Record rail tunnel break through in Malaysia Nov 2010
Don Hall, Head of Tunnel Dept, Gamuda
A final blast last Monday, 1 November 2010, completed excavation of what is believed to be the longest drill+blast rail tunnel in South East Asia. At 2.5km long, the twin tube Berapit tunnel is a key element on the electrification and double-track upgrading of the Ipoh-Padang Besar railway line in Malaysia. Constructed by two of Malaysia's heavy civil contractors, the Gamuda-MMC JV, the Berapit tunnel, and the second shorter Larut tunnel, replace four tunnels and two bridges on the existing single track alignment and completes several highway crossings on their passage through the hills.
- For the past one year and three months, crews of the Gamuda-MMC JV have been mining the twin tube Berapit tunnel on the Ipoh-Padang Besar railway line upgrade project in Malaysia. On 1 October, the first bore saw daylight. At a ceremony on the north side of the mountain, workers excavating the northbound bore of the tunnel initiated a last blast completing the tunnel about a month ahead of schedule. Significantly, more than 470,000 work hours were completed without a lost-time injury among the 220 employees. On 1 November crews completed the parallel single-track tunnel.
The parallel tunnel broke through on Monday, 1 November
- Workers will continue to install the waterproofing membrane and cast the final 500mm concrete lining before fitting ventilation and drainage systems and laying the rail track towards completion of the tunnel by the end of 2011.
- Gamuda-MMC JV was awarded the contract to electrify and double-track the 329km Ipoh-Padang Besar railway line at a fixed cost of MYR12.5 billion (US$ 4 billion). The design phase of the project is worth MYR420 million. The track doubling of the northern portion of the Kuala Lumpur-Thai border line, which forms a key section of the planned rail link from Singapore to Kunming in China, includes the Larut tunnel and the Bukit Berapit tunnel, Southeast Asia's longest rail tunnel. Electrification of the line will permit train speeds of 160km/h.
- The Berapit and Larut tunnels for the project are situated between the towns of Padang Rengas and Taiping. The Larut tunnel (390m long) and the Berapit twin-tunnels of 2.5km long each are 10km apart and sit respectively at the north and south gateways into this hilly region of Perak. The alignment carries the new tunnels under the old single-track line as it winds up over the hills as well as under the major Plus Highway twice and under a federal trunk road (Figs 1 and 2).
- One of the shallow depth crossings of the Plus Highway required a pipe arch presupport system, which was constructed using the microtunneling method. These microtunnel drives of up to 92m long for a total of 4,400m, are the longest in Southeast Asia. Construction of the Berapit tunnel Taiping portal required diversion of the federal trunk road and of a river for a length of about 1.5km. Land acquisition for construction of the south portals was a key issue with numerous owners of small land parcels creating a complex matter to resolve.
Padang Rengas portals of the Berapit tunnel
- The twin tunnels were constructed about 80% by drill+blast with the balance by cut-and-cover. The tunnels encountered varying geology ranging from extremely hard granitic rock to residual soil and included unpredictable interfaces between rock and conglomerate.
- The 9m high x 9m wide horse shoe shaped twin tunnels (average 50-60m2) are about 20m apart and will be fully concrete lined and connected with nine cross passages.
- Drill+blast excavation of the long twin tube Berapit tunnel advanced from the four portals. To start excavation of the Padang Rengas portals, massive earth works were required as well as diversion of a stream, which in storm conditions would have caused flooding of the works. The initial 150m advance of tunneling was in very soft, poor ground conditions in which high water flows, several large boulders, and alluvium and highly weathered granite were encountered.
- To reduce the water in flow, dewatering pipes were drilled from within the tunnel and wells were installed on the surface.
Pipe umbrella presupport
- Pipe umbrellas were installed for tunnelling through the highly weathered granite residual soil. These comprised 114mm diameter x 10mm wall thickness steel pipes, installed on a 3m overlap. The pipes were inclined at 4° and inserted at spacings of 300mm, 400mm and 500mm depending on the quality of the ground. Each set of 10 pipes installed was fully grouted before the next set was inserted. Fibreglass face nails were also used to increase stability and in extremely poor ground conditions, the pipe umbrella overlap was increased.
- Excavation of a top heading was then carried out in 1m rounds with steel ribs and shotcrete support and the bench was excavated once the tunnel was in competent granite. Boulders when encountered were either removed mechanically or blasted.
- Blasting pattern
Once into competent granite, drill+blast tunnelling progressed. A blast in good quality granite would normally pull a full charge-hole length of 4.3m. To achieve this, the drill pattern comprised a total 134 drill holes of 45mm diameter plus a set of 110mm diameter burn holes.
- Emulex 150 cartridges and Bulk Emulex 1000 UG explosive was used. Emulex is an emulsion explosive consisting of droplets of saturated oxidizer solution tightly packed in a homogenous fuel mixture. A typical blast consumed a about 365kg of explosive and 134 detonators. About 400 tonne of explosive was used on the twin Berapit tunnels.
- River diversion for pipe arch twin tunnel
A particularly complex set of work was the main Plus Highway underpass. This required construction of pipe arch presupport of each tube but to make way for this work an existing 3m x 3m drainage box culvert had to be demolished and the drainage flow of a river and several streams diverted.
- Drainage calculations determined that the box culvert needed to be replaced by three 3m diameter pipes installed under the highway using microtunneling techniques. With only 4m overburden, this was a major achievement. The three pipes were constructed using a bentonite slurry microtunnelling/pipejacking machine, the slurry pressure being used to support the face and avoid surface settlement of the highway.
- As the site investigation showed no indication of granite, a RASA 3.5m diameter machine with soft ground cutterhead was chosen to work through compacted fill and alluvium. Constant surface monitoring was carried out during all three drives and only minimal settlement was recorded.
- Once completed and the river and streams diverted to their new course, the existing box culverts under the highway were hacked and back-filled to allow for the construction of the two pipe arches.
- Pipe arch construction
At another passing under the Plus Highway, extremely low cover of only 3m required extra support measures to avoid settlement. The solution was to pipe-jack an arch of microtunnel presupport. Each arch comprised steel pipes of 6m long x 780mm diameter x 10mm wall thickness welded together for each 90-92m long drive (Fig. 3 and 4). Once installed, the full pipe length was backfilled with lean mix grout. A total length of 4,400m of pipe jacking was installed to presupport both tunnel tubes.
- Unfortunately the geological condition was not homogeneous with granite at one end of the drive coming to within 2m of the crown. Due to the 780mm diameter of the machine, disc changes would not be possible and there was the possibility that excessive wear could bring the machine to a standstill with retrieval unlikely from under the highway.
- To avoid this problem, a Herrenknecht AVN 500 microtunnelling machine was chosen with a sacrificial skin that upgraded to an AVN 600 for the correct cutting diameter.
- Should the machine be unable to continue, the outer ring of the cutterhead and the sacrificial skin can be discarded and the main body of the machine pulled back through the pipe.
Excavation of the Larut tunnel started at the south portal with two overlapping pipe umbrellas. Due to close proximity of the existing rail track tunnel, blasting under the umbrellas could only take place once a line block had been granted. The line block was usually between 1-5pm daily. Monitoring of the existing tunnel was carried out before, during and after each blast.
- Excavation was carried out on a top heading and bench operation. Apart from pipe umbrellas at each portal, rock support was limited to spot bolting and shotcrete sealing.
- A drained waterproofing membrane system was placed prior to casting the final concrete lining. After testing of the integrity of the membrane, the final lining was placed using 9m long, custom built steel forms.
- Once the tunnels are completed with the finishing M&E and track laying work, the new upgraded line is expected to be commissioned by the end of 2011.
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