Simplified prediction of changes in shear strength in geotechnical use of drinking water sludge

Drinking water sludge is the aggregation of clay and organic compounds which is formed in flocculation and sedimentation process. This study focused on the decomposition of the bonding by flocculating agent and organic matter, and proposed a simplified method for the prediction of changes in shear strength caused by DWS decompositions. The changes in shear strength of DWS were investigated by triaxial compression tests. The specimens were produced using the DWS which was mainly decomposed by H₂O₂ solutions. As a result, volumetric strain became large in the large axial strain range, and the maximum deviator stress decreased concomitantly with the decrease in ignition loss. After the organic matter was decomposed until 1.38%, the internal friction angle decreased from approximately 38.8° to 37.6°. The changes of shear strength were related to the substantial period in geotechnical works such as road infrastructures. The decompositions of the mechanical bridging and organic matter were described based on diffusion-controlled Al leaching and aerobic biodegradation, respectively.