Hypoplastic Model And Numerical Simulation Of Anisotropic Sand And Sand-structure Interface

Anisotropy and roughness are important factors affecting the mechanical properties of sand and sand-structure interface.The description of the macroscopic mechanical behaviour of sand and sand-structure interface must take into account the effects of anisotropy and roughness.Therefore,it is of great research significance and application to develop a sand and sand-structure interface constitutive model which can reflect the effects of anisotropy and roughness.Based on the classical hypoplastic model proposed by Wu and Bauer,this paper establish an anisotropic sand hypoplastic model by considering the influence of fabric anisotropy and its evolution.On the basis of the established model,an anisotropic critical state hypoplastic model is proposed by introducing anisotropic state parameters to the sand density function.Meanwhile,an anisotropic sand-structure interface hypoplastic model is established by considering the shear characteristics of the interface under plane strain conditions and further considering the influence of roughness based on the Gudehus-Bauer hypoplastic model.The content and conclusions of the study are as follows:(1)Based on the classical hypoplastic model proposed by Wu and Bauer,an anisotropic hypoplastic model of sand considering the fabric evolution and its relation with anisotropic parameters during loading is established.The simulation results are compared with the experimental results and existing theories.The results show that the improved anisotropic hypoplastic model can better describe the macroscopic mechanical behaviour of drained and undrained triaxial tests on anisotropic sand.(2)The effects of the variation of the fabric tensor on the position of the critical state line and relative density are analyzed,and on this basis the density function associated with the anisotropic state is introduced into the improved anisotropic sand hypoplastic model,and an anisotropic critical state hypoplastic model for sand is established within the framework of anisotropic critical state theory.The reliability and accuracy of the anisotropic sand hypoplastic model is verified by comparing the simulation results with existing models and experimental data.The results show that the improved anisotropic critical state hypoplastic model can better reflect the triaxial undrained mechanical response of anisotropic sand at large strain state.(3)Based on the Gudehus-Bauer eight-parameter hypoplastic model,an interface hypoplastic model is established under the assumption of plane strain conditions taking into account the effects of sand anisotropy and structural surface roughness.The UMAT subroutine code for the improved interface model is written using the FORTRAN language and applied to the numerical analysis of the direct shear test of the sand-structure interface.(4)On the basis of the UMAT subroutine,the pile-soil interaction problem of the Qingshui River mega bridge is simulated.The variation characteristics of the top settlement,lateral friction resistance,axial force of the pile and pile-soil stress are analyzed in detail.The reliability and accuracy of the improved interface hypoplastic model are further verified through the analysis of the actual project.