盐分影响重塑黄土渗透性的微观机制试验研究

Experimental study on the micromechanism of salt influence on the permeability of remolded loess

“治沟造地”修建水库,导致土地盐渍化,而盐渍土的渗透性是影响工程设计、施工安全的重要因素,因此阐明不同盐分含量及类型条件下的重塑黄土渗透性至关重要。通过制备不同盐分含量的钠、钙盐重塑黄土试样,开展一系列室内变水头饱和渗透试验,探析重塑黄土渗透系数随盐分含量的变化规律。结果表明:随盐分含量增加,重塑黄土饱和渗透系数逐渐减小,两者呈负指数相关,含盐重塑黄土渗透系数与不含盐重塑黄土相比均有不同程度减小;同一盐分含量条件下,钙盐黄土的渗透系数小于钠盐黄土的渗透系数。采用核磁共振(nuclear magnetic resonance,NMR)技术,测取重塑黄土的孔隙水赋存状态与孔隙结构随盐分含量与类型的变化;当盐分含量小于2%时,随盐分含量增加,孔隙水赋存状态与孔隙结构的变化使重塑黄土渗透系数迅速减小;当盐分含量大于2%时,随盐分含量增加,孔隙水赋存状态变化使重塑黄土渗透性增加,而孔隙结构变化使重塑黄土渗透性减小且对渗透性的影响占主导,因此重塑黄土的渗透系数缓慢减小;同一盐分含量条件下,钙盐重塑黄土的孔隙水赋存状态和孔隙结构的变化比钠盐重塑黄土更显著。

The construction of reservoirs by"gully land consolidation"leads to soil salinization,and the permeability of saline soil is an important factor affecting engineering design and construction safety.Therefore,it is important to clarify the remolded loess permeability under different salt content and type conditions.In this study,a series of indoor variable head permeability tests was carried out to investigate the variation of permeability coefficient of remolded loess with salt content by preparing sodium and calcium salt remolded loess specimens with different salt contents.The results indicated that with the increase of salt content,the saturation permeability coefficient of remolded loess gradually decreases,and the two are negatively correlated.Moreover,the permeability coefficient of salt-containing remolded loess decreased to varying degrees compared with that of remolded loess without salt.Under the same salt content,the permeability coefficient of calcium-salt loess was smaller than that of sodium-salt loess.The variation of pore water fugacity and pore structure with salt content and type within the specimen was tested using nuclear magnetic resonance(NMR)techniques.When the salt content was below 2%,the permeability of remolded loess decreased rapidly with the increase of salt content,due to the changes in pore water occurrence state and pore structure.However,when the salt content exceeded 2%,the permeability of the remolded loess increased with the change of pore water occurrence state,while the permeability of the remolded loess decreased with the change of pore structure,and the change of pore structure had a dominant influence on the permeability,thus the permeability coefficient of the remolded loess decreased slowly.Furthermore,under identical salt content,the changes in the pore water occurrence status and pore structure of the calcium salt remolded loess were more significant than those in the sodium salt remolded loess.