New-design TBM ready for Malaysia challengeNov 2012
Peter Kenyon, TunnelTalk
The world's first Variable Density TBM (VD-TBM) for the twin-running 9.5km tunnelled section of the Klang Valley MRT is completed and ready for disassembly and shipment to Kuala Lumpur, Malaysia.
World's first VD-TBM ready for shipment to Malaysia
The machine, the first of six specially designed for the Mass Rapid Transit Corporation (MRT Corp) in a collaboration between Herrenknecht and its selected tunnelling contractor MMC-Gamuda, has been specifically designed for coping with the specific challenges presented by Kuala Lumpur's extreme karstic limestone geology.
A total of six VD-TBMs will be used to tunnel through the highly unpredictable karstic Kuala Lumpur Limestone Formation between Bukit Bintang Sentral station and the Maluri Portal (Fig 1), for approximately half the total alignment. Four EPBMs will be used to drive through the more homogeneous and stable Kenny Hill geological formation that will be encountered on the northern and western half of the alignment.
The VD-TBM evolved as a direct result of MMC-Gamuda's experience as a tunnelling contractor on the Kuala Lumpur SMART project, also through Kuala Lumpur Limestone. The slurry TBMs used there frequently encountered chambers or fissures into which the slurry would escape, resulting in high volume and pressure loss (Fig 3, below).
"To overcome this problem the MMC-Gamuda JV, with its TBM adviser Richard Lewis, and Herrenknecht, worked together to design the Variable Density TBM," said MMC-Gamuda Construction Manager Gus Klados.
Fig 1. Two distinct geological formations
Fig 2. VD-TBM specially designed for karstic limestone
"The variable density slurry shield enables the TBM to alter the density and viscosity of the slurry according to soil condition when tunnelling. Slurry of higher viscosity can stop slurry of lower viscosity from escaping into cavities or blowing out from fissures leading to the surface. This in turn preserves the face pressure of the TBM, keeps the terrain stable during the excavation process, and prevents upwards flows of slurry, reducing the risk of slurry fountains on the built-up surface," he added.
Fig 3. Kuala Lumpur's extreme karstic geology presents challenges
Encik Amir Mahmood Razak of MRT Corp said: "The factory acceptance test is an important milestone in the MRT project as it marks the completion of the TBM's manufacturing process. MRT Corp and MMC-Gamuda has inspected the TBM to ensure that it complies with its required specifications and that it functions properly. The TBM is now ready for action in Malaysia."
"The designing of the Variable Density TBM is the result of combined Malaysian and German ingenuity. This is something which Malaysians can be truly proud of," he added.
Table 1. Breakdown of the Klang Valley MRT tunnel drives
2 x EPBM
North Portal (Sementan) to KL Sentral Station
2 x EPBM
Pudu- KL Sentral Station
2 x VD-TBM
2 x VD-TBM
2 x VD-TBM
The machine, which took nine months to manufacture at Herrenknecht's factory in Schwanau, is now being dismantled and will be shipped to Malaysia with a second similar machine. Arrival in Malaysia is scheduled for March 2013, and the two machines will be reassembled in the Cochrane launch shaft in Kuala Lumpur before launching on drives towards Pasar Rakyat Station.
In all 10 TBMs have been ordered - six of the Variable Density type plus two further EPBMs from Herrenknecht, and two more from China Railway Tunnel Engineering. The Chinese TBMs are expected to be ready for factory acceptance testing in January 2013.
The Malaysian MMC-Gamuda JV won the MYR8.2 billion (US$2.65 billion) contract for the tunnelled section of the 51km line in March (2012) following a Swiss Challenge method of procurement. In the event the JV submitted the lowest bid, and did not need to exercise its right to meet or better rival qualifying bids.
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