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Ground movements observed during foundation installation and basement construction of a residential 53-story RC tower are presented. The One Museum Park West building is located in Chicago, Illinois, and was developed using a combination of bottom-up methods, used for the construction of a central concrete core of the building, and top-down methods to build five levels of basements. The excavation extended 13-15 m below grade and was made through soft to medium-stiff clays. The building was supported by drilled shafts and a perimeter wall formed by secant piles that transitioned to tangent piles below the bottom of the cut. The system was laterally braced with RC floor slabs structurally connected to the secant pile walls and the RC core. Field performance data were collected by means of settlement points and inclinometers located close to the walls on two sides of the excavation. The construction sequence and attendant ground movements during each main activity are summarized. As much as 160 mm of settlement was recorded in the adjacent streets throughout construction. Wall and foundation installation accounted for approximately 35% of the total settlements during construction, whereas top-down construction of the basement resulted in approximately 40% of the total settlements. These data emphasize the importance of considering all construction activities when making predictions of ground movements adjacent to deep supported excavations. [ABSTRACT FROM AUTHOR]

Because of its large size ( in plan), the 17.85- to 25.89-m-deep foundation pit of the 492-m-high Shanghai World Finance Center building was excavated by the central-island technique, i.e., bottom-up construction of the central cylindrical shaft first and then top-down construction of the peripheral rectangular pit. As part of the comprehensive study on the characteristics of this large-scale foundation pit, this study mainly focuses on the behaviors of the peripheral pit via the following investigated items: (1) lateral wall deflections; (2) vertical wall movements; (3) lateral ground movements; (4) axial forces in the cast floor slabs and braced struts; (5) lateral earth pressures on both sides of retaining walls; (6) variation of pore pressures along depth and deep artesian water levels; (7) ground settlements; (8) subsurface settlements; (9) basal heaves; (10) vertical column movements; and (11) column stresses. To explore the potential effects of pit sizes on the excavation behaviors, field data from another 33 top-down excavations in Shanghai were also included for comparison. The comprehensive comparisons show that in addition to the well-known factors (e.g., excavation depths, supporting system stiffness, and factor of safety against basal heave), pit sizes in plan played a key role in determination of the pit behaviors. The large-scale pits with the areas in plan of experienced wall deflections and ground settlements three to five times those of regular building basement and metro station excavations with the sizes in plan no more than , and the corresponding influence zones behind the large-sized pits were also much wider. Different from the braced struts that just carried the load because of soil removal in the proximity, the floor slabs sustained the load induced by exposure of the entire retaining wall along the depth. For the top-down excavations in Shanghai soft clay, the lateral earth pressure envelopes behind the retaining walls were trapezoidal, but their magnitudes were significantly smaller than those predicted by the methods available in the literature, and the corresponding peak values occurred at a greater depth. The influence zones of basal heave caused by soil removal (stress relief) extended much deeper below the excavation bases than those assumed in the conventional slip circle basal stability models. [ABSTRACT FROM AUTHOR]

A large amount of field and experimental data has been devoted to rectangular excavations thus far. In contrast, very few data were available for cylindrical excavations, especially those with large diameters in thick soft clay deposits. Via a comprehensive instrumentation program on a unpropped (self-supported) cylindrical excavation constructed by the bottom-up method in Shanghai soft clay, the characteristics of this large-sized circular excavation were extensively investigated. This cylindrical shaft was a part of a large-scale deep foundation pit excavated by the central-island technique. The investigated items included (1) lateral wall deflections, (2) vertical wall movements, (3) lateral ground movements, (4) ground settlements, (5) subsurface settlements, (6) basal heaves, (7) vertical column movements, (8) column stresses, and (9) variation of pore pressures along depth and artesian water levels. Analysis of the field data indicates that discharging of the deep artesian water was one of the key factors affecting the excavation behaviors. The influence zone of basal heave caused by soil removal (stress relief) reached very deep soil layers, far beyond the depths reported in literature. Column movement and stress were shown to be reliable indicators of the relative movement between basal soils, diaphragm walls, and interior columns. Finally, the comparisons of this study with other bottom-up excavations in Shanghai, including 11 cylindrical excavations, 92 building basement excavations, and eight metro station excavations, demonstrate that self-supported (unpropped) cylindrical excavations had much stronger capabilities of resisting deformation than both multipropped regular basement excavations (in terms of deformation magnitudes) and long and narrow metro station excavations (in terms of scale of influence zones). For cylindrical shafts, their diameters, and not wall penetration ratios, played a dominant role in the determination of excavation behaviors. However, when the shaft diameter reached 90 m or more, the advantage of cylindrical shafts over rectangular pits in constraining wall deflection was no longer obvious. [ABSTRACT FROM AUTHOR]

This paper presents the results of 150 finite-element simulations conducted to define the effects of excavation geometry, i.e., length, width, and depth of excavation, wall system stiffness, and factor of safety against basal heave on the three-dimensional ground movements caused by excavation through clays. The results of the analyses are represented by the plane strain ratio (PSR), defined as the maximum movement in the center of an excavation wall computed by three-dimensional analyses normalized by that computed by a plane strain simulation. A simple equation for PSR is presented based on excavation geometry, wall system stiffness, and factor of safety against basal heave. This PSR equation reasonably represents trends in results of the 150 simulations as well as those simulations reported in literature. When the excavated length normalized by the excavated depth of an excavation wall is greater than 6, results of plane strain simulations yield the same displacements in the center of that wall as those computed by a three-dimensional simulation. [ABSTRACT FROM AUTHOR]