Abstract
This paper investigates the performance of a top-down deep excavation in soil-rock composite stratum. The behavior of the excavation bracing system, consisting of ground anchors and end-suspended piles, has not been well understood due to the lack of relevant research. Based on the observed data of a typical deep excavation case history for the May Fourth Square Station in Tsingtao, China, the characteristics of the horizontal and vertical pile displacements, ground surface settlements, building settlements, axial forces in ground anchors, earth pressure, and pore water pressure during excavation were analysed. Two-dimensional finite element simulations were carried out to further explore the deformation and internal force responses of end-suspended piles and to capture the effects of pile diameter, embedded depth, and rock-socketed depth on the horizontal displacement and bending moment distributions along the pile shaft. It was found that the pattern of the vertical pile displacements could be categorized into three types: rapid settlement, slow settlement, and rapid heave. The magnitudes of the ground and building responses can be well controlled within allowable limits by combining the top-down method with the adopted bracing system. Among the investigated parameters, pile diameter is dominant in affecting the horizontal pile displacement. The primary influence zone for pile bending moment varies, depending on the parameters. It is recommended that a combination of top-down method, ground anchors, and end-suspended piles be adopted for restraining excavation deformation and lowering construction costs of similar deep excavations in soil-rock composite stratum.
Highlights
Excavations are generally made for constructing metros, mass rapid transit systems, high-rise buildings, underground oil tanks, and other facilities
Within the primary area, the bending moment increases with increasing pile diameter; and the rate of increase in the bending moment decreases with increasing pile diameter
The performance of top-down deep excavation braced with ground anchors and end-suspended piles in a soil-rock composite stratum was investigated by analysing the observed data for a typical case history in Tsingtao, China, and performing a series of finite element simulations
Summary
Excavations are generally made for constructing metros, mass rapid transit systems, high-rise buildings, underground oil tanks, and other facilities. In the past several decades, extensive studies have been conducted to investigate the performance of deep excavations in terms of excavation-induced deformation and internal force characteristics of retaining walls and bracing structures [9,10,11], ground movements [12,13,14], and response of preexisting structures that are adjacent to the excavations [15,16,17] These studies are based mainly on numerical simulations [18, 19], empirical or semiempirical methods [20, 21], analytical solutions [22, 23], in situ monitoring data analysis [24, 25], centrifuge or scaled model testing [26, 27], and machine learning [28, 29]. Due to the difficulty of constructing castin-place pile in hard rock stratum and the limitation of Elevation (m)
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