考虑渗流条件下开挖面失稳离心试验研究

Centrifugal model tests of tunneling face failure under seepage flow

当土压平衡盾构穿越高水位地层(如穿越江河)时,地下水与土舱之间的高水压差会产生过大的渗透力,导致开挖面失稳。为了研究渗流条件下开挖面失稳问题,开发了一套隧道离心模型试验装置,主要包括刚性模型箱、模型盾构、开挖面伺服加载系统、水位控制系统、储水箱。针对饱和砂质粉土地层,开展了一系列不同水位高度的稳态渗流开挖面失稳模型试验。结果显示,开挖面失稳过程中随着开挖面位移的增加,有效支护压力迅速下降;在达到最小值limP?之后缓慢回升并趋于稳定;极限有效支护压力limP?与水头压力?h/D呈线性关系。

When the earth pressure balanced shield is tunneling in the stratum with a high water table(for example, a tunnel constructed below the river by the shield), the hydraulic head difference between the ground and the shield's chamber can produce seepage force acting on the tunnel face. The seepage force can lead to the failure of the tunneling face, in order to investigate the failure of the tunneling face considering the seepage flow. A device for the centrifugal model tests is developed, including: rigid model container, tunnel model, loading system, water table control system and water storage tank. The size of the rigid model container is 1 000 mm in length, 450 mm in width and 1 000 mm in height. Due to the symmetry, the tunnel model is made from a D-shape steel tube. The diameter of the tunnel model D is 100 mm the tunnel face is a D-shape aluminium plate with the drainage holes. The drainage holes allow the seepage water to flow into the tunnel. Loading system consists of a hydraulic actuator, a cylindrical loading rod, a linear variable differential transformer(LVDT) and control software. The loading system is used to fulfill the tunnel face retreating. The water table control system consist a flow pump, some hoses, a metal pipe with some holes and a solenoid valve. The water table control system allows keeping an invariant water table and steady seepage during the tests. Water storage tank is used to store seepage water. A series of the model tests with different water tables are conducted. The depth between the crown of the tunnel model and the water table are 1D, 2D and 3D. The depth of the overburden is 1D. The silty sands are used in the tests. The sands are collected from the beach on Qiantang River. A pressure cell is placed between the tunnel face and the loading rod. It is used to measure the support pressure. The armature of LVDT is connected to the loading rod. The LVDT is used to measure the horizontal displacement of the tunnel face. The results show that the effective support pressure decreased when the face plate is retreating. The effective support pressure increased slowly after reaching the minimal value. In the limit state, effective support pressurelimP? increased linearly with the hydraulic head ?h/ D.