关键词: 卵砾石地层; 双隧洞; 地层变形; 盾构开挖; 离散元方法;

Abstract: With the development of subway shield construction, it is significant to study the influence of tunnels excavation on deformation of gravel stratum.The deformation characteristics of gravel stratum caused by tunnels excavation and shield tail gap are studied by using discrete element method, and influences of single tunnel and twin tunnels excavation on the stratum deformation are compared and analyzed.The results show that the surface deformation of gravel stratum can be divided into three stages: initial deformation stage, accelerated settlement stage and the settlement completed stage.The surface settlement deformation on the central axis of the tunnel is the largest.With the increase of the horizontal distance and the decrease of buried depth, the stratum deformation reduces gradually.In the twin tunnels excavation, due to the prior excavation of the left tunnel, the influence scope of the stratum deformation caused by the right tunnel excavation increases.The surface settlement and the effective influence scope both increase with the increase of twin tunnel space.The tunnel excavation results in the rapid settlement of particles on the top of the outer wall of the shield shell, and the hysteresis effect of the particle movement leads to a reduction in the particle contact force and an increase of porosity above the tunnel during the initial deformation stage.As the hysteresis effect dissipates, the particle contact force increases and the porosity decreases.

Key words: gravel stratum; twin tunnels; stratum deformation; shield excavation; discrete element method;