A comparison of shear strength measurements using two sizes of shearbox

A study was undertaken to compare the results of tests performed on specimens of a uniformly graded medium sand using 60 mm and 300 mm shearboxes. The results of the tests obtained from the 300 mm shearbox were adversely affected by the design of the hydraulic system that applied the normal load to the specimens. This problem was overcome by replacing the original hydraulic cylinder with one which had a very low frictional resistance, and by measuring the applied normal load with a load cell. Details of the test procedure and equipment, including the modifications to the 300 mm shearbox are provided. Following these modifications, good agreement between test results from both shearboxes was obtained. The results from both shearboxes showed that the angle of friction of the sand could be broken down into two parts; a constant volume component and a particle interlock component. The constant volume component had a value of approximately 33.6 degrees. The maximum value of the particle interlock component was governed by the initial density of the specimens and could be related to the maximum value of the ratio of the rate of vertical to the rate of horizontal movement. (A)