CORRELATION BETWEEN INDEX PROPERTIES WITH SHEAR STRENGTH PARAMETERS FOR HAWASSA SOIL

Abstract

Shear strength parameters (angle of internal friction and cohesion) are the key engineering properties of soil. In every situation finding these parameters by laboratory testing or by using advanced equipment may be uneconomical for clients during the preliminary design phase. So it is a common practice in geotechnical engineering to estimate these parameters by employing empirical equations from easily found engineering properties of soil. Correlations and empirical equations developed are site specific, and a good result will be found using them for soils from which they are developed. In this study an attempt was made to correlate shear strength parameters (angle of internal friction and cohesion) for Hawassa city soil from index properties. Detailed analysis was carried out by randomly taking thirty four samples from seven sub cities of Hawassa city. The sampling pits were dug manually using hand tools with plan area of 1.50 m by 1.50 m at depth of 3.0 m from the ground surface. From laboratory test results, most samples were found to be with very low values of density and no plasticity. The soil was classified as cohesionless soil of fine to medium sized sand with group name silty sand, sandy silt, silty, clayey sand, silty, clayey sand with gravel and well graded sand with gravel consecutively. Due to the nature of the soil, cohesion was exempted from correlation. The Influence of easily found index properties of soil on its shear strength parameter was studied, and a regression carried out for the selection of most influencing variables. This parameters identified as the grain size distribution, density, and water content of the soil