EFFECT OF VOID RATIO AND GRADATION ON SHEAR STRENGTH PARAMETERS OF GRANULAR SOILS

Abstract

This paper was mainly focused on an experimental study conducted to investigate the effects of changing grain size distribution on shear strength characteristics of sandy soils. Ravi sand, Chenab Sand and Lawrencepur sand were mixed with each other in varying proportions to constitute sand samples of varying gradations. Grain size analysis (GSA), specific gravity, index
density and direct shear tests were performed to investigate the effects of changing gradation on void ratios and the shear strength parameters, respectively. Based on the experimental results of GSA and direct shear tests, multivariate regression analysis was carried out and correlation between GSA parameters and internal friction angle ()was proposed. In order to validate  the proposed model, and independent set of data based on testing of thirty sand samples was used. The value of internal friction angle measured experimentally differed by about ±5% from value predicted by the proposed
correlation. It was also observed that by changing the mean grain size, the void ratios first decreased and afterwards it increased. In addition to this, direct shear tests were also performed on sand samples by adding non plastic fines up to 30% in three basic sands to examine their effect on shear strength parameters of sandy soils. The friction angle decreased as fine content increased where as the apparent cohesion increased with the increase in the fines within the range of fine contents investigated.