Sunday, 19 January 2014

Mining method for cripple siding

A cripple siding is an extra track that is used to facilitate withdrawal or storage of trains that are not part of revenue service. For instance, trains that are on standby for emergency situations as evacuation trains or trains that are faulty and not fit for passenger service. The Downtown Line has several cripple sidings along its 42-km route length and most are constructed using the open cut technique, known as cut-and-cover (the process of excavating the earth - cut; and subsequently back-filling over the completed tunnel - cover). However, there lies one section of cripple siding that is being constructed using the mining method.

Cripple siding near Bedok North station

The siding falls under the work scope of Contract 927 and contractor CMC di Ravenna, who are building Bedok Reservoir station. The cripple siding is located near to Bedok North station. In the mining method, the rock matter is cut away and a rebar cage installed. A mix called shotcrete is then sprayed over to hold the ground in place, forming the shape of the tunnel. Subsequently, tunnel rings are installed in this portion or concrete is poured directly into formwork to form the permanent tunnel. Other areas where mined tunneling have been used along the DTL are at Promenade (towards Bayfront as it crosses under the Circle Line), Little India (towards Rochor as it crosses under the North East Line) and at Fort Canning (towards Chinatown as it approaches the Singapore River for the TBMs to be able to launch). Here are a few photos showing the extent of work on the cripple siding at Bedok North.

The location of the cripple siding, in between the main line tunnels. On the left is the Expo bound tunnel bored by Tierra
and on the right is the Bukit Panjang bound tunnel bored by Kaida.

A head-on view of the cripple siding mined tunnel.

Installation of rebar for spraying of shotcrete to act as a firm support for the soil above.

Photo credit - Friends Keeper

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