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.
