海涂盐碱地灌排工程边坡水盐运移及其对浅层坡体失稳的作用机制

The banks of irrigation-drainage channels that form a vital part of an engineering system that is intended to reclaim coastal saline land often undergo frequent wet-dry cycles. These cycles affect the processes of salt leaching and uprising by rainwater percolating through the soil, the intensive evaporation and groundwater fluctuations. Consequently, they readily cause the formation of original and secondary cracks in the channel banks, which become unstable possibly leading to severe slumping or “shallow landslides”. However, the affecting mechanisms of soil water-salt transport on these shallow landslides remain unclear, which restricts studies related to the eco-slope-engineering in the coastal saline land areas. The proposed project will consider the channel banks in the coastal reclamation area in Jiangsu Province. Based on the results of the study’s experiments and a theoretical analysis, this project aims to study the factors and processes that govern the soil mechanics and hydraulic characteristics of the soils forming the banks of the irrigation-drainage channels, as well as their responses to changes in soil sodicity and salinity. With a series of simulated rainfall experiments and field plots monitoring, the study will obtain important experimental data about the changes in water allocation and quality, and soil and sodic-saline characteristics as well as noting the glide plane deformation in the shallow layer, during the processes of soil water-salt transport. Using the acquired data, the study will further investigate the hydrodynamics mechanisms involved in the glide plane deformation under the influence of various soil-water-salt transport conditions. Finally, the study proposes to identify the critical parameters involved in achieving soil improvement and to recommend slope reinforcement techniques that could involve the utilization of lime/polymeric stabilizers on the saline soils. Furthermore, simulations of the dynamic processes involved in shallow landslides would be created that take into account the responses of the soil mechanics and hydraulic characteristics to changes in the soil salt status. Finally, it would analyze the contribution of salt-water regulation to increased slope stability. The results should provide useful information that can compensate for the current deficiencies of studies about the mechanisms involved in shallow landslides in coastal saline land areas. This would provide a scientific basis for the planning and designing of engineered irrigation-drainage channel systems, as well as information that could ensure the ecological systems in the coastal reclamation region are protected from the adverse effects of the shallow landslides.

海涂盐碱地灌排工程边坡在降雨淋洗、强烈蒸发和地下水波动影响下经历频繁干湿交替与脱盐-返盐过程，浅层土体易产生原生或次生裂隙，失稳滑塌严重。现阶段，边坡水盐运移对浅层坡体失稳的作用机制尚不明确，制约了海涂盐碱土生态固坡研究。本项目拟以江苏沿海围垦区沟渠（河）边坡为对象，通过试验与理论分析，研究灌排工程边坡水土力学特性演变规律及其对土壤盐分动态的响应；结合定位监测和室内模拟试验，获取边坡水盐运移过程中水-土-盐特性变化与浅层坡体滑动变形的重要试验数据，探索海涂盐碱地边坡浅层土体随水盐运移过程变形失稳的水动力学机制；基于水盐调控角度分析，提出盐碱地掺石灰/高分子稳定剂改土固坡技术的关键参数，并将土水力学参数与盐分动态响应关系引入边坡失稳过程模型模拟，分析改土固坡水盐调控对提高边坡稳定性的贡献。研究成果可弥补海涂盐碱地边坡失稳机理研究的不足，并可为围垦区灌排工程规划设计及边坡生态防护提供科学依据。

海涂盐碱地土壤钠盐含量高、结构松散、粘聚性差，海涂灌排工程边坡在降雨淋洗、强烈蒸发和地下水波动影响下经历频繁干湿交替，坡体土壤在吸水过程中基质吸力下降、孔隙水压力上升，浅层土体的土壤骨架之间受到孔隙水压力挤压而产生原生或次生裂隙，诱发坡体发生失稳滑塌。现阶段，边坡水盐运移对浅层坡体失稳的作用机制尚不明确，制约了海涂盐碱土生态固坡研究。基于此，本研究以江苏沿海围垦区沟渠（河）边坡为对象，通过试验研究与理论分析，围绕围垦区土壤水盐动态影响下盐分-结构-土力特征传递关系、土壤结构与土力学、水力学性质关系、应力-应变本构模型、坡面失稳过程机理与模拟开展了为期4年的研究。项目通过野外监测，明确了围垦区土壤盐分-结构-土力特征传递影响关系。通过试验研究明确了盐分动态影响下土壤抗剪强度的变化，结合控制盐分因子的三轴压缩与剪切试验，将盐分对抗剪强度作用引入应力-应变本构关系，构建考虑盐分变化的非饱和土弹塑性本构模型。通过添加生物炭和PAM改良围垦区盐渍土壤，明确了结构改良下土壤结构、水力学性质和土力学性质的变化，构建了基于图像分析的改进PSF模型模拟土壤水力性质。通过模拟降雨试验，开展地下水位变化对不同坡长、坡度的坡面侵蚀与崩塌过程模拟，明确了水盐动态影响下坡体侵蚀与失稳过程发展的机理。提出盐碱地掺施聚丙烯酰胺/生物炭改土固坡技术的关键参数，并将结构改良后的土壤土水力学参数与盐分动态响应关系引入边坡失稳过程调控。基于灌排工程小尺度工程边坡的侵蚀与失稳的相互作用，通过耦合元胞自动机与离散元理论构建边坡径流-侵蚀-崩塌的一体化三维模型，探索海涂盐碱地边坡浅层土体失稳动态机制。研究成果可弥补海涂盐碱地边坡失稳机理研究的不足，并可为围垦区灌排工程规划设计及边坡生态防护提供科学依据。