基于核磁共振技术的黄土内部孔径分布对逾渗特性的影响

Effect of Pore Size Distribution on Percolation Characteristics of Loess Based on Nuclear Magnetic Resonance Technique

为研究重塑黄土渗透性的临界效应,开展了变水头试验来分析黄土渗流过程中的逾渗现象,然后利用核磁共振技术对试样进行孔隙分布评价,据此来分析孔径分布对于黄土逾渗特性的影响。结果表明:原状黄土由于原生结构较好,孔隙大小的分布较重塑黄土更为集中。重塑黄土由于丧失了结构性,部分土颗粒会产生黏聚,从而导致土体内的微孔与大孔的比例比原状黄土中的多,且随着干密度的增加,大孔隙逐渐减少,小孔隙逐渐增多;由于原状黄土孔径分布更为集中,更不容易透水,所以更易达到临界状态从而发生逾渗,其临界水头比相同干密度的重塑黄土也更高。而重塑黄土则是干密度越大,孔隙率越低,孔隙越小,临界水头越高。试验结果可为黄土重大工程的基础建设中的有关渗流问题提供理论指导。

In order to study the critical effect of remolded loess permeability,a variable head test was carried out to analyze the percolation phenomenon in the process of loess seepage,then the effect of pore size distribution on seepage percolation of loess was analyzed for by nuclear magnetic resonance(NMR).Water head tests and NMR scanning were conducted,and the critical effect of remodeling loess permeability was determined,by which the influence of pore size distribution on percolation characteristics of loess was obtained.The experimental results show that undisturbed loess featured good integrity of original structure and the distribution of pore size was more concentrated than that of the remolded loess,while remolded loess particles have lost the integrity of original structure and partial cohesion occurred,resulting in the slight increases of micropores or macropores.Pores of undisturbed loess were more concentrated and the internal pores were less permeable,by which the critical state was easier to reach at a rapid decline in permeability.In addition,the critical water head of undisturbed loess was higher than that of remolded loess in the same dry density,while for remolded loess,the higher the dry density,the smaller the pores,and the higher the critical water head.The results could provide theoretical direction for the seepage problems in the foundation construction of loess major projects.