Influence of relative density on deformation and failure characteristics induced by tunnel face instability in sandy cobble strata

Abstract

This paper aims at influence of relative density on deformation and failure characteristics for a shield tunnel in sandy cobble strata. A series of model tests were performed for tunnels with different relative densities of 0.35, 0.55, and 0.75. The evolution law of the stratum deformation during the instability process of the tunnel face was analyzed. The soil disturbance range of tunnel face instability with different relative densities was explored. The results show that relative density has a significant impact on the extent of surface subsidence. The stratum deformation caused by the instability of tunnel face in the medium dense and dense sandy cobble strata only occurs significantly behind the tunnel face, while the stratum with loose sandy cobble has significant stratum deformation behind and in front of the tunnel face. The method of improving the relative density can be used to reduce the deformation of the sandy cobble strata.