深埋隧道内超前深孔降水模型试验

针对弱胶结富水粉细砂岩极易突水涌砂导致的隧道掌子面坍塌和初期支护开裂变形, 研究了深埋隧道内超前深孔降水方法, 建立了模拟隧道内超前降水的实体模型, 分析了3种降水管和3种抽水泵功率下各时刻模型的水位面变化, 采用三轴试验分析了粉细砂岩在高含水率下的破坏状态。研究结果表明: 降水试验模型切向断面上同一标高测点处中间水头低, 两侧水头逐渐升高, 呈抛物线形式, 反映了超前深孔降水规律; 粉细砂岩在高、低含水率下均呈塑性破坏, 破坏时的轴向应变小于5%;降水过程中地层含水率从20%下降到11%时, 粉细砂岩强度、黏聚力和内摩擦角达到最优稳定状态, 实现了开挖面无水状态; 隧道内超前降水参数应采用管径为65 mm的真空降水管和抽水功率为7.5 kW的真空泵, 且降水管应布置在超前掌子面20 m的隧道两侧边墙处; 在富水粉细砂岩深埋隧道内超前深孔预先降水并辅以注浆加固, 能够实现开挖期间粉细砂岩稳定, 为隧道顺利施工奠定了基础, 也避免了大埋深隧道从地表进行深井降水的困难。 

Dewatering model test of advanced deep hole in deep-buried tunnel

For the problem of tunnel palm surface collapsing and initial support cracking deformation caused by the sudden water surge in the weak glue-rich water powder fine sandstone, the advanced deep hole dewatering method in deep-buried tunnel was studied. A solid model for simulating the tunnel advanced dewatering was established. The water level surface changes of the model at each moment under 3 kinds of dewatering tubes and 3 kinds of pumping powers were analyzed. The three-axis test was used to analyze the failure state of powder fine sandstone with high water content. Research result shows that the water head in the middle part of dewatering test model at the same elevation measuring point on the tangent section is low, rises gradually on both sides, and is in a parabola form, reflecting the dewatering laws of advanced deep hole. The powder fine sandstone failures plastically under high and low water contents, and the axial strain at the failure is less than 5%. In the dewatering process, when the stratum water content decreases from 20% to 11%, the strength, cohesion, and internal friction angle of powder fine sandstone reach the optimal stable states, realizing the waterless state of excavation surface. The advanced dewatering parameters in the tunnel should be the vacuum dewatering pipe with the diameter of 65 mm and the vacuum pump with the pumping power of 7.5 kW. The dewatering pipe should be arranged at the side walls on both sides of tunnel and at 20 m ahead of tunnel palm surface. The advanced deep hole dewatering supplemented with grouting reinforcement in the deep-buried tunnels with rich water powder fine sandstone can achieve the stability of powder fine sandstone during the excavation. It lays the foundation for the smooth construction of tunnel, and avoids the difficulty of deep well dewatering from the surface in the deep-buried tunnels.