Large Extrusion Deflection Control Technology for Tunnel in Active Fault Zone

Abstract

The Wushaoling tunnel passes the active engineering fault 7(simply called F7 below), where the surrounding rock is broken, mainly composed of fault boulder clay and rubble with very low strength/geostress ratio, resulting in remarkable deflection. Measures have been taken to control the large deflection of the primary support effectively and to ensure safety of the lining structure so that the F7 can be passed as early as possible . Two small-section roundabout drifts for left and right line each, affected less by the high geostress, are excavated in order to continue the construction ahead, to release partial geostress and to conduct experimental study guiding the design &construction of the main tunnels. At the same time, in-situ experiments are carried on against different pattern and parameters of support structure. Based on the above study, the measures are finally determined such as adopting circular multiple-support composite lining, setting deformation joints per segment to absorb the movement of the active fault, adhering the construction principle of “rapid excavation, rapid support, rapid closure and timely lining”, etc. As a result, the large deflection is controlled effectively in subsequent construction and the large-scale active fault rarely encountered domestic and abroad has been passed successively.