Tunneling-induced longitudinal responses of existing tunnel with discontinuities in structure stiffness

Abstract

Owing to a change in construction method, the existence of a reinforcement section, or a settlement joint, an existing tunnel is likely to have discontinuities in its longitudinal stiffness. An analytical solution for the new tunneling-induced responses of the existing tunnel with stiffness discontinuities is derived in this paper. The existing tunnel is modelled as a series of Timoshenko beams connected by elastic springs for considering various connection types and possible discontinuous deformations at the locations of the stiffness discontinuities. The accuracy and applicability of the proposed solution are successfully verified by numerical models. Two hypothetical examples are used to further study the normalized response of the existing tunnel with single stiffness discontinuity or with a reinforcement section. The results show that when the location of the new tunnel is around the position of the stiffness discontinuity, the normalized internal force of the small-stiffness section of the existing tunnel becomes larger. The reinforcement length and the longitudinal stiffness of the reinforcement section should match each other to control abrupt increases in the normalized internal force and ensure the effectiveness of the reinforcement measures.