全吸力范围南阳膨胀土的土-水特征曲线

Soil-water characteristic curve of Nanyang expansive soil in full suction range

膨胀土的失水收缩、吸水膨胀过程分别对应着土-水特征曲线的脱湿和吸湿阶段。土-水特征曲线对于研究非饱和土的水力与力学特性有着重要作用。用压力板法(吸力范围0～1.5 MPa)、滤纸法(吸力范围0～40 MPa)和蒸汽平衡法(吸力范围3～368 MPa),分别对南阳膨胀土进行了土-水特性试验,得到全吸力范围内的土-水特征曲线。试验结果表明:初始孔隙比大致相同土样的土-水特征曲线,在低吸力范围内脱湿曲线与吸湿曲线具有明显的滞回现象。当吸力大于300 MPa时,土-水特征曲线的滞回效应基本消失,即脱湿曲线与吸湿曲线基本重合。滤纸法所测出的土-水特性落在主脱湿和主吸湿曲线的滞回圈内。当吸力等于367.54 MPa时,含水率仅为0.325%,几乎近于0。孔隙比随着吸力的变化规律中,不仅受到吸力大小的影响,还受到吸力历史和吸力路径影响;孔隙比与吸力关系中,相同吸力时吸湿路径的孔隙比要比脱湿路径的大;在吸力低范围,吸湿路径与脱湿路径的孔隙比相近。孔隙比与饱和度关系因吸力路径的不同也存在着明显的滞回效应,接近饱和时趋近一致。变吸力情况条件下,饱和度随着孔隙比的增加而增加,蒸汽平衡法得出的孔隙比与饱和度的关系具有明显的线性关系,而压力板法做出来的低吸力范围内的线性关系不明显。

The processes of dehydration shrinkage and water-swelling of expansive soil correspond to the drying and wetting stages of the soil-water characteristic curve（SWCC）.The SWCC plays an important role in defining the hydro-mechanical behavior of unsaturated soils.In order to study the SWCC of Nanyang expansive soil in full suction range,three suction control or measurement methods are used： the pressure plate method for low suction range of 0-1.5 MPa,the filter paper method for suction range of 0-40 MPa,and the vapor equilibrium technique for high suction range of 3-368 MPa.The results show that the SWCC has obvious hysteresis phenomenon during the drying and wetting in the low suction range.When the suction is greater than 300 MPa,the hysteresis effect of SWCC disappears;and the drying and wetting curves are almost overlapped.Test data of soil-water characteristic by the filter paper method are located between the main drying and wetting curves of the SWCC.When the suction of is 367.54 MPa,the soil water content is only 0.325%,and it almost approximates to zero.Void ratio not only changes with suction,but also it is influenced by the suction history and suction path.In the relation between void ratio and suction,the curve of wetting path is above that of the drying path;and they become the same at low suction.There is a clear hysteresis of the relation between void ratio and saturation degree,due to the different suction paths;and they will be consistent when close to saturation.The saturation degree increases with the increasing void ratio when suction changes.The experimental data obtained by the vapor equilibrium method have an obvious linear relationship between void ratio and saturation degree;while the test data obtained by the pressure plate method are no an obvious linear relationship in the low suction range.