封闭气泡对一维积水入渗影响的试验研究

Experimental research on the effect of entrapped air on one-dimensional ponded water infiltration

非饱和土体中的部分气体极容易在入渗过程中被封闭在孔隙或裂隙中,形成互不连通的与外界隔绝的封闭气泡。封闭气泡的存在阻碍了水相的流动,使土体的渗透性能降低,从而对土体的入渗速率产生不可忽视的影响。在分析前人研究成果的基础上,结合室内一维积水入渗试验结果,初步探讨了封闭气泡的形成原因,及其对土体入渗性能的影响机制,对研究非饱和土中水气二相流规律有重要指导意义。试验结果表明:积水入渗时,土体中存在封闭气泡,封闭气泡的含量与土性、干密度和初始含水率等有关。干密度越大,封闭气泡占据孔隙空间越大,阻渗作用越明显,干密度相同时,黏性土中封闭气泡对入渗的阻碍作用较砂性土明显;初始含水率较小时,封闭气泡含量相对较大。由于封闭气泡的存在,入渗稳定时的传输区土体含水率只有土样饱和含水率的80%左右。

A part of air in soil is easily surrounded by water flow and entrapped in the pores of unsaturated soil in the infiltration progress.The entrapped air is neither continuous with each other nor with the external atmosphere.Thus the water flow is encumbered and the permeability is decreased,which results in great influence on infiltration.Based on the previous research and the results of one-dimensional ponded water infiltration in the laboratory,a preliminary research on the formation of entrapped air and its influence mechanism on infiltration are conducted.This research is important to understand the water-air two phases flow in unsaturated soil.The test results show that the entrapped air is found in all ponded water infiltration tests,which is related to soil type,dry density,and initial water content.The entrapped air occupies more void in larger dry density sample and has greater influence on water flow.Under the same dry density condition,the entrapped air in clay soil affects infiltration greater than that in sand soil.The less the initial water content is,the greater the entrapped air volume is.At the steady state of infiltration,the water content is about 80% to the saturated water content.