Introduction
Secant piles are a widely adopted deep foundation and retaining system in modern geotechnical engineering. Constructed by overlapping reinforced and unreinforced piles, they form continuous walls capable of providing both structural stability and groundwater cutoff. Due to their adaptability in difficult ground conditions and tight urban spaces, secant piles are extensively applied in tunnels, basements, and infrastructure projects.
This article highlights the field applications of secant piles across these domains, supported by case-specific advantages.
1. Secant Piles in Tunnel Construction
1.1 Temporary and Permanent Tunnel Shafts
- Secant piles form circular or rectangular shaft enclosures for tunnel boring machine (TBM) launches and retrievals.
- Provide groundwater cutoff in high water table conditions.
- Ensure shaft wall stability during excavation and lining installation.
1.2 Cross-Passage Construction
- Used for small cross-passages between twin tunnels.
- Enable construction in weak soils or mixed-face conditions without ground collapse.
1.3 Advantages in Tunnel Projects
- Low noise and vibration, suitable for urban tunneling.
- Effective in controlling inflow and soil settlement near sensitive structures.
2. Secant Piles in Basement Excavations
2.1 Deep Basements in Urban Areas
- Provide retaining wall support for high-rise basements in congested city centers.
- Minimize ground movements that could damage adjacent buildings or utilities.
2.2 Groundwater Cutoff for Basement Waterproofing
- Act as a permanent waterproof barrier, reducing the need for expensive external tanking systems.
2.3 Applications in Multi-Level Parking and Commercial Complexes
- Enable construction of basements below the water table.
- Allow safe excavation for multi-level underground car parks and malls without extensive dewatering.
3. Secant Piles in Infrastructure Projects
3.1 Bridge Abutments and Underpasses
- Provide earth retention and groundwater control for cut-and-cover underpasses.
- Stabilize slopes and approaches to bridges.
3.2 Ports and Marine Structures
- Used in quay walls and marine excavations where water retention and stability are crucial.
- Can resist both lateral earth and hydrostatic pressures.
3.3 Road and Railway Cuttings
- Control ground movement in urban transport projects near sensitive structures.
- Support excavations for metro stations, utility tunnels, and underground corridors.
4. Case Study Examples
- London Crossrail Project (UK): Secant piles used for deep station boxes and shaft enclosures in water-bearing soils.
- Metro Rail Basements (India): Employed to stabilize deep basements adjacent to existing buildings in congested city cores.
- Urban Underpasses (Europe): Provided retaining walls for cut-and-cover tunnels below groundwater level, with minimal settlement impact.
5. Key Benefits Across Applications
- Dual Functionality: Acts as retaining wall and groundwater barrier.
- Adaptability: Works in mixed soils, gravels, and soft rock.
- Urban Suitability: Low vibration, minimal disturbance to surrounding structures.
- Durability: Long-term resistance to groundwater and aggressive soil environments.
Conclusion
Secant pile systems have become indispensable in tunnel shafts, deep basements, and infrastructure projects where excavation stability and groundwater control are critical. Their versatility in diverse soil conditions, combined with their economic and environmental benefits, makes them one of the most reliable solutions in modern geotechnical engineering. With increasing urbanization and underground construction, the use of secant piles is expected to expand further in global infrastructure development.
