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

在城市高层建筑的开挖中，最近的趋势是使用围堰，这有时是造成大部分地面移动的原因。由于这些项目，地下管理机构规定的允许的地面移动已大大减少，要求改进移动控制计划中使用的观察和分析方法。该奖项支持了城市围堰分析和设计方法的基础研究，并为深基坑土-结构相互作用行为的研究提供了机会。在美国，目前还没有考虑到围堰性能影响的设计建议。两个城市围堰作为这项研究的试验台：第一个是为美国最高建筑的结构而建造的，并且在该结构提出的城市中建造了最深的地下室；第二个是为伊利诺斯州芝加哥的One Museum Park West建筑建造的。在这项研究中发展的基础知识将激发新的分析和设计近海结构、深基础、码头和挡土结构的方法，并将促进对其他类型岩土工程中土-结构相互作用的理解。知识将产生在城市围堰板桩联锁在压缩载荷下的行为，混凝土材料对钢筋混凝土环梁支撑的围堰行为的时间依赖效应，以及板桩联锁在城市围堰与节段钢环梁支撑的滑移和旋转。采用先进的本构土模型，结合土的小应变特性，对城市围堰进行三维全耦合流动-变形数值分析。面向实践的新设计方法将被开发，以将以下因素纳入设计过程：钢筋混凝土环梁的材料时间依赖性，钢环梁和板桩的结构遵从性，板桩联锁处的滑移和旋转，以及深基础和围堰内部其他结构的安装。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具可持续性和弹性的城市环境，这些基础设施往往在过度变形时受到损害。

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.