| The unsaturated-saturated fluid flow result in the complex existence of liquid and gas and the time varying saturation, which is the root cause for the poor diversion of liquid and gas in the landfills in China. The saturation variation law of municipal solid waste (MSW) in the landfills is determined by its water retention characteristics, which can be expressed by its soil water characteristic curve. The coupled effect of biodegradation and compression resules in the time varying particle size distribution and pore ratio, which leads to the change of water rentention characteristics in MSW. Therefore, Research on soil water characteristic curve of MSW under coupled bio-mechanical effect is of great significance for the analysis of unsaturated-saturated fluid flow, design and optimization of diversion system in landfills. Synthetic MSW was prepared for laboratory research. The value of C/L, particle size distribution, specific gravity and content of cellular water, kitchen and non-kitchen waste of the MSW with different degree of biodegradation were tested, in order to provide theoretical support for the study of the influence of biodegradation on the water characteristic curve of MSW. A large-scale SWCC testing apparatus was designed to test the SWCCs of MSW samples with different degree of biodegradation and void ratio. And at last, the influence of matric suction on the MSW’s skeleton deformation was analyzed through the volume change rule of the MSW sample in the soil water characteristic curve test and the shrinkage test. The main research works and conclusions are as follows:(1) The value of C/L was used to characterize the degree of biodegradation of the waste samples in the test. The experimental results showed that the average value of C/L was 5.15,4.63 and 4.28 in the initial state, thirtieth and sixtieth days respectively, which decreased with the increase in degree of biodegradation.(2) The feasibility of combining the absorbent paper method and the dryin gmethod to measure the content of cellular water in MAW was proved. This method combining absorbent paper and drying was used to measure the content of cellular water, kitchen and non-kitchen waste of the MSW in different degr ee of biodegradation. The experimental results showed that, in the sixtieth day, thecontent of cellular water, kitchen and non-kitchen waste of the MSW was 2.23%,1.33% and 90.52% of that in initial state respectively.(3) The particles of kitchen waste containing cellular water were considered as whole solid particles. The particle size distribution curve of waste samples with different degree of biodegradation were tested was obtained by screening method. The experimental results showed that, the content of the particles whose diameter were bigger than 10mm decreased from 83.5% to 68.%, while that whose diameter were smaller than 0.5mm increased from 3.8% to 7.4% after 2 months. The vacuum drainage method was used to measure the value of specific gravity of the MSW samples, and the resules showed that the values of specific gravity of kitchen and non-kitchen waste were 1.01-1.07 and 1.37～1.43 respectively, and were not significantly changed in first 2 months, while that of the whole sample increased from 1.11 to 1.41.(4) A large-scale SWCC testing apparatus was designed to test the SWCCs of MSW samples with different degree of biodegradation and void ratio. The results of SWCC tests showed that the saturated and residual water content of the MSW were 52%～81.4% and 22%～33.8% respectively, and the SWCC curve was steep when matric suction was relatively low. The air-entry values of the MSW were too low to be measured, and were considered lower than 0.25kPa. Some of the test results showed that the water retention characteristics increased with the increasing degree of biodegradation and void ratio while some of others didn’t. Simulation results showed that van-Genuchten model could satisfactorily model the SWCC of Chinese MSW.(5) The water absorbing capacity of three 2-months-old MSW samples was tested using a capillary rise open tube. The heights of wetting front were quite different from one position to another even in one sample. The capillary water tends to stop rising after 30 days, and the average height of wetting front of each sample varying from 3.6cm to 3.82cm.(6) The total vertical strain was less than 0.6% in each 2-months-old MSW samples in the secong drying soil-water characteristic curves test. And the total vertical strain was only about 0.83% in a shrinkage test of a 2-years old MSW sample obtained from a borehole drilled into a landfill in Jing cun gou, while the volumetric water content decreased from 0.47 to 0.07. |
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