Predictive model for the surface settlement caused by the excavation of twin tunnels

Abstract

It is of great difficulty to accurately predict the stratum deformation caused by double-track or twin-tunnel construction because of the complex coupled interaction of the two tunnels. Although green-field ground movements can be well fitted using established empirical methods, the disturbance caused by the excavation of the first tunnel is expected to affect the soil deformation close to the second tunnel. Due to the lack of consideration of the influence of secondary disturbances, the computed results of conventional prediction methods often lead to large errors when compared to measured results. Based on the Peck formula, this paper first clarifies the influence mechanism of twin-tunnel excavation. The model is then calibrated using field data from a twin-tunnel excavation in Wuhan city. With the concern of disturbance due to prior tunnel excavation, the disturbance correction factor η(x) is introduced to deduce a prediction formula for the ground surface deformation caused by twin-tunnel construction. Finally, the proposed theory is verified based on the field measurements of a practical case study of the Changsha Metro Line 2 Project.