Tunneling in the MRT Sungai Buloh-Kajang Line


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A 9.5km stretch of the MRT Sungai Buloh-Kajang Line when it traverses the city centre of Kuala Lumpur will be underground. The northern end of the MRT tunnel is at the Semantan Portal at Jalan Duta opposite Parliament House while the southern end of the tunnel is at the Maluri Portal near the Sri Sabah Flats in Cheras.

There will be seven underground stations, namely Muzium Negara, Pasar Seni, Merdeka, Bukit Bintang, Tun Razak Exchange (TRX), Cochrane and Maluri.

The main method of construction for the underground alignment is by tunneling using tunnel boring machines (TBM) while stations will be built by excavating the station box from the surface.

Tunneling was chosen because the city center of Kuala Lumpur is already well developed. By tunneling, there will be minimal disturbance to existing roads and the city landscape. It will also will minimise the impact of the traffic and business activities during the construction period.

CHALLENGES

The geological condition of the Klang Valley makes tunneling beneath Kuala Lumpur extremely challenging.

The MRT Sungai Buloh-Kajang Line's underground alignment will cut through 2 different geological formations, namely the Kenny Hill Formation which consists sedimentary rocks such as mudstone, shale, phylite and sandstone, and the Kuala Lumpur Limestone Formation with erratic Karstic features comprising eroded limestone rock beneath a layer of top soil.


This graphics shows the different geological formation under Kuala Lumpur which tunnel boring machines have to excavate through for the MRT tunnel.

The transformation zone between these two geological conditions is at Bukit Bintang, with the Kenny Hill Formation lying to the west of this zone while the Kuala Lumpur Limestone Formation lying to the east.

Because of the erratic Karstic feature, the Kuala Lumpur Limestone formation is extremely challenging to tunnel through. Erosion of the limestone mass has created deep cavities and underground caverns, which, if not discovered beforehand, can pose considerable danger when tunneling activities are carried out.

To overcome this, meticulous soil investigation work has to done to gather as much information as possible about the soil condition of the tunnel path. On top of that, the correct type of TBM has to be deployed for the correct type of geological formation, and specifically for the Kuala Lumpur Limestone Formation, a special type of tunnel boring machine was developed to overcome the challenges posed.

TUNNEL BORING MACHINES

Two types of TBMs are being used to excavate the tunnel for the MRT Sungai Buloh-Kajang Line. In the portion of the alignment going through the Kenny Hill Formation, Earth Pressure Balance (EPB) TBMs will be used while Variable Density TBMs, which was specially developed joinly by world renowned TBM manufacturer Herrenknecht AG of Germany and MMC Gamuda joint venture, will be used to excavate in the Kuala Lumpur Limestone Formation portion of the alignment.

 

 

Earth Pressure Balance TBM

The EPB TBM uses excavated material to provide support for the drill face, thereby preventing soft ground from falling in during the tunnelling process. Nozzles at the front of the drill head inject foam into the soil before the drill face cuts into it, and turns the excavated earth into a more liquid and malleable substance.

The substance is stored behind the drill face, and applies an outward pressure equivalent to the combined inward pressure exerted by external forces, preserving what engineers call "face control". An operator monitors the pressure and releases excess excavated earth to the surface using a corkscrew conveyor to maintain the pressure between the TBM face and the external terrain.

 

Variable Density TBM

The high groundwater table and erratic Karstic feature renders EPB TBMs not suitable to tunnel in Kuala Lumpur Limestone Formation conditions. Slurry Shied TBMs are usually used for such conditions but lessons learnt from the SMART Project also revealed that the standard Slurry Shied TBMs not able to prevent incidences of sinkhole formation and blowouts.

The Karstic environment means that the standard Slurry Shield TBM frequently encountered chambers or fissures into which the slurry will escape resulting in high volume and pressure loss. If the fissures lead to the surface, the slurry will escape to the surface, resulting in a blowout. On the other hand, if the slurry escapes into an underground cavity, it will result in a loss of face pressure, thereby creating sinkholes on the surface.

 

 

To overcome these situations, the Variable Density TBM was developed which enables the density and viscosity of the slurry to be varied. This prevents the slurry from escaping into cavities or blowing out from fissures leading to the surface. With this, the face pressure of the TBM is preserved, and the terrain is kept stable during the excavation process.

 

Download Video (Tunnel Boring Machine - 49mb)

 



UNDERGROUND STATIONS

An artist impression of how the Variable Density Tunnel Boring Machine will tunnel beneath Kuala Lumpur.

There are seven stations along the underground alignment of the MRT Sungai Buloh-Kajang Line. They are Muzium Negara, Pasar Seni, Merdeka, Bukit Bintang, Tun Razak Exchange (TRX), Cochrane and Maluri.

Construction of underground stations is by way of excavating the station box from the surface to the desired depth of the station. Any existing building or structure on the surface will have to be demolished before excavation begins. Buildings which construction on top of underground stations can only be built at the same time or after the station has been built.

Surface land is also required to construct exits for underground stations to ground level. Connecting underground walkways can also be constructed to connect underground stations with the basements of adjacent buildings, allowing MRT users to access buildings directly without needing to walk at street level.

 

 

For more information on tunneling for the Klang Valley MRT Sungai Buloh-Kajang Line, please see the website of MRT Project's underground works package contractor MMC Gamuda KVMRT (T) Sdn Bhd at http://www.mymrt-underground.com.my/

 

Underground Project Updates Download Video (Underground Works - 97mb)

 



             


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