论文部分内容阅读
泥膜是维持泥水盾构开挖面稳定的关键因素。通过渗透柱试验研究了加压泥浆向砂土渗透、并在砂土表面形成泥膜的行为,获得了泥膜渗透性与时间的关系。结果显示泥水盾构在开挖时,由于刀盘不断切削泥膜,开挖面上只能形成微透水的泥膜;当拼装管片时,刀盘停止转动,开挖面上则会形成难透水的泥膜。建立了在开挖面上设置微透水的泥膜的二维数值模型,通过瞬态渗流分析获得土体孔压的最大值。根据地层孔压计算了失稳区域内的渗透力,获得了不同泥浆压力下在泥膜表面和地层中的分配比例。当有效泥浆压力越大,孔压在泥膜和失稳区以外地层的下降幅度就越大,对维持开挖面稳定的贡献越小。基于极限平衡法,提出了泥水盾构开挖面极限泥浆压力的计算方法,结果显示目前工程中采用的方法高估了开挖面极限泥浆压力。
Mud membrane is the key factor to maintain the stability of slurry shield excavation surface. The infiltration of pressurized mud into sand and the formation of mud on the surface of sand were studied by means of permeation column. The relationship between mud permeability and time was obtained. The results show that when the mud shield is being excavated, the muddy film can only be formed on the excavated surface due to the continual cutting of the mud film on the cutterhead. When the segment is assembled, the cutterhead stops rotating and the excavation surface will be formed Permeable mud membrane. A two-dimensional numerical model of mud membrane with micro-percolation on the excavation surface was established. The maximum pore water pressure was obtained by transient seepage analysis. According to the formation pore pressure, the seepage force in the area of instability was calculated and the distribution ratio in the muddy surface and formation under different mud pressures was obtained. When the effective pressure of the mud increases, the pore pressure decreases more in the strata beyond the mud and instability zones, and contributes less to maintaining the stability of the excavation face. Based on the limit equilibrium method, the calculation method of the ultimate mud pressure of the excavation face of the muddy water shield is proposed. The results show that the method adopted in the current project overestimates the ultimate mud pressure of the excavation face.