Ground deformation and three-dimensional simulation during sequential excavation of unsupported tunnel in a sedimentary soft rock

Abstract

Unsupported excavation for a horseshoe shaped tunnel with 5.0m height was carried out in sedimentary soft rock under 45m depth, and the ground deformation during the excavation was measured by high resolution equipment installed prior to the construction work. In order to simulate the ground deformation, soft rock samples retrieved from the same site and tested at a laboratory. Three-dimensional elasto-plastic FEM analysis was carried out to investigate the observed behavior, where the soil parameter values were assigned based on the results from laboratory tests and in-situ measurements. The FEM analysis showed that the absolute value of settlement at the tunnel crown caused by the unsupported tunnel excavation was only slightly influenced by the ground strength parameters. The majority of the influence was due to the deformation modulus in the elastic region. The settlement characteristic may have been also affected by non-uniformity, the confining pressure and creep.