The Coupled Thermo-hydro-chemo-mechanical Peridynamics For Rock Masses And Numerical Study

With the rapid development of social economy,the stability of rock mass in engineering construction has attracted great attention.In recent years,such as deep-buried geological disposal of highly radioactive nuclear waste,deep-buried tunnel construction,geothermal resource development,freeze-thaw cycle of tunnels in cold region,CO2 geological storage and unconventional oil and gas exploitation,etc.The problems encountered in the construction of these projects urgently need the support of the thermo-hydro-chemo-mechanical(THMC)coupling theory and analysis technology,so as to improve the engineering properties of rock mass,improve the efficiency of resource exploitation,save the investment in engineering construction and enhance the disaster prevention and reduction ability.The study on crack initiation,propagation and connection mechanism of fractured rock mass under thermo-hydro-chemo-mechanical coupling can not only effectively predict the stability of rock mass in underground engineering.In addition,technologies related to the development of new energy production can be rationally developed,such as unconventional oil and gas(oil,shale gas)extraction schemes for deep rock mass,clean geothermal energy extraction schemes and seabed energy extraction schemes.With the development of computer,numerical algorithm has many advantages over the traditional test method in simulating the fracture mechanism of rock mass under the coupling action of multiple physical fields.For example,numerical simulation algorithm has the advantages of low cost and repeatability.In addition,the numerical algorithm overcomes the limitation of single test conditions in traditional experiments.Peridynamics is a numerical method based on nonlocal continuum mechanics theory.In the theory of peridynamics the differential-integral governing equations without spatial differential terms are used.Therefore,based on the theory of peridynamics,a numerical model of peridynamics with thermo-hydro-force-chemical coupling is proposed in this paper to simulate the fracture of fractured rock under the coupled action of thermo-hydro-force-chemical.In order to simulate the fracture of rock under loading condition and overcome the limitation of poisson ratio fixed in traditional peridynamics theory.In this paper,a numerical model of conjugated-bond-pair based peridynamics is established.In this model,the problem of fixed poisson's ratio in traditional numerical theory of peridynamics is overcome by the introduction of tangential force density.The model is used to study the fracture characteristics of rock with multiple fractures under uniaxial loading.Compared with the experimental results and the traditional discrete element numerical results,the correctness and accuracy of the conjugated-bond-pair based peridynamics numerical model in predicting crack initiation,propagation and coalescence under the condition of rock loading are proved.In order to simulate the fracture of rock under temperature load,a numerical model of thermo-mechanical coupling peridynamics is established.In this model,the multi-scale time integration is proposed to overcome the multi-scale problem under the condition of multi-field coupling.The fracture characteristics of several brittle solids under different thermal loads were predicted and compared with the experimental results and traditional discrete element numerical results.The correctness and accuracy of the proposed model for simulating rock thermal energy under different conditions are illustrated.In order to simulate the rock fracture under water pressure,a numerical model of "bond" base peridynamics under hydro-mechanical coupling is established in this paper.In this model,the Biot porous media seepage theory and the corresponding cubic law of fracture seepage were applied to establish the porous media seepage model.Through the law of conservation of mass and the law of conservation of momentum,the numerical calculation model of hydro-mechanical coupling bond-based peridynamics is established.The model can solve the seepage problem of fractured porous media completely and avoid the trouble of setting inner boundary or reconstructing meshes around fractures in traditional numerical methods.By comparing the results of different seepage calculation examples and hydraulic fracturing calculation with the mature numerical results,the correctness and accuracy of the numerical calculation model of hydro-mechanical coupling bond-based peridynamics in simulating the seepage problem of fractured rock and hydraulic fracturing under different conditions are illustrated.In order to simulate the fracture of rock under the condition of chemical corrosion,a force-chemical coupling peridynamic model is established.In this model,the chemical corrosion degree of material particle points is determined by the concentration of chemical ions in the chemical solution,and it is substituted into the corresponding attenuation function of elastic stiffness and fracture threshold,so as to realize the fracture prediction of rock materials under the force-chemical coupling effect.Finally,the numerical model of peridynamics under the coupled action of thermo-hydro-chemo-mechanical is proposed.And it is applied to the energy extraction of geothermal energy mining.The temperature and water pressure changes in the process of geothermal energy mining are simulated.It shows that the application of peridynamics theory in deep complex environment has broad prospects.