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.