粉煤灰地层隧道开挖卸载应力路径数值模拟与试验

Numerical Simulation and Laboratory Tests of Unloading Stress Path of Fly Ash Stratum Tunnel Excavation

隧道在动态开挖过程中,土体的变形与其应力路径密切相关。针对这一问题,运用FLAC3D有限差分软件构建了隧道动态施工三维模型,模拟了大断面隧道采用双侧壁导坑法开挖的施工流程,测得了开挖卸载引起的土体应力状态变化规律。基于数值模拟获得的土体应力状态变化规律简化结果,对粉煤灰水泥加固土进行不同应力路径下的室内三轴试验,研究了隧道开挖卸载过程中土体单元受力变形情况,并对比了未掺入水泥的试件变形情况,以分析水泥加固对粉煤灰土卸荷变形的影响。数值模拟及室内试验结果表明:隧道进行三导洞法施工开挖过程中,围岩监测点的单元土体的应力路径较为复杂且存在明显差异,但大致可以简化为两类,即恒围压卸轴压以及恒围压升轴压的加卸载的过程;在模拟围岩单元土体不同位置的应力路径试验中,未经掺加水泥的试件存在变形破坏,而经水泥加固的试件变形量较小,未发生破坏。

The stress path of soil is closely tied to deformation during dynamic tunnel excavation.A three-dimensional model of tunnel construction was created using the FLAC3D finite difference software.The double-side wall guide pit method was used to simulate the excavation process of a large-section tunnel and measure the resulting soil stress state.The changing laws of the stress state were then investigated based on the numerical simulation results.Indoor triaxial tests were conducted on soil reinforced with fly ash cement under different stress paths to replicate the stress and deformation of soil units during tunnel excavation and unloading.Unreinforced soil specimens were used as a control group.The numerical simulations and laboratory test results reveal that the stress paths of the surrounding rock unit soil at monitoring points are complex,and can be roughly divided into two categories:the process of constant confining pressure unloading axial pressure and constant confining pressure rising axial pressure.The cement-reinforced specimens showed less deformation and no signs of failure,while the unreinforced specimens were damaged during the stress path tests of different soil positions within the simulated surrounding rock unit.