饱和城市固废一维降解固结解析解
Analytical solution for one-dimensional degradation-consolidation of saturated municipal solid waste
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摘要: 填埋后的城市固废因降解产生固相质量损失,从而造成在外力作用下的固结是一个相当复杂的过程。为研究饱和城市固废的降解固结特性,建立了一维降解固结普遍模型;基于已有城市固废降解、压缩和渗透特性研究,获得了考虑可降解固相水解、胞内水释放为孔隙水及降解导致压缩性衰变的一维降解固结简化模型;基于简化模型,针对饱和城市固废填埋层底部淤堵不透水和顶部自由排水工况,获得了一维降解固结解析解。针对国内填埋场新鲜城市固废的计算结果表明:在瞬时常荷载作用下,固结初期,填埋层底部的超静孔压值会超过初始值,这主要是因为降解引起固相质量损失导致骨架疏松、压缩性增大;固结后期,整个填埋层出现负的超静孔压,这是因为后期填埋层孔隙比因固相质量损失而增大,而压缩性衰变相对较小。参数敏感性分析表明:降解引起的次压缩速率越大,固结初期超静孔压越大;增加填埋层的先期固结压力会延缓超静孔压的消散。Abstract: Owing to loss of solid mass of municipal solid waste (MSW), the consolidation under external loading is complex. In order to study the degradation-consolidation behavior of saturated MSW, the universal model for the one-dimensional (1-D) degradation-consolidation is established. A simplified 1-D degradation-consolidation model considering hydrolysis of degradable solid, formation of pore water due to intra-particle water release and degradation-dependent compressibility is derived based on the existing research achievements of degradability, compressibility and permeability of MSW. The top and bottom boundary conditions of waste layer are assumed to be free-draining and impervious, respectively. The analytical solution to a simplified 1-D degradation-consolidation model is derived. Case studies are carried out for the fresh MSW in landfills of China. The results show that the excess pore water pressure being larger than the initial value is found in deeper waste layer during the early stage of consolidation under an instantaneous constant loading. This is mainly due to loosened soild skeleton, increasing compressibility associated with loss of solid mass. The excess pore water pressure is found to be negative in the whole waste during the later stage of consolidation. The reason is that the loss of solid mass causes the increasing void ratio, while the increase of compressibility is relatively smaller. The sensitivity analysis shows that an increase of the secondary compression rate causes the increasing excess pore water pressure during the early stage of consolidation, and its dissipation will be delayed with the increasing preconsolidation pressure.