超浅埋超高断面暗挖隧道地层变形控制技术

Control Technology for Strata Deformation of Ultra-shallow-buried and Ultra-high Sectional Tunnel with Underground Excavation

研究目的：通过建立ANSYS仿真模型，研究隧道开挖引起的地层扰动对地表沉降和拱顶下沉2个重要安全控制指标的影响规律，从而控制地层应力重分布对施工安全和结构稳定带来的不利影响；实施地层变形仿真结果与实测结果的对比分析和反馈设计，优化隧道开挖步序，从而实现复杂环境、软弱富水围岩条件下超浅埋超高断面暗挖隧道的成功修建。研究结论：通过仿真计算与实测变形绝对值对比，实测和仿真计算预测的地层竖向变形值在各级控制范围之内。故针对软弱富水围岩下的超浅埋超高断面隧道施工，建立以100％应力释放的平面应变模式的ANSYS仿真模型，适合现场施工过程控制和优化的需要；针对超浅埋超高断面暗挖隧道施工采用的CRD工法，仿真结果显示在软弱富水围岩条件下2、4、5和7部开挖引起的沉降量占总量的85％～90％，以此进行优化，即所述各部采用台阶式预留核心土法开挖，隧道断面以2、4和5、7部的分界面控制台阶高度，采用先贯通上部断面后贯通下部断面的分台阶CRD法施工，该方法安全可靠。

Research purposes： Through the establishment of simulation model based on ANSYS, the two influence laws for control of surface and arch subsidence caused by the strata disturbance due to the excavation of tunnel were researched for control of the unfavorable effects on construction safety and structure stability caused by stress redistribution of strata. The space - time sequence of tunnel excavation was optimized through the comparative analysis of simulation results with measured results and feedback design for construction of the ultra - shallow - buried and ultra - high sectional tunnel with underground excavation under the conditions of complex environment and weak - water rock.Research conclusions： Compared with the absolute measured deformation, all calculated deformations were in the controlled ranges stipulated in the codes and standards based on the pre - measured and simulated results. Therefore, for construction of ultra - high sectional and ultra - shallow - buried tunnel under the condition of weak - water rock, the establishment of ANSYS simulation model with 100 percent of the stress release by the plane strain mode could meet the demands of the process control and optimization. For construction of the tunnel with CRD method, the simulation results showed that settlement of 2, 4, 5 and 7 subsections accounted for 85 - 90 percent of total settlement under the complex conditions. Based on this, the space - time sequence of excavation was optimized in the ways that the excavation method of the reserved core soil was used along with the stepped CRD method. The sequence was firstly to cut through the upper step is and then to cut through the lower step. The practice has proved that this optimized method is safe and reliable.