Impact of gradation on the shear strength-dilation behavior of well graded sand-gravel mixtures

A total of 27 large scale direct shear tests have been conducted to investigate the shear strengthand dilatancy of well graded sand-gravel mixtures. this paper focuses on the differences in behaviorbetween three soils: sandy gravel with a specified gradation as the base soil, and two other ones withequivalent scalped or parallel gradations. direct shear tests were conducted on three considered soils.maximum grain size is 25.4mmin base soil, and is limited to 12.5mmfor equivalent scalped and parallelgradations. test results are considered in terms of frictional and dilatancy contributions to the shearstrength as a function of relative density and applied surcharge pressure. according to the results, thegradation of tested soils affects their shear strength by a change in maximum friction angle, which can berelated to both dilatancy at failure and the constant volume friction angle. scalped gradation is found as abetter approximate gradation compared to the parallel one for determination of peak shear strength forcoarse grained soils. finally, empirical equations are developed to relate the shear strength characteristicsof the base gradation to scalped and parallel ones.