Study On A Three-dimensional Continuum-Discontinuum Method Where The Lagrangian Element Method With The Discrete Element Method Are Combined And Its Application

Failures and instabilities of tunnel surrounding rock restrict the safe and highly efficient mining of minerals.Under the impact disturbance,mining disasters often cause huge casualties and economic damages.Hydraulic supports can effectively compensate for the lack of support strength of conventional methods.It is beneficial to study the deformation-cracking process of three-dimensional tunnel surrounding rock under the action of impact and the hydraulic support by use of a numerical simulation method.Considering shortcomings of continuum methods and discontinuum methods,the method based on the combined continuum method and discontinuum method has significant advantages in studying above problems.A three-dimensional continuum-discontinuum method coupling the Lagrangian element method(a continuum method)with the discrete element method(a discontinuum method)was proposed.Using the proposed method,uniaxial tensile tests of rock samples under force-controlled loading or displacement-controlled loading,a three-point bending rock beam test and dynamic and static distribution characteristics of unloading stress waves in tunnel surrounding rock were simulated;under plane strain conditions(only one layer element was applied normal constraints in the thickness direction),propagation processes of unloading stress waves in linear elastic tunnel surrounding rock and the deformation-cracking process of tunnel surrounding rock under displacement-controlled loading were simulated;under progressive excavation,deformation-cracking processes of three-dimensional tunnel surrounding rock with normal constraints on the front and back surfaces were simulated;under the action of half-sinusoid periodic impact and the hydraulic support,the deformation-cracking process of three-dimensional tunnel surrounding rock with normal constraints on the front and back surfaces was simulated.The main conclusions are listed as follows.(1)In the proposed method,based on the principle of coordinate transformation,a normal vector expression of the three-dimensional theoretical crack surface was derived to determine the propagation direction of a three-dimensional crack;by judging relationships between surfaces and edges of two hexahedral elements in contact,the common-body method was proposed to deal with the three-dimensional contact problem.(2)Elastic moduli and Poisson's ratios of rock samples in uniaxial tensile tests under force-controlled loading or displacement-controlled loading,the load-time curve of the loading point in the three-point bending rock beam test and dynamic and static distribution characteristics of unloading stress waves in tunnel surrounding rock are basically the same as input values,theoretical solutions and numerical solutions obtained by the finite element method,which verify the correctness of the proposed method.(3)Under plane strain conditions,increasing local nonviscous damping is beneficial to the rapid balance of the model,but not beneficial to the propagation of the unloading stress wave;with the increase of unloading time,the crack distribution of tunnel surrounding rock changes from continuous to interval.Under compressive displacement-controlled loading,tunnel surrounding rock firstly cracks;then,roof caving and floor heave occurr;and eventually tunnel surrounding rock collapses.(4)Under the condition of progressive excavation,shorter excavation footage and longer excavation interval are beneficial to reduce the disturbance caused by excavation to tunnel surrounding rock.Stress concentrations are easily formed at four corners of the tunnel and in front of the working face in vicinity of two sides,the roof and the floor of tunnel surrounding rock.When the tunnel will penetrate the model,stress transferring toward surroungding rock in front of the working face during excavation leads more cracking here.(5)Under the condition without impact and without support,the action of excavation leads to a small number of tensile cracks in tunnel surrounding rock.Under the condition with impact and without support,the number of cracks on two sides of the tunnel is larger than that on the floor,but less than that at the roof;some elements at the roof of the tunnel are isolated from the tunnel surrounding rock and fall into the tunnel.Under the condition with impact and with support,the number of cracks on two sides of the tunnel are less than that under the condition with impact and without support;there are no new cracks on the roof and the floor of the tunnel.The action of the hydraulic support can make tunnel surrounding rock resist the disturbance caused by impact,reduce cracking,and improve the safety of the tunnel.There are 78 figures,15 tables and 262 references in this thesis.