DEVELOPMENT OF SURFACE SETTLEMENT OF TWIN TUNNELS UNDER THE INFLUENCE OF THE RIVER

Abstract

Soft soil poses more challenges to the construction of shallow-buried tunnels than other soils: the surrounding rock mass is more easily disturbed, and the tunnel stability is more influenced by groundwater seepage. The research is based on the Zizhi Tunnel project, a shallow-buried twin tunnel in soft soil. This paper divides the research area into the inside and outside river-affected areas respectively. From the field monitoring data, the settlement law can be summarized, which found that for a single monitoring point, outside a river-affected area, the entire settlement development stage can be clearly divided into three stages: slow growth, rapid growth stage, and gradual convergence; however, inside the river-affected area, the settlement in the last stage will not converge but will continue to develop. Compared with the vault settlement, the surface settlement inside the river-affected area develops slower than that outside the river-affected area, which shows good consistency with the monitoring data. The synchronization of the sinking rate and stability of vault settlement and surface settlement verifies that the river over the tunnel has an impact on the development of surface settlement by the groundwater seepage in the soft soil. Based on field monitoring data, a numerical model is established to investigate the influence of the river on the surface settlement of the twin tunnels, of which the numerical results show the same development law as the monitoring data.