隧道突涌水机制与渗透破坏灾变过程模拟研究

Study on tunnel water inrush mechanism and simulation of seepage failure process

针对岩体渐进破坏和充填体渗透失稳两种典型突涌水灾害,阐述了动力扰动、开挖卸荷与高水压三者联合作用下岩体渐进破裂机制,以及高渗透压作用下充填体"变强度-变渗透性-变黏度"的渗透破坏机制。针对渗透破坏突涌水的变黏度机制,采用DEM-CFD耦合计算方法,开展了流体黏度对渗透破坏机制影响的定性模拟研究,分析了流体黏度对平均接触力、流量(流速)、孔隙率、颗粒运移过程、运移轨迹以及临界水力梯度的影响规律。结果表明,低黏度条件下的临界水力梯度比高黏度条件下的要小,换言之,低黏度条件下充填体更容易发生渗透破坏;平均接触力对水力梯度临界值的响应最为敏感,而流量难以准确反映该信息。从渗透破坏突涌水的变黏度机制这单一角度出发(不考虑渗透性增大的影响),随着黏性介质流入水体,流体黏度会增大,但流动速度会降低,两者共同作用下反而阻碍了渗透破坏过程的发展。最后,采用DEM-CFD计算方法,对工程尺度突涌水过程进行了模拟,再现了突涌水优势通道的形成与扩展过程,并指出了实现突涌水灾变机制模拟所需解决的参数选取与定量分析难题。

In view of the two typical modes of water inrush disasters,progressive fracturing of rock mass and seepage failure of filling structure,the mechanism of progressive fracturing of rock mass under the combined effects of dynamic disturbance,excavation unloading and high water pressure is described.The seepage failure mechanism of the variable strength-variable permeability-variable viscosity of the filling structure under osmotic pressure is also expounded.For the variable viscosity mechanism of water inrush caused by seepage failure of filling structure,a qualitative simulation study on the effect of fluid viscosity on seepage failure mechanism is carried out using the DEM-CFD coupled simulation method.The effects of fluid viscosity on the average contact force,flow rate(flow velocity),porosity,particle migration process,migration trajectory and critical hydraulic gradient of the simulation model are analyzed.The results show that the critical hydraulic gradient of fluid with low viscosity is smaller than that with high viscosity.In other words,seepage failure of filling structure is more likely to occur under the action of fluid flow with low viscosity;the average contact force is especially sensitive to the response of critical value of the hydraulic gradient,however it is difficult to be accurately reflected by the flow rate.Considering only the variable viscosity mechanism of water inrush due to seepage failure(regardless of the effect of increasing permeability),as the viscous medium flows into water,the fluid viscosity would increase,but the flow velocity would decrease,and the combined action of these two changes would actually hinder the development of seepage failure process.Finally,the phenomenon of water inrush process in engineering scale is simulated using DEM-CFD method,and the formation and expansion process of the dominant channel of water inrush is reproduced.The problems of parameter selection and quantitative analysis are identified to realize the simulation of water inrush mechanism.