In-situ test on synergistic mechanical behavior of steel pipe nested piles in soil-rock dual-stratum deep excavations
HAO Zengming1, BAI Xiaoyu1, YAN Nan1, LIU Junwei1, ZHANG Qijun1, 2
(1. School of Civil Engineering, Qingdao University of Technology, Qingdao, Shandong 266520, China;
2. Qingdao Yegao Construction Engineering Co., Ltd., Qingdao, Shandong 266022, China)
Abstract：To effectively address the challenges of low efficiency and difficulties in rock-socketing construction faced by traditional large-diameter bored piles, this study pioneered the application of the steel pipe nested pile support structure to deep excavation engineering in soil-rock dual strata. A systematic in-situ test study on the support performance of steel pipe nested piles was conducted, clarifying the dynamic evolution of internal forces in pile shafts during the excavation process, revealing the synergistic load-bearing mechanisms of composite support structures, and proposing an optimized support scheme for steel pipe nested piles. The results show that as the excavation depth increases, the bending moments of cast-in-place piles evolve into a “wave-shaped” multi-peak distribution along the depth direction, with significant fluctuations near the excavation face and a gradual downward migration of extreme bending moment points; the application of prestressed anchor cables reduces peak bending moments by 11%–34%. The bending moments of steel pipe piles evolve into a nonlinear “S” shaped distribution along the depth direction, with significant increases within 1.0 m above and below the interface, accompanied by noticeable stress concentration. Front-row steel pipe piles bear the majority of hydrostatic and soil pressures, while the bending moment fluctuation range of rear-row piles is approximately 90% of that of front-row piles. The supporting effect of the reserved side ramp significantly mitigates the excavation-induced unloading effect, and the upward shift of the slightly weathered rock layer interface effectively restricts the development of negative bending moments at the base of cast-in-place piles. The variation in the interface position between cast-in-place piles and steel pipe piles significantly influences the mechanical behavior of the piles. As the interface position shifts upward, the bending moments of cast-in-place piles and steel pipe piles evolve into a “lateral-spoon-shaped” single-peak distribution and a “wave-drum-shaped” multi-extremum distribution, respectively, gradually activating the load-bearing characteristics of steel pipe piles. Under similar geological conditions, it is recommended that subsequent excavation projects prioritize the optimized support scheme for steel pipe nested piles, with the interface between cast-in-place piles and steel pipe piles set within 0.5 m below the soil-rock stratum boundary and positioned between anchor cables MG–4 and MG–5. This design can fully utilize the support performance of steel pipe nested piles, ensuring the stability of the support structure and construction efficiency.
郝增明1，白晓宇1，闫 楠1，刘俊伟1，张启军1，2. 土岩二元深基坑钢管嵌套桩支护协同受力特性现场试验[J]. 岩石力学与工程学报, 2025, 44(9): 2515-2532.
HAO Zengming1, BAI Xiaoyu1, YAN Nan1, LIU Junwei1, ZHANG Qijun1, 2. In-situ test on synergistic mechanical behavior of steel pipe nested piles in soil-rock dual-stratum deep excavations. , 2025, 44(9): 2515-2532.
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2025, Vol. 44 
