ABSTRACT
With the rapid underground infrastructure construction, multi existing tunnels undercrossed by new tunnels become increasingly crucial, which incorporates high complexity of tunneling influence and soil-structure interaction in multi-tunnel conditions. In this paper, an infrequent real case of 4 parallel overlapped subway lines undercrossed closely by new shield tunnelling in Tianjin, China was investigated. The settlements of existing tunnels are monitored with high precision and frequency using VDMS, a novel vertical deformation monitoring system. The construction process is divided into 9 stages and then classified into 4 risk levels. The study demonstrates the capability of VDMS to achieve timely detection of potential risks. Furthermore, a refined 3D numerical model was established to analyze the undercrossing effect. The result indicates that the extensive reinforcement on surrounding soil by multiple structures tends to unify soil and structures into a single unit that collaboratively withstands new tunneling disturbance.
