Observed Performance and FEM-Based Parametric Analysis of a Top-Down Deep Excavation in Soil-Rock Composite Stratum

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.

Rational design solutions for deep excavations using soil nail wall systems

“…Many researchers have contributed to numerous studies aimed at addressing the stability issues associated with soil and rock layers during cutting, excavation, and mining operations [6]- [9]. These studies have significantly benefited the mining and construction industries by developing support systems that ensure stability in excavations and slope faces.…”

Study on Design and Deformation Law of Pile-Anchor Support System in Deep Foundation Pit

“…The literature [50][51][52][53] studied the deformation and stress changes of the supporting structure, caused by the failure of the pile-anchor in a deep foundation pit, by the finite difference method and put forward that the failure of the local anchor had a great influence on the stability of the foundation pit. The literature [54][55][56][57] used the finite difference principle to study the frost heaving force on the foundation pit pile-anchor support system and discussed the stress change and deformation law of foundation pit pile-anchor support under low-temperature conditions. The literature [58,59] optimized the supporting structure of the pile-anchor foundation pit, considering the corner effect.…”