Beneficial Use of Water Treatment Sludge in Geotechnical Applications as a Sustainable Alternative to Preserve Natural Soils

Abstract

This paper explores the feasibility of employing drinking water treatment sludge (WTS) mixed with soils, lime, or rock powder in geotechnical applications, as well as discusses the sustainability of the approach based on experimental results, aiming at the beneficial reuse of waste and the preservation of natural geomaterials. The selected materials were two soils largely used in earthworks, two WTSs, a high purity calcium hydrated lime, and rock powder from a granitic–gneissic quarry, all occurring in São Paulo State, Brazil. The mixtures were chemically, mineralogically, and geotechnically characterized, and the geotechnical properties permeability, shear strength, and deformability were investigated. Soil-WTS mixtures showed hydraulic conductivity (10−10–10−6 m/s, depending on soil and WTS), effective cohesion (10–30 kPa), friction angle (34°–40°), undrained strength (>50 kPa), and compression index (0.1–0.4) compatible with those of soils usually employed in earthworks. Lime:WTS and rock powder:WTS mixtures achieved 50 kPa undrained strength for WTS contents lower than 24% and 8%, respectively, and could be used as daily and intermediate covers of waste landfills, as well as in other applications with low soliciting stresses. The possibility of WTS being pumped instead of transported by trucks was analyzed in the light of results from rheological tests.