Numerical Modeling Method Of Sand And Finite Element Analysis

The theory of soil constitutive relations is the base of geotechnical engineeringdesign and computation. The mechanical properties of geological medium are verycomplex. They are nonlinear, shear dilatancy, anisotropy and the stress condition, stresspath also have influence to the soil constitutive relations. In order to understand them,tests and observations should be done to acquire the mechanical response data, and thenthe rules of deformation and failure are abstracted from the data. In traditional modelingmethods, the expressions of mathematical model are induced from the experimental databy plastic potential theory and empirical assumptions. In these methods,the parameters ofmodel are determined by some certain stress path,therefore the influence of stress pathcan not be reflected. Based on the theory of inverse problems, the elastoplastic constitutive model ofsand is built up through the numerical method of modeling the constitutive law for rockand soil, which utilizes the characters of mapping high-nonlinearly and self-learning inartificial neural networks (ANN). Trial curves of εv ~ q , εs ~ q are drawn by theconventional triaxial tests of eight saturated sand samples.The stress-strain relation ofsand is obtained by the numerical method of modeling. The three-dimensional surfacesof the stress-strain relations are drawn through visualization and the relative yieldingtraces are also given. The deformations under three stress paths have been calculatedthrough the finite element program of axial symmetry. By comparing the results forexperiments and computations, the effectiveness of this numerical method for modelingconstitutive law has been verified. In order to put the model into practical application, theelastoplastic matrix of plane strain is derived for finite element analysis, and the finiteelement program is compiled, in which the constitutive model is inserted. The foundationsettlements under three stress paths have been calculated. By the results of settlements,itproves that the influence of stress path to the constitutive law could not be neglected. The numerical method of modeling proposed in this thesis is quite different from thetraditional modeling method of mechanics. The explicit Gauss function is obtained to IIdescribe the constitutive law for rock and soil. (1) The numerical method of modeling theconstitutive law for soil and rock could overcome the difficulties to find plastic potential,and the stress-strain behavior can be abstracted from test data. (2)Stress paths can bearbitrarily chosen in the numerical modeling method and the reflection of stress paths canbe expressed quantificationally, which provides an effective approach for simulating thereal stress paths of the soil in geotechnical engineering.