An MRT system best serves its function by providing connectivity to the busiest population pockets, but these pockets are also extensively developed with narrow corridors and dense structures. An above-ground route especially in the heart of KL city for the MRT is simply unfeasible.
The most challenging task in the underground tunnelling works for the Klang Valley Mass Rapid Transit (KVMRT) Sungai Buloh-Kajang Line (SBK Line) is the tough geological formations found underneath Kuala Lumpur city. The underground alignment for the KVMRT SBK Line will navigate past two distinctly different geological settings, with the extreme karstic limestone accounting for almost 50% of the underground alignment. Extreme karst is a geological formation consisting of weakly soluble bedrock such as limestone eroded by mildly acidic water over millions of years, leaving behind an elaborate labyrinth of unstable caverns, cliffs and pinnacles in the depth of Kuala Lumpur city.
Thus, maintaining the equilibrium of the sub-surface geological system containing underground reservoirs and water-filled cavities is a challenge as any disturbances from underground activities could cause karst sinkholes and ground subsidence. Another possible consequence is bentonite blowouts, resulting in mudflows that rise to the surface during the boring process.
This is a cross section of the soil formation underlying Kuala Lumpur city that the KVMRT SBK Line will be passing through. The interface between the more consistent Kenny Hill formation and the highly unpredictable extreme karst formation is somewhere beneath the centre of Jalan Bukit Bintang. About 4.5km of the 9.5km-long underground tunnelling works will bore past this “Swiss cheese” of karst.
With significant improvement in the knowledge of karst terrain and using the world’s most sophisticated tunnel boring machine, and information gathered from extensive ground investigations and pre-tunnelling soil treatment, our tunnelling team is expected to safely bore through the delicate extreme karstic limestone stretch of the SBK Line underground alignment at an average depth of 30m.