基于离散元的浅埋偏压隧道施工细观机理研究

Microscopic Mechanism Analysis of the Construction of ShallowBuried Bias Tunnel Based on DEM

浅埋偏压隧道受力性质复杂,施工危险程度较高。以齐家庄隧道为研究对象,采用离散单元法模拟了浅埋偏压隧道开挖过程,分析了不同工况下围岩应力、位移的变化规律,并着重从微细观角度研究了开挖引起的围岩内部的裂隙发展、接触力分布和强弱力链演化规律,进而阐释了锚杆支护的作用机理。结果显示:隧道开挖引起围岩应力转移,使强力链产生了明显的拱效应,而弱力链仍表现为各向同性;系统锚杆的挤压加固作用促进了隧道附近拱效应的形成,提高了隧道的稳定性;拱效应引起隧道上部应力沿压力拱传递到隧道的拱腰和拱脚,使其附近颗粒接触力增大,主方向偏转;现场监测数据与模拟结果规律一致,且与有锚杆三台阶工况结果接近。

The mechanical properties of shallow buried biased tunnel are complicated and the construction risk is high.Taking Qijiazhuang Tunnel as the research object in this paper,discrete element method is used to simulate the construction process of the shallow buried bias tunnel.The variation law of stress and displacement of tunnel surrounding rock under different working conditions are analyzed.The cracks development,contact force distribution and evolution law of strong and weak force chain in surrounding rock caused by tunnel excavation are analyzed emphatically from the microscopic point of view,and then the mechanism of bolt support is explained.The results show that,(1)The stress transfer of surrounding rock caused by tunnel excavation makes the strong force chain produce obvious arching effect,while the weak force chain is still isotropic.(2)The reinforcing effect of the system bolt promotes the formation of arch effect near the tunnel,thus improving the stability of the tunnel.(3)Due to the arch effect,the stress in the upper part of the tunnel is transmitted along the pressure arch to the arch waist and arch foot of the tunnel,which increases the contact force of the particles around it and deflects the main direction.(4)The simulation results are consistent with the field monitoring data,and close to the results of three-step method with systematic bolt support.