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人们对地下空间产生了巨大的需求。地下建设提供了可持续发展的好处，包括在现有基础设施的地区创造公共交通和商业空间，捕获排放的能力，以及通过将交通系统和其他结构转移到地下来保护绿色空间的机会。然而，地下空间的开发可能会对邻近的基础设施造成破坏。此外，地下空间的规划和建设是一个漫长的过程，需要大量的预算，而且大多数地下建筑都是公共的、纳税人资助的项目。在地下空间的设计和建造中可以提高的效率将给美国带来巨大的经济利益。快速反应研究（Rapid）项目将开发工具，推动地下建筑行业的最新技术和实践，以便在城市地区创建地下空间，使该过程对相邻结构和公用设施的影响最小。最近由美国国家科学基金会资助的研究在预测、监测和控制挖掘过程中地面运动的技术方面取得了进展。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成分。工程师需要对挖掘引起的地面运动有准确的预测，因为过度的运动（通常是1英寸或更小）会对邻近的基础设施和结构造成破坏。一个准确的运动估计将允许工程师调整他们的设计，以限制运动到一个可接受的水平。在典型城市开挖的规划区域周围，天然土壤具有非均质性，Go值呈横向和深度变化。该项目将确定在华盛顿州西雅图的一个大型挖掘周围Go的空间变化，特别是华盛顿州会议中心扩建（WSCCA），并量化变化对挖掘过程中产生的测量和预测地面运动的影响。该项目由西北大学、德克萨斯大学奥斯汀分校、佛罗里达大学和GeoEngineers公司合作完成。与国内领先的岩土工程咨询公司GeoEngineers以及WSCCA项目记录在案的岩土工程工程师进行合作，确保其成果将对地下施工界产生直接影响，不需要项目承担任何成本。WSCCA的挖掘提供了许多独特的机会。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先前建筑活动的影响。因此，在开挖后对Go进行评估时，可以直接测量土壤性质的变化。这些测量很少被执行，如果有的话。项目团队将在施工开始前使用NHERI@UTexas现场设备和SASW阵列获得与空间相关的Go值；通过先进的三维全波形层析成像技术分析地震数据，绘制出Go的三维地图；采用先进的三轴和组合式动扭共振柱和循环扭剪装置在薄壁管和块状试样上进行详细的实验方案；根据实验室数据和挖掘过程中收集的现场测量数据，利用优化技术，为包括小应变刚度在内的高级本构模型开发土壤参数；收集和记录现场表现，并将其与施工活动联系起来；并采用有限元法对开挖过程进行了模拟。虽然解决了与深挖有关的地面变形，但项目结果适用于任何岩土工程施工活动。关于西雅图地区冰川固结土的应力-应变-强度特征的详细信息很少，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。项目小组将通过期刊出版物和会议报告的方式向科学界和专业团体传播其成果。GeoEngineers, Inc.专业人员、NU、UT和UF参与者之间通过项目互动和研讨会的互动，将自动促进这些进步的快速技术转移。实地研究期间还将举办NHERI@UTexas用户讲习班。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。

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.