在黄河流域高质量发展的国家战略引导下，黄土地区工业化和城市化稳步推进，工业废水、煤矿废水、城市污水等弱酸性水入渗黄土的情况逐渐增多；黄土受多孔隙、弱胶结、强水敏性等特征和弱碱性沉积环境影响，地表弱酸性水极易入渗黄土发生地质灾害。开展弱酸溶蚀型黄土工程性质劣化机理研究，对于黄土地区防灾减灾工作提升具有重要的理论意义。论文以原状黄土为研究对象，开展弱酸淋滤试验研究，重点关注原状黄土中可溶盐阳离子迁移及矿物成分变化规律，深入分析弱酸溶蚀作用下原状黄土的微-细观结构损伤演化过程及机制。主要研究成果包括：

（1）淋滤后，原状黄土中方解石、白云石、钠长石变化较明显，但在不同淋滤条件下，上述矿物变化率存在一定差异：①在pH较高的淋滤条件下有如下关系：钠长石≈方解石˂白云石，且白云石溶蚀反应更易生成Mg离子；②当pH较低时，钠长石˂绿泥石˂白云石˂方解石，而绿泥石溶蚀反应释放Si离子较释放Fe、Al、K离子更迅速、更剧烈；借助SEM图像并配合EDS功能，可观察到方解石和钠长石（层状）逐层剥蚀导致各层颗粒轮廓逐渐清晰甚至在其表层出现细小颗粒聚集，石英和白云母逐层磨蚀造成层间梯度下降和轮廓磨圆。

（2）利用SEM对淋滤前后颗粒间接触情况进行分析后，发现颗粒间直接接触方式主要为面-面和线-面接触；胶结连结的变化体现为：①细颗粒团聚体消失；②絮凝状胶结结构随淋滤时间增加交替出现；利用Image Pro Plus（IPP）图像分析软件获得了淋滤前后颗粒的圆度和分形维数，其中分形维数变化不大，而圆度则随淋滤时间延长或淋滤液pH降低而增大，且淋滤液pH降低时此现象更显著。

（3）基于试样各层位淋滤前后孔隙结构定量参数、孔隙灰度比区间频数占比变化可知，试样内部不同位置孔隙发展均存在2种演化规律：①横向扩展甚至贯通或萌生；②横向闭合且纵向堵塞；随淋滤时间延长，蒸馏水和pH=5弱酸淋滤时，孔隙交替出现上述2种演化趋势，而pH=3弱酸淋滤时，试样各层位较深孔隙始终以第1种演化规律发展，而较浅孔隙则交替出现上述2种演化规律。

（4）借助工业CT和Avizo图像处理软件对Ф100×150mm规格的黄土内不同孔径占比情况进行统计，并由自相似性假设在其累积占比曲线中确定了黄土大、中、小、微孔隙界限分别为>330μm、200~330μm、120~200μm、˂120μm，并利用核磁共振、液氮吸附测试掌握了更小微孔隙（˂10μm）的分布情况；分析其随时间增长的变化趋势后发现，不同孔隙间存在往复单向发展的现象，且蒸馏水和pH=5弱酸淋滤时，率先出现较大孔隙向较小孔隙发展的趋势，而pH=3弱酸淋滤时则相反，且在微孔隙区间内，相对较大微孔隙首先向较小微孔隙发展，且此后仍往复发展。

（5）弱酸淋滤原状黄土孔隙结构损伤特征表现为：初始孔隙、孔洞扩展的脆性损伤和较浅孔隙萌生的韧性损伤；蒸馏水淋滤时，孔隙扩展系集料胶结丧失、粒间错动所致；而弱酸淋滤时除上述内在机制外，还需考虑方解石和钠长石等矿物晶格滑移破裂后为孔隙提供的扩展空间、骨架颗粒间胶结包衣的脱落。

Under the guidance of the national strategy of high-quality development of the Yellow River Basin, industrialization and urbanization in the loess region have been steadily promoted, and the infiltration of weakly acidic water, such as industrial wastewater, coal mine wastewater and urban sewage, into the loess has been gradually increasing. Due to the characteristics of multi-porosity, weak cementation, strong water sensitivity and weak alkaline sedimentary environment, the loess is prone to geological disasters caused by weakly acidic water infiltration. It is of great theoretical significance for the improvement of disaster prevention and reduction in the loess area to study the degradation mechanism of engineering properties of the weakly acid dissolved loess. Taking undisturbed loess as the research object, this paper carried out weak acid leaching experiments. We focused on the cation migration of soluble salts and the changes of mineral composition, and deeply analyzed the micro-meso-structural damage evolution process and mechanism of undisturbed loess under the action of weak acid dissolution. The main research results include:

(1) After leaching, the changes of calcite, dolomite and albite are obvious. However, under different leaching conditions, the relative changes of the above minerals are different. Under higher pH leaching conditions, the relationship is as follows: albite ≈ calcite ˂ dolomite, and the dissolution reaction of dolomite is easier to generate Mg ions;When the pH is low, albite ˂ chlorite ˂ dolomite ˂ calcite, but the dissolution reaction of chlorite releasing Si ions is faster and more intense than the release of Fe, Al, K ions. By means of SEM images and EDS function, we can observe that layer-by-layer denudation of layered calcite and albite leads to gradually clear outline of particles in each layer, and even small particles gather in the surface layer. Layer-by-layer erosion of quartz and muscovite results in gradient descent between layers and contour grinding.

(2) The contact of the particles before and after leaching were analyzed by SEM. It was found that the direct contact between particles were mainly surface-surface contact and line-surface contact. The changes of cementation bonding are as follows: ① fine particle aggregates disappear; ② The flocculated cementation structures appear alternately with the increase of leaching time. The roundness and fractal dimension of the particles before and after leaching were obtained by image analysis software Image Pro Plus (IPP). The fractal dimension did not change much, while the roundness increased with the lengthen of leaching time or the decrease of leaching solution pH, and this phenomenon was more significant when the leaching solution pH decreased.

According to the changes of quantitative parameters of pore structure and frequency ratio in the interval of pore gray ratio before and after leaching at each layer of the sample, there are two evolution trends in the development of different depths pores: ① lateral expansion or even coalescing or initiation; ② lateral closure, longitudinal plugging; With the prolongation of leaching time, the above two evolution trends appear alternately when leaching with distilled water and weak acid at pH=5. When leaching with weak acid at pH=3, the deeper pores in each layer of the sample mostly develop in the first evolution trend from beginning to end, while the shallower pores still show the above two evolution trends alternately.

(4) With the help of industrial CT and image processing software (AVIZO), the different pore size ratios of Ф100×150mm soil body were calculated, and the boundaries of macropore, mesopore, fine pore, and micropore were determined as >330μm, 200~330μm, 120~200μm and ˂120μm in the cumulative ratio curve based on the self-similarity hypothesis. The distribution of smaller micropores (˂10μm) was also obtained by using NMR and liquid nitrogen adsorption tests. To analyze its growth over time, we found that there is a reciprocating and unidirectional development phenomenon between different pores. In the leaching process of distilled water and weak acid with pH=5, the larger pores develop to smaller pores first, while in the leaching process of weak acid with pH=3, the larger pores develop to smaller pores first, and in the micropore interval, the relatively larger micropores first moved towards smaller pores and then continue to develop in a reciprocally manner.

(5) The damage characteristics of the pore structure of the undisturbed loess leached by weak acid are as follows: brittle damage caused by the expansion of initial pores and holes and toughness damage caused by the initiation of shallow pores. During the leaching of distilled water, the pore expansion is caused by the loss of aggregate cementation and the dislocation between grains. In addition to the above internal mechanism, the expansion space for pores after lattice sliding and rupture of calcite and albite, and the shedding of cementing coating between skeleton particles should also be considered in the leaching process of weak acid.