THE world’s first Variable Density Tunnel Boring Machine completed its job and broke though at the Pasar Rakyat Station site at about 2.30pm on 9 January 2014.

The tunnel boring machine known as Cochrane 2 was launched from the Cochrane Launch Shaft on 22 July 2013. The machine excavated around 1km through karstic limestone formation, going under the SMART Tunnel and Jalan Tun Razak.

The breakthrough marks the completion of the first section of twin tunnels between Cochrane and Pasar Rakyat. Tunneling of this section was without any major issues. The event was marked with a celebration organized by the MRT Project underground works package contractor MMC Gamuda (T) Sdn Bhd.

Designed together by MMC Gamuda and Herrenknecht AG, the Variable Density TBM is specially built to handle excavation through the transition between two geological formations – the Kuala Lumpur Limestone Formation and the Kenny Hill Formation – by being able to switch between slurry and earth pressure balance modes.

Using slurry of higher density and viscosity, the TBM is also designed to cater of the karstic limestone formation, minimizing the risk of blow-outs and sinkholes.

To date, the underground portion for the Sungai Buloh-Kajang MRT project has reached 50% completion while the project overall has reached 33% completion. With the completion of Cochrane 2, six TBMs are currently in operation. Tunneling works are expected to be completed by mid-2015.