Abstract
A new form of retaining system for use in deep excavations in crowded cities is proposed in this paper. The new system, which we have coined the herringbone retaining system (HRS) involves the use of vertical and batter piles, capping beams, and wales. A numerical study was conducted (using the finite difference tool FLAC3D) to investigate various aspects of the behavior of the new system and reveal the mechanisms responsible for it. The HRS method was compared subsequently to two other commonly-used systems: the cantilever retaining structure (CRS) and horizontal-strutted retaining structure (HSRS). The results show that using the HRS method significantly reduces the deformation of the vertical piles and bending moments acting on them. More specifically, the maximum values of the deformation and bending moment were calculated to be 4.5% and 23.1% of the corresponding CRS values, respectively (the corresponding figures calculated for the HSRS method are 5.3% and 19.7%, respectively), so the HRS and HSRS methods provide similar levels of support. Finally, a real-world application of the system was presented to provide a valuable reference for the future use of HRS.
Highlights
In metropolitan areas such as Beijing and Shanghai, booming populations and a scarcity of urban land lead to excessive congestion
The following conclusions can be drawn from the analyses reducing lateral pile deflection and bending moment
(1) When herringbone retaining system (HRS) is used, the vertical piles rotate around the wale during excavation
Summary
In metropolitan areas such as Beijing and Shanghai, booming populations and a scarcity of urban land lead to excessive congestion. To help alleviate such congestion, cities are tending to build more high-rise buildings and develop the space available underground. This, in turn, is leading to an increase in the number of deep excavation projects being undertaken (for building basements and other underground engineering structures). Excavation induces soil movement and, sometimes, collapse of the land. This can result in adjacent buildings and utilities becoming damaged and even produce casualties [1,2]. Suitable retaining structures need to be employed in these deep excavations and so engineers are facing severe challenges with respect to the design and construction of excavation support measures
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