Study On Numerical Method In Modeling The Elastoplastic Constitutive Relationships Of Expansive Soil And Sands

Most existent elasto-plastic models of constitutive relation for rock and soil are constructed based on the plastic potencial theory. Seeking the analytical expression of the plastic potencial has become a unique approach of modeling. However, these existent models can't completely and exactly reflect the effects of hydrostatic pressure, the dilatancy and particularly the dependence of stress path. For this reason, the authors have done the reserches on the numerical method of modeling of constitutive relation for expansive soil and sand. The numerical method has many advantages that are better than the traditional one: it is overcome to seek the ananlytical expression of plastical potencial. Since the constitutive relation is directly abstracted from the data of triaxial tests; the initial states for soil and loading paths can be freely selected in the modeling, so their effects on the constitutive relation of soil can be reflected in the constructed models. The water content is a very important factor which affects the strength and expand-shrinkage characteristic. It is proved that the transformation of water is caused by the weather, geology environment and the construction, and the behavior of expansive soil is changed by the water transformation. The variation of the shear strength of expansive soil relative to the water changing. The deviator stress would appear due to the anisotropism which caused by the suction of water in expansive soil. Meanwhile the expansive soil could be destroyed by the asymmetric swell. So the water content is one of the most important criterions to predict the potential of swelling behavior of expansive soil. For the expansive soil, firstly the physical character tests, mineral and chemicals component tests were fulfilled, then the drained and undrained trixal compression test under different initial states, such as water content etc., was carried out. The elasto-plastic equations of constitutive relation of expansive soil under different water contents were constructed by using the numerical method of modeling, which are inserted into finited element program. The stress-strain curves were obtained through the analyses of deformation of triaxial test samples. Comparision the calculated values of stress-strain relation with the values of the tests, two ones coincide well with each other. Through visualization, the three dimension surfaces of stress-strain relationship for two water content in the whole stress field (p, q) are plotted, it is found that the differences between them is obvious, which proved the influence of water content on constitutive law is notable. Three sets of tests for sands were carried out under the path of constant proportion of principle stress, conventional triaxial compression(CTC) path and p=constant (TC) path; The elasto-plastic equations of constitutive relation of sand under three stress psths above were construted by using the numerical method of modeling, which are inserted into finited element program. The stress-strain curves were obtained through the analyses of deformation of triaxial test samples. Comparing the calculated values of stress-strain relation with the values of the tests, two ones are consistent well with each other. Meanwhile, the three dimension surfaces of stress-strain relationship and the yield loci in the whole stress field (p, q) obtained under the path of constant proportion of principle stress, CTC and TC stress path were plotted. By comparing the surfaces and the yield locus, it is found that the difference among those of the three stress paths are obvious, which demonstrates that the influence of stress path on constitutive law is not neglected. Finally, the research results shown that the numerical method in modeling of the stress-strain relation has advantages, and is better than the traditional method. i.e., it can not only describe the effects of hydrostatic pressure, the dilatancy but also reflect the effects of initial states and dependence of stress paths, which is feasible, effective and promising.