SQUEEZING POTENTIAL OF JOINTED ROCKS IN TUNNELS

Abstract

Rock squeezing is the deformation of the boundary of underground opening that reduces cross section of the opening. The squeezing is recently receiving great attention in the field of rock mechanics and tunneling. Rock squeezing problems such as the inward movement, invert heaving and the buckling of the walls / crown have been experienced during tunneling through low strength rock. Higher overburden pressure, orientation of the discontinuities, condition of the joints, number of joint sets and frequency of the joints affect the squeezing of rock mass around the tunnel. In this dissertation, a methodology has been suggested, to asses the excepted squeezing of a circular tunnel in jointed rock mass. The methodology is based on the constitutive modeling of jointed rock masses presented by Huang et al. (1995). The model uses the normal and shear stiffnesses of the joints, their orientation and spacing in addition to the intact rock properties to model the stress-strain behavior of the mass. In the present report two models are developed: the first one is two dimensional model under biaxial loading and the second is three dimensional model under triaxial loading to take into account the effect of intermediate confining stress a2. Effect of dilation of joints is also considered in this model. Tangential and radial stresses surrounding the tunnel are estimated using theory of elasticity. This model is applicable for only small deformations and elastic ground conditions, having unfilled joints, Uniform joint spacing and the same geological condition are assumed throughout the length within the joint set.