| The bioreactor landfill is a new type of waste landfill technology, which developed from the traditional landfill, and possesses with the merits of accelerating the degradation of organic matter of waste in landfill, improving the rate and production of methane, speeding up the settlement of landfill, increasing the effective volume of landfill, shortening the maintenance period of landfill, reducing the pollution period of landfill. The study on the bioreactor landfill has important theoretical and practical value. Based on the laboratory test and theoretical analysis, the primary compression and secondary compression settlement mechanism and characteristics were presented. The models of primary compression and secondary compression settlement were established correspondingly.Some existing bioreactor landfill settlement models were classified and commented. Based on geotechnical theory, the compression settlement was divided into immediate settlement, primary settlement and secondary settlement. But in this paper, it was divided primary settlement and secondary settlement. Based on the primary compression and secondary compression settlement mechanism and characteristics, it was proposed that the bioreactor landfill settlement is a double function of mechanical compression and organic matter degradation.The mechanical properties of domestic waste in landfill were reflected by its basic soil parameters. A set of experiments were carried out, which consisted of organic matter content, moisture content, specific gravity, dry density and void ratio of domestic waste through in-situ sampling. The results of geotechnical test of waste were obtained. The basic soil parameters of domestic waste were studied based on the collation and analysis of test results, which provided an important basis and foundation for primary compression and secondary compression settlement tests of domestic waste.A primary compression settlement apparatus of bioreactor landfill was designed. The primary compression settlement experiment of landfill in the stabilization process was conducted by this apparatus in laboratory. The compression rule of waste was studied, based on the results of primary compression settlement experiment of domestic waste. The primary compression curve of domestic waste was obtained. And the mechanical properties of primary compression of domestic waste were mastered. The computational model of primary compression settlement of domestic waste was established using the linear relationship of σ/ε-σ. There exist positive correlations between a, b of the calculating parameters of the model and the dry density of waste samples.A fully functional secondary compression settlement apparatus was designed based on primary compression settlement experiment. The gas collection system, leachate collection system and treatment system were added in the set of experiment equipment. And an experiment protocol of secondary compression settlement of bio reactor landfill was designed: the first group was pre-treatment leachate recirculation landfill (PLRL); the second group was raw leachate recirculation landfill (RLRL); the third group was no leachate recirculation landfill (NLRL). There was a leachate treatment center in the first set of experiment. The results showed that PLRL shortened the degradation time of organic matter significantly and accelerated the settlement process of landfill.The bioreactor landfill was simplified as a one-dimensional gas seepage field. Incorporating Darcy’s law, ideal gas law, the principle of effective stress and the theory of fluid dynamics in porous media, a mathematical model was developed for the secondary compression settlement under the action of gas pressure in a bioreactor landfill according to the air pressure difference between atmosphere and landfill during gas dissipation. Finite difference method and finite grid method were used to solve the model. The theoretical results were basically consistent with experimental results. |
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