Effects of organic content on sewage sludge compression behaviour

Five sewage sludge specimens with different organic contents were prepared by mixing mass ratio 0%, 5%, 10%, 20% and 40% of dry soil powder into raw sewage sludge. The addition of dry soil powder can reduce the organic content of sewage sludge without significantly changing its particle composition. Oedometer tests were conducted, starting from a small effective vertical stress σ v′ = 3 kPa. It is observed that the e-logσ v′ compression curves show an inverse ‘S’ shape due to suction pressure resisting deformation. The suction pressure decreases exponentially with the organic content, a regressed equation for which has been provided. Burland’s concept of intrinsic compression line (ICL) is adopted for correlating the compression curves of sludgewith various organic contents. It is found that the ICL with high organic content lies above the low one, that is, the higher the organic content, the greater the void index. In addition, the shape of the ICL for organic sludges is an inverse ‘S’ rather than slightly concave upwards for inorganic reconstituted clays. An average ICL is provided to normalize the compression curves of sludges with different organic contents. The intrinsic compression parameters e * 100 and C c * can be correlated with the organic content, which increase linearly with the organic content, and the regressed equations for them were provided.