Abstract
For a long time, deep foundation pit support engineering has primarily utilized reinforced concrete and steel structure supports, with reinforced concrete being particularly widespread. However, with advancements in engineering technology, the limitations of reinforced concrete support systems in terms of cost, construction period, and environmental impact have become apparent. Today, the PC (Pile Combination) method pile construction technology has matured and is suitable for deep foundation pit support in coastal soft soil areas. This technique employs various materials such as steel sections, steel plates, and steel pipe piles, which can be flexibly combined to form different types of retaining piles. The optimal combination can be selected based on specific project requirements. This article focuses on the application and analysis of PC method combined steel pipe piles in foundation pit engineering.
Keywords: PC method, combined steel pipe piles, foundation pit engineering, application, analysis
Introduction
The PC method combined steel pipe pile is an innovative retaining pile technology, evolving from traditional Larssen sheet piles. Conventional sheet piles—whether U-shaped, Z-shaped, or straight-web—have small cross-sectional stiffness, necessitating multi-layer bracing in deep foundation pits, which increases construction difficulty and undermines their efficiency. The PC method integrates Larssen sheet piles with steel pipes and sections to form composite piles with enhanced load-bearing and waterproofing capabilities. Depending on the project’s needs, different combinations can be deployed.
1. Project Overview
The case study involves an underground parking garage in Wenzhou, Zhejiang Province, located east of Huimin Road and south of Yueluoyang Road. The reinforced concrete frame structure spans a total construction area of 5,370 m². The basement, roughly rectangular (80 m × 31 m), covers 939 m² with an excavation depth of 4.3–4.7 m. The west side borders Huimin Road, where municipal pipelines (e.g., rainwater and sewage lines) are buried, while the other three sides are open land. Geological layers include miscellaneous fill, clay, silt, and muck.
2. Application of PC Method Piles
2.1 Construction Technical Arrangement
(Refer to Figure 1 for the workflow.)
2.2 PC Method Combined Steel Pipe Pile Construction
The project employs the PC method combined with steel pipe piles—a recyclable, steel continuous wall system integrating steel pipes and Larssen sheet piles. Key construction equipment and methods include:
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First-Stage Pile Driving: A Hitachi 470H full-revolution hydraulic vibratory hammer was used for initial steel pipe and Larssen sheet pile installation, offering high precision and efficiency.
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Second-Stage Pile Driving: A 28RF electric vibratory hammer (786 kN vibratory force, 400 kN extraction force) mounted on a crawler crane ensured seamless continuation.
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Noise Control: ICE’s 28RF resonance-free hammer minimized noise and soil disturbance, aligning with eco-friendly construction practices.
Challenges & Solutions:
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Steel Pipe Piles: High rigidity allowed smoother penetration with heavy-duty hammers.
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Larssen Sheet Piles: Lower rigidity caused deformation during driving, leading to interlock jamming. Pre-drilling and optimized pile stiffness mitigated these issues.
Construction Steps:
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Survey & Layout: Align pile centers using control networks, verified by engineers.
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Alignment & Verticality: Two theodolites ensured ±90° verticality checks. Piles were adjusted within 3 m of penetration; deviations required re-driving.
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First Pile Installation: Critical for maintaining axis alignment due to the limited lateral adjustability of guide slots.
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First-Section Driving: The hydraulic hammer vibrated the pile until 1 m remained above the trench, with continuous verticality monitoring.
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Pile Connection: A 2 m inner sleeve with high-strength bolts provided temporary fixation before full welding. Four 20 cm × 20 cm curved plates reinforced with joints for future extraction.
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Second-Section Driving: Welded segments were cooled before driving.
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Larssen Pile Installation: Driven into pre-attached locks on steel pipes, with alignment checks.
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Closure: Custom-cut steel plates resolved dimensional mismatches during final sealing.
Conclusion
PC method combined steel pipe piles offer superior bending and shear resistance, enhancing foundation pit stability while controlling deformation risks. Their reusable nature reduces material costs, shortens timelines, and lowers equipment expenses, delivering significant economic and environmental benefits.
