Research On Settlement, Static And Dynamic Stability Of Landfills For MSW

Recently Municipal Solid Waste (MSW) aggrandized rapidly in China. Landfill has become the main means to deal with MSW in this country and it will be exist as the final disposal method in the long run. This thesis focuses on MSW's compression and shear strength characteristics, settlement and capacity of landfills, static and dynamic stability as well as seismic permanent deformation of landfills.There is no appropriate model to analyze settlement of landfills so far, especially when bio-chemical decomposition was taken into consideration. Organism decomposition rules of MSW are generalized and an equation to evaluate the variation of organic substance with time (depth) is proposed at the first time in this thesis. The equation is verified when compared with the results from field-test. Large-dimension compression tests are performed in laboratory and void ratio梔epth curve are obtained by means of in-situ sampling. By comparison of in-situ tests results and laboratory tests results, an opinion that organic biodecomposition doesn't change the void ratio of MSW during compression by and large is proposed. On this basis, a method to calculate settlement during and after filling and an equation to estimate the capacity for landfills are also presented. The proposed methods are simple and parameters are tended to be determined with accuracy. The effects of organic content and decomposition rate on the settlement and capacity of landfills are quantitatively analyzed. Through calculations, it's found that MSW is highly compressive and the settlement of landfills is significantly influenced by organic biodegration; especially when decomposition rate increases up to the 0.1/year level, decomposition will contribute much to the capacity of landfills; the design density depends on many factors such as the height of landfills^ filling rate, decomposable organic content and the organic decomposition rate.The mechanism of MSW's shear strength is stated in this thesis. The underlying cause for the phenomenon that the cohesion of MSW increases with depth while angle of shear resistance doesn't is detailed explained in this paper. It's found by means of calculation that the form and the maximum thickness of the profile of the liquidsurface are highly influence by the integrality of the leachate system. The static stability is also analyzed by USAP in this paper. To explore the dynamic properties of landfills further more; Rayleigh wave tests on landfills are performed by a self-developed RSA system. By means of frequency analysis; shear wave velocity varied with depth curves of landfills are obtained. The seismic response is analyzed with total stress method; and it's found that the positions of the most dangerous slide surfaces are fairly stable though the precision for searching is very high. The idea of Newmark method is induced to calculate permanent deformation on circular sliding surfaces. The precision is increased and the complexity of searching is lessened. This method can also be applied to the seismic analysis of different kinds of dams and embankments. It's concluded by analysis that the increment of unit weight can restrain the permanent deformation during earthquakes.With the presented methods; the settlement and stability of an extended landfill in Hangzhou are analyzed systematically. Geomembranes and liner system between the extended landfill and the old one especially above the toe of the old dam are probable failure places due to ununiform settlement. Some suggestions about the design of liner systems are also put forward in this thesis.