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

地震会导致地下水位以下的松散沙子液化，表现得像重液体，导致支撑在沙子上的建筑物、桥梁和港口下沉、滑动或翻倒。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，工程师们可以将所有可液化的沙子压实，或者使用穿透可液化沙子的深地基，但这些方法非常昂贵，特别是对于住宅区。一种更经济的策略正在世界范围内被广泛研究，那就是压缩一个12到20英尺厚的表层，即使在它下面的深层仍然会发生液化，也能安全地支撑一座建筑。为了研究这种方法，在不等待地震发生的情况下，我们将在地表压实20英尺厚的土层，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的克赖斯特彻奇，那里的液化破坏导致1万多户家庭被谴责。液化沉降将与相邻未处理区域的相同试验进行比较。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际应用中是否安全。土壤压实将使用一种创新的方法，即向地面注入膨胀的聚氨酯。与大多数土壤改良技术不同，这种方法可以安全地在现有结构下使用。新西兰政府将支付土壤改良的费用，而美国国家科学基金会将支付液化试验的费用。利用来自两国的资金，扩大了工作范围，超出了任何一个国家独立完成的范围，并增加了研究的国际影响。这些基准案例历史将帮助工程师设计安全且具有成本效益的基础解决方案，以最大限度地减少地震破坏。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。几乎在每次地震中，松软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对社会来说是巨大的代价，新西兰最近就证明了这一点。超过1万所房屋因液化而受损，经济正在努力恢复。新西兰的工程师们正在试验一种改善地面的方法，使不可液化的地表地壳变厚和变硬，以最大限度地减少地壳下的液化造成的沉降差异。最近在新西兰开发了一种名为树脂注入的创新液化缓解方法，并在三个地点进行了测试。2013年，作为一项价值500万美元的研究的一部分，已经测试了18种其他地面改善方法，即爆炸诱导液化。聚氨酯树脂通过安装在三角形网格中的垂直管道自下而上注入。低粘度树脂通过软弱面或水力压裂渗透到周围土壤中。树脂的膨胀使周围土体变密，增加了侧土压力。这种方法可用于处理现有结构下的土壤，并且对难以用振动方法密实的粉质砂有效。大量的后处理现场测试表明，相对于以前的方法，这种新技术是非常有效的；然而，没有一个树脂注入试验点进行了爆破试验，以评估可液化砂上覆改善地面的性能。这使得无法将该治疗方法的整体系统性能与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点和邻近的未经处理的区域进行爆炸液化试验。在爆破之前，将安装仪器来测量孔隙压力的产生和消散，土壤沉降与时间和深度的关系，剪切波速与孔隙压力比，侧土压力与孔隙压力比，以及爆炸引起的剪切应变。本项目将：(1)直接比较树脂处理层与未处理层的超孔隙压力和土壤沉降；(2)为数据库增加地表地壳厚度和刚度对地壳上建筑物沉降和变形的影响；(3)提供侧土压力和剪切模量随孔隙压力产生和消散变化的基础原位测量。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知识价值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.