| Soil is multiphase consisted of solid particles, water and gas, which makes the research of its stress-strain relations greatly difficult. Recently, the theory of soil constitutive relations has been widely concerned and developed, because of the impulse of engineering which caused people to make research on the characters of the soil and the advancement of the computer science. Progress of the laboratorial equipment and calculational methods makes it possible to find out the comparatively authentic constitutive relations of the soil. Now scholars of many countries have brought forward many elastoplastic constitutive models of soil, however, most of which are based on plastic potential theory, so finding the plastic potential function becomes the basic approach of building the stress-strain relations. Numerous experiments indicate that soil distortion caused by the load is not only decided by its material but also has great correlation with exoteric conditions, in the other words, which has relationship with the stress path. Although an experiment is began and finished at the same loading conditions, its stress-strain loci differ according to the stress paths. However, most of constitutive models nowadays neglect the effect of the stress paths, even though some scholars have made researches of the effect, few of them have advanced corresponding models. In fact, there is much information about stress-strain relations in test data obtained under different complicated loading conditions. So the key is how to abstract the constitutive law form it, which is just the contents of the inverse problem theory. In traditional elastoplastic constitutive models, the main task is to find the plastic potential function, through which the increment relations of stress-strain could be set up. Since the characters of soil are affected by many factors, it is difficult to find an analytic expression of plastic potential. Therefore, it is necessary to seek new modeling methods to satisfy the need of engineering practical application. Based on the numerical method of the inverse problem theory in modeling the constitutive relations of rock and soil, the numerical modeling for the elastoplastic constitutive relations of sand is studied. According to the result of triaxial tests under the stress paths of K 0? ctc, the stress-strain relations in the whole stress field (p, q) are obtained by using the numerical method in modeling. The three-dimensional surfaces of the stress-strain relations are drawn through visualization and the corresponding yielding locis are also given. Through a comparison of the calculated curve of stress-strain relation and the experimental one, it is found that two ones well coinside,which approved the effectiveness of the numerical method in modeling. The constitutive model proposed in this paper is different from the traditional mathematical modeling, and it reflects the complex constitutive relations effectively. (1) The numerical modeling for the elastoplastic constitutive relations of sand under the stress paths of K 0? ctc was set up, which has profound function on the analysis of foundational sedimentation. (2) The method reflects the effects of confining pressure, shear expansion, shear shrinkage and stress paths. Moreover, the stress paths in modeling are not designed but can be chosen freely, which provides an effective way to simulate the actual stress paths in soil. |
