Vane shear strength of dewatered sludge from Hong Kong

The vane shear strength and total solids content of dewatered sludge from Hong Kong were determined in order to evaluate their geotechnical suitability for disposal in landfills. The results obtained indicate that (i) the total solids and vane shear strength of dewatered sludge from different treatment plants varied considerably depending on the type of sludge and dewatering method; and, (ii) percent total solids alone is not sufficient to guarantee geotechnical stability in terms of vane shear strength. The critical state model for soils provided a good fit for the characteristic relationship between vane shear strength and total solids, which can be used to estimate vane shear strength from total solids only. No relationship between volatile solids and vane shear strength was found. The results of the laboratory vane shear test correlated well with those obtained by a pocket shearmeter indicating the usefulness of this method for rapid determination of vane shear strength on site. Some factors that influence vane shear strength were briefly evaluated. Implications of the results for sludge management with special emphasis on dewatering and landfilling were discussed.