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

快速重复荷载作用下产生的有效应力损失引起的松散无粘性土的液化是引起地震中土木基础设施破坏的重要原因。虽然有许多因素会影响土壤的抗液化性，但实验室研究和现场观察都支持这样的结论，即塑性细粒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，这是一个深入的调查使用的触变流体，特别是膨润土为基础的悬浮液，用于处理砂土液化敏感性缓解。这个想法，起源于NSF赞助的研讨会，重点是在土木工程中使用自适应媒体，是由NSF通过探索性研究计划的小额赠款资助的一个短期项目的结果支持。这项研究表明，存在5%的膨润土（干质量的砂）显着增加了抗液化性的松散砂。由于膨润土悬浮液的流变特性，将膨润土输送到砂孔中的难度也很大。所提出的研究建立在该初步研究的结果的基础上，以a）提供对砂-膨润土系统的行为的更深入的调查;和B）解决以时间释放方式将膨润土递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小组进行。第一部分研究的具体目标不仅是扩大试验条件的范围（CSR和循环加载过程中施加的荷载频率，围压应力水平，膨润土百分比等），调查，而且还解决更根本的问题的微观机制（S）负责增加抗液化性的砂在膨润土的存在。此外，还将开展工作，以评估膨润土处理在重复循环事件下的自我修复性质，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砂的孔隙中，本研究将探索一种基于用壳聚糖包覆膨润土颗粒的新型处理方法，壳聚糖是一种广泛可用且廉价的可生物降解的阳离子碳水化合物。壳聚糖将用于抑制膨润土的溶胀，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，该化合物将降解，恢复膨润土的膨胀性能。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一个创新的和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具有与许多其他应用相关的潜力。将创建一个交互式网页，以托管用于教学粘土的微观/纳米结构的复杂性的图像集合。该网页将辅之以一本手册，说明其在初中至大学课程教育中的用途。将继续与数学教师一起开发用于K-12教育的模块，由于NSF的RET（教师研究经验）赠款，已经与数学教师进行了初步工作。

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.