RAPID/Collaborative Research: Spatial Variability of Small-Strain Stiffness, Go, and Effects on Ground Movements Related to Geotechnical Construction in Urban Areas

美国日益密集的城市化和交通拥堵促使对地下空间的巨大需求。 地下建筑提供了可持续发展的好处，包括在现有基础设施的地区创建公共交通和商业空间、捕获排放的能力以及通过重新安置地下交通系统和其他结构来保护绿色空间的机会。 然而，地下空间的开发可能会导致邻近基础设施的破坏。 此外，规划和建设地下空间是一个漫长的过程，需要大量的预算，而且大多数地下建筑都是由纳税人资助的公共项目。 提高地下空间设计和施工的效率将为美国带来巨大的经济利益。 该快速响应研究补助金 (RAPID) 项目将开发工具，推动地下建筑行业的最先进技术和实践，以便在城市地区创建地下空间，同时将这一过程对邻近结构和公用设施的影响降至最低。 最近，美国国家科学基金会资助的研究取得了预测、监测和控制挖掘过程中地面运动技术的进步。 这些努力表明，土壤的小应变剪切刚度 Go 及其随应变的变化是用于预测地面运动的模型的关键要素。 工程师需要准确预测挖掘引起的地面运动，因为过度运动（通常为英寸或更小）可能会对邻近的基础设施和结构造成损坏。 对运动的准确估计将使工程师能够调整其设计，将运动限制在可接受的水平。 天然土壤具有异质性，Go 值会随着典型城市开挖规划区域的横向和深度而变化。 该项目将确定华盛顿州西雅图大型基坑周围的空间变化，特别是华盛顿州会议中心扩建部分 (WSCCA)，并量化这些变化对挖掘过程中测量和预测的地面运动的影响。 该项目是西北大学、德克萨斯大学奥斯汀分校、佛罗里达大学和 GeoEngineers, Inc. 之间的合作项目。该项目与美国领先的岩土工程咨询公司 GeoEngineers 以及 WSCCA 项目记录的岩土工程师进行免费合作，确保结果将对地下建筑界产生直接影响。 WSCCA 发掘提供了许多独特的机会。 该场地的很大一部分是绿地，因此，大部分场地的初始 Go 变化基本上不会受到之前施工活动的影响。 因此，当开挖后评估 Go 时，可以直接测量土壤性质的变化。 这些测量很少（如果有的话）进行。 项目团队将在施工开始前使用 NHERI@UTexas 现场设备和 SASW 阵列获得空间相关的 Go 值；通过先进的 3D 全波形断层扫描分析地震数据，以开发 Go 的 3D 地图；使用先进的三轴和组合动态扭转共振柱和循环扭转剪切装置对薄壁管和块样品进行详细的实验计划；使用基于实验室数据和开挖过程中收集的现场测量的优化技术，开发高级本构模型的土壤参数，其中包括小应变刚度；收集并记录现场表现并将其与施工活动联系起来；并利用有限元方法模拟开挖过程。 在解决与深基坑特别相关的地面变形时，该项目结果适用于任何岩土施工活动。 关于西雅图地区冰川固结土壤的应力-应变-强度特征的详细信息非常少，作为该项目的一部分开发的信息将对附近的任何大型项目有用。 项目团队将通过期刊出版物和会议演讲的方式向科学和专业界传播其成果。 GeoEngineers, Inc. 专业人士、NU、UT 和 UF 参与者之间通过项目互动和研讨会自动进行的互动将促进这些进步的快速技术转让。 实地研究期间还将举办 NHERI@UTexas 用户研讨会。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Increased dense urbanization and traffic congestion in the US is prompting a significant demand for underground space. Underground construction provides sustainable development benefits in terms of creating mass transit and commercial space in areas with existing infrastructure, the ability to capture emissions, and the opportunity to preserve green space by relocating transportation systems and other structures underground. However, development of underground space may result in damage to adjacent infrastructure. Furthermore, planning and constructing underground space is a lengthy process that requires large budgets, and most underground construction are public, taxpayer-funded projects. Efficiencies that can be developed in design and construction of underground space will have a large financial benefit to the US. This Grants for Rapid Response Research (RAPID) project will develop tools that will advance the state-of-art and practice in the underground construction industry so that underground space can be created in urban areas in such a way that the process will have minimal impact on adjacent structures and utilities. Recent NSF sponsored research has resulted in advances in techniques to predict, monitor, and control ground movements during excavation. These efforts have shown that small-strain shear stiffness of soil, Go, and its variation with strain is a key ingredient in a model used to predict ground movements. Engineers need to have accurate predictions of ground motion caused by excavations because excessive movements (often and inch or less) can cause damage to adjacent infrastructure and structures. An accurate estimate of movement will allow engineers to adjust their design to limit the movement to an acceptable level. Natural soils are heterogeneous and Go values vary laterally and with depth around the plan area of typical urban excavations. This project will determine the spatial variations of Go around a large excavation in Seattle, WA, specifically the Washington State Convention Center Addition (WSCCA), and quantify the effects of the variations on measured and predicted ground movements that arise during excavation. The project is a collaboration between Northwestern University, the University of Texas at Austin, the University of Florida and GeoEngineers, Inc. Collaboration, at no cost to the project, with GeoEngineers, a leading geotechnical consulting firm in the country and the geotechnical engineers of record for the WSCCA project, ensures that results will have an immediate impact in the underground construction community. The WSCCA excavation provides a number of unique opportunities. A large portion of the site is green space, and as such, the initial Go variation in most of the site will mostly be unaffected by previous construction activities. Therefore, when Go is evaluated after excavation, a direct measure of the change in the soil properties will be available. These measurements are rarely, if ever, performed. The project team will obtain spatially dependent Go values prior to start of construction using NHERI@UTexas field equipment and SASW arrays; analyze the seismic data via advanced 3-D full waveform tomography to develop a 3-D map of Go; conduct detailed experimental programs using both advanced triaxial and combined dynamic torsional resonant column and cyclic torsional shear devices on thin-wall tube and block samples; develop soil parameters for an advanced constitutive model that includes small-strain stiffness using optimization techniques based on the laboratory data and the field measurements collected during excavation; collect and record field performance and relate it to construction activities; and simulate the excavation process using the finite element method. While addressing ground deformations specifically associated with deep excavations, the project results are applicable to any geotechnical construction activity. There is very little detailed information concerning the stress-strain-strength characteristics of the glacially consolidated soils in the Seattle area, and information developed as part of this project will be useful for any large project in the vicinity. The project team will disseminate its results to the scientific and professional communities by means of journal publications and conference presentations. The interactions among GeoEngineers, Inc. professionals, NU, UT and UF participants via project interaction and seminars automatically will foster the rapid technology transfer of these advances. A NHERI@UTexas user workshop also will be held during the field study.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.