准饱和多孔介质中圈闭气体对渗透系数的影响

含圈闭气体的地下水流称为准饱和流，准饱和流中的圈闭气体对含水层渗透系数有重大影响。通过柱试验开展了粉砂、细砂、中砂和粗砂4种介质圈闭气体饱和度与准饱和渗透系数关系的研究。结果表明:圈闭气体饱和度明显受介质的粒径影响，在细粒介质中圈闭气体饱和度明显较大；4种介质圈闭气体饱和度在0~15%范围内，准饱和渗透系数与完全饱和相比减少了32.82%~56.38%，且准饱和渗透系数与圈闭气体饱和度之间可表达为一个负线性相关的经验公式；该公式与Faybishenko公式等效，但形式简单，参数较少，使用方便；准饱和渗透系数的变化规律可概化为圈闭气体占据了原有的有效孔隙，造成原有效孔隙度减少，从而使渗透系数减小。利用该理论，Kozeny-Carman方程能较准确地描述准饱和渗透系数的变化规律，而基于哈根-泊肃叶方程的渗透系数公式则存在较大误差，不适用于描述准饱和渗透系数；试验结果证明了室内测定饱和渗透系数时排除圈闭气体的必要性。

Effect of entrapped air on hydraulic conductivity in quasi-saturated porous media

The groundwater flow with entrapped air was termed as quasi-saturated flow. The entrapped air in quasi-saturated flow of aquifer had a significant influence on hydraulic conductivity of porous media. In this paper,the relation between entrapped air saturation and hydraulic conductivity was studied by the column experiments with respect to four medium,silt,fine sand,medium sand and coarse sand,respectively. The results illustrated that the entrapped air saturation in a quasi-saturated aquifer was related to the particle size of the medium,and the entrapped air saturation in the fine-grained media was greater than that in the coarse-grained. Within a saturation range of 0-15% of entrapped air saturation,the hydraulic conductivity decreased by 32.82%-56.38% compared with that at entrapped saturation,and the hydraulic conductivity can be expressed as a negative linear correlation with entrapped air saturation. The results also showed that the variation of the quasi-saturated hydraulic conductivity could be generalized as the entrapped air occupied the original effective poresand resulted in a decrease in the original effective porosity and hence in hydraulic conductivity. According to this air entrapment theory,the Kozeny-Carman equation could accurately exhibit the variation of the hydraulic conductivity with entrapped air saturation in the quasi-saturated aquifer,and furthermore,the results illustrated the hydraulic conductivity formula based on the Hagen-Poiseuille equation was not suitable for quasi-saturated hydraulic conductivity. In Addition,the experimental results also showed it was necessary to remove entrapped air in laboratory measurement of hydraulic conductivity.