Soil Treatment with a Thixotropic Fluid: An Autoadaptive Design for Liquefaction Prevention

使用触变流体处理土壤：预防液化的自适应设计

• 批准号: 0408739
• 负责人: Antonio Bobet
• 金额: --
• 依托单位: Purdue University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-08-01 至 2008-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0408739&HistoricalAwards=false
• 关键词: Soil; Treatment; Thixotropic; Fluid; Autoadaptive

Liquefaction of loose cohesionless soils, associated with the effective stress loss produced by rapid repeated loading, is an important cause of damage to civil infrastructures during earthquakes. While many factors affect the liquefaction resistance of soils, both laboratory studies and field observations support the conclusion that the presence of plastic fines reduces the liquefaction susceptibility of a site. This concept is the premise for the work proposed here which is an in-depth investigation of the use of thixotropic fluids, specifically bentonite-based suspensions, for treatment of sands for liquefaction susceptibility mitigation. This idea, which originated from an NSF sponsored workshop focused on the use of autoadaptive media in civil engineering, is supported by the results of a short term project funded by NSF through the Small Grant for Exploratory Research Program. This study demonstrated that the presence of 5% bentonite (by dry mass of sand) dramatically increased the liquefaction resistance of a loose sand. It also highlighted the difficulties of delivering the bentonite into the sand pores due to the rheological properties of bentonite suspensions. The proposed research builds on the results of this preliminary study to a) provide a more in depth investigation of the behavior of sand-bentonite systems; and b) to tackle the challenge of delivering the bentonite to the pore space in a time-release fashion. The work will be performed by an interdisciplinary team from Purdue University's School of Civil Engineering and Department of Chemistry. The specific objectives of the first component of the research are not only to expand the range in testing conditions (CSR and frequency of load applied during cyclic loading, confining stress level, bentonite percent, etc.) investigated, but also to address the more fundamental question of the micromechanism(s) responsible for the increased liquefaction resistance of sands in presence of bentonite. In addition, work will also be performed to assess the self healing nature of the bentonite treatment under repeated cyclic events, which potentially makes the sand-bentonite system a truly autoadaptive material. For delivering the bentonite to the pore space of sands, the research will explore a novel treatment based on coating the bentonite particles with Chitosan, a widely available and inexpensive biodegradable cationic carbohydrate. Chitosan will be used to inhibit swelling of the bentonite thus facilitating permeation of the suspension into the porous medium. The compound will then degrade due to the action of soil bacteria restoring the swelling properties of the bentonite. One broader impact of this research is to develop an innovative and cost-effective solution for a problem that has great significance to society. The novel approach for treating bentonite by means of a biodegradable compound has the potential of being relevant for a number of other applications. An interactive web page will be created to host a collection of images for use in teaching the complexity of the micro/nanostructure of clays. The web page will be complemented by a manual that will describe its use for education in junior high through university level courses. Work will continue on the development of modules for use in K-12 education with the mathematics teacher with whom initial work has already been conducted thanks to a RET (Research Experience for Teachers) grant from NSF.

松散无粘性土的液化，与快速重复加载产生的有效应力损失有关，是地震期间土木工程基础设施破坏的重要原因。虽然影响土的液化抗力的因素很多，但实验室研究和现场观测都支持这样的结论，即塑料微粉的存在会降低场地的液化敏感性。这一概念是这里提出的工作的前提，该工作是深入研究使用触变流体，特别是膨润土基悬浮液来处理砂子以缓解液化敏感性。这一想法源于NSF赞助的一个研讨会，重点是在土木工程中使用自适应媒体，并得到了NSF通过小额探索性研究计划资助的一个短期项目的结果的支持。这项研究表明，在松散砂土中加入5%的膨润土(按干砂质量计)，可显著提高其抗液化能力。它还强调了由于膨润土悬浮液的流变性，将膨润土输送到砂孔中的困难。拟议的研究建立在这一初步研究结果的基础上，以a)更深入地调查砂-膨润土体系的行为；以及b)解决以时间释放的方式将膨润土输送到孔隙空间的挑战。这项工作将由普渡大学土木工程学院和化学系的一个跨学科团队进行。研究的第一部分的具体目标不仅是扩大测试条件的范围(循环加载过程中施加的荷载的CSR和频率、约束应力水平、膨润土含量等)。研究不仅是为了解决更根本的问题，也是为了解决在膨润土存在下砂子抗液化能力增强的微观机制(S)。此外，还将进行工作，以评估膨润土处理在反复循环事件下的自愈性质，这可能使砂-膨润土系统成为真正的自适应材料。为了将膨润土输送到沙子的孔隙空间，这项研究将探索一种新的处理方法，即用壳聚糖包裹膨润土颗粒，壳聚糖是一种广泛存在的廉价可生物降解的阳离子碳水化合物。壳聚糖将被用来抑制膨润土的膨胀，从而促进悬浮液渗透到多孔介质中。然后，由于土壤细菌的作用，化合物会降解，恢复膨润土的膨胀特性。这项研究的一个更广泛的影响是为一个对社会具有重大意义的问题开发出一种创新的、具有成本效益的解决方案。通过生物可降解化合物处理膨润土的新方法有可能与许多其他应用相关。将创建一个互动网页，以托管一系列图像，用于教授粘土微米/纳米结构的复杂性。该网页将由一本手册补充，该手册将介绍其在初中教育中通过大学一级课程的使用情况。将继续与数学教师一起开发用于K-12教育的模块，由于国家科学基金会提供了RET(教师研究经验)赠款，该教师已经开展了初步工作。