CONSTITUTIVE MODEL FOR JOINT SHEAR STRESS-DISPLACEMENT AND ANALYSIS OF DILATION
(1. Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education，Tongji University，Shanghai 200092，China；2. Department of Geotechnical Engineering，Tongji University，Shanghai 200092，China)
Abstract：Laboratory direct shear tests show that shear stress-displacement curve usually follows the pre-peak hardening and post-peak softening rule. When the asperities overriding effect is dominant，the curve shows stress hardening；and while damage and wear is accumulated to a certain extent，it will result in stress softening behavior. The hardening and softening effects together control the joint shear behavior. A new generalized hardening- softening constitutive model is put forward after detailed analysis of the existing model?s limitations. One function is used to describe the features of the pre- and post-shear curves and its advantages are as follows：(1) Don?t need discuss the characteristics of shear displacement curves for several segments and its fitting parameters separately. (2) Throughout the entire shear displacement range，this function has only one peak and at this point，its slope is zero. (3) Shear stress tend to residual strength when shear displacement is large enough which reflects the basic features of the joint material. The new model is suitable for analysis three types of shear displacement stress curves，which are shear stress hardening curve，hardening-softening curve and curve with an initial shear stress. Meanwhile，the limitations of the existing dilation models are that they cannot reflect negative dilation and the real point where the joint starts to dilate. So，a new normal-shear displacement coupling model is derived which takes two types of functions to express the different phenomena during direct shear test. At last，validity of the two proposed constitutive models is verified through applications to several existing laboratory test results. There is a high fitting accuracy between fitting results and experimental results.
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2011, Vol. 30 
