THE Klang Valley Project reached yet another important milestone on 24 December 2013 as one of the Tunnel Boring Machines (TBMs) used to construct tunnels for the MRT Sungai Buloh-Kajang Line made its first breakthrough at the underground KL Sentral Station.

A breakthrough is the process where a TBM emerges from underground after completing the tunnel excavation process. This usually occurs inside a station box or a retrieval shaft which is specially dug to enable a TBM to breakthrough.

The Earth Pressure Balance TBM was launched at the Semantan North Portal on 13 June 2013. The machine excavated about 1.4km of tunnel for trains that will head north towards Sungai Buloh. The diameter of the tunnel is about 6m.
After the breakthrough the TBM will undergo maintenance works at the KL Sentral Station worksite before being re-launched for tunnelling through to Pasar Seni MRT Station.

Currently, there are seven TBMs which are operational for the MRT Project at various stages of tunnelling. These machines are monitored by personnel who are stationed directly above where the TBMs excavate.

A total of 10 TBMs are going to be used to construct the 9.5km long underground section of the alignment. They comprise of four Earth Pressure Balance TBMs that will be used for the Kenny Hills geological formation and six Variable Density TBMs for the Kuala Lumpur Limestone geological formation.