Deformation Based Design Methodology for Excavation Support Systems

摘要：地下建筑和改造工程在全国许多城市普遍存在。由于邻近的基础设施非常接近，这些项目工地的建筑活动空间通常有限。涉及深挖工程的一个主要问题是与开挖有关的地面移动对邻近建筑物和公用事业的影响。开挖区域边缘的过度横向移动可能会导致邻近结构物发生显著的位移和旋转。因此，控制侧向位移是开挖支撑系统的主要设计考虑因素。在许多城市地区，工程场地被软粘土覆盖。这需要额外的考虑，因为土壤的固结和蠕变的贡献。许多城市工程往往需要严格的变形控制，以最大限度地减少对邻近结构的破坏。变形的控制通常是通过刚性开挖支撑系统来实现的。传统的开挖支护系统是采用表观土压力图进行设计的。使用这种方法，支撑系统设计成为最大预期土压力的函数，并由整体结构稳定性控制，而不是最大允许的水平或垂直变形。这种方法产生的支撑系统在防止结构破坏方面是足够的，但可能会导致过度的墙变形和地面移动。现有的考虑变形的方法将侧向墙体移动与开挖支撑系统的刚度和地基稳定性联系起来。然而，这些都是使用有限数量的墙类型和配置来开发的，并且没有考虑不同的开挖支撑系统的材料；墙结构的三维效应；不同支撑类型的影响；开挖几何形状和顺序的影响；或复杂的场地地质。由于开挖支撑体系和开挖过程的复杂性，很容易得出结论：为了真实地分析土体与开挖支撑体系之间的相互作用，需要建立三维有限元模型。这项研究的学术价值在于，最新的研究表明，开挖引起的地表移动和复杂的土-结构相互作用在本质上是三维的。然而，到目前为止，对深基坑进行全三维有限元分析的文献报道的数据有限。此外，还没有人提出一种包括建造支撑墙和安装支撑系统的三维影响、开挖和回填场地的三维影响(包括基础设施建设的时间延迟)以及三维地面变形影响的开挖支撑系统的设计方法。这项研究将提供三个案例的三维有限元分析，并将发展一种基于变形的设计方法。这项研究的更广泛影响是，基于变形的设计方法可能会节省数百万美元，通常用于修复和减轻挖掘对邻近基础设施的破坏。此外，本文的研究成果将直接或间接地应用于隧道设计、挡土墙设计、围堰设计和深基础设计(如土石方工程)。钻孔竖井、旋挖桩、砂箱等)。还预计这些研究成果将扩展到评估结构对顶管和施工降水等施工活动引起的地面移动的反应。这项研究的另一个合乎逻辑的扩展是评估建筑物和公用事业对动态荷载引起的地面移动的响应，如爆炸荷载、建筑振动和地震荷载。这项研究还将促进本科生研究人员的参与，特别强调代表性不足的群体的参与。

Abstract:Underground construction and rehabilitation projects are prevalent in many urban areas across the country. Space for construction activities is usually limited at these project sites because of the close proximity of adjacent infrastructure. A major concern for projects involving deep excavations is the impact of excavation-related ground movements on adjacent buildings and utilities. Excessive lateral movements at the edge of the excavated area can lead to significant displacements and rotations in adjacent structures. Consequently, control of lateral displacements is a major design consideration for excavation support systems. In many urban areas, the project site is underlain by soft clays. This requires additional considerations because of the contributions from consolidation and creep of the soil. Strict deformation control is often required to minimize damage to adjacent structures for many urban projects. Control of deformations is typically achieved with stiff excavation support systems. Traditionally, excavation support systems are designed using apparent earth pressure diagrams. Using this approach, the support system design becomes a function of the maximum anticipated earth pressure and is governed by overall structural stability as opposed to maximum allowable horizontal or vertical deformation. This approach produces a support system that is adequate with regard to preventing structural failure, but may result in excessive wall deformations and ground movements. Existing methods that do consider deformations relate lateral wall movements to excavation support system stiffness and basal stability. However, these were developed using a limited number of wall types and configurations, and do not include considerations for differing materials of an excavation support system; the three-dimensional effects of the wall construction; the effects of different support types; the influences of the excavation geometry and sequencing; or complex site geology. Due to the complexity of the excavation support system and the excavation process, it is easily concluded that for a realistic analysis of the interaction between the soil and the excavation support system, a three-dimensional finite element model is required. The intellectual merit of this research is that the most recent studies have shown that excavation-induced ground movements and the complicated soil-structure interactions of the excavation support system are three-dimensional in nature. However, to date limited data has been reported in the literature that presents a fully three-dimensional finite element analysis of a deep excavation. In addition, no one has presented a design methodology for excavation support systems that incorporate the three-dimensional influences of constructing the support wall and installing the support system; the three-dimensional influences of excavating and backfilling the site (including time delays for infrastructure construction); and the influences of three-dimensional ground deformations. This research will provide the three-dimensional finite element analysis of three case histories and will develop a deformation-based design methodology. The broader impact of this research is that a deformation-based designed methodology will potentially save millions of dollars typically expended for repairs and mitigation of excavation-induced damage to adjacent infrastructure. In addition, the results of this research will directly and indirectly be applicable to tunnel design, design of earth retaining walls, cofferdam design, and deep foundations design (eg. drilled shafts, auger-cast piles, cassions, etc.). It is also envisioned that these research results will be extended to evaluating structure response to ground movements resulting from construction activities such pipe jacking and construction dewatering. Another logical extension of this research is evaluating the building and utility response to dynamic loading-induced ground movements such as blast loads, construction vibrations, and earthquake loading. This research will also facilitate participation of undergraduate researchers, with special emphasis on participation of underrepresented groups.