Scale dependence of shear strength for a coarse granular soil using a superimposition-nest type of direct shear apparatus

摘要

This study applies a modified superimposition-nest type of direct shear apparatus (DSA) to exploring the scale dependence of shear strength from the direct shear test (DST) of soil. The modified apparatus enables the variation of the diameter D and height H of specimens and can adjust the gap T between the upper and lower shear box halves. The DSTs in different combinations of T, D, and H were conducted under a constant vertical normal stress sigma for a coarse granular soil. In each combination situation, five sets of tests were performed in parallel under the same sigma value to validate the reproducibility and reliability of testing. The gap effect results show the influence of T on the failure shear stress tau (f). The diameter and height effect results reveal the dependence of tau (f) on the D and H of specimen. The reasonable values of T, D, and H relative to the maximum particle diameter d (max) of the soil are evaluated for the coarse granular soil as well as the reasonable shear strength envelopes.