Experimental Investigation on the Effect of Volume Loss on Ground Movements Induced by Tunnelling in Sand

Abstract

Complex ground conditions or support failures during tunnel construction can lead to high ground loss, which may cause damage to surrounding structures. In this paper, a series model tests are carried out in order to clarify tunnelling-induced ground deformation at high ground loss conditions. The model tunnel in this test is shallowly buried in loose sand and the tunnel volume loss (Vl,t) is set from 4% to 10%. The Vl,t is controlled by a water-filling-drainage system and the ground deformation is monitored by digital image correlation (DIC) system. The results show that the Peck-Gaussian function can be used to fit the settlement data well, and the increase of Vl,t has no significant effect on the width of the settlement trough, while the horizontal displacement can be described by modified empirical method. The width of influence aera caused by tunnelling decreases linearly with depth, and the width near the tunnel crown is about 78% of that on the surface. For loose sand ground, it is the shear band rather than the soil arch that dominates the ground deformation. Furthermore, excavation leads to a volume contraction of the ground, which suggests predictions based on tunnel over-excavation trend to underestimate the ground deformation, and that should be taken seriously in consideration of the safety of the engineering project. This study can provide a better understanding of ground deformation induced by tunnelling.