Study on launch tunnelling parameters of a shield tunnel buried in pebble soil with existing pipelines base on discrete continuous coupling numerical method

A computational scheme coupling the particle flow code in three dimensions and fast Lagrangian analysis of continua in three dimensions techniques is implemented to evaluate the coupling effects of different discrete and continuous coupling computing modes under a gravity stress field. Based on the optimal coupling mode that can consider the computational efficiency and coupling effect, a three-dimensional discrete-continuous coupling numerical model is established to realize the dynamic excavation of a shield tunnel. The effects of launch excavation chamber filling rates and shield tunnelling control parameters on the ground surface and pipeline settlement in the initial stage are examined. With the increase in the initial chamber filling rate, the convergence rate of the surface and pipeline settlements increases, and the total settlement significantly decreases. Moreover, although the disturbance range of shield tunnelling to the strata decreases, the thrust and torque of the shield machine increase. As the cutter head speed varies, the settlement of the surface and pipeline and thrust of the shield machine do not significantly change. However, the torque of the shield machine significantly increases with the increase in the cutter head rotation. The tunnelling speed, ground disturbance range, and shield torque are weakly correlated; however, as the tunnelling speed increases, the thrust of the shield machine increases and the stratum displacement tends to be uplifted. With the increase in the screw conveyor rotation speed, the settlement of the surface and pipeline increases, and the thrust of the shield machine decreases. The torque of the shield machine, range of ground disturbance, and screw conveyor rotation speed are only weakly correlated. The thrust and torque calculated using the coupling numerical model are close to the measured values, which demonstrates the reliability of the coupling numerical model.