Shear Strength Assessment of Moist Sands Using Direct Shear Tests

Abstract

Granular materials are commonly used to backfill buried structures due to its free-draining property and higher shearing resistance. Conventional analysis of soil-structure interaction is performed assuming soil parameters based on typical values available in published literature for the standard and natural soils. Engineers often require replacing natural sand with locally manufactured sand as a backfill material for buried structures due to the scarcity of material and environmental considerations. This thesis presents a laboratory investigation of a locally manufactured sand which is classified as well-graded clean sand. Considering the various factors on which the strength parameters of soil depend, a series of direct shear tests are performed with varying density, normal stress, moisture content, shear displacement rate. As the soil used as a backfill for the buried structure is usually moist (unsaturated), the entire test program focuses on investigating the behavior of moist sand. The conventional test apparatus is used in this study as the special apparatus typical used in the research with unsaturated soil is not readily available to the practicing engineer. The study reveals that the conventional test apparatus can reasonably be used to estimate the design parameters for moist sand. For the manufactured sand used in this study, the effect of capillary suction on the shear strength parameters is found to be less significant. While the strength parameters depend on the degree of saturation, these depend extensively on the dry density of the soil with a higher angle of internal friction for the soil with higher dry density.