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.