Study On A Continuum-discontinuum Method Considering The Dynamic Constitutive Model And Its Application

It is important to study failures of rocks under dynamic loads for expounding mechanisms of geological disasters and for predicting and preventing these disasters on theoretical and practical aspects.Owing to advantages of numerical simulation,numerical methods applicable to modeling dynamic fracturing processes must be especially emphasized.Based on the combined Lagrangiandiscrete element method,a continuum-discontinuum method considering the dynamic constitutive model is presented,in which the Zhu-Wang-Tang constitutive model is used to replace the general Hooke’s law.The continuum-discontinuum method considering the dynamic constitutive model is validated through modeling uniaxially compressive experiments of sandstone rock specimens for different loading velocities.Deformation-cracking processes of granite specimens for different loading velocities are modeled by use of the continuum-discontinuum method considering the dynamic constitutive model,and fracturing mechanisms of rock specimens are revealed.Shear bands include en echelon shear cracks.The minimum principal stress of the node exhibits a fluctuant decrease,followed by an increase in the oscillation form.The increasing stage corresponds to the strain-softening stage of the rock specimen.A large oscillatory amplitude of the minimum principal stress is found for the separating node,which is due to the fact that large stress waves are induced by node separations and contact between elements.Shear separations of nodes occur due to concentrations of the minimum principal stresses at the shear band tip.Motion of the triangle wedge of the rock specimen leads to tensile separations of nodes whose stress states are similar to those of the compact tension experiment.Deformation-cracking processes of tunnel surrounding rock under different impact amplitudes are modeled by use of the continuum-discontinuum method considering the dynamic constitutive model.Shear cracks first occur at two sides of the tunnel,forming V-shaped notches,and then occur at the roof.Tensile cracks mainly occur at the roof and floor.The impact load amplitude has a great influence on distributions of shear and tensile cracks at the roof and has a little effect on the depth of V-shaped notches at two sides of the tunnel.For larger amplitude,shear cracks near left and right shoulders of the tunnel present a banded distribution.For smaller amplitude,shear cracks near left and right shoulders of the tunnel present a continuous distribution.The number of shear cracks is more than that of tensile cracks after impact loading.As the amplitude increases,the number of shear crack segments in the tunnel surrounding rock increases.Deformation-cracking processes of tunnel surrounding rock under the action of impact and the hydraulic support are modeled by use of the continuum-discontinuum method considering the dynamic constitutive model.Shear cracks near left and right shoulders of the tunnel with supports appear later and distribute in a smaller scope.At the sharp increase stage of the number of crack segments,the increase rate of the number of crack segments with supports is fewer than without supports.At the constant stage of the number of crack segments,the number of crack segments with supports is fewer than without supports.The hydraulic support can resist the impact,restrain expansion of shear and tensile cracks in the roof,and improve the safety of the tunnel.There are 44 figures,4 tables and 85 references in this thesis.