黄土真三轴剪切屈服与强度破坏条件

Shear yield and shear failure characteristics of loess under true triaxial condition

【目的】分析真三轴应力条件下黄土的剪切屈服和强度破坏规律,为黄土塑性变形和强度稳定性研究提供参考。【方法】利用自主研发的真三轴仪,对西安黄土进行了控制中主应力比值的真三轴剪切试验,分析不同固结围压(50,100,150,200kPa)和中主应力比值(0,0.1,0.3,0.5,0.7,0.9,1.0)条件下体应变与应力比的关系,探讨不同中主应力比值对屈服和破坏状态的体应变、应力比差异,研究子午平面和π平面上屈服线和破坏线形状及塑性应变的增量方向。【结果】不同中主应力比值下,屈服状态体应变ε_(vy)为0.53%~3.30%,应力比(q/p)_y为1.34~0.33;破坏状态ε_(vf)为5.13%~15.9%,(q/p)_f为1.67~0.70。子午平面内屈服线斜率远低于破坏线,π平面内屈服线和强度线相似且呈曲边三角形状,塑性应变矢量与强度面呈非正交关系。【结论】通过黄土真三轴试验验证了三维应力条件下黄土处于剪切屈服和破坏状态时应力和应变差异性。

【Objective】The rules of shear yield and strength failure of loess were analyzed under true triaxial condition to provide basis for investigating plastic strain and strength stability of loess.【Method】Experimental researches on Xi＇an loess were conducted by true triaxial apparatus,developed by Xi＇an University of Technology independently.The relationships between volumetric strain and stress ratio were analyzed with different consolidation pressures（50,100,150,and 200 kPa）and intermediate principal stresses（0,0.1,0.3,0.5,0.7,0.9,and 1.0）.The differences in volume strain and stress ratio of yield state and failure state with different b-values were discussed,and the corresponding limit lines in the meridian andπplanes as well as plastic strain increment direction in theπplane were investigated.【Result】The ranges of volume strain and stress ratio in the yield state were 0.53%-3.30% and 1.34-0.33,and those in the failure state were 5.13%-15.9% and 1.67-0.70 with different intermediate principle parameters.The slope of yield line in the meridian plane was lower than that of failure line.In theπplane,the shape of failure plane was similar as a curved-edge-triangle.The relationships of plastic strain increment vectors and strength surface of loess in the special states were non-associative.【Conclusion】The significant differences in stress and strain of loess in the yield state and failure state were testified through true triaxial test.