离子型稳固剂对膨胀土缩-裂进程的调控机理研究

Expansive soils shrink and crack easily in dry environment, which in turn has an adverse impact on engineering properties of soil mass. The aim of this project is to explore the effect of a novel ionic soil stabilizer (ISS. abbreviation) on the shrinkage-cracking process of expansive soil.In this proposed project, two different type of strong expansive soil will be studied. A combined method to quantitatively describe the dehydration state of expansive soil was firstly proposed based on experimental analysis of water vapor desorption isotherm, dehydration thermodynamics and water structure vibration spectrum. Based on such method, analysis of dynamic connection between dehydration，shrinkage and desiccation cracking was performed to investigate the influence of ISS on the process of shrinkage-cracking of expansive soil in terms of dehydration behavior, suction and pore structure evolution. From a perspective of micro-interaction between soil and water, a micro-shrink stress model of modified soil is expected to be set up, which takes fully account of the coupling effect of “clay layer surface property-exchangeable cation-solute osmosis-electrostatic field force-clay particle unit fabric” on the shrinkage potential. Combining the micro-shrink stress model and macro-tensile strength behavior, a crack criterion model is finally proposed to reveal the mechanism of ISS inhibiting the shrinkage and desiccation cracking. Overall, these project achievements would provide theoretical basis and useful reference for controlling crack behavior of expansive soil. It would also provide a strong promotion to the engineering construction in expansive soil area and problematic soil stabilization theory. Therefore, this project possesses enormous academic value and broad prospect in engineering applications.

膨胀土在干燥环境下极易收缩龟裂，对土体工程性质产生重要不利影响，本项目探索一种新型离子稳固剂对膨胀土缩-裂性状的抑制过程及调控机理。以两种典型强膨胀土为研究对象，立足于”缩-裂”进程中水分迁出这一主线，首先实验建立“水汽等温脱附-脱湿热区间-水分子结构振动光谱分析”的水分迁出形态界定量化方法，在此基础上，开展失水-收缩-缩裂动态关联特征分析，从水分迁出-吸力发展-孔隙结构演化多角度探讨固化剂对“缩-裂”发生发展的影响机制；从干燥过程中土/水作用的微细观层面，构建“晶层表面-吸附阳离子-溶质渗透-静电场力-粘土单片组构”多因素耦合的微观缩应力模型，结合抗拉强度测试，提出改性土起裂判据模型，从而揭示离子稳固剂对膨胀土缩-裂性状改变的本质机理。项目的成功实施可为膨胀土“裂隙性”控制方法研究提供理论依据和有益借鉴，可有力推动膨胀土地区工程建设及特殊土改良理论发展，具有重要科学价值和广阔应用前景。

膨胀土在干燥环境下极易收缩龟裂，对土体工程性质产生重要不利影响，本项目探索了一种新型离子稳固剂对膨胀土缩裂性状的抑制过程及调控机理。以两种典型强膨胀土为对象，立足于水分迁出这一主线，首先实验建立了“水汽等温脱附-脱湿热区间-水分子结构振动光谱分析”的水分迁出形态界定量化方法，解析了粘土矿物表面水合机制，研究了稳固剂改性膨胀土持水模式的变化趋势。在此基础上，对比分析了改性前后膨胀土收缩特征曲线及缩裂发育程度的差异。通过改性前后膨胀土表面物化参数及水化活性因子分析，从粘土水合能量的转化平衡角度，构建了改性膨胀土收缩吸力势的数学模型。基于水分迁出机制与孔隙结构演变的动态关联分析，结合抗拉强度测试，从“水-力-结构”互馈角度揭示了离子稳固剂对膨胀土缩-裂性状调控的本质机理。研究表明，离子稳固剂通过与膨胀性粘土矿物发生物化作用，降低了晶层间阳离子数量、占据了阳离子交换位置，束缚了晶层表面的水化活性中心，从而降低了阳离子水化能和晶层表面水合能。在阳离子水化阶段（极高吸力段），改性土吸力势的减小源于阳离子的水化势降低，在晶层表面水合阶段（中等吸力段），则源于比表面积的减小以及水分子与晶层极化吸引力的降低（范德华力）。改性土孔隙结构更为密实，片聚体单元厚度更大，干燥过程中大颗粒之间的孔隙虽发生一定程度收缩，但由于厚层片聚体刚度大，导致颗粒的相互靠拢和结构调整阻力增大；此外，结合水脱失阶段，晶层间距基本保持稳定，不能为粘土片聚体或团聚体之间的孔隙收缩提供足够的空间。改性土抗拉强度随吸力的增加速率显著高于素土，且颗粒内部收缩吸应力整体小于抗拉强度，导致其起裂时间更晚且裂隙发育程度更低。本项目相关成果为膨胀土“裂隙性”的控制方法研究提供了理论依据和有益借鉴，可有力推动膨胀土地区工程建设及特殊土改良理论发展，具有重要科学价值和广阔应用前景。