Hydro-mechanical Coupling Models For Water And Mud Inrush Induced By Suffusion Of Filling Material And Failure Of Surrounding Rock

With the vigorous development of national infrastructure construction and the implementation of the Belt and Road strategy,traffic and hydropower construction of our country are being distributed all over the world.A large number of long tunnels will be constructed under complicated geological environment.According to relevant statistics,80%of serious accidents are induced by water and mud inrush in tunnel construction in karst areas,which has caused heavy losses to personal safety,national economy and environment.Water and mud inrush is difficult to control due to lack of scientific understanding and systemic research of the mechanism.Numerical simulation are indispensable to investigate the mechanism and evolution progress of water and mud inrush.Actually water and mud inrush is a hydro-mechanical coupling problem.Present numerical simulation for water and mud inrush cannot work effectively and efficiently during whole tunnel excavation mainly due to hydro-mechanical coupling models cannot describe the progressive process of water and mud inrush induced by suffusion of filling material and failure of surrounding rock,respectively.Thus,the aim of thesis is establishing the hydro-mechanical coupling models for water and mud inrush induced by suffusion of filling material and failure of surrounding rock in tunnel,respectively.(1)An erosion law expressing variation of erosion ratio with hydraulic gradient and with time is proposed based on investigation of influences of hydraulic gradient,hydraulic load history and time on variation of soil erosion by suffusion.Then an exponential permeability evolution equation is developed according to Kozeny-Carman equation for suffusion.The proposed erosion law and permeability equation are verified by suffusion test data,which can be applied to simulate seepage flow and hydro-mechanical behavior in embankment dam,slope and tunneling engineering,etc.(2)The proposed erosion law and permeability evolution model are implemented in our in-house finite element code PANDAS to simulate seepage flow with suffusion.It is further applied in simulating and analyzing the influences of erosion of mud and sand in a fault on water inflow when tunnel excavation suffered the fault in rain.When considering the influence of rain on water inflow,a determination method of hydraulic pressure head in rain is proposed.This application verifies the reasonability and practicability of this simulation method.(3)The effective stress principle is improved for suffusion based on an assumption that the change rate of interfacial contact area between particles is linearly related to erosion ratio.Equations of effective stress,solid partial stress and strain related to erosion ratio of suffusion are derived,which can describe the behaviors that solid partial stress increases and extra strain occurs as fine particles are washed away.Then equilibrium and seepage continuity equations for suffusion are established for hydro-mechanical coupling model.In addition,the Mohr-Coulomb criterion of suffusion is derived,which indicates that soil is more subjected to failure as the soil particles are washed away.Finally,the proposed hydro-mechanical coupling model is verified by comparing with Biot’s theory.(4)A hydro-mechanical coupling model for progressive water and mud inrush of tunnel induced by failure of surrounding rock is developed.Firstly an adaptive elastoplastic strain-softening model(AESS model)is developed in order to overcome the problem that single constitutive model,which is applied to the most simulation software,cannot describe post-peak stress-strain behaviors at arbitrary confining pressure.Secondly an adaptive trilinear volumetric dilatancy model(ATVD model)at arbitrary confining pressure is established according to AESS model.The trilinear model is divided into elastic contraction,softening dilatation and constant stages,which are corresponding to elastic,strain-softening and residual stages of stress-strain curves.respectively.Thirdly a volumetric strain-dependent permeability evolution model is put forward based on the ATVD model.(5)The evolution process of water and mud inrush subjected to a high pressure karst cave is simulated using hydro-mechanical coupling model based on PANDAS.Taken Qiyueshan tunnel as the engineering background,the behaviors of principal stresses,displacement,water pressure and fluid velocity of tunnel surrounding rock with a high pressure karst cave are studied-In addition,effects of position and size of the karst cave,and of distance between the tunnel and the karst cave on principal stresses and displacement of surrounding rock are further studied.