导致直接剪切实验强度偏高的原因及改进办法

对次生红粘土、粉质粘土和全风化泥岩进行了直接快剪实验和三轴不排水剪切实验，并对实验结果进行了分析．实验结果显示，直接快剪实验获得的岩土体的抗剪强度指标——粘聚力和内摩擦角明显高于三轴实验结果．分析其原因，在于直剪实验中法向力与剪切力(剪切面)不垂直，使试样的应力状态改变，从而导致直剪实验获得的岩土体抗剪强度指标偏高．最后，根据力的平衡原理，提出了直剪仪加载装置的改进办法——改一端加载为两端加载．

Reason for Resulting in High Direct Shearing Strength and Improvement of Loading Unit

Direct and triaxial shearing tests were carried out for deuterogenic adamic earth, silty clay and completely weathered mudstone, and the experimental results were analyzed. The result shows that shear strength of rock or soil, cohesive force and internal friction angle, obtained through a direct shearing test is markedly higher than that through a triaxial shearing test. The reason for this phenomenon is that normal force in direct shearing tests is not usually vertical to the shear force (shear surface) to lead to the change in stress state in samples, as a result, higher shearing strength than triaxial shearing strength is obtained. Finally, an improved measure for the loading unit was proposed based on the principle of force equilibrium, i.e. loading at its two ends instead of one end.