After completion of mining works in bored tunnels, cross passages & in pump sumps, , the permanent works such as first stage concrete, SWC bracket installation, Cast in-situ reinforced concrete lining of cross passages & Pump sumps are undertaken in order to bring them for live tunnel operation.

First Stage or First Bed Concrete in Bored Tunnel

First stage or First bed concrete is a concrete layer which is placed between the precast segment lining and the track concrete lining cast by the track work contractor.

After completion of TBM mining, there are numerous preparations prior to this casting. They are, removing the TBM supply line, dismantling the temporary tracks, cleaning the slurry from the inverts, grinding the segments, cleaning and protecting the segment grooves and so on.

This casting work is considered as a massive concreting operation in Tunneling works.

SWC Bracket Installation

After the first stage casting, the precast segment lining is drilled at dimple locations to install various brackets that will be used for cabling of live tunnel operation.

The brackets are fixed at the segment face by means of bolt and expansion anchors hammered into the drilled holes.

Cast in-situ reinforced concrete lining of cross passages & Pump sump

Cross passages are constructed to connect the twin tunnels, which will act as an emergency escape route; whereas the pump sumps are constructed in lower elevation of bored tunnels or of the cross passages to receive the water and will be pumped out throughout the lifespan of the bored tunnels.

The design opening is achieved by using aluminium or conventional formwork systems.

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