湿胀条件下合肥膨胀土土-水特征研究

膨胀土在吸水时会产生体积膨胀,研究湿胀条件下膨胀土的土-水特征具有重要意义。以合肥地区9种弱膨胀土为研究对象,采用滤纸法和渗析法试验测定了膨胀土的土-水特征,采用蒸汽加湿法试验测定了膨胀土在吸湿过程中的体积变化。基于土-水特征曲线(SWCC)试验及加湿试验,获得了膨胀土在吸湿过程中的体积变化规律,得到了湿胀条件下膨胀土的重力含水率-基质吸力曲线(w-ψ曲线)及体积含水率-基质吸力曲线(θw3-ψ曲线),分析了膨胀土吸湿过程中的体积变化对体积含水率-基质吸力曲线的影响,探讨了w-ψ与θw3-ψ曲线拟合参数的变异性及参数间的相关性。结果表明:蒸汽法加湿土样是一种较为理想的增湿方式;湿胀条件下,w-ψ曲线与考虑体变的θw3-ψ曲线的差异程度与吸湿结束后的土样含水率有关;w-ψ曲线的变异性小于θw3-ψ曲线的变异性;拟合参数n的变异性小于参数a及m的变异性;w-ψ曲线及θw3-ψ曲线的对应拟合参数间呈线性关系。

Study of soil-water characteristics of Hefei expansive soil under moisture-expansion condition

Expansive soil will appear volume expansion under moisture adsorption condition. It is very important to study the soil-water characteristics of expansive soil under moisture adsorption and expansive conditions. Considering nine Hebei expansive soils as the study objects, soil-water characteristic curve (SWCC) tests by osmotic method and filter paper method are carried out. Filter paper method is used to measure the lower suction range, while osmotic method is used to measure the higher suction range. Moisture adsorption tests are carried out by steam humidification method. Based on soil-water characteristics tests and moisture adsorption tests, the volume change rules of expansive soils under wetting condition can be obtained. The experiment data are then curve fitting by using Matlab, and the gravity water content-suction curves (w-ψ curves) and the volumetric water content-suction curves (θw3-ψ curves) are obtained. The influence of the volume change of expansive soil under moisture adsorption condition on the θw3-ψ curves is analyzed; and the variability and correlation between curve fitting parameters of w-ψ curves and θw3-ψ curves are also studied. The results show that the steam humidification method is a good approach for moisture adsorption test. During the steam humidification process, the moisture is adsorbed slowly and uniformly, and the shape of soil sample remains unchanged. The void ratio?gravity water content curve can be divided into four stages, which are initial stage, approximate linear stage, nearly horizontal stage, and ascent stage along the saturation line. The difference between the two types of SWCCs (w-ψ curves and θw3-ψ curves) is due to the volume change of expansive soil samples during the wetting process, and the extent of volume change depends heavily on the water content of expansive soil samples after the moisture adsorption process. The variability of w-ψ curves is less than that of θw3-ψ curves. For both of the two types of SWCCs, the variability of parameter n is relatively small, which means that the slopes of SWCCs are close to each other for different soils. The variabilites of parameters a and m are larger than that of parameter n. The corresponding curve fitting parameters of w-ψ curves and θw3-ψ curves are linearly correlated. Therefore, the curve fitting parameters of θw3-ψ curves can be preliminary estimated by those of w-ψ curves.