非饱和粘性土中气体渗透特征

由于气体的进入形成了非饱和带，饱和土层中的气体渗透实质上是非饱和渗透问题。本文借助基于多孔介质气体渗流理论并考虑气体压缩性的、描述非饱和土中气体渗流运动的本构方程，试验研究了上海地区饱和粘性土层中的气体渗透规律。结果表明，饱水粘性土层中，气体渗透存在起始压力值，数值为100～200kPa, 与上海地区粘土的非饱和进气值较为接近；气体渗透速度与外界所施加的压力平方差梯度之间存在明显的分段特征。后者可能与在充满结合水的微孔隙通道中，只有一部分结合水在气压梯度的作用下发生流动，从而形成气体通道，施加的外力越大，形成的气体通道也越大，气体渗流也越明显。非饱和粘性土中气体渗透规律的研究，对于饱和粘土中的气压法施工，具有重要的理论与工程实践意义。

LABORATORY TESTS ON THE CHARACTERISTICS OF AIR-PERMEATION IN UNSATURATED SHANGHAI SOFT SOIL

After air entrance, an unsaturated area is formed in saturated soil. So, in fact, air permeation in saturated soil aquifer is an unsaturated permeation problem. Based on the constitutive equation, which is deduced from porous media theory with consideration of the compressibility of air, the characteristics of air permeation in saturated soil aquifer in Shanghai area is studied through laboratory tests. Results show that the air permeation in saturated clayey soil has a threshold of pressure about 100~200 kPa, which nearly equals to the air-entry value of the corresponding soil. The air permeation velocity and pressure gradient curve in the soil show clearly in step-phase. The main reason for this phenomenon may be due to that in saturated porous soil, all the channels are full of water. At the initial stage of air entrance, only a small mount of absorbed water can move under low air pressure. And with the air pressure increases, the air permeation channel expands, more air can be transmitted. The study of air permeation in saturated soft soil is helpful for air pneumatic underground engineering construction activities in saturated soft soils.