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

在美国的几个地区发现了富含硫酸盐的粘性土壤。当用钙基石灰和水泥稳定剂处理富含硫酸盐的土壤以改善土壤时，土壤中的硫酸盐与稳定剂中的钙和粘土中的氧化铝发生反应，形成结晶矿物钙矾石。这种矿物在水化作用下，在土壤中会发生大量的起伏。这种隆起在文献中被称为硫酸盐引起的隆起。在水泥和石灰处理过的含硫酸盐土壤上建造的建筑物、人行道、跑道和堤防受到了这次隆起的影响。修理和维护这些破旧的建筑每年要花费数百万美元。由于越来越多地使用工业硫废料来稳定和固化土壤，未来可能会出现潜在的隆起问题。因此，有必要从根本上了解硫酸盐-稳定剂在土壤中引起硫酸盐隆起运动的反应机制。本项目旨在研究土壤组成和环境因素对富含硫酸盐的土壤的隆起机制的影响，并建立各种土壤组成和环境变量的问题硫酸盐水平。四种不同类型粘土矿物的粘土土，两种水泥和石灰处理水平，五种硫酸盐含量，两种含水量水平和三种温度条件将被研究。将制备处理过和未处理过的土样，必要时采用不同温度的加速固化方法进行固化，然后在各种矿物学、化学和工程膨胀、吸力势和抗剪强度试验下进行试验。测试结果将进行分析，以了解硫酸盐隆起机制的可能原因，并研究钙矾石在土壤中形成的时间周期。此外，将开发模型来预测土壤中有问题的硫酸盐水平，在这种情况下，对给定的化学处理可以预期产生起伏。这些模型将通过将其预测结果与现场已知的隆起灾害进行比较来验证。该项目将对土壤中硫酸盐引起的起伏机制的基本认识作出重大贡献。本研究项目的潜在好处是：(1)为不同的粘性土开发出有问题的硫酸盐条件，在这些条件下，水泥和石灰处理会引起起沉；(2)针对影响钙矾石形成的因素，在未来开发出更好的化学处理方法；(3)促进硫废物在稳定中的回收利用。此外，应用游离氧化铝和电导率测量在土壤中，以确定有问题的硫酸盐将进行评估。这个项目也会对研究人员的教育活动产生很大的影响。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，以及数据采集、数据简化和分析以及数据表示概念。研究生和本科生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项目的网址提供给感兴趣的个人。全年将公布最新的研究情况和研究结果。此外，研究结果将在各种期刊和会议论文中传播。

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.