Research On The Visco Elasto-plastic Creep Constitutive Theory Of Artificial Frozen Soil And The Mechanical Property Of Frozen Wall

With the deepening of underground mineral resources exploitation and the expansion of the comprehensive utilization for urban underground space development,artificial freezing method has been widely used in underground engineering.As temporary supports in the shaft excavation process,frozen wall frequently have large deformation due to the rheological properties of frozen soil,which lead to the freezing pipe fractured and shaft lining damaged,that caused lots of problems for shaft construction.Therefore,it has great significance for freezing engineering and shaft excavation to research the rheological properties of frozen soil and the mechanical properties of frozen wall.In this paper,the creep properties of frozen soil and the deformation characteristics of frozen wall were analyzed by the combination of theoretical research method and numerical simulation method.The visco elasto-plastic creep constitutive of artificial frozen soil was established based on rheological theory of element model.The mechanical properties of frozen wall was studied based on twin shear unified strength theory,which considering the creep of frozen soil,unloading effect and the heterogeneity of frozen wall.The deformation characteristics of frozen wall was analyzed by the finite element software ANSYS.The main research work and achievements obtained in this dissertation can be summarized as follows:(1)Based on the twin shear unified strength theory,the unified strength criterion of artificial frozen soil was established on the consideration of the influence of confining pressure.The Nishihara model was improved by substitute the non-Newtonian visco pot for the Newtonian visco pot,nonlinear Newton element for the linear one,the twin shear unified strength theory for saint-venant body.Based on the improved Nishihara model,the visco elasto-plastic creep constitutive of artificial frozen soil was deduced.The results show that the constitutive has considered the influences of nonlinearity,it can describe the whole creep process of frozen soil,and the result can be applied to different materials.(2)Based on the twin shear unified strength theory,the visco elasto-plastic stress and displacement field of frozen wall were established on the consideration of the creep of frozen soil and the intermediate principal stress.The frozen wall in excavation process was simulated by using finite element software ANSYS,and the radial displacement of frozen wall was compared with out of consideration of the creep.The results show that the deformation of frozen soil wall is increased with time,and the creep deformation can not be neglected.The viscoelastic limit load is increased with the strength criterion parameter;The radial displacement of frozen wall is parabolic distribution along the excavation height,the maximum displacement is in the upper middle;the radial displacement is increased compared with out of consideration.(3)Considered the intermediate principal stress and unloading effect,the united analytical solutions of the elastic-plastic stress and displacement,the elastic limit load,the plastic limit load and external load were derived.the influence of the parameter of unified strength theory was investigated.The results show that the external load of unloading state is decreased compared with the tradition method,the stress and displacement distribution is decreased as well;The elastic limit load and the plastic limit load are increased with the strength criterion parameter.(4)Considered the intermediate principal stress and functionally graded material frozen soil,the analytical solutions of the elastic limit load,the elastic-plastic stress and the plastic limit load are derived.the influence of the parameter of unified strength theory was investigated.The results show that the stress distribution of FGM frozen soil wall changed more evenly compared with that of homogeneous frozen soil wall;the elastic limit load is relatively increased and the plastic limit load is relatively decreased with that of homogeneous frozen soil wall;The elastic limit load and the plastic limit load are increased with the strength criterion parameter.