砂层盾构隧道泥水劈裂试验与数值研究

Experimental and numerical study on slurry fracturing of shield tunnels in sandy stratum

开展砂层盾构隧道泥水劈裂平面模型试验,研究不同覆土厚度条件下的泥水劈裂破坏机制、土体表面竖向位移和土体内部土压力变化规律.结果显示,劈裂机制为加压泥浆向掘削空间表面砂层渗透形成致密砂层及其表面泥膜(泥膜-砂层结构),泥膜-砂层结构在泥浆挤压作用下发生拉剪破坏.劈裂压力随覆土厚度的增加呈近似线性增大.劈裂扩展从刀盘顶部起始分别呈“斜直线”或“先竖直后斜线”型向上扩展.基于自主开发的模拟泥水劈裂的有限元计算程序,参照模型试验建立二维数值模型,计算获得与模型试验较一致的劈裂扩展形态以及土体内部竖向位移与水平位移的变化规律.结果表明,土体竖直向位移主要分布在刀盘上方以劈裂面为边界的“三角形”区域内,土体水平位移主要分布在掘削面土层.

A series of 2D model tests on slurry fracturing of shield tunnels in the sandy stratum with different cover depths were conducted to investigate the slurry fracturing mechanism,the displacements of the ground surface,and the earth pressure distribution in the stratum.According to the test results,the slurry fracturing mechanism is that the dense sandy stratum and the filter cake on its surface(the filter cake-sandy stratum)is formed due to the pressurized slurry penetrating into the sandy stratum around excavation space,and then the filter cake-sandy stratum is pushed by the slurry to tensile and shear failure.The fracture pressure increases linearly with the increase of the cover depth.The fracture initiates on the top edge of the cutter head and propagates up to the ground surface in acclivitous direction directly,or first in straight and then in acclivitous direction.Based on a self-developed finite element program for simulating slurry fracturing,the 2D numerical models were established referring to the model tests,the numerical results including the morphology of the fracture propagation which agreed with the test results,and the vertical and horizontal displacements in the stratum were obtained.The numerical results show that the vertical displacement mainly distributes in a triangle region bounded by the fracture surface above the cutter head,while the horizontal displacement mainly distributes in the excavation face.