离子土固化剂改性强膨胀土微细观水合—膨胀模型研究

As a new type of material for improving soil property, Ionic Soil Stabilizer (ISS. abbreviation) can effectively inhibit the soil swelling potential. However, the unknown mechanism of ISS modifying the expansive soil greatly limits its application in engineering practice. In this proposed project, a strong expansive soil collected from the South-to-north water transfer project will be studied. Experimental research will be firstly performed to set up a combined method, i.e. "water vapor desorption isotherm-DSC, TG -infrared spectroscopy analysis", to quantitatively define the soil hydration form. On the basis of such method, the volume swelling behavior as well as pore size distribution tests at different stages of hydration-expansion will be then carried out to investigate the mechanism of ISS affecting the volume swelling in terms of hydration form, absorbed water content and evolution of pore structure during hydration-expansion. Through the systematic experimental analysis on the change of physicochemical property and orientation characteristic of clay mineral particle after being treated by ISS, A hydration-swelling force model of modified soil is expected to be established, taking fully account of the coupling changes of "clay layer surface hydration-cationic hydration-potential energy of solute penetration-electrostatic surfaces hydration -microscopic particles fabric". From a perspective of micro-interaction between soil and water, the mechanism of ISS modifying the hydration potential and swelling characteristic is expected to be revealed. This proposed project is expected to provide a scientific basis and theoretical support for the application of ISS in treating engineering problem induced by expansive soils, and consequently, to be valuable and significant in advancing the construction project in expansive soil distribution area and in promoting theoretical development of modifying problematic soil as well.

离子土固化剂是一种新型土壤改良材料，能有效抑制土体膨胀潜势，但改良机理的不明确限制了其实践推广应用。本项目以南水北调中线"引江济汉"工程段强膨胀土为对象，首先实验建立"水汽等温脱附-差热、热重测试-红外光谱分析"相结合的膨胀土水合形态定量界定方法，在此基础上，开展膨胀特性试验，并测试水合-膨胀不同阶段的孔隙分布，从水合形态、结合水含量及水合孔隙结构演化综合分析固化剂对膨胀土体积膨胀的调控机制。通过对改性前后粘土矿物表面物化参数及颗粒排列分布参数测试分析，建立离子土固化剂作用下"晶层表面水合-阳离子水化-溶质渗透势-静电场吸附势-颗粒微观组构"耦合变化的改性土水合-膨胀力模型，从土水结合作用的微细观角度，揭示固化剂对膨胀土水合能态及膨胀性状改变的本质机理。研究可为离子土固化剂应用膨胀土治理的实践提供科学依据和理论支持，对推动膨胀土地区工程建设及特殊土改良理论发展有着重要价值和现实意义。

膨胀土与水相互作用过程中产生的胀缩体变、结构劣化及强度衰减对工程建设安全构成极大威胁，离子土固化剂(Ionic soil stabilizer，简写ISS)是一种新型粘土改良材料，能有效抑制土体膨胀潜势，但改良机理的不明确限制了其推广应用。为深入揭示ISS对膨胀土“水合–膨胀”过程的调控机理，本项目以南水北调中线安阳段膨胀土为对象，首先从黏土矿物表面水汽吸附势与膨胀势内在关联角度，提出了采用85%相对湿度下吸湿含水量对膨胀土分级判别的新方法，分析了浸水膨胀时程曲线特征及膨胀速率参数的提取方法，研究了水合膨胀中孔隙水、孔隙气两相动态变化过程及其对最终膨胀变形的影响机制，在此基础上，构建了考虑压实度–含水率–上覆压力耦合关联影响的k0（侧限）、三轴膨胀本构模型。通过室内膨胀试验及离心模型试验，比较分析了ISS改良前后膨胀土胀缩变形及力学强度变化规律，并从微细观层面研究了ISS对膨胀性黏土矿物组分、晶层结构、表面性质、孔隙结构的作用机制。通过“水汽等温吸附–差热、热重测试–红外光谱定性分析”提出了膨胀土水合形态界定与量化方法，分析了ISS改性前后膨胀土水合历程、结合水含量的变化特征，建立了ISS改性膨胀土“水合–膨胀”理论概化模型。水合–膨胀试验表明，水汽吸附指标与胶粒含量、塑性指数及自由膨胀率等关键分级指标具有良好的线性相关性，能反映水合势与膨胀势之间的本质关联，膨胀过程受控于水合总量及孔隙中“水–气”两相的体积置换度。改性试验表明，ISS未改变黏土矿物组分（晶层结构）及相对含量，但弱化了黏土颗粒表面水化能（表面水合能、阳离子水化能，静电吸附势等），ISS微观改性机理为：解离的弱水合能阳离子基与土颗粒表面及矿物层间吸附阳离子进行非可逆交换、亲水头与离子的化学键合束缚、与矿物表面及层间的氢键连接、以及疏水基团对于水分子的吸附阻碍等。研究发现，ISS一方面使黏土矿物层间水合能力、结合水数量降低，有效抑制了晶层基面扩张的“晶格膨胀”，另一方面，通过疏水尾对水分子的阻隔，减小土粒表面弱结合水膜的分布厚度，从而一定程度抑制了黏土团块中相邻颗粒和颗粒集合体被结合水膜“楔开”而产生的不均匀应变膨胀。本项目研究成果为ISS应用于膨胀土治理的实践提供了科学依据和理论支持，对推动膨胀土地区工程建设及特殊土改良理论的发展有着重要价值和意义。