Twin EPB tunneling-induced deformation and assessment of a historical masonry building on Shanghai soft clay

Abstract

This paper presents a comprehensive geotechnical and structural investigation of a historical multistory masonry building undercrossed by twin mechanized metro tunnels. The prototype is the case of the Shanghai Metro Line 11, which was recently constructed in Shanghai clay using two EPB machines. Field instrumentation is conducted before, during and after tunneling. The settlements along the greenfield surface and building sections are measured. A detailed three-dimensional finite element (FE) model is developed to reproduce the twin tunneling process under the masonry building characterized by the presence of uneven settlements to capture the interaction phenomenon occuring between the twin tunnels during construction. An advanced constitutive model, capable of simulating the behavior of Shanghai clay under the excavation, is employed for the numerical analyses. The FE model is first validated against a set of field instrumentation data, including both greenfield and building surface settlements in cases of single-tunnel passage and double-tunnel passage. Further analyses of the effect of the building presence on the ground movements are subsequently conducted. The results highlight that the presence of the building affects the settlement profiles and that significant differences are observed compared to greenfield conditions. The volume loss of the surface settlement trough after the passage of first tunel and twin tunnels is observed to be approximate 0.58% and 1.02%, respectively. A quantified assessment of the additional deformation of the historical building considering the existing deformation is conducted. No obvious damage to the building is observed during and after the tunnel drives, which confirms the successful tunnel passage beneath the historical building.