含水率对黄土渗气性影响及其微观机理

Influence of water content on loess air permeability and its microcosmic mechanism

利用改进的渗气仪对风干原状土和重塑马兰黄土进行渗气性试验,分析初始含水率、增湿和减湿过程对渗气率ka的影响,并结合概念模型、超景深显微镜和扫描电子显微镜揭示其微观机理。研究结果表明:当试验含水率w<18%,干密度ρd≤1.6g/cm^3时,由于团聚体的形成、颗粒软化和基质吸力阻滞作用,重塑试样的渗气率随着初始含水率的增大而增大;而当ρd>1.6g/cm^3时,渗气率开始随着初始含水率增大而减小。由于原状和重塑黄土增湿过程中水、气的渗透作用和烘干减湿过程中微小裂缝的形成,在相同含水率下,减湿过程渗气率始终大于增湿过程渗气率。重塑黄土的增湿级数与渗气率之间没有显著关系。当干密度为1.4~1.7g/cm3时,增湿过程中含水率与渗气率关系曲线呈反S型。随着含水率的增大,大孔的平均直径、大孔和总孔面积也呈现明显增大趋势,致使对应的渗气率也逐渐增大。

The air permeability tests were performed on the undisturbed and remolded loess samples by using the improved air permeameter. The impacts of initial water content, wetting and drying processes on the air permeability ka were analyzed. The conceptual model, super depth of field microscope, and scanning electron microscope were applied on loess samples to investigate the microcosmic mechanism of air permeability. The results show that when water content w<18%, dry density ρd≤1.6 g/cm^3, the air permeability of the remolded samples increases with the increase of the initial water content, whereas when ρd>1.6 g/cm^3, the air permeability decreases with the increase of initial water ratio. Due to the permeation of the air and water during the wetting processes of the undisturbed and remolded loess samples and the formation of micro cracks during the drying process, the ka in the drying process is always greater than the ka in the wetting process at the same water content. There is no significant relationship between the wetting stage and the air permeability for the remolded loess. When ρd is 1.4.1.7 g/cm3, the water content and the ka show an inverse Sshaped relationship in the wetting process. With the increase of water content, the average diameter of macropores and the areas of macropores and the total pores also increase, leading to a gradual increase in ka.