Study On Damage Failure Mechanism And Mechanical Model Of Limestone Under Hydro-mechanical Coupling Effect

With the rapid development of infrastructure construction,the high water pressure tunnels in northwest and southwest China are growing.In high water pressure tunnel construction,the coupling effect of high water pressure and ground stress and frequent occurrences of tunnel gushing and leakage result in huge economic losses and casualties.Thus,the multi-scale physical characteristic tests and mechanical tests are made with adopting microscopic,meso and macroscopic methods.Based on the test results,the mechanisms and relevance theories of mechanic-percolating interaction of limestone without confining pressure are studied.The main contents are as follows:(1)The limestone immersion test under different seepage pressures are made.Based on the test results,the changes of mineral compositions,pore characteristics and AE(acoustic emission)characteristics etc.caused by seepage pressure are analyzed,moreover,the mechanisms and evolution laws of limestone's physical and chemical water-rock interaction under different seepage pressures are studied.Furthermore,the contact scouring model considering seepage water and the infiltration pore model considering bubble are built to analyse the influence of seepage pressure on physical and chemical water-rock interaction.(2)To reveal the physical performance,mechanical properties and the fracture mechanisms of limestone under the interaction of uniaxial load and seepage pressures,the uniaxial compression tests of dry limestone and saturated limestone under different seepage pressures are made with the new permeability apparatus.Then under different seepage pressure conditions,the complete stress-strain curves,the fracture characteristics and the limestone's AE characteristics in the failure evolution process are analyzed.The physical and chemical reactions between water and limestone and the guidance effect of seepage pressure on micro-crack propagation are used to analysis the effect of seepage pressure on mechanical properties of dry and saturated limestone under uniaxial compression.(3)The step cyclic loading tests and the constant cyclic loading tests of limestone under six level seepage pressures are carried out.Based on the test results,the Felicity effect of limestone under different seepage pressures are analyzed to obtain the fatigue damage thresholds and reveal the impacts of seepage pressure on limestone fatigue failure.The physical and chemical reactions between water and limestone and the guidance effect of seepage pressure on micro-crack propagation are used to explain the mechanism of water-rock interaction.(4)With micro-meso analysis methods,the parameter of leakage dissolution is introduced into statistical damage theory to establish the uniaxial statistical damage constitutive model of rock considering seepage pressure.By establishing a new porous rock deformation model and damage threshold predictive equation,the new model is improved to reflect the rock deformation characteristics in void compaction stage and elastic stage under the interaction of uniaxial load and seepage pressures.Furthermore,the model parameters are fitted according to the complete stress-strain curve of limestone in the uniaxial compression test.On this basis,the constitutive model is established to predict the deformation characteristics in each stages of limestone under uniaxial load and seepage pressures.The model is secondary redeveloped by using the ABAQUS finite element software,and the applicability of the new model is verified by simulation.(5)Based on the modified Nishihara constitutive model,the change rule of fatigue mechanical parameters caused by seepage pressure is analyzed.Considering rock mechanical properties deterioration and rock accelerated fatigue caused by seepage pressure,the functional relationship between rock mechanical parameters,rock porosityand seepage water pressure is established.On this basis,an nonlinear Visco-elasto-platic fatigue model is established to reflect the mechanical properties of limestone under the interaction of cyclic load and seepage pressures.The fatigue failure procedures of limestone under different seepage pressures are simulated by numerical analysis to verify the rationality and feasibility of the new model.