游离氧化铁对红黏土持水特性的影响

分别以红黏土去铁前后的原状样为研究对象,采用压力板仪和饱和盐溶液蒸气平衡法测得全吸力范围内的土水特征曲线并同时量测体变;利用压汞试验测量不同吸力下的孔径分布,以探讨去铁前后红黏土的孔隙结构,并解释宏观持水特性。试验结果表明:低吸力范围(0～1MPa),去铁前原状样的持水曲线下降较为明显,而去铁后原状样的持水曲线较平缓,尤其是吸力–饱和度的关系,到1MPa时基本上仍为饱和状态,所以去铁后土样进气值增大;去铁后的原状样随着吸力的增大收缩明显,而原状样的收缩相对较缓,主要原因是游离氧化铁以包膜和桥的形式分布在颗粒表面,加强了颗粒之间的连接和包裹作用,使得土骨架抵抗变形的能力增强。高吸力范围(9～367MPa),去铁前后红黏土持水和收缩特性相差不大,此时游离氧化铁的作用不明显。去铁前后的红黏土原状样基本上存在单峰孔隙结构,主要原因是在自然经过无数次胀缩变形,相对较大的孔隙收缩,最终使孔径分布相对均匀;随着吸力的增加,这两种土样孔隙结构基本上不变。

Effects of free iron oxide on water retention behavior of lateritic clay

In order to obtain the soil-water characteristic curve (SWCC) of two types of undisturbed lateritic Guilin specimens with and without free iron oxide in full suction range, two measurement methods are used: the pressure plate method and the vapor equilibrium method with saturated salt solution, and the volumes of specimens are measured during the process. The mercury intrusion porosimetry (MIP) tests are used to investigate the pore-size distributions. The test results show that in the low suction range, the SWCC of undisturbed specimens where the free iron oxide is removed is gentle. Especially in the relationship of suction-saturation, it's still saturated when the suction is 1 MPa. But the SWCC of undisturbed specimens declines obviously. Compared with the undisturbed specimens, the undisturbed specimens where the free iron oxide is removed shrink obviously. The main reason is that the free iron oxide is distributed on the particle surface in the form of film enveloping and bridge, which strengthens the connection and the coat effect between particles, so as to enhance the capability of the soil skeleton to resist deformation. In the high suction range, the water retention and shrinkage characteristics of the two types of undisturbed specimens have little difference, indicating that the absorbed water in the soil is dominant. The undisturbed specimens with and without free iron oxide exhibit a unimodal pore-size distribution, and they are different from the traditional understanding of a double-porosity microstructure. There are mainly intergranular pores with a diameter of 40 nm in compacted samples.