干湿不同路径下黄土的土水特征试验研究

Experimental Study of Soil-Water Characteristics of Loess Under Different Wetting and Drying Paths

摘要:

为了全面认识在干、湿两种不同路径下黄土持水特性的联系和区别，针对豫西三门峡原状黄土展开了全吸力范围内的土水特征试验，采用渗析法（低吸力段）和气相法（高吸力段）逐级控制吸力，获得了在增湿和干燥两种不同路径下，黄土在0.01~309 MPa 吸力范围内的土水特征曲线（SWCC）。结果表明：黄土的土水特征曲线呈“S”型，含水率随吸力的增加而递减，且递减趋势呈现中间变化较大而两端变化小的现象，由此可通过进气值和残余饱和度将黄土土水特征曲线分成三个阶段：边界效应段、过渡段和非饱和残余段；黄土残余含水率为9.6 %，进气值为30 kPa，残余饱和度对应的吸力值约为300 kPa；在100~1 000 kPa吸力范围内，黄土的土水特征曲线存在明显的回滞现象，即相同吸力下的干燥路径曲线对应的含水率明显超过增湿路径曲线，特别在吸力为100 MPa附近数据差异最为显著，同吸力大小条件下含水率之差为5 %。最后基于Fredlund-Xing模型对增湿和干燥两个路径上的试验曲线进行拟合，得到了黄土的SWCC拟合公式及参数。

Abstract:

To better understand the relationship and differences in the water retention characteristics of loess under two different wetting and drying paths， this paper conducted soil-water characteristic tests over the full suction range on undisturbed loess in Sanmenxia， located in western Henan province. The suction was controlled step by step using the osmotic method （for low suction range） and the vapor phase method （for high suction range）. The results were obtained for both wetting and drying paths. The soil-water characteristic curve （SWCC） of the loess in the suction range of 0.01 to 309 MPa shows an “S” shape， Water content decreases， as the suction increases， with a significant change in the middle suction and a minimal change at both two ends. Based on the air entry value and residual saturation， the SWCC of loess can be divided into three stages：the boundary effect section， the transition section， and the unsaturated residual section. The residual water content of loess is 9.6 %， the air entry value is 30 kPa， and the suction corresponding to the residual saturation is about 300 kPa. In the suction range of 100 to1 000 kPa， the soil-water characteristic curve of loess has obvious hysteresis phenomenon， that is， the water content corresponding to the SWCC of loess exhibits notable hysteresis： the water content along the drying path curve is significantly higher than that along the wetting path curve for the same suction， especially in the vicinity of the suction of 100 MPa， where the difference in water content is 5 % . Finally， using Fredlund-Xing model， the experimental curves for both wetting and drying paths were fitted， and the corresponding SWCC fitting formula and parameters for loess were obtained.