Influence of Compost Amendment on Shear Properties of Topsoils Used in Highway Slopes

Abstract

Erosion of highway slopes is of the utmost importance because it can lead to a decreased quality of the soil underneath, reduced water quality, and exacerbated air quality. Current highway slopes are implemented using compacted inorganic topsoil or occasionally by placing a layer of compost above the existing topsoil layer. The single topsoil layer can be susceptible to erosion but, if blended with compost materials, may potentially yield vegetation that reinforces the strength of the soil. The potential implementation of compost-amended topsoil on highway slopes is a sustainable practice due to larger amounts of compost use in construction but requires additional research to evaluate the geotechnical properties of these systems. A research study was undertaken to evaluate the changes in shear strength of topsoil upon amending with two common composts. Four mixtures were prepared at varying percentages of composts and one topsoil. Direct shear tests were performed on pure topsoil, composts, and the blends. Shape properties of the materials were defined using digital image analysis. The results indicate that the drained friction angle increased from 360 to 440, and the angularity increased from 2608 to 3127 due to addition of the compost material. The shape parameters of Form 2D, flatness, sphericity, elongation, angularity, and texture were compared with the respective friction angles; angularity and Form 2D were found to have the greatest correlation displaying high R^2 values ranging from 0.816 to 0.940, regardless of compost type.