EFFECT OF SILICA FUME ON THE SHEAR STRENGTH OF COHESIONLESS SOIL

Utilization of waste materials in geotechnical applications reduces the environmental problems of factories wastes. Silica fume is a by-product of the extraction of silicon or ferrosilicon manufacturing. Using silica fume as an additive to the soil can significantly increase the strength and decrease the permeability of the mixture. In this study silica fume is used to improve the mechanical properties of cohesionless soil, with special attention when used as backfill material for reinforced earth retaining walls. Biaxial geogrid prototype was used as reinforcement sheets in prepared bed of sand-silica fume mixture. The effect of adding silica fume was evaluated based on the results of Pull-out tests under various overburden pressures. From this study it was concluded that, adding silica fume to the sand had reduced the pull-out displacement of the geogrid by about 30% to 91% depending on the applied overburden pressure. That interlocking between the sand and silica fume particles is the main cause of densifying the sand by minimizing the lateral movement of the particles. Reduction in geogrid elongation reflects the increase in shear resistance interaction of the geogrid-backfill, and consequently the increase in the stability of the reinforced earth retaining walls under static and earthquake actions