渗滤液水位以下垃圾体产气对孔隙压力影响研究

为了研究渗滤液水位以下产气对孔隙压力的影响，从孔隙气在渗滤液水位以下特定的流动状态出发，采用峰值产气模型，结合了达西定律、理想气体状态方程和多孔介质流体动力学理论，建立了渗滤液水位以下考虑产气作用的气液迁移模型。运用差分法对产气引起的气液迁移问题进行了数值求解。计算结果表明，渗滤液水位以下垃圾体的产气对孔隙压力的影响主要有渗滤液渗流引起的附加孔隙压力和水位升高引起的附加孔隙压力，按孔隙气所处阶段的不同可以分为孔隙气被封闭时孔压积聚阶段、孔隙气突破孔隙水封闭时的孔压急剧消散阶段以及由对流作用控制的气液运移阶段；高产气速率、高渗滤液水位和低渗透系数都会使得垃圾体内产生较高的孔隙压力；降低填埋场内渗滤液水位是减小产气对孔隙压力影响的有效措施。

Research on effect of landfill gas generation on pore pressure below leachate level

In order to study the effect of landfill gas on pore pressure below the leachate level in wet municipal solid waste landfill, a new model for predicting the time and depth dependent development pore pressures due to the formation of landfill gas is derived. Considering the specific flow conditions of pore gas below the leachate level, the model combines the Darcy law, the ideal gas law and the theory of dynamics of fluids in porous media. A finite difference solution is obtained for the liquid-gas migration problem, which is caused by the continuous formation of landfill gas within the wet waste. The calculation results show that the pore pressure below leachate level is mainly influenced by the additional pore pressure caused by the increasing of phreatic surface and the excess pore pressure due to the continuous formation of gas. The pore pressure varied over time during the gas generating period. At the beginning, a maximum gas pressure is identified because of gas eruption, and then, gas escaped from the surface leading to an immediate pressure reduction along with a significantly increased gas permeability; finally, the pore pressure is depended by gas-liquid convection. In the landfill, high gas yield rate, high leachate level and low permeability make waste to form high pore pressure. Drawdown of leachate level is found to be the most effective and workable emergency measure to reduce the pore pressure in wet landfill, which is caused by the continuous formation of landfill gas.