Performance of precast bolted tunnel lining through physical and numerical modelling

Abstract

Designing a tunnel is significantly different from designing a normal building. Tunnels not only require maximum strength but also need for stability due to movement which incorporate stress redistribution in the surrounding soil. To allow tunnel deformation, a number of precast concrete segments are lined together and joined with curved bolts to form a tunnel ring. Due to jointing conditions and the curving shape of the segment, complex flexural movement in the segment joints is not yet fully understood. It is crucial to examine angular joint stiffness as previous researchers assumed that each segment joint has a unique value, even though they change non-linearly. This study examines angular joint stiffness in lining segments to produce a realistic model of soil-structure interactions. The behaviour of individual (non-jointed) segments and dual-jointed segments were investigated in the laboratory with a transversal vertical line load supported by two different boundary conditions to attain a moment reduction factor, MR and angular joint stiffness, k?. MR was in the range of 0.132 - 0.85 for pin-roller and 0.62 for pin-pin. The k?? of dual-joints for pin-pin conditions was 6000 to 7000 kNm/rad and k??for pin-roller conditions was 1035 kNm/rad. Three-dimensional segmental lining models were developed using ABAQUS 6.10 software. Initial results were validated with an analytical Unit Load method for selected load and support conditions. The model was compared with laboratory data. It was observed that the segmental tunnel lining model with nonlinear jointed stiffness for hinge interaction matched laboratory results. The simulation was successfully extended into a full soil-tunnel model for a case study. Validation was carried out with published field data from a case study for Mass Rapid Transit (MRT) Circle Line Projects in Singapore. A new level of understanding for tunnel linings was achieved from the effect of segment lining joints. When compared to a continuous ring model (tie-model), less tangential bending was observed in the simulated segment tunnel model (hinge-model), indicating a reduction in joint stiffness with increased loads and a significant effect on overall tunnel responses. A practical method to solve the soil-structure interaction of segmental bolted tunnel linings using nonlinear angular joint stiffness was achieved from this study.