Elastic-Plastic Constitutive Model For Sand Under Constant Principal Stress Ratio Path

The constitutive relations of rock and soil are the base of engineer design and simulation. For several years,specialists and scholars bring forward many constitutive models of soil to reflect its real properties. However,the properties of soil is so complicated and includes confining pressure effects,expansion,dependence of stress path. Moreover,its properties alternate much with the loading condition. In traditional elastoplastic models,the main task is to find out the analytical expression of plastic potential function,through which the increment relations of stress-strain is set up. To the characters of soil influenced by many factors,it is difficult to find an analytical expression of plastic potential to describe the constitutive relation entirely.The inverse problem theory gives a new way to solve the constitutive modeling of rock and soil which actually is an inverse problem. The data observed by experiment in several kinds of conditions involve much information about strain-stress relations of materials. So it is possible to build a constitutive model from the data to simulate the factual characters.To simulate the deformation of soils in filling construction,it is necessary to build up the constructive model under the stress path of constant ratio of principal stress. Based on the numerical method of modeling the constitutive relations of rock and soil,the model for the elastoplastic constitutive relations of sand is build up,which provides possibility to figure out the stress and strain in filling construction. According to the result of triaxial tests under the stress paths of constant ratio of principal stress,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 traces are also given. Through the comparison with CTC stress path,we can easily find that the difference of three-dimensional surfaces between them is obviously. We can draw a conclusion that the impact on constitutive relation by stress path can't be negligible. It is inaccurate to simulate the deformation of soils in filling construction using the Duncan-Chang model which based on CTC stress path. Through a comparison of the calculated curve of stress-strain relation and the experimental one,it is found that two ones well coincide,which approves the effectiveness of the numerical method in modeling.The constitutive model proposed in this paper is different from the traditional modeling,it is more simple and more practicable and reflects the complex constitutive relations more effectively, especially the effect of stress path. (1)The model can reflect the effects of confining pressure and stress path. Moreover,it can be extended to other stress path. Through this way,the actual stress path can be simulated effectively. (2) The strain-stress relations can be abstract from the experimental curve which makes it practicable to use. So it can be used more widely.