宽广吸力范围内弱膨胀土的抗剪强度及其预测

Shear strength of weakly expansive soils and its prediction in a wide range of suction

在宽广吸力范围内对不同吸力的非饱和弱膨胀土进行了一系列吸力控制的三轴剪切试验。关于吸力的施加,较低吸力采用轴平移技术;高吸力采用蒸汽平衡法。试验结果表明:在净应力相同的条件下,试样的应力应变关系曲线随着吸力的增大而升高、剪缩量变小,并且随着吸力的增大其偏应力–应变关系和体变明显地表现出类似超固结土的特性。主要原因是试样受到较大的吸力,弱膨胀土试样失水收缩、孔隙比减小均明显,使试样剪切过程中表现出类似超固结黏土的特性。在宽广吸力范围内,吸力所引起弱膨胀性土体积收缩明显,不可忽视。根据压汞试验结果确定的微观饱和度引入有效饱和度中,再将试验结果与修正后的Bishop非饱和土强度公式的预测值进行比较,证明了修正后的Bishop非饱和土强度公式在宽广吸力范围内可较为准确地预测非饱和弱膨胀土的抗剪强度。

A series of suction-controlled triaxial tests are conducted on unsaturated weakly expansive soils experiencing different suctions in a wide range of suction. With regard to the suction applied, the low and high suctions are imposed by using the axis translation technique and the vapor equilibrium method. The test results show that under the same net stress, the specimen experiencing larger suction shows a higher stress-strain relationship and small contractive volumetric strain shearing, and its deviatoric stress-strain relationship and volumetric strain behavior become more and more similar to deformation characteristics of overconsolidated soils with the increase of the imposed suction. The reason of the above phenomenon is that when the specimen experiences a larger suction, the weakly expansive soils shrink significantly due to the loss of water, and its void ratio decreases obviously, thus the specimen exhibits the deformation characteristics of overconsolidated soils during shearing. In a wide range of suction, the volume shrinkage of weakly expansive soils is significantly caused by the suction, and it cannot be ignored. In addition, on the basis of test data of the mercury intrusion porosimetry（MIP）, the Bishop＇s equation for unsaturated soils is modified by introducing the concept of the effective degree of saturation. A comparison between the measured and the predicted results shows that the modified equation can predict the strength of unsaturated Nanyang weakly expansive soils well in a wide range of suction.