干湿-盐侵蚀耦合作用下黄土劣化效应与边坡演化机理研究

The environment of wetting-drying cycle and salt erosion due to the climate characteristics of concentrated rainfall and intensive evaporation with its typical and universal is an important influencing factor of deterioration of loess and deformation and failure of loess slope in loess plateau of China. There is less preliminary research at home and abroad. The fixed-point observation for typical deterioration of loess based on investigation in the region of eastern Gansu, northern Shaanxi and western Shanxi. The capillary migration of unsaturated loess was conducting for the activity of soluble salt. A series of tests to measure the variation of physical, mechanical and hydrological properties and microstructure of loess that mixed with different types, percentage and contents of soluble salt under wetting-drying cycles were performing to quantify responding behavior of deterioration of macroscopic properties and changes of microstructure. And the relationship between macroscopic properties indexes and microstructure characteristic parameters were establishing. The evolution patterns induced by deterioration of loess were proposing and the evolution mechanism of different evolution patterns were revealing for loess slope. This research can further enrich and perfect deterioration of loess, and also useful for controlling and monitoring deterioration of loess and its impact on stability of loess slope.

黄土高原地区典型、普遍的集中降雨与快速蒸发的气候特征，为黄土创造的干湿交替与盐侵蚀共同作用的赋存环境，是黄土劣化以及边坡变形破坏的重要影响因素，对此国内外前期研究较少。本项目拟在对甘肃陇东、陕西陕北和山西晋西等地区黄土劣化及其作用影响下边坡变形破坏调查基础上，对典型黄土边坡的黄土劣化定点观测；通过非饱和黄土毛细水盐迁移试验，研究毛细迁移过程中盐分活动规律；开展不同土性、不同盐分类型和复盐比例、不同含盐量并经历不同干湿循环次数的黄土的物理、力学和水理等性质指标、微结构分析试验和波速测试，定量化确定干湿交替与盐侵蚀双重作用下黄土宏观性质劣化响应行为和微观结构变化规律，并建立宏观性质指标与微结构特征参数之间的内在联系；提出黄土劣化作用影响下黄土边坡演化模式，探索不同演化模式进程机制。研究成果进一步丰富和完善黄土劣化研究，对防治、监测黄土劣化的发生和发展及其对边坡稳定造成影响提供科学依据。

黄土赋存典型的干旱、半干旱气候环境条件，经历黄土高原地区最为普遍和典型的夏、秋两季短暂而集中降雨并伴随快速强烈蒸发的气候过程，导致干湿和盐侵蚀耦合作用下黄土发生劣化行为响应，黄土劣化效应对边坡作用影响由量变发展为质变的缓慢变化过程，致使黄土边坡发育阶段性病害，控制黄土边坡变形破坏模式与进程。本项目基于不同地区、不同土性黄土劣化的现场调查，研究干湿-盐侵蚀耦合作用下黄土劣化及其黄土边坡的基本特征与形成地质环境条件，概化由黄土劣化引起边坡变形破坏的演化模式；开展非饱和黄土毛细水迁移试验和KCl、Na2SO4和混合液（KCl：Na2SO4=1：1）等3种不同盐溶液的黄土土柱盐分迁移试验，研究非饱和黄土毛细水迁移过程中水分迁移规律及其影响因素、盐分运移和结晶规律；开展干湿-盐侵蚀耦合作用下黄土劣化试验，研究不同干湿循环次数（0、5、10和15次）作用下硫酸盐、碳酸盐和氯盐等3种不同盐分、0.1%、0.2%和0.3%等3种不同盐分含量、氯盐与碳酸盐（1:1、1:2和2:1）等3种不同比例复合盐对黄土性质的影响；基于轴向压裂法开展原状与重塑黄土抗拉强度试验，研究不同含水率、不同高径比和不同衬垫直径对原状和重塑黄土抗拉强度的影响，初步探讨冻融循环作用对原状和重塑黄土抗拉强度的影响，借助离散元程序PFC3D模拟再现基于轴向压裂法黄土抗拉试验；建立黄土抗拉强度的悬臂梁模型，通过黄土抗拉强度的现场试验，研究长度、厚度对抗拉强度的影响，分析黄土抗拉强度的尺寸效应；针对黄土的裂隙对黄土边坡演化的影响，开展贯通和非贯通裂隙黄土的无侧限抗压强度试验与数值模拟研究，分析裂隙形态对黄土力学性质的控制效应。干湿-盐侵蚀耦合作用下黄土边坡演化进程可概括为毛细水迁移使盐分富集、黄土剥落使坡脚掏蚀内凹，坡体上部开裂、下部失去支撑，最终边坡失稳破坏。