黄土地区盐蚀型崩塌灾害发生机理及预测判据研究

Salification erosion will cause damage to the micro-structure of loess,which will lead to collapse under the influence of repeated dry-wet and freeze-thaw cycles. However, the mechanism of this type of collapse is still not clear. In this project, water and salt migration tests in loess will be carried out with dry-wet tests and freezing-thawing tests in undisturbed saline loess. Based on the test results, the regularity of salt migration inside loess will be studied. The relationship between the deformation and strength characteristics and dry-wet and freeze-thaw parameters will be determined. A computational model that can simulate water and salt migration in loess will be bulit. Moreover, a elasto-plastic constitutive model simulating the mechanical properties of salification erosion-damaged loess under the influence of dry-wet and freezing-thawing cycles will also be established.The above two models will be combined to establish a coupled heat-moisture-salt-stress formulation of salification erosion-damaged loess.Based on this, the mechanical mechanism of salification erosion collapse induced by dry-wet and freeze-thaw cycles will be analyzed both analytically and numerically.The critical conditions of the collapse will be determined during the analysis.Further analysis will be carried out using a numerical model to investigate the deformation velocity, slump route, and area influence of the collapse to establish the prediction criterion of the destruction caused by the collapse.The achievements of the project will aid to critically evaluate this type of collapse hazard and provide theoretical support for prevention and prediction of this kind of collapse.

盐蚀作用会对黄土结构造成损伤，在干湿循环、冻融循环等因素的影响下会诱发盐蚀型崩塌灾害，然而目前对该类崩塌的机理认识尚不清楚。本项目通过开展黄土体水盐迁移试验和含盐原状黄土试样的干湿循环与冻融循环试验，确定黄土体含盐量的动态变化规律及量化分析方法，建立含盐黄土应力应变关系、强度和变形指标与干湿循环及冻融循环参数之间的定量关系；建立黄土水盐迁移的计算程序，提出可以描述干湿循环、冻融循环及其耦合作用下黄土盐蚀损伤特性的弹塑性本构模型，并将两者结合起来构建含盐黄土的水-热-盐-力耦合关系式；然后通过理论和数值分析揭示黄土边坡在干湿循环、冻融循环及其耦合效应下产生盐蚀型崩塌灾害的力学机理，确定崩塌发生的临界条件，进一步利用数值模型分析其运动速度、滑塌路径及影响范围，最终提出对该类崩塌危险性及破坏力的预测判据。研究成果有助于更加合理地评价黄土盐蚀型崩塌灾害，为该类崩塌的防治及监测预报提供理论依据。

对黄土地区边坡盐蚀病害常见类型及其水盐迁移特征测试结果进行了分析和总结，结果表明：盐蚀剥落病害按剥落形态可分为条带状、片块状及凹腔状盐蚀剥落，引起盐蚀病害的易溶盐主要成分为硫酸钠。基于自然蒸发作用下黄土水热盐迁移试验，分析了黄土蒸发速率随光照、风速、气温、气压及相对湿度等气象因素的变化规律；确定了蒸发过程黄土体内部温度场、水分场及盐分场的动态耦合变化规律；确定了外界气象因素与黄土体内部水热盐多物理场之间的耦合变化规律。基于冻结条件下黄土水热盐迁移试验，确定了冻结过程黄土体内部温度场、水分场及盐分场的动态耦合变化规律；编制了冻结条件下黄土水热盐耦合迁移计算程序。对干湿循环及冻融循环条件下Na2SO4原状黄土的三轴剪切和CT细观扫描试验结果进行了全面分析，试验结果表明：含盐原状黄土应力应变曲线呈应变硬化型；粘聚强度随干湿或冻融循环次数增加呈指数形式衰减；干湿循环条件下粘聚强度随含盐量增加近似表现出线性衰减特征，冻融循环条件下粘聚强度随含盐量增加近似呈抛物线形式衰减；干湿循环损伤因子与盐蚀损伤因子的比值随干湿循环次数增大近似呈抛物线变化规律，随含盐量增大逐渐减小；盐蚀与冻融损伤之比随着冻融循环次数增加近似呈指数衰减，随含盐量增大逐渐增加；CT细观损伤变量与三轴剪切强度指标表现出相似的变化规律。建立了干湿及冻融循环作用下黄土边坡盐蚀风化数值计算模型，揭示了盐蚀黄土边坡体塑性区、最大主应力及位移场演化规律：概化了黄土盐蚀型崩塌灾害破坏模式可分为拉裂-滑移式、拉裂-坠落式及拉裂-倾倒式三种类型，并进一步构建了基于离散元法的黄土边坡盐蚀型崩塌数值计算程序，对盐蚀型崩塌破坏模式及位移场进行了计算分析；基于极限平衡理论分析法，分别给出了不同类型盐蚀型崩塌破坏模式的预测判据及崩塌体运动速度、致灾范围及破坏力的定量评估方法。