RAPID: Blast Testing to Investigate Resin-Injection Treatment for Liquefaction Mitigation

地震震动会导致地下水位以下的松散沙子液化，表现为重液体，导致支撑在沙子上的建筑物、桥梁和港口下沉、滑动或倾覆。液化造成的直接和间接经济损失是社会的巨大代价。为了应对这种危险，工程师可以将所有可液化的沙子压实到位，或者使用穿透可液化沙子的深基础，但这些方法非常昂贵，特别是对于居民区。世界各地正在深入研究的一种更经济的策略是，在建筑物的表层压实12至20英尺厚的表层，即使下面的深层仍发生液化，也能安全地支撑建筑物。为了研究这种方法，在不等待地震的情况下，我们将压实一层20英尺厚的表层，并使用一系列小型炸药来液化下面的沙子。现场测试地点将在新西兰克赖斯特彻奇，那里的液化破坏导致1万多户家庭被谴责。液化产生的沉降将与邻近未处理区域的相同测试进行比较。这些测试的结果将使工程师能够确定这种经济的解决方案在实践中是否真的安全。土壤压实将使用一种创新的方法进行，在这种方法中，将膨胀的聚氨基甲酸酯注入地面。与大多数土壤改良技术不同，这种方法可以在现有结构下安全地使用。新西兰政府将支付土壤改良费用，而美国国家科学基金会将支付液化测试费用。利用这两个国家的资金将工作范围扩大到任何一个国家都无法独立完成的范围，并增加了这项研究的国际影响。这些基准案例将帮助工程师设计安全、但具有成本效益的基础解决方案，以将地震损失降至最低。此外，美国研究生将通过参与这项研究获得重要的国际经验。在几乎每一次地震中，松散的饱和砂土的液化都会对民用基础设施造成重大破坏。液化造成的直接和间接经济损失是社会的巨大代价，最近在新西兰就证明了这一点。超过10,000所房屋因液化而受损，经济正在艰难复苏。新西兰的工程师们正在试验地基改良方法，这种方法可以加厚和硬化不可液化的表层结壳，以最大限度地减少结壳下液化造成的差异沉降。新西兰最近开发了一种名为树脂注射的创新液化缓解方法，并在三个地点进行了测试，作为一项耗资500万美元的研究的一部分，2013年曾使用爆炸诱发液化测试了其他18种地基加固方法。通过安装成三角形网格图案的垂直管道自下而上注入聚氨酯树脂。低粘度树脂通过软弱面或水力压裂渗透到周围土壤中。树脂的膨胀使周围的土体变得密实，增加了侧向土压力。该方法可用于现有构筑物下面的土的处理，对难以用振动法密实的粉砂土有效。一系列广泛的后处理现场试验表明，与以前的方法相比，这项新技术非常有效；然而，没有一个树脂注射试验点进行过爆破试验，以评估在深层覆盖可液化砂土的改良地基的性能。这使得无法将该处理方法的整体系统性能与先前在2013年试验中评估的其他系统进行比较。为了弥补这一缺陷，我们将在其中一个树脂注射地点和邻近的一个未经处理的区域进行爆炸液化测试。在爆破前，将安装仪器来测量孔压的产生和消散、土体沉降随时间和深度的变化、剪切波速与孔压比、侧向土压力与孔压比以及爆炸引起的剪切应变。该项目将：(1)提供树脂处理层和未处理场地中超额孔压和土壤沉降的直接比较；(2)增加定义地表地壳厚度和刚度对建筑物在地壳上的沉降和变形的影响的数据库；以及(3)提供侧向土压力和剪切模数随孔压的产生和消散而变化的基本现场测量。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Earthquake shaking can cause loose sands below the water table to liquefy and behave like heavy liquid, causing buildings, bridges and ports supported on the sand to settle, slide or tip over. Direct and indirect economic losses resulting from liquefaction are substantial costs to society. To deal with this hazard, engineers can compact all the liquefiable sand in place or use deep foundations that penetrate through the liquefiable sand, but these methods are very expensive, especially for residential areas. A more economical strategy, being intensively studied around the world, is to compact a surface layer 12- to 20-ft thick that can safely support a building even if liquefaction still occurs in the deeper layers below it. To investigate this approach, without waiting for an earthquake, we will compact a surface layer 20-ft thick and use an array of small explosive charges to liquefy the sand below. The field test site will be in Christchurch, New Zealand, where liquefaction damage caused over 10,000 homes to be condemned. Settlement from liquefaction will be compared with an identical test at an adjacent untreated area. The results from these tests will allow engineers to determine if this economical solution is actually safe to employ in practice. The soil compaction will be peformed using an innovative approach in which expanding polyurethane is injected into the ground. Unlike most soil improvement techniques, this method can be safely used under existing structures. The New Zealand government is paying the cost of the soil improvement while the US National Science Foundation will pay the costs of the liquefaction test. Leveraging funding from both countries expands the scope of work beyond what either country would accomplish independently and increases the impact of the research internationally. These benchmark case histories will help engineers to design safe, yet cost effective foundation solutions to minimize earthquake damage. In addition, U.S. graduate student will gain significant international experience by participating in this study. Liquefaction of loose saturated sands results in significant damage to civil infrastructure in nearly every earthquake event. Direct and indirect economic losses resulting from liquefaction are substantial costs to society as was recently demonstrated in New Zealand. Over 10,000 homes were damaged as a result of liquefaction and the economy is struggling to recover. Engineers in New Zealand are experimenting with ground improvement methods that thicken and stiffen a non-liquefiable surface crust to minimize differential settlement from liquefaction below the crust. An innovative, new liquefaction mitigation method known as resin-injection was recently developed and tested in New Zealand at three sites where 18 other ground improvement methods were previously tested using blast induced liquefaction in 2013 as part of a $5 million study. Polyurethane resin is injected from the bottom-up through vertical pipes installed in a triangular grid pattern. The low-viscosity resin penetrates the surrounding soil through planes of weakness or by hydrofracturing. Expansion of the resin densifies the surrounding soil and increases the lateral earth pressure. This method can be used to treat soils below existing structures and is effective in silty sands that are difficult to densify with vibratory methods. An extensive set of post-treatment in-situ tests demonstrate that this new technique is very effective relative to previous methods; however, none of the resin injection test sites has been subjected to blast testing to evaluate the performance of the improved ground overlying the liquefiable sand at depth. This makes it impossible to compare the overall system performance of this treatment method with the other systems previously evaluated in the 2013 trials. To remedy this deficiency, we will conduct blast liquefaction tests at one of the resin injection sites and an adjacent untreated area. Prior to blasting, instrumentation will be installed to measure pore pressure generation and dissipation, soil settlement vs. time and vs. depth, shear wave velocity vs. pore pressure ratio, lateral earth pressure vs. pore pressure ratio, and blast-induced shear strain. This project will: (1) provide a direct comparison of excess pore pressure and soil settlement in the resin-treated layers with an untreated site, (2) add to the database defining the effect of surface crust thickness and stiffness on the settlement and distortion of buildings on the crust, and (3) provide fundamental in-situ measurements of lateral earth pressure and shear modulus variation with the generation and dissipation of pore pressure.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.