穿越煤系地层隧道预留岩墙破坏力学行为与安全厚度研究

Failure Mechanical Behaviors and Safety Thickness of Reserved Rock Walls in Coal Seam Tunnels

为研究穿越煤系地层隧道在瓦斯压力和地应力作用下的力学行为变化,以贵州的天成坝隧道的瓦斯煤系地层为工程案例,通过相似模型试验搭建三维试验物理模型,分别研究预留岩墙在2种不同隧道跨度下的力学行为变化,并与数值模拟相结合研究不同因素下隧道开挖岩墙厚度变化规律。结果表明:1)隧道开挖改变了围岩的原始应力状态,在隧道掌子面前方的岩墙出现应力集中,且隧道在开挖后掌子面一侧的应力卸载使竖向应力和水平应力差值最大。2)隧道所在的地质环境相同时,预留岩墙上部垂直地应力越大,隧道的开挖跨度越大,预留岩墙的厚度越小,预留岩墙发生破坏失稳的可能性越大。3)隧道开挖过程中,预留岩墙垂直应力与位移监测点竖向位移同步变化;垂直应力达到峰值时,竖向位移变形最大;随后垂直应力减小,竖向位移变形趋于稳定;垂直应力突变导致预留岩墙破坏,位移量急剧增大。4)建立不同瓦斯压力、不同围岩等级、不同隧道跨度情况下的数值计算模型,通过正交试验法,设计8种不同工况,得到不同因素组合下预留岩墙厚度的变化规律;最后通过多因素回归分析法,拟合得到最小预留岩墙厚度的计算经验公式。

To investigate the mechanical behaviors of tunnel crossing coal seam strata under the action of gas and ground stress,a case study is conducted on the Tianchengba tunnel in Guizhou,China.A three-dimensional experimental physical model is constructed using a similar model test to examine the mechanical behaviors of the reserved rock wall under two tunnel spans.The variation patterns of the rock wall thickness during tunnel excavation under different factors are studied using numerical simulations.The findings are the following:(1)Tunnel excavation changes the initial stress state of the surrounding rock.This results in stress concentration in the rock wall ahead of the tunnel face.The unloading of stress on the side of the tunnel face after excavation leads to the maximum difference between vertical and horizontal stresses.(2)Under identical geological conditions,the greater the vertical stress on the upper part of the reserved rock wall and the tunnel span,the thinner the reserved rock wall becomes.This increases the likelihood of failure and instability of the reserved rock wall.(3)During tunnel excavation,the vertical stress of the reserved rock wall ahead of the tunnel face and the vertical displacement at the corresponding monitoring point increase simultaneously.When the vertical stress of the reserved rock wall ahead of the tunnel face reaches a peak,the vertical displacement deformation measured at the monitoring point also reaches a peak.Then,the vertical stress of the reserved rock wall decreases,whereas the vertical displacement deformation measured at the monitoring point gradually stabilizes.A sudden change in vertical stress can lead to the failure of the reserved rock wall ahead of the tunnel face,resulting in the sudden and rapid increase in the displacement at the tunnel monitoring point.(4)Numerical calculation models are established under different gas pressures,rock mass ratings,and tunnel spans.Through orthogonal experimental design encompassing eight different scenarios,the variation patterns of the reserved rock wall thickness under different factor combinations are obtained.Finally,a multiple regression analysis method is used to fit an empirical formula for calculating the minimum reserved rock wall thickness.