三轴应力条件下原状黄土的渗气特性

用改装的三轴渗气仪,在三轴应力条件下对不同含水率原状黄土进行渗气试验,分析了平均应力、偏应力及含水率变化对渗气系数与饱和度关系的影响,提出了考虑三者影响的渗气函数。研究结果表明:偏应力、平均应力及含水率对渗气系数与饱和度关系皆有较大的影响。平均应力(应力比相同)或偏应力(平均应力相同)作用引起饱和度增大时,渗气系数线性减小,且减小程度与含水率的大小有关;含水率增大时渗气系数随饱和度增大而减小的速率比应力增大时的小。不同应力状态下,相对渗气系数与饱和度关系,渗气系数与修正气体饱和度关系皆可归一,且可分别用以总饱和度为参量的P-v G-M模型及本文提出的修正气体饱和度幂函数(MAPL)模型描述,但相比较而言,MAPL模型参数较少,更便于实际工程应用。MAPL模型对渗气系数的预测结果与试验结果吻合较好。

Gas permeability of intact loess under traixial stress conditions

The gas permeability tests on intact loess with various water contents are performed under traixial stress conditions using the refitted triaxial gas permeability equipment. Influences of changes in the mean stress, deviator stress and water content on gas permeability as a function of liquid saturation are analyzed. The gas permeability function considering their effects is proposed. The results show that the relationships between gas permeability and liquid saturation are affected clearly by the deviator stress and mean stress as well as water content. The gas permeability decreases linearly with the increase of liquid saturation resulted from the mean stress with constant stress ratio or deviator stress with constant mean stress, and the decreasing degree is dependent on the value of water content. The decreasing rate of gas permeability with the increase of liquid saturation is smaller during the increasing water content than that during increasing stress. There are all unique relationships between the relative gas permeability and the liquid saturation between the gas permeability and the modified gas saturation at different stress states. These relationships can be predicted by the P-vG-M model in term of the total liquid saturation and proposed modified gas saturation power law (MAPL) model, respectively. In comparison with the P-vG-M model, the MAPL model with less parameters is more convenient for engineering application. The predicted results of gas permeability by MAPL model are in good agreement with the test ones.