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.