Study on Segment Loosening of Shield Docking Method Based on the Coupling of Stress-Seepage

Shield docking is that two tunneling machines dig opposite to each other to a certain point, and then discarding shell in the stratum, which is suitable for waters, mountains and dense urban areas. Through establishment of stress-seepage coupling model, influence of subsequent tunnel excavation and thrust unloading of propulsion jack on annular joints of preceding tunnel was studied, and design parameters of anti-loosening ring were proposed based on opening amount of circumferential. The results show that the opening amount increases with the increase of excavation steps, and misdisplacement amount fluctuates two times due to stratum subsidence at the top of tunnel and opening of segment. In the process of subsequent tunnel excavation, opening amount increases with the increase of tunnel excavation steps, while displacement decreases with the increase of tunnel excavation steps. Secondly, the influence of excavation disturbance can be effectively reduced by increasing thrust size. However, when the abandoned shell is disintegrated, there will be obvious secondary opening of annulus. In order to control the opening amount in a reasonable range, increasing ring thickness can effectively reduce the stress and deformation of anti-loose ring.