RUI: Effects of Pre-Excavation Activities on the Performance of Urban Cofferdams

最近城市高层建筑开挖的趋势是使用围堰，而围堰有时是导致地面移动的主要原因。这些项目的结果是，地下监管机构实施的允许地面移动已大大减少，需要改进移动控制计划中使用的观测和分析方法。该奖项支持城市围堰分析和设计方法的基础研究，并为深基坑的土-结构相互作用行为提供了一个进步的机会。考虑到对围堰性能的影响的设计建议目前在美国还不存在。两个城市围堰是这项研究的试验台：第一个围堰是为一座预计将成为美国最高建筑的建筑建造的，地下室也是该建筑拟建城市有史以来最深的；第二个围堰是为伊利诺伊州芝加哥的One Museum Park West大楼建造的。本研究发展的基础知识将启发近海结构、深基础、码头和围护结构分析和设计的新方法，并将促进对其他类型岩土工程中土-结构相互作用的理解。将产生关于城市围堰板桩联锁在压缩荷载作用下的性能，混凝土材料对钢筋混凝土环梁支撑围堰性能的时变效应，以及城市节段钢环梁支撑的板桩联锁的滑移和转角的知识。采用先进的土体本构模型，结合土体的小应变特性，对城市围堰进行了三维流动-变形全耦合数值分析。新的设计方法将面向实践，将钢筋混凝土环梁的材料时效性、钢环梁和板桩的结构柔度、板桩联锁处的滑移和转动以及围堰内深基础和其他结构的安装等因素纳入设计过程。这项研究的最终目标是通过保存和保护现有的基础设施来创造更可持续和更具弹性的城市环境，当过度变形发生时，这些基础设施往往会受到影响。

The recent tendency in urban excavations for high-rise buildings is the use of cofferdams which at times are responsible for the majority of the resulting ground movements. As a result of these projects, the allowable ground movements imposed by underground regulatory agencies have been drastically reduced, calling for improvements in the observational and analytical methods used in movement control plans. This award supports fundamental research on the methods of analysis and design of urban cofferdams and presents an opportunity for advances in soil-structure interaction behavior of deep excavations. Design recommendations considering the proposed effects in the performance of cofferdams do not currently exist in the United States. Two urban cofferdams serve as the test bed of this research: the first was built for a structure projected to be the tallest building in the United States, and to have the deepest basement ever built in the city where the structure was proposed; the second was built for the One Museum Park West building in Chicago, Illinois. The fundamental knowledge developed in this research will inspire new methods of analysis and design of offshore structures, deep foundations, wharfs, and retaining structures, and will advance the understanding of the soil-structure interaction in other types of geotechnical projects.Knowledge will be produced on the behavior of sheet pile interlocks in urban cofferdams under compression loading, the concrete material time-dependent effects on the behavior of cofferdams braced with reinforced concrete ring beams, and slippage and rotation at sheet pile interlocks for urban cofferdams braced with segmental steel ring beams. Three-dimensional fully-coupled flow-deformation numerical analyses of urban cofferdams using advanced constitutive soils models and incorporating the small strain behavior of soils will be used in the analyses. New design methodologies oriented for practice will be developed to incorporate the following factors into the design process: the material time-dependency of reinforced concrete ring beams, the structural compliance of steel ring beams and sheet piles, the slippage and rotation at sheet pile interlocks, and the installation of deep foundations and other structures inside of cofferdams. The ultimate goal of this research is to create more sustainable and resilient urban environments by preserving and protecting existing infrastructure, which is often compromised when excessive deformations occur.