Multi-scale Model Analysis And Finite Element Secondary Development Of Soil Deformation

Soil is a discontinuous and heterogeneous granular medium composed of mineral particles of different scales,water and air.The deformation of soil has significant granular and structural multi-scale characteristics.However,the classical continuum theory is only based on the macro scale,which lacks the description of the soil particle size and its rotation,while the discrete mechanics method is mostly suitable for the uniform particle system of a single scale,and there is a problem of massive calculation.The strain gradient theory was originally proposed for the study of metal materials,but whether it can be applied to discrete multi-scale granular media needs to be further studied.Due to the shortcomings of the above theories in the analysis of soil multi-scale properties,the intrinsic scale and rotational variables are introduced into the classical continuous constitutive relation,and the multi-scale model of soil is established based on Drucker-Prager yield criterion.The finite element subroutine UPE8 W embedded in calculation is developed by ABAQUS,and the mechanism of intrinsic scale and particle rotation on the macroscopic deformation behavior of soil is expounded.The main research work and achievements of this paper are as follows:(1)Using the soil cell structure model and introducing intrinsic scale and particle rotation into the classical constitutive relation,a soil multi-scale model considering particle size and rotation effect is established based on Drucker-Prager yield criterion.(2)Develop the corresponding multi-scale model finite element method.With the help of the secondary development platform of ABAQUS,the finite element subroutine UPE8 W is embedded in the modeling INP file for calculation.The correctness of the program is verified by simulating the problem of stress concentration in circular holes.It is explained that the phenomenon of stress concentration is related to the intrinsic scale and the particles rotation of soil.(3)The multi-scale model of soil and its finite element method are used to simulate the phenomenon of soil deformation localization.The correctness and validity of the soil multiscale model are verified by comparing with the results of Alshibli plane strain test.Through the comparison of different meshing models,it is shown that the multi-scale model can solve the numerical calculation difficulties and element sensitivity problems of classical continuous mechanics.The influence of intrinsic scale on the thickness of shear band and the stress-strain relationship in the localized region is analyzed.(4)The numerical simulation of slope sliding and foundation bearing capacity with engineering size is carried out,the whole process calculation of nonlinear deformation of soil softening is realized,and the element sensitivity problem in classical continuous mechanics is solved.The influence of the intrinsic size of particles on the strength and deformation characteristics of soil is discussed,which provides a theoretical reference for guiding the practical engineering application.