城市生活垃圾填埋场固液气耦合一维固结模型

建立了一维固、液、气三相耦合的大孔隙垃圾固结数学模型。把垃圾视为大孔隙介质,假定基质吸力等于0,即孔隙气压等于孔隙液压,把填埋场简化为非稳定单向渗流场。模型中采用了Gibson和Lo一维压缩流变模型及Landgem产气方程,结合了达西定律、气体状态方程、有效应力原理和多孔介质流体动力学理论。填埋场的沉降按封场前和封场后两个阶段分别计算,封场前填埋场接受垃圾,导致堆载压力增加,而封场后的填埋场堆载压力保持不变。垃圾堆填时产生的超孔隙压力按Hilf分析法计算。运用差分法对固、气耦合问题进行了数值求解。计算结果表明:气压随深度增加而增大,透气率大的填埋场其气压消散速率快。在堆填期,气压随时间增加而增大;封场后,气压逐渐消散。气压增加,导致填埋场沉降速率和容量减小。

One-dimensional consolidation model for landfills considering solid-liquid-gas interaction

A preliminary study on the solid-liquid-gas interaction in the landfill of municipal solid waste(MSW) was carried out by use of the numerical modeling.It was assumed that the mechanical effect of suction in the MSW could be ignored because macro-pores were dominant in the MSW.On the basis of this assumption,a theoretical model considering solid-liquid-gas interaction was developed to compute the compression of landfill of MSW.The model incorporated Gibson and Lo’s biodegradation and creep model,the Landgem’s gas production equation,Darcy’s law,the ideal gas law,the dynamics of fluids in porous media and the principle of effective stress.It was assumed that the migration of landfill gas only occurred vertically,and hence the theoretical model could be simplified to a one-dimensional compression model.The compression model could be used to calculate the settlement during the filling stage and the closed stage.During the filling stage,the landfill continually received the refuse which led to the increasing of the loading pressure.During the closed stage,the loading pressure kept constant.The excess pore pressure caused by the loading pressure was calculated by Hilf’s analysis.A finite difference solution was obtained for the solid-liquid-gas interaction problem,which was a special case of solid-liquid-gas interaction problem.The results showed that the gas pressure increased along the depth.During the filling stage,the gas pressure increased.During the closed stage,the gas pressure dispersed gradually.In the landfill with high permeability,the pore gas pressure dispersed quickly.The quick decrease of the settlement rate,caused by the increasing of the gas pressure,would decrease the capacity for the landfill.