直剪实验剪切面积的修正及误差分析

针对现行直剪实验没有考虑剪切面积不断减小对实验结果的影响,本文从理论上推导了计算有效剪切面积的公式,然后通过实验并采用最小二乘法对数据进行处理.结果表明,土体的抗剪强度误差随着环刀面积的增大而减小,当环刀面积为30 cm~2时,随着剪切位移的增大,土体的抗剪强度误差增大;当剪切位移达到4 mm和6 mm时,抗剪强度误差可达8.2%和12.38%.现行方法测得的黏聚力和内摩擦角均比真实值小,低估了土体的抗剪强度,因而需要修正.

CORRECTION OF THE SHEAR AREA AND ERROR ANALYSIS IN DIRECT SHEAR TEST

In the direct shear test, the effect of the gradual decrease of the shear area is not duly considered. The accurate formula of the effective area is derived in this paper. Then, the method of Least Squares is used to deal with the experimental data and it is found that the shear strength error of the soil decreases with the increase of the area of the cutting ring and increases with the shear displacement when the area of the cutting ring is 30 cm2; when the shear displacements are 4 mm and 6 mm, the error is increased as much as 8.2% and 12.38%. The sticky cohesion and the internal friction angle measured by the current method are smaller than the true value, so the shear strength and the parameters of the soil are underestimated and should be corrected.