Engineering the Pore Fluid of Sands with Highly Plastic Nano-Particles for Liqefaction revention

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。在地震中，液化是破坏民用基础设施的一个重要原因，在不产生地面扰动的情况下最小化场地液化易感性的技术可以极大地影响岩土地震工程实践。虽然有许多因素影响液化阻力，但实验室和现场观察表明，塑料颗粒的存在降低了液化敏感性。在此前提下，之前的工作探索了使用膨润土基触变浆料来缓解液化。这项工作表明，在砂孔隙中存在3%的膨润土时，循环阻力增加了10倍或更多；证明了用焦磷酸钠处理粘土可以使浓膨润土悬浮液渗透；并确定了循环阻力的增加是由于在膨润土存在下形成的孔隙流体的流变性。这项工作有可能通过使用拉脱土进一步推进，拉脱土是一种合成的、惰性的、高纯度的、高塑性的纳米粘土，尺寸比膨润土小十倍。作为膨润土，拉脱土不会造成环境问题，并且受益于粘土岩土工程的经验基础。早期结果表明，与膨润土相比，更小比例的拉脱土可能需要获得相同的循环阻力改善；而且，由于凝胶时间的延迟，无需对粘土进行化学处理就可以渗透（尽管可能需要化学改性来延长渗透的时间窗口）。这项研究是基于一种全新的土壤改良方法。一种依赖于工程孔隙流体，而不是土壤骨架的方法。这也是在土木工程中首次尝试利用拉铁矿。因此，这项研究有可能具有变革性，为缓解液化的土壤改善问题提供下一代解决方案。研究的总体范围是为这种治疗的有效性提供可靠的实验室证据，并解决能够进行现场试验的关键问题。具体目标是：量化拉土渗透后砂的循环阻力改善；确定导致这种行为的机制；确定可优化处理的拉脱土化学物理改性；并探索验证拉土在砂基质内输送的方法。这些目标将通过一个实验方案来实现，该方案将包括：循环三轴试验和对渗透了拉土的砂样进行共振柱试验；laponite悬浮液在实验室砂柱中的渗透试验利用先进的流变学技术和低温扫描电镜对拉脱土孔隙流体的流变学和微观结构进行表征；通过XRD、FTIR和热分析研究了拉土的表面化学性质；通过实验规模的测试，探索处理后砂体的电学、物理和化学性质的变化，这可能有助于确定现场验证方法。

This award is funded under the American Recovery and Reinvestment Act of 2009(Public Law 111-5).Liquefaction is an important cause of damage to civil infrastructures during earthquakes, and techniques that can minimize the liquefaction susceptibility of a site, with no ground disturbance can greatly impact geotechnical earthquake engineering practice. While many factors affect liquefaction resistance, laboratory and field observations demonstrate that the presence of plastic fines reduces liquefaction susceptibility. With this premise, previous work explored the use of bentonite-based thixotropic slurries for liquefaction mitigation. This work showed a ten fold or greater increase in cyclic resistance in presence of 3% bentonite in the sand pores; demonstrated that permeation of concentrated bentonite suspensions is possible through treatment of the clay with Na-pyrophosphate; and established that increased cyclic resistance is due to the rheology of the pore fluid formed in presence of bentonite.This work has the potential to be further advanced through the use of laponite, a synthetic, inert, high purity, highly plastic nano-clay, ten times smaller in size than bentonite. As bentonite, laponite does not pose environmental concerns and benefits from the experience base in geotechnical engineering with clays. Early results suggest that, compared to bentonite, smaller percentages of laponite may be required to obtain the same improvement in cyclic resistance; and that, thanks to the delayed gel time, permeation is possible with no chemical treatment of the clay (although chemical modification may be necessary to extend the time window for permeation). The research is based on an absolutely novel approach to soil improvement ? one that relies on engineering the pore fluid, rather than the soil skeleton. It also represents the first attempt in civil engineering to utilize laponite. Hence, the research has the potential to be transformational providing a next generation solution to the problem of soil improvement for liquefaction mitigation.The overall scope of the research is to provide sound laboratory evidence of the effectiveness of this treatment and address key issues that will enable field testing. The specific objectives are to: quantify the improvement in cyclic resistance of sand following permeation with laponite; identify the mechanism(s) responsible for this behavior; determine the chemo-physical modification of the laponite that can optimize treatment; and explore means by which to verify the delivery of the laponite inside a sand matrix. These objectives will be pursued through an experimental program that will include: cyclic triaxial tests and resonant column tests on sand specimens permeated with laponite; permeation tests of laponite suspensions in laboratory prepared sand columns; characterization of the rheology and of the microstructure of the laponite pore fluid using advanced rheometrical techniques, and cryo-scanning electron microscopy; study of the surface chemistry of laponite through XRD, FTIR and thermal analyses; and bench-scale tests exploring changes in electrical, physical and chemical properties of the treated sand volume, that may be helpful to define field verification methods.