Support provided to rock excavations by a system of two liners

Abstract

The support provided by a system of two liners to a cylindrical excavation which is subjected to a shear stress at infinity is considered. The tensile, shear and normal stresses and the rotation of a material element at the surface of the excavation before and after the liners are applied are calculated to second order in the thickness parameter ɛ using the theory of plane strain in elasticity. Stress is transferred from the rock mass to the liners. To first order in the thickness parameter ɛ the changes in the stresses and the rotation do not depend on the order in which the liners are bonded to the surface of the excavation. A small dependence on the order in which the liners are attached was found at second order in ɛ . Effective boundary conditions on the shear and normal stress at the surface of the excavation which could replace the liner system were obtained.