of 6m length
RAILWAY TUNNEL
steel pipes each one to be welded successively by MIG welding
after every jacking. (Fig. 12) The annulus of the jacked-in steel
4.1 The Railway Tunnel Crossing under North-South Expressway pipe is grouted to consolidate the outside surrounding. Once the
machine breaks through at receiving shaft, the microtunnelling
machine is dismantled and transported back to the jacking shaft
The concept of the pipe arch tunnel is referring to steel pipes of for the next drive until the maximum possible number of drives
780mm diameter acting as primary support that need to be in- for the pipe arch is completed. The maximum possible number of
stalled first before the tunnel can be excavated. drives per pipe arch tunnel is 20 ± 7 steel pipes depending on the
Before construction of the steel pipe arch and eventually the geology. (Fig. 13)
tunnel can be carried out, extensive soil investigation is commis-
sioned. Apart from drilling borehole on each of four shafts at the
embankment, seismic refraction and resistivity surveys, laborato-
ry tests, as well as probe holes also help to investigate the geolog-
ical profile beneath the expressway. (Fig. 10 and 11)
The soil investigation shows granite formation on each left
and right bore of the twin-bore railway tunnel. Higher bedrock
profile on the right bore requires a combination of methods of
umbrella tubes cum steel ribs installation and rock splitting cum
manual excavation before microtunnelling and full face excava-
tion can be carried out. Rock splitting is required at high bedrock
profile as blasting under the expressway is not allowed.
Fig. 12. The microtunnelling machine with retraction mechanism
(top) and successive welding of the 780mm diameter steel pipe
Fig. 10. Left-bore profile of twin-bore pipe arch railway tunnel
Fig. 13. Typical cross section of the twin-bore pipe arch tunnel
Fig. 11. Right-bore profile of twin-bore pipe arch railway tunnel
with 20 ± 7 steel pipes of 780mm diameter

4. 4.2 Pipe Arch Tunnel in Progress
The microtunnelling machine is launched from the jacking shaft
excavated within a three-sided 1 m diameter bored pile wall and a
thrust wall for the jacking. The receiving shaft consists of similar
three-sided bored pile wall. The jacking and receiving shafts have
to be excavated in each stage of 2m depth for each possible num-
ber of drives. (Fig. 14)
Before microtunnelling operation, the perimeter of 800mm
diameter in steel bar and shotcreted reinforcement of the bored
pile wall starting face have be cored and hacked out on each of
the receiving and jacking shaft to prepare as soft eye for the mi-
crotunnelling advance and breakthrough. (Fig. 15) Fig. 15. The soft eye prepared for microtunnelling advance
Where the bedrock profile is high at the right bore, an addi-
tional primary support of mini pipe arch consisting of 61 ± 34
numbers of horizontal umbrella tubes at 24m length, 139mm di-
ameter and 10mm thick fully grouted have to be installed first to
secure the weathered granite at top of the bedrock. (Fig. 16)
The tunnel is then mined in by rock-splitting method in pro-
gression of 1m advance. After the rock face is drilled with a se-
ries of holes of 110mm diameter, a hydraulic splitter is inserted
inside the drilled holes to split open the rock.
On completion of every 1m advance of mining, a single steel
rib of 203 x 135 x 31mm (31.3kg/m) is installed. Bullflex strip of
320mm diameter by 12m length is then installed on top of the
steel rib and inflated with pressurized grout to provide immediate
support. Crown face of the tunnel at the steel rib is then shot-
creted 200mm thick with double layers of BRC A6. Fig. 16. Installation of mini pipe arch ongoing
This mini pipe arch operation is repeated until it has mined in
20m. The rock face is also further secured with 6m length rock
bolts for complete stabilization in order for the pipe arch micro-
tunnelling machine to breakthrough at this face of the receiving
shaft. (Fig. 17)
The extent of steel pipe from jacking to receiving shafts aver-
ages about 90m in length. Total length of all steel pipes to be
jacked in for each left and right bore of pipe arch tunnel is more
than 2700m. The internal of the pipes are to be backfilled with
lean concrete before commencing excavation of the tunnels. (Fig.
18)
Once the pipe arch of 780mm diameter steel pipes have been
completely installed, the tunnel will be able to be excavated un-
derneath the expressway embankment every 1m in advance with
double steel rib of 203 x 135 x 31mm (31.3kg/m), supported by
bullflex and shotcrete. Fig. 17. Installation of single steel rib ongoing
During the progress of pipe jacking, the surface of the ex-
pressway embankment is monitored by optical targets.
Fig. 18. Installation of pipe arch ongoing
Fig. 14. The thrust wall and three-sided bored pile wall forms
jacking shaft for microtunnelling

5. 5 CONCLUSION
It is quite a challenge to construct a twin-bore tunnel through
such varying geology in shallow overburden. Debris from the ex-
pressway embankment such as tree trunks and steel bars apart
from soil and gravels are not uncommonly encountered during
microtunnelling. Excavation of the tunnel under a live express-
way also calls for innovative construction methods, as well as ex-
treme caution.
At the time of writing, microtunnelling works is still ongoing
on the right bore of the Bukit Berapit twin-bore railway tunnel.
The construction process calls for close cooperation and
teamwork amongst all members of the site team.
ACKNOWLEDGMENTS
The authors would like to express their gratitude to Keretapi Ta-
nah Melayu Bhd (KTMB), Projek Lebuhraya Utara-Selatan Bhd
(PLUS) and the whole site team of MMC-Gamuda Joint Venture
Sdn Bhd based at Package N6 of EDTP Ipoh-Padang Besar, in-
volved in the construction of the twin-bore, pipe arch railway
tunnel.