Purposes of subdivision of tunnelling faces in Sprayed Concrete Linings (SCL) method

In using sprayed concrete lining methods for lining a large tunnel in soft ground, tunnelling face is generally divided into many parts owing to the following reasons:

(i)  It allows early closure of part of the invert of the tunnel.

(ii) With the excavation in every part occurring at different times, it helps to decrease the area of exposure of the tunnel face so that there is better control on tunnel stability.

(iii)For unit advancement in any part of the tunnel excavation, amount of excavation and sprayed concrete is decreased. Hence this allows for early provision of primary support.