Experimental Investigations on Chemically Treated Sulfate Soils For Fundamental Understanding of Heaving Mechanisms

在美国的几个地区都发现了富含硫酸盐的粘性土壤。当富含硫酸盐的土壤用钙基石灰和水泥稳定剂进行土壤改良时，土壤中的硫酸盐与稳定剂中的钙和粘性土壤的氧化铝反应生成结晶矿物钙矾石。这种矿物在水化后，在土壤中经历了大量的隆起。这种隆起在文献中被称为硫酸盐诱导隆起。在水泥和石灰处理过的硫酸盐土壤上建造的建筑物、人行道、跑道和路堤都受到了这场隆起灾害的影响。受损结构的维修和维护每年要花费数百万美元。未来可能会出现潜在的隆起问题，因为用于土壤稳定和固化的工业硫磺废物的使用量增加。因此，有必要从根本上了解土壤中硫酸盐稳定剂引起硫酸盐隆起的反应机理。该项目旨在研究土壤成分和环境因素对富含硫酸盐土壤中硫酸盐膨胀机理的影响，并为各种土壤成分和环境变量建立有问题的硫酸盐水平。将调查四种不同粘土矿物类型、两种水泥和石灰处理水平、五种硫酸盐用量、两种含水率水平和三种温度条件的粘性土。经过处理和未经处理的土样将在不同的温度下通过加速养护方法进行准备，必要时进行养护，然后在各种矿物学、化学和工程膨胀、吸力和剪切强度测试下进行测试。将对测试结果进行分析，以了解硫酸盐膨胀的可能原因，并调查土壤中钙矾土形成的时间段。此外，还将开发模型来预测土壤中有问题的硫酸盐水平，在该水平下，给定的化学处理可能会发生隆起。这些模型将通过将它们的预测与已知的野外场地隆起压力进行比较来验证，该项目将为从根本上理解硫酸盐在土壤中诱导隆起的机理做出贡献。这项研究项目的潜在好处是：(1)为水泥和石灰处理导致隆起的不同粘性土壤开发有问题的硫酸盐条件；(2)针对影响钙矾石形成的因素，开发未来更好的化学处理方法；以及(3)促进硫酸盐废物在稳定剂中的回收应用。此外，还将评估游离氧化铝和土壤电导率测量在识别有问题的硫酸盐方面的应用。这个项目也将对研究人员的教育活动产生强烈的影响。该项目的一个组成部分是向研究生和本科生教授膨胀、收缩、矿物学和化学表征方法以及数据获取、数据简化和分析以及数据呈现概念。研究生和本科生都将被鼓励作为一个团队来完成研究任务。研究项目信息将通过岩土工程方案的网址提供给感兴趣的个人。研究状况和研究结果的最新情况将在全年发布。此外，研究结果将在各种期刊和会议记录文章中传播。

Sulfate-rich cohesive soils are found in several regions of the United States. When the sulfate-rich soils are treated with calcium based lime and cement stabilizers for soil improvements, the sulfates in soils react with the calcium of stabilizers and alumina of clayey soils to form a crystalline mineral, ettringite. This mineral, upon hydration, undergoes a large amount of heave in the soils. This heave is termed as sulfate induced heave in the literature. Buildings, pavements, runways and embankments built on cement and lime treated sulfate-bearing soils have been affected by this heave distress. Repair and maintenance of the distressed structures costs millions of dollars annually. Potential heave problems may arise in the future due to the increased use of industrial sulfuric waste products for soil stabilization and solidification. Hence, it is necessary to fundamentally understand sulfate-stabilizer reaction mechanisms in soils that cause sulfate heave movements. This project is designed to investigate the influence of soil compositional and environmental factors on the heave mechanisms in sulfate rich soils and establish problematic sulfate levels for various soil compositional and environmental variables. Four types of clayey soils with different types of clay mineralogies, two cement and lime treatment levels, five sulfate amounts, two moisture content levels, and three temperature conditions will be investigated. Treated and untreated soil samples will be prepared, cured if necessary, by accelerated curing methods at different temperatures and then tested under a variety of mineralogical, chemical and engineering swell, suction potential and shear strength tests. Test results will be analyzed to understand the possible causes of sulfate heave mechanisms and investigate time periods at which ettringite formation takes place in soils. Additionally, models will be developed to predict problematic sulfate levels in soils at which heave distress can be expected for a given chemical treatment. These models will be verified by comparing their predictions with the known heave distresses of field sites.This project will make a strong contribution to the fundamental understanding of the sulfate induced heaving mechanisms in soils. Potential benefits of this research project are: (1) develop problematic sulfate conditions for different clayey soils at which cement and lime treatments cause heave distress, (2) develop better chemical treatment methods in the future by targeting the factors that influence the ettringite formation, and (3) facilitate the use of sulfuric wastes for recycling applications in stabilization. Also, applications of free alumina and electric conductivity measurements in soils to identify problematic sulfates will be evaluated. This project will also have a strong impact on the researchers' educational activities. An integral part of this project is to teach swell, shrink, mineralogical and chemical characterization methods as well as data acquisition, data reduction and analysis and data presentation concepts to graduate and undergraduate students. Both graduate and undergraduate students will be encouraged to work as a team in performing the research tasks. The research project information will be made available to interested individuals through the web address of the geotechnical program. Updates on research status and findings will be posted throughout the year. Also, the research findings will be disseminated in various journals and proceedings articles.