各向异性砂土剪切带角度的理论分析

Theoretical analysis of shear band angle for anisotropy sand

针对平面应变条件下各向异性砂土剪切带角度的试验规律,采用传统的3种理论和分叉理论进行对比分析。将平面应变条件下剪切带角度的试验结果按照传统3种理论整理发现,尽管传统3种理论可以估算同种砂剪切带角度的极小、中间和极大值,但无法解释其各向异性规律。砂土在平面应变条件下破坏时会产生明显的剪切带,当剪切带方向和砂土沉积面方向接近时,会较早诱发剪切带的产生,使材料强度降低,造成了平面应变条件下各向异性强度规律明显不同于常规三轴条件下的试验规律,采用分叉理论结合各向异性模型则可以有效解释这个规律。随砂土沉积面角度的变化,模型可以从细观角度解释常规三轴条件下剪切带角度的单调变化的试验规律,结合分叉理论可以描述平面应变条件下其先减小然后增大的规律。通过几种理论对比分析表明,模型结合分叉理论不但能够描述多种应力状态下的平面应变和常规三轴应力条件下剪切带角度表现的不同规律,而且能够从细观角度解释其各向异性成因。

Aiming at the test results of shear band angle under plane strain conditions for anisotropy sand,a comparative analysis was carried out based on the three traditional theories and bifurcation theory.The results of shear band under plane strain condition described by the three traditional theories showed the traditional theories could estimate the minimum,middle and maximum values of the shear band angle of sand,whilst it could not t explain the anisotropy behaviors of shear band.The shear band under the plane strain conditions was easily observed,and it induced shear bands that reduced material strength when the directions of shear band and sand deposition were the same.It resulted in the different anisotropy characteristics in the conventional triaxial conditions and plane strain conditions. Such different characteristics could be explained using bifurcation theory together with anisotropy model. With the direction variation of sand deposition,the model ccould explain the monotonic behaviors of shear angled under conventional triaxial condition from microscopic viewpoint,the bifurcation theory combined with themodel could describe the behavior of shear angled under plane strain condition which decreased first and then increased.The comparative analysis of four theories showed that bifurcation theory together with anisotropic model well explained the different shear properties between plane strain and conventional triaxial under various stress conditions,and one could well explain it from the microscopic viewpoint.