A 16–18 m deep excavation for a metro station with in-plane dimensions of approximately 20 m wide by 290 m long was constructed by using the cut-and-cover technique in soft clay in the Shanghai metropolitan area, in which many high-rise buildings and utilities exist. To investigate the performance of this deep excavation and the associated effect on the adjacent buildings and utility pipelines, a long-term comprehensive instrumentation program was conducted during construction. Field observations included deflections of diaphragm walls, vertical movements at wall tops, ground settlements, and settlements of surrounding buildings and utilities. Analyses of field data indicated that overexcavation (i.e., removing more soil than designed) and a long construction duration caused the diaphragm walls to develop substantial deflections. The base and middle floor slabs played dominant roles in suppressing postexcavation wall deflections and ground settlements. This excavation in general exhibited different behavi...

Observed Behaviors of a Long and Deep Excavation Constructed by Cut-and-Cover Technique in Shanghai Soft Clay

Via a long-term comprehensive instrumentation program, the performance of a 26 m deep metro station excavation constructed by the top-down method in downtown Shanghai was extensively examined. The ...

Measured performance of a 26 m deep top-down excavation in downtown Shanghai

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 100-m-wide×25.89-m-deep 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 art...

Characteristics of a Large-Scale Deep Foundation Pit Excavated by the Central-Island Technique in Shanghai Soft Clay. I: Bottom-Up Construction of the Central Cylindrical Shaft

Because of its large size (30,000 m2 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...

Characteristics of a Large-Scale Deep Foundation Pit Excavated by the Central-Island Technique in Shanghai Soft Clay. II: Top-Down Construction of the Peripheral Rectangular Pit

Basement excavation may induce unsymmetrical and highly skewed loadings and (or) stress changes in an existing tunnel, not only in the transverse, but also in the longitudinal direction of the tunn...

Three-dimensional centrifuge modelling of basement excavation effects on an existing tunnel in dry sand

The characteristics of wall deflections and surface ground settlements at six deep multi-strutted excavations in Shanghai soft soils were studied and compared with those of similar case histories r...

Characteristics of wall deflections and ground surface settlements in Shanghai

Closure of "Observed Performance of a Deep Multistrutted Excavation in Shanghai Soft Clays"

To meet the increasing demand for underground space for economical development and infrastructural needs, more and more deep excavations have been constructed in Shanghai. In this paper, field perf...

G.B. Liu

Papers

Characteristics of wall deflections and ground surface settlements in Shanghai

Closure of "Observed Performance of a Deep Multistrutted Excavation in Shanghai Soft Clays"

Deformation characteristics of a 38 m deep excavation in soft clay

Three-dimensional deformation behaviour of a multi-propped excavation at a “greenfield” site at Shanghai soft clay

Long-Term Tunnel Settlement Mechanisms of Metro Line 2 in Shanghai