EFFECT OF PARTICLE GRADATION AND RELATIVE DENSITY ON THE SHEAR STRENGTH OF COMPACTED SAND SOILS

Abstract

This study presented in this paper investigates the effects of particle gradation and relative density on the shear strength of compacted sand samples with different grain size characteristics. Samples representing poorly and well graded sand soils of different origins were considered and prepared in the laboratory at initial relative densities of 40, 70 and 90% and their shear strength was determined by direct shear method. The grain size analysis tests performed on the samples showed that the average (Dav) and mean (D50) grain size diameters are closely interrelated despite the differences in the soil gradation patterns. Sound linear relationships were developed between the soil minimum dry density (Dmin) and the above two grain size parameters. The effect of grain size on shear strength was investigated but no useful correlation was found between the parameters Dav and D50 and the peak shear strength of studied soils. The study results indicated that there is a linear relationship between peak shear strength (τ) and the relative density (Dr) such that the soil strength increases as the Dr value increases. However, the relationship between Dr and τ is dependent on the normal stress (σn) applied on soil samples during testing. The effect is more pronounced and the relationship between τ and Dr is more reliable for soil samples subjected to lower than to higher normal stresses. Furthermoresince the sand samples tested were unsaturated the influence of Dr on shear strength might have also been overshadowed by their initial matric suctions.