Measurement Of Geotechnical Properties For Sewage Sludge At A Disposal Site And Evaluation Of Its Influence On Slope Stability Of MSW Landfill

The operation of many landfills has been seriously influenced by the sludge reservoir simply trenched in the landfill which reduces storage capacity of the landfill and will trigger waste mass instability. As the disposal of MSW, increases available storage of landfill is limited. Nowadays different treatment measures are undertaken in many landfills to assure subsequent disposal on the sludge reservoir. The predecessors have mainly researched into the geotechnical characteristics of fresh sludge and ultra-soft soil reinforcement disposal The improvement of the sludge in the reservoir and storage restoration is an unsolved problem by which many landfills in China are confronted, In this paper, for solving the problems of reinforcement disposal of sludge reservoir and restoring the capacity of Phase II project in Chengdu MSW landfill, the geotechnical properties of the sewage sludge taken from the disoposal site were measured, then the its influence on slope stability of MSW landfill were evaluated. Finally, the reinforce disposal methods of sludge reservoir was proposed.The major studies and achievements in this thesis are as following:(1)A thorough geotechnical investigation consisted of borehole sampling, laboratory tests, cone penetration tests and vane shear tests were conducted to get the engineering properties of sludge in the reservoir, the result showed that: the sludge could form hard crust layer, fluid layer and fluid plastic layer with different geotechnical characteristic, to place in the sludge reservoir for a considerable period. The sludge had much lower strength than the muddy soil. The sleeve friction, tip resistance and shear strength was of the order 10-1-101kPa, as well showed an increasing trend with depth.(2)The geotechnical test was conducted on the sewage sludge with different depth, the study founded that: the sewage sludge with biodegradation was an organic soil with the characteristic of high values in organic content, water content, plasticity index, compressibility as well as the low values in permeability, consolidation coefficient and shear strength. The organic content and water content of sludge in the sludge reservoir showed a decreasing trend with the depth; specific gravity and density showed an increasing trend with depth. The consolidation of the sewage sludge showed a non-linear behavior.(3)A conventional and air-boosted vacuum-preloading model tests were conducted to explore the consolidation settlement, strength improvement of degraded sewage sludge with vacuum preloading technique and its feasibility.(4)Experiments results of large-scale model tests were compared with that of conventional consolidation theory and non-linear consolidation theory, and a new design method suitable for sewage sludge was proposed, which was applied to subsequent analysis of consolidation settlement and strength improvement of sludge in Chengdu landfill reservoir.(5)The software Geo-Slope was made used to analyze the second phase design plan of storage capacity restoration of Chengdu landfill, and two optimized design schemes on waste mass slope angle and corresponding controlling measures on stability were obtained, based on which required undrained shear strength of sludge after treatment was proposed.(6)According to gain in undrained shear strength of sludge in model tests and required strength to assure slope stability of second phase storage restoration project, the method of vacuum preloading combined with surcharge load on sludge reservoir was proposed.