Effects of organic content on sewage sludge compression behaviour

Abstract

Five sewage sludge specimens with different organic contents were prepared by mixing mass ratios of 0, 5, 10, 20 and 40% 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 [Formula: see text]. It is observed that the [Formula: see text] compression curves show an inverse ‘S’ shape due to suction pressure resisting deformation. The suction pressure decreases exponentially with the organic content, a regression equation for which is provided. Burland’s concept of the intrinsic compression line (ICL) is adopted for correlating the compression curves of sludge with various organic contents. It is found that the ICL with a 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 normalise the compression curves of sludges with different organic contents. The intrinsic compression parameters [Formula: see text] and [Formula: see text] can be correlated with the organic content, which increase linearly with the organic content, and the regression equations for them are provided.