黄土崩塌是西北黄土高原地区最常见、最严重的一种地质灾害。黄土是一种松散沉积物，是在第四纪特殊的气候条件下形成的，具有大孔隙、垂直节理发育等特殊性质，在水的作用、切坡卸载、地震等外在触发因素作用下黄土高原地区崩塌灾害频繁发生。在水的作用下，黄土崩塌的形成，首先是由于土体内裂隙的发育、发展以及贯通；其次由于边坡坡脚发生破坏从而失去支撑力，最终在其共同的作用下导致崩塌的形成。因此开展水的作用下黄土体的节理裂隙的发育以及物理力学性质的变化规律等方面的机理研究，对治理防护黄土地区崩塌等灾害具有重要的指导意义。 在收集已有黄土地区崩塌灾害的研究成果以及对黄土地区黄土崩塌灾害进行补充调查的基础上，以延安市洛川塬边缘为典型研究场地，通过野外踏勘、测绘以及相关资料的收集，总结阐述了水的作用对黄土体自身表现出的工程特性具有重要影响，研究分析了黄土体的工程特性对于导致黄土崩塌灾害具有一定内在联系；通过干湿循环试验，利用CT扫描研究水的物理作用—干湿循环对黄土内部结构劣化的影响规律；针对干湿循环后土样的强度力学试验，研究干湿循环次数、干湿循环幅度与土体强度劣化等相关参数的关系；通过室内物理力学试验，研究在水的化学作用—溶蚀作用对黄土体的物理力学性质的影响；并利用Abaqus软件，结合理论分析与数值模拟等方法，对黄土边坡形成崩塌机理进行数值模拟分析。研究表明：由于黄土边坡的开挖，坡体内垂直节理的张开，形成的拉张裂隙促进水的入渗，在水的物理化学作用以及黄土的水理特性等共同作用下，使得黄土体的物理力学性质发生了改变，黄土体的强度降低，导致黄土边坡发生塑性变形，由局部破坏发展为整体破坏，最终造成不同类型的崩塌破坏模式。总之，黄土边坡在切坡卸荷引起垂直裂隙发育的基础上，解释了在干湿循环以及水的化学溶蚀的综合作用下造成垂直节理裂隙扩展变形，黄土体内部应力分布不均匀以及土体自身的物理力学性质的劣化，导致边坡整体变形，最终形成崩塌灾害的力学机制，认为水的作用是黄土崩塌形成的主导因素。

Loess collapse is the most common and dangerous geological disaster in the Loess Plateau of Northwest China. Loess is a kind of loose sediments which has special properties such as large pores and vertical joint development and was formed under special climate conditions in quaternary. On the effect of water, slope unloaded and earthquake, the collapse of Loess Plateau accurr frequently. Loess collapse on the effect of water has two reasons, on the one hand due to the development of earth fissures in vivo, as well as through the development, on the other hand due to the toe of the slope failure occurs and thus lose the support force, resulting in the formation of collapse. Study on the joints and fissures of loess body development and the change rule of physical and mechanical properties has a important guiding meaning for the governance and protection of loess collapse in loess area. On the basis of the research results of loess collapse in loess area, taking yan’an luochuan tableland edge as the typical research area, through the collection of field reconnaissance, surveying and mapping information, this paper summarized that the effection of water has an important influence on the engineering properties of loess, and analyzed that the engineering properties of loess has internal relations with loess collapse. By dry-wet cycle test and CT scan, this paper research the physical action of water---the influence law of dry-wet circulation to loess structure degradation. According to the mechanical strength test of dry-wet circulation loess, this paper revealed the related parameters between dry-wet circulation circulation rate, dry-wet circulation amplitude and the intensity of soil degradation. Through indoor physical and mechanical test, this paper discussed the chemistry properties of water--dissolution effect on the physical and mechanical properties of loess. By using Abaqus software, combining theoretical analysis and numerical simulation method, the loess slope collapse and stability has been analyzed. The research result shows that: Due to the excavation of the loess slope and the slope vertical joints, with water entering the tensile fracture, under the physical and chemical action of water, it leads to local damage of loess slope become overall damage and finally form different failure mode of loess slope. The action of water leads to reduce the the safety factor and stability of loess slope.