Hydro-mechanical behavior of fiber reinforced dredged sludge

Abstract

Dredged sludge has poor mechanical properties and its safe disposal is highly risky. Fiber has been considered as an effective additive for soil reinforcement because of its cost effectiveness, easy adaptability, and reproducibility. The main objective of this research is to investigate the effects of polypropylene fiber on hydro-mechanical behavior of dredged sludge. A series of compression and direct shear tests were performed on dredged sludge samples with different percentage contents of polypropylene fiber 0%, 0.05%, 0.1%, 0.2%, 0.4%, and 0.8% by weight of dredged sludge and the direct shear tests were performed at vertical stresses of 50, 100, 200 and 400 kPa. The test results indicate that inclusion of fiber improves shear strength of sludge with increasing compression, void ratio, consolidation coefficient and hydraulic conductivity. The optimum fiber content for these improvements was found to be 0.1%. Presumably the post-consolidation moisture content of sludge after consolidation is minimal at this fiber content, although the shear strength continues to increase with fiber content even after consolidation. The shear strength of samples with the fiber contents of 0.8% is 1.48, 1.58, 1.42, 1.27 times that of the non-reinforced samples under respective consolidation pressures of 50, 100, 200 and 400 kPa, and the reinforcement efficiency is most significant under a pressure of 100 kPa. The strain hardening tendency is more pronounced with the increase of fiber content in the late shear failure process. The results of this study indicate that the mechanism of fiber reinforcement for the consolidation test is “bridging” as different from the shear strength test, which is “friction”. This realization should impact upon the failure patterns of fiber reinforced materials.