An experimental study of the effect of local contact loss on the earth pressure distribution on existing tunnel linings

This study presents the results of the experimental investigation that has been conducted to examine the effect of local contact loss between a tunnel lining and the surrounding ground on the earth pressure distribution acting on the tunnel liner. An experimental setup has been designed using a mechanically adjustable tunnel model to simulate the initial lining pressure that results from shield tunnelling. A local separation between the lining and the surrounding soil was introduced at different locations around the tunnel and the changes in contact pressure were measured. Results indicated significant changes in earth pressure in the close vicinity of the area that has experienced the contact loss. The changes in earth pressure differed greatly depending on the location of the induced separation. When located at the invert and haunches results showed an increase in pressure by about 28%, whereas a pressure decrease of about 75% was measured immediately above the separated section when located at the springline. The above results suggest that the presence of a small lining area that is not in direct contact with the surrounding ground can have a significant impact on the performance of the tunnel lining.