PECASE: The Role of Specific Surface Area and Cation Exchange Capacity in Understanding and Predicting Expansive Soil Behavior

PECASE：比表面积和阳离子交换能力在理解和预测膨胀土行为中的作用

• 批准号: 0746980
• 负责人: Amy Cerato
• 金额: $ 40万
• 依托单位: University of Oklahoma Norman Campus
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-02-01 至 2014-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0746980&HistoricalAwards=false
• 关键词: PECASE; Role; Specific; Surface; Area

Expansive unsaturated soils cover one-fourth of the United States and undergo large amounts of heaving and shrinking due to seasonal moisture changes. These movements often lead to cracking and buckling of the infrastructure built on expansive soils, and result in billions of dollars of damage annually (e.g., Wray & Meyer 2004). Although not life-threatening or cataclysmic as compared to other natural events, expansive soils are certainly a natural hazard. Even though expansive soils have been studied for several decades, all of the idealized models presented to date to predict shrink-swell potential of expansive soils have failed to predict actual soil movement under real conditions where the presence of several cations and clay minerals can influence soil behavior (Hillel 1998). The research goal of this award is to advance the understanding of and prediction methods for macroscopic unsaturated expansive soil behavior through microscopic fundamental soil surface phenomena, such as specific surface area (SSA) and cation exchange capacity (CEC). This will be achieved by improving existing 1-D empirical models and extending the application of a physicochemical discrete element method (DEM) computer model to incorporate expansive soil movement. Understanding expansive soil behavior under various environmental conditions will allow the design of robust foundation systems using life-cycle performance as the driving factor in choice of design. This innovative unsaturated soils research program will be woven into several important high-impact educational components in order to bridge the gap between geotechnical theory and geotechnical practice. Understanding expansive soil behavior using microscopic soil surface phenomena will advance the state-of-knowledge and practice in geotechnical engineering by allowing researchers and practitioners to accurately and repeatedly predict macroscopic expansive soil behavior in a way that is not currently available. The improvement on existing empirical models for expansive soil movement prediction using microscopic soil parameters, such as SSA and CEC, is an immediate practical necessity for the geotechnical engineering profession. It is also essential to develop a physically meaningful mathematical model that utilizes a microlevel understanding of particles and interparticle forces to further advance our fundamental knowledge of expansive soil behavior. Merging physicochemical and unsaturated soil mechanics theories into a DEM will provide insight into observed laboratory and in situ behavior and speed progress toward a solution to a complex and expensive problem. The topic of expansive soils is not only compelling from a scientific perspective, but a social perspective as well. The microscopic, particle-particle understanding of expansive soil behavior will help to predict the macroscopic shrink-swell behavior that causes in the United States an estimated $15 billion dollars in annual damage to infrastructure. To initiate this improvement, students will be taught about the important role that geotechnical engineer?s play within our society to broaden their career path opportunities as well as increase, enhance and diversify our undergraduate civil engineering population. This enhanced undergraduate student population will feed a more talented and diverse graduate student population which will produce a more educated workforce. In time, this extensive network of civil engineers can dispel the poor public perception of engineers and increase their status in society. Similar to current practices and successes, the PI will focus on the recruitment and retention of women and minorities in order to enhance and diversify the engineering experience.

膨胀的非饱和土壤覆盖了美国的四分之一，由于季节性的湿度变化，它经历了大量的起伏和收缩。这些运动经常导致在膨胀土壤上建造的基础设施开裂和屈曲，每年造成数十亿美元的损失（例如，Wray & Meyer 2004）。与其他自然灾害相比，膨胀土虽然不会危及生命或造成灾难性后果，但它确实是一种自然灾害。尽管对膨胀土的研究已经进行了几十年，但迄今为止所有用于预测膨胀土收缩膨胀势的理想化模型都无法预测在实际条件下的实际土壤运动，在实际条件下，几种阳离子和粘土矿物的存在会影响土壤的行为（Hillel 1998）。该奖项的研究目标是通过微观土壤表面基本现象，如比表面积（SSA）和阳离子交换容量（CEC），推进对宏观非饱和膨胀土行为的理解和预测方法。这将通过改进现有的一维经验模型和扩展物理化学离散元方法（DEM）计算机模型的应用来实现，以纳入膨胀土的运动。了解膨胀土在各种环境条件下的行为，将有助于设计出以生命周期性能作为设计选择驱动因素的坚固基础系统。这个创新的非饱和土壤研究项目将被编织成几个重要的高影响力的教育组成部分，以弥合岩土工程理论和岩土工程实践之间的差距。通过微观土壤表面现象来理解膨胀土的行为，将使研究人员和从业人员能够以目前无法获得的方式准确、反复地预测宏观膨胀土的行为，从而提高岩土工程的知识水平和实践水平。改进现有的基于细观土体参数的膨胀土运动预测经验模型，如SSA和CEC，是岩土工程专业迫切需要的。开发一个物理上有意义的数学模型，利用对粒子和粒子间力的微观理解，进一步推进我们对膨胀土行为的基本知识，也是至关重要的。将物理化学和非饱和土壤力学理论合并到DEM中，将提供对观察到的实验室和原位行为的洞察，并加快解决复杂而昂贵问题的进展。膨胀土的话题不仅从科学的角度来看是引人注目的，而且从社会的角度来看也是如此。对膨胀土行为的微观、颗粒-颗粒的理解将有助于预测宏观的收缩-膨胀行为，这种行为在美国每年对基础设施造成的损失估计为150亿美元。为了开始这一改进，学生将被教导岩土工程师的重要作用？在我们的社会中发挥作用，拓宽他们的职业发展机会，以及增加、加强和多样化我们的土木工程本科人数。本科学生人数的增加将为更有才华和多样化的研究生提供更多的食物，从而产生受过更好教育的劳动力。随着时间的推移，这个广泛的土木工程师网络可以消除公众对工程师的不良看法，提高他们在社会中的地位。与目前的做法和成功经验类似，该计划将侧重于招聘和留住妇女和少数族裔，以提高工程经验并使其多样化。