Applicability And Effect Evaluation Of Quasi-static Calculation Of Dilatancy-Softening Constitutive Model

In natural disasters and engineering disasters,landslides and foundation pit collapses have always caused great economic losses and even posed a threat to people’s lives.Many disasters are mostly caused by external disturbances to the original stable geotechnical system,such as earthquakes,floods,overloading of vehicles,overexploitation of underground resources,etc.,which lead to progressive failure of underground soil and shear band(sliding surface,interface layer),leading to soil sliding along the shear zone and causing accidents.Most of the shear bands are caused by the softening of soil during shear.Therefore,in geotechnical engineering,it is particularly important to adopt constitutive laws that can comprehensively reflect the hardening,softening and volume change characteristics of soil,in order to explore the mechanical behavior of geotechnical engineering in the process of deformation and failure,the formation and development of strain localization shear band and interface layer.Based on the unified model of dilation softening and shrinkage hardening,this paper discusses the applicability of the model in quasi-static simulation,and then evaluates the engineering effect.The dynamic explicit algorithm can solve the problem that the static implicit algorithm does not converge in the calculation of soft rock and soil materials.The fluctuation ratio of the load-displacement curve is proposed in this research to evaluate the effect of quasi-static calculation.First of all,the plane strain simulation test of elastic materials is conducted to analyze the effect of the elastic modulus,density,Poisson’s ratio and confining pressure on the value of quasi-static load speed.The findings indicate that the increase of elastic modulus,Poisson’s ratio and confining pressure will increase quasi-static load speed,while the increase of density will reduce the quasi-static load speed.Correlation analysis between each influence factor and quasi-static load speed gives the empirical formula of quasi-static load speed.Then the formula is extended to the unified model material of dilatancy softening and shrinkage hardening with the adjustment coefficient,which provides reference for the subsequent explicit quasi-static simulation calculation of nonlinear materials.Through quasi-static simulation calculation,the engineering effect of the unified constitutive model of dilatancy softening and shrinkage hardening is evaluated.In this paper,LS-DYNA is used to simulate the earth pressure of retaining wall and the bearing capacity of foundation.In the simulation,Mohr-Coulomb constitutive model,softening and hardening constitutive model are used to simulate,and the analytic solutions of Rankine earth pressure theory and Taisha base ultimate bearing capacity theory are compared.The results show that the quasi-static calculation method of dilatancy softening constitutive model can be reasonably applied to engineering simulation with softening characteristics.The non-convergence problem of softening constitutive in the solution of statics implicit algorithm is solved by using dynamic display algorithm.This method reduces the fluctuation effect of the results of dynamic algorithm and optimizes the balance between the accuracy of the results and the consumption of computing resources.This constitutive model can well reflect the characteristics of soil hardening,softening and volumetric deformation,and meet the comprehensive requirements of actual geotechnical engineering simulation.The application of quasi-static method to the constitutive model breaks through the limitation of the traditional theoretical analysis based on the assumption that the point on the failure surface reaches the limit state at the same time.It can reflect the process of soil strain localization to overall failure.The research results have important guiding significance for stability analysis and control of geotechnical engineering.