Storage sludge has high water content and low shear strength, which limits the capacity expansion of overlying municipal landfilling. Few studies have addressed the field treatment of large amounts of storage sludge due to the variability of the depth of geotechnical property. This paper proposes a stratified treatment method for storage sludge, based on the in situ characterization of layered sedimentary patterns of the storage sludge acquired from the Qizishan landfill in China. Additionally, the stability of the landfilling above the sludge pond is analyzed using the Morgenstern–Price and limit equilibrium slice method, which considers the layered strength properties of solidified sludge. The treated sludge has a significant decrease in average water content from 1398% to 88% and an increase in average cohesion to 23.52 kPa. The high content of clay particles, low amount of solidification products, and high water content together result in the high sensitivity to the water content of the strength of deep solidified sludge. For a 40-m high waste body, stability analysis suggests a sliding surface across the raw sludge pond, while the critical surface remains outside the treated sludge pond and the safety factor is increased from 0.934 to 1.464. The validated stratified treatment provides valuable references for the treatment of deep sludge.
Low-strength sludge takes up a lot of space in landfills, creating an environmental concern and a resource waste that needs to be treated right away. A novel mixed solidifying agent in this work is introduced to the geotechnical characteristics’ improvement of sludge for the first time. The role of each component in the mixed agent is explored by a series of different additive dosages in solidification. According to water content tests, shear wave velocity tests, unconfined compression strength tests, direct shear strength tests, X-ray diffraction, and scanning electron microscopy, the strength development of solidified sludge is comprehensively analyzed under different dosages and curing ages. The micro-analysis result shows that the geotechnical characteristics improved mostly due to hydration products such as ettringite, calcium silicate hydrate gel, aluminum gel, and hydrogarnet. Besides, the generation of hydration products consumes the water in sludge, fills soil particle pores, and connects the soil particles, which makes the structure of solidified sludge compacted, hence, improving the strength of the solidified sludge. Furthermore, the relationship between the shear wave velocity and undrained shear strength parameters follows the power function and indicates that the shear wave velocity can characterize the strength level of the solidified sludge.
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