Undrained shear strength–water content relationship for sewage sludge Available to Purchase

Micro-fibrous organic clays include sludges and residues derived from municipal and industrial treatment processes. This paper studies the relationship of water content w against remoulded undrained shear strength s_ur of one such material, namely sewage sludge (biosolids), and the factors affecting the coefficients a and b in the equation w=as⭑b−bur. Data for s_ur in fall-cone, vane shear and triaxial compression (TC) tests were examined, considering the material's mineralogical, physiochemical and biological properties. The effects of the different shearing modes, rates and confinement pressure on the mobilised strength were studied, since the different apparatuses approach the estimation of strength in different ways. The scalar relating the deduced s_ur values in vane shear to TC was not singular, but was particularly sensitive to the confining pressure (σ₃) applied in TC tests, and also to the difference in strain rate between the different tests. The deduced s_ur from the miniature vane was between 1·19 and 1·40 times that mobilised in quick-undrained TC of 38 mm diameter specimens under σ₃ of 100 kPa. New methods of analysis are presented to estimate the strength contribution of the gel-like pore fluid to the mobilised s_ur, and also to determine more accurately the water content corresponding to the fall-cone liquid limit condition.