Objective In water-rich weathered diorite strata, earth pressure balance （EPB）shield tunneling is prone to stratum water loss and water gushing. Therefore, it is necessary to study the water loss pathways and treatment measures for metro shield tunneling.

Method  Based on the Gangzicun Sta.- Huayuan Road Sta. shield tunnel section of Nanjing Metro Line 6, a research framework of "gushing characteristic analysis – water loss pathway identification – treatment measure evaluation" is established combined with stratum properties and field water loss conditions. Firstly, the gushing characteristics of the screw conveyor before and after the installation of water stop ring, as well as the evolution pattern of key tunneling parameters, including total thrust force, cutterhead torque and earth chamber pressure, are analyzed emphatically. Secondly, field tests are carried out to monitor the response pattern of pore water pressure with shield advancing after the water stop ring installation, and the water inflow in different sections is calculated to further clarify the specific water loss mode of the stratum. Finally, treatment measures for stratum water loss are discussed.

Result & Conclusion  After the installation of the water stop ring, water gushing is greatly alleviated and the fluctuation of earth chamber pressure weakened, while the total thrust increased. Since the stratum of the studied section presents high stability and low permeability coefficient, tunneling exerts limited influence on pore water pressure, and seepage is hardly to form in front of the excavation face. The water loss pathway is mainly the longitudinal seepage behind segment linings, which flows into the earth chamber through over-excavation gaps and triggers screw conveyor gushing. The permeability coefficient of moderately weathered diorite in fracture zones is high, where the water inflow is significantly greater than that in intact moderately weathered diorite. Therefore, water stop rings need to be installed more frequently to block water inflow. Installation of water stop rings and active drainage are effective measures to mitigate water loss during shield tunneling.