基于优势流及各向异性随上覆压力变化的填埋体饱和渗流模型

Modeling saturated permeability of municipal solid waste based on compression change of its preferential flow and anisotropy

生活垃圾由于组成成分的多样性及分层填埋,其孔隙呈不均匀分布,并且水平向多于竖向。填埋体中的渗流存在明显的优先流效应,各向异性显著并受上覆压力等因素影响。基于Poiseuille方程,根据上覆压力作用下生活垃圾孔隙形状、孔隙尺寸分布及孔隙排列方向分布特征,提出了基于优先流及各向异性的饱和渗流模型。揭示了新鲜生活垃圾分布变化规律,0~200 k Pa,大孔隙逐渐消失,平均孔隙直径与可排水孔隙率呈指数下降,孔隙排列角度逐渐水平向倾斜。采用新建饱和渗流模型进行分析计算,确定采用可排水孔隙率可比总孔隙率更好地模拟垃圾孔隙渗流特性。渗流由大孔隙优先流主导,0~600 k Pa内计算获得新鲜垃圾水平向饱和渗透系数变化范围为10^(-2)~10^(-5)cm/s。给出了渗流各向异性值的计算公式,渗流各向异性值大体随上覆压力增加而增大,并与初始孔隙排列角度相关;0~600 k Pa内计算得新鲜垃圾渗流各向异性值变化范围为1~10。

It is generally accepted that landfilled municipal solid waste（MSW）exhibits heterogeneity and anisotropy because of the diverse composition and the layered placement, causing that the distribution of pores prefers to be horizontal. In the landfill, the preferential flow is obvious, and the anisotropy is significantly affected by the overburden pressure. According to the changes of pore shape, pore size distribution and pore alignment under compression, a saturated permeability model is derived based on the Poiseuille equation, which mainly relates to the dominant flow and its anisotropy. The pore distribution changes of fresh MSW are revealed. Under the overburden pressure of 0～200 k Pa, with the collapse of larger pores, the pore average size and drainable porosity decrease according to the negative exponent, and the pore alignment tends to be horizontal. When calculated by the new model, the drainable porosity can well simulate the variation of permeability. The preferential flow is dominated by the large pores. Under the overburden pressure of 0～600 k Pa, the saturated horizontal permeability of fresh MSW is in the range of 10～（-2）～10～（-5） cm/s. The formula for the permeability anisotropy is given. The calculated permeability anisotropy of fresh MSW increases for the correction to the direction of pore alignment. Under the overburden pressure of 0～600 k Pa, the value is in the range of 1～10.