应力-渗流-损伤耦合作用下管道型岩溶隧道突水灾变规律研究

Research on the law of water inrush disasters in pipeline-type karst tunnels under the coupling effect of stress-seepage-damage

为研究管道型岩溶隧道的突水灾变规律,以毕节市大寨隧道为工程背景,考虑围岩的应力-渗流-损伤耦合作用,采用FLAC 3D对管道型岩溶隧道掘进过程中围岩位移、塑性区、渗透系数以及涌水量变化规律展开数值模拟研究,在此基础上了对比分析了无岩溶管道以及不同岩溶水压对隧道突水灾变特征的影响。数值模拟结果表明:(1)隧道掌子面距岩溶管道4 m以上时,隧道围岩稳定性良好,而隧道开挖一旦全部揭露岩溶管道,则管道内充填岩体会逐渐塑性屈服并发生整体滑移失稳,导致隧道出现突水突泥事故,这与实际工程状况保持一致。(2)管道型岩溶隧道掘进过程中的涌水量大致呈“S型曲线”变化,表现出很强的突发性和较大的体量性;(3)溶洞承压水通过岩溶管道向隧道内发生突水存在一个启动压力,只有超过这个启动压力,隧道才会发生突水突泥事故,且其突水量与岩溶水压呈现出明显的指数递增关系。

With the strategy of"advancing the development of China's western regions",the construction of tunnels in karst areas has increased significantly.Among these tunnels,the karst pipeline is a kind of structure prone to disasters caused by the filling which is developed under the action of surface rainfall and groundwater dissolution.Generally,this kind of structure is small with sufficient water supply,so it is not easy to be found in the early geological survey.Once the karst pipeline is exposed by tunnel excavation,under the combined action of groundwater pressure and construction disturbance stress,the filling medium in the karst pipeline will be damaged,resulting in the decrease of its anti-sliding force and the increase of permeability.Consequently,it is easy to cause an accident of water and mud inrush.However,previous research rarely focuses on the sudden change of mechanical and permeability properties of surrounding rock and pipeline filling medium after the rock and medium have been damaged.This is inconsistent with the actual complex evolution process of water inrush disasters in pipeline-type karst tunnels.Aiming at water inrush disasters in pipeline-type karst tunnels,some scholars take the influence of tunnel excavation disturbance into consideration,and study the evolution process and disaster mechanism of water inrush disasters in pipeline-type karst tunnels through theoretical analysis,physical model test and numerical simulation.Taking the different occurrence forms of karst pipelines into account,some other scholars analyze the influence of the location and size of karst pipeline development as well as the influence of the water level of water-bearing body on the safety of karst tunnel excavation by establishing a geological model of water inrush in karst pipelines.These research results greatly ensure the excavation safety of pipeline-type karst tunnels.However,they rarely focus on the mechanical and permeability properties of the surrounding rock and pipeline filling medium after they have been damaged.In this study,we took Dazhai Tunnel in Bijie City as an example and took the stress-seepage-damage coupling effect of surrounding rock into consideration to explore the law of water inrush disasters in pipeline-type karst tunnels.Furthermore,using FLAC 3D,we studied the displacement of surrounding rock,the plastic zone,the permeability coefficient and the variation law of water inrush during the tunneling process of pipeline-type karst tunnels.On this basis,we conducted a comparative study of the effects of karst-free pipelines and different karst water pressures on the characteristics of water inrush disasters in tunnels.The numerical simulation results show that:(1)When the tunnel face is more than 4 m away from the karst pipeline,the maximum displacement of surrounding rock on the left wall,right wall,bottom arch,top arch and tunnel face will be stabilized at 25.0 mm,24.5 mm,14.1 mm,18.2 mm and 34.1 mm respectively.However,once the karst pipeline is completely exposed by tunnel excavation,the filling rock body inside the karst pipeline will be prone to plastic yielding,and thus cause the overall slipping and instability.This phenomenon will result in accidents of water and mud inrush in tunnels.The result is consistent with the actual engineering situation,indicating the rationality of the mathematical model established under the coupling of stress-seepage-damage in this study.(2)The amount of water inflow during the tunneling process of the pipeline-type karst tunnel roughly changes in an"s-shaped"curve,showing strong suddenness and a large volume.When some karst pipelines are exposed by tunnel excavation,water inflow increases from 5.9 m^(3)·h^(−1) to 256.0 m^(3)·h^(−1);when all karst pipelines are exposed by tunnel excavation,water inflow reaches 588.7 m^(3)·h^(−1).(3)If there are no karst pipelines,large displacement as well as large water inflow will not be generated by tunnel excavation through the karst cave when it is far away from the tunnel.This result indicates that the existence of karst pipelines provides a potential water-conducting channel for water inrush from karst cave to tunnel.(4)There is a starting pressure when a water inrush occurs from the karst pipeline to the tunnel.Only when the starting pressure is exceeded,will an accident of water and mud inrush occur in the tunnel,and the water inrush amount presents an obvious exponential increasing relationship with the karst water pressure.