Long-term settlement behaviour of metro tunnels in the soft deposits of Shanghai

Flood risk assessment in metro systems of mega-cities using a GIS-based modeling approach.

Longitudinal structural modelling of shield tunnels considering shearing dislocation between segmental rings

This paper presents a generalized approach for predicting the diameter of jet grout columns based on the theoretical framework of turbulent kinematic flow and soil erosion. The proposed calculation method is applicable to all conventional jet-grouting systems and takes into account the full range of operational parameters, fluid properties, soil strength, and particle size distribution, including the effect of the injection time on erosion distance. It was demonstrated that the increase in the jet grout column diameter arising from the use of a compressed air shroud in the double and triple fluid systems is approximately 27–81% for the typical range of air pressure of 0.5–1.5 MPa. The proposed method was applied to four case histories involving four variants of jet-grouting systems, i.e., single fluid, double fluid, triple fluid, and an enhanced triple fluid system. Comparison between the calculated and the measured jet grout column diameters indicated that the proposed method can produce reasonab...

Generalized Approach for Prediction of Jet Grout Column Diameter

Perspectives for flood risk assessment and management for mega-city metro system

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

Four metro stations with similar supporting systems and pit geometries in Shanghai soft clay were excavated using different soil removal procedures, which led to distinctly different pit behaviors. Through analyzing and comparing the well-documented field data from these four bottom-up excavations, the significances of quick excavation, promptly propping, timely casting of floor slabs, and segmented construction in control of pit deformations were identified and their influences were comprehensively quantified. As to these four pits, the measured time-dependent wall deflections and wall heaves in 20–35 days at relatively deep excavation levels were up to 47–94% the magnitudes at completion of excavation to the final depths. The measured postexcavation wall deflections in about 20–30 days were up to 36–45% the maximum wall deflections at completion of excavation and the corresponding postexcavation deflection rates were up to twice those during excavation. The poorly excavated pits, which featured ...

Lessons Learned from Construction of Shanghai Metro Stations: Importance of Quick Excavation, Prompt Propping, Timely Casting, and Segmented Construction

Characterization of semi-top-down excavation for subway station in Shanghai soft ground

This paper examines the performance of an overexcavated metro station in soft clay within Shanghai metropolitan area, in which there are many high-rise buildings and buried utility pipelines in the proximity. The excavation was supported by stiff concrete diaphragm walls braced by steel pipes. The measured performance included deflections of diaphragm walls, ground settlements, and settlements of the adjacent buildings and utility pipelines. On the basis of daily monitored data, the effects of overexcavation on wall deflections, deflection rates, and the locations in which the maximum wall deflections and the maximum wall deflection rates occurred were investigated. For those buildings in the proximity, the heavy high-rise steel-reinforced concrete buildings supported by deep foundations experienced limited uniform settlements, whereas the light brick buildings resting on shallow foundations experienced substantial total and differential settlements. For the adjacent utility pipelines, the excavation-induced settlements were relatively uniform.

Performance of an Overexcavated Metro Station and Facilities Nearby

By analyzing the field data from nine metro-station pits with aspect ratios (AR) of pit length to width of 6.6–19.4 in Shanghai soft clay, this paper investigates the potential corner effects (i.e., the retaining walls near pit corners have stronger capabilities to resist deformation than those distant away as a product of spatial arching effects across the pit corners) of long and narrow multipropped metro station excavations. Contrary to the two-dimensional (2D) plane-strain assumption widely adopted in practice for analysis of a metro station excavation (i.e., deformations of the pit in which the displacements of all points along the longitudinal sides are assumed to be parallel to a given plane in the transverse direction and the values of these displacements do not depend on the distance perpendicular to the plane), seven out of the nine metro station pits exhibited apparent corner effects and only two showed plane-strain conditions. Because of the stiffening effects from the pit corners, the...

Bin Wei

Papers

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

Lessons Learned from Construction of Shanghai Metro Stations: Importance of Quick Excavation, Prompt Propping, Timely Casting, and Segmented Construction

Characterization of semi-top-down excavation for subway station in Shanghai soft ground

Performance of an Overexcavated Metro Station and Facilities Nearby

Spatial Corner Effects of Long and Narrow Multipropped Deep Excavations in Shanghai Soft Clay