The influence of grading on the shear strength of loose sands in stress-controlled ring shear tests

Abstract

Three silica sand samples-well graded, intermediately graded, and narrowly graded-having different uniformity coefficients, were constituted to allow the investigation of the influence of particle size distribution on their mechanical behavior. Using a ring shear apparatus, samples were tested under a wide range of laboratory conditions. Results of the tests clearly indicate that, for specimens confined under identical stress conditions, well-graded specimens have higher values of peak and steady state strengths than the rest of the specimens. A relationship between uniformity coefficient and shear strengths shows that the higher the uniformity coefficient, the higher the shear strength. On account of these, well-graded specimens have higher static liquefaction resistance than the poorly graded specimens. Within the range of normal stresses employed in the tests, results reveal that not only are poorly graded sands more likely to suffer higher postfailure strength reduction, but that their steady-state strengths are easily reduced to zero, the magnitude of the confining stress notwithstanding. This reduction of shear resistance to zero has been described as complete liquefaction in this paper. While almost all of the narrowly graded specimens suffered complete liquefaction, widely graded ones did not; an observation that seem to highlight the influence of grading on the mechanical behavior of the sands. © Springer-Verlag 2007.