非饱和含砂细粒土的气体渗透特性研究

Air permeability of unsaturated fine sandy soil

为了探讨非饱和含砂细粒土的气体渗透规律,制备不同含水率和干密度试样进行气体渗透试验,并基于多孔介质渗流理论分析进气压力、孔隙比和饱和度等对气体渗透率的影响规律,总结了非饱和土中渗透率的经验公式。试验结果表明,随着进气压力的增加,土样气体渗透率测试值逐渐趋于稳定值;含水率较高时,进气压力对土样气体渗透率的影响程度较大;含水率较低时,土样气体渗透率随进气压力增加而变化幅值较小。气体渗透率随土样含水率的增加(或饱和度的增加)呈减小趋势;当含水率低于最优含水率时,气体渗透率变化较小,但当含水率大于最优含水率后,气体渗透率急剧降低;在最优含水率两侧,土样微观结构的差异(絮凝结构和分散结构)是导致气体渗透率发生突变的主要原因;气隙比可有效表征土体孔隙比与饱和度对气体渗透率的影响规律,气体渗透率与气隙比呈良好的幂函数关系,并采用已有文献中试验数据验证了经验公式的合理性。

To investigate the gas permeability performance of unsaturated fine sandy soil, a series of samples with different moisture contents and different dry densities is prepared and air permeability tests are conducted. Based on the porous media permeation theory, the effects of inlet pressure, void ratio, saturation on the air permeability of samples are analyzed, and an empirical formulation of air permeability is proposed. The experimental results demonstrate that air permeability tends to a stable value with the increase of the inlet pressure. The effect of inlet pressure on air permeability is far more obvious for samples with high moisture content than for samples with low moisture content. The increases of moisture content or degree of saturation can result in a decrease in air permeability of sample. When the moisture content is lower than the optimum moisture content, the variation of the air permeability is negligible; however, a rapid decrease in air permeability is observed when the moisture content is higher than the optimum moisture content. The difference of soil microstructure （flocculation structure and dispersion structure） accounts for the air permeability mutation at the two sides of the optimum moisture content. Air void ratio can effectively represent the influence of void ratio and saturation on air permeability. A power function relationship well adapts the relationship of air permeability with air void ratio. Test dates from the literatures also demonstrate the effectiveness of proposed empirical formulation.