Blast-induced waves in soil around a tunnel

Abstract

The paper is concerned with the numerical modelling of waves in saturated granular soil around a cylindrical tunnel with a tubbing-type lining. The waves are induced by a short-term large-amplitude load on the tunnel wall. The soil is assumed to be fully saturated or contain a small amount (a few volume percent) of free gas in the pore water. The behaviour of the solid skeleton is described by a constitutive relation of the hypoplasticity theory. The presence of gas makes the soil stiffness stronger pressure dependent and leads to the formation of a shock front in the soil in the immediate vicinity of the tunnel. Free gas in the pore water is shown to be an adverse factor from the viewpoint of both the residual state of the soil and the deformation of the lining. A permanent reduction of the effective stresses in the soil caused by the wave is stronger for the soil with gas. For a sufficiently large loading amplitude, the wave may lead to the vanishing of the effective stresses and liquefaction of the soil. It is also shown that the presence of gas increases the displacement and the velocity of the tubbings.