Introduction
Contiguous piles are widely used in urban and infrastructure projects where deep excavations and foundation support are required. Their ability to provide lateral stability, excavation support, and load transfer makes them highly suitable for basement construction, underground facilities, and high-rise foundations. Effective integration of contiguous piles with basement excavations and deep foundations ensures both construction safety and long-term structural performance.
1. Role of Contiguous Piles in Basement Excavations
(a) Retaining Wall Function
- Act as temporary or permanent retaining walls during deep basement excavation.
- Resist lateral earth and hydrostatic pressures, reducing soil movement.
(b) Excavation Safety
- Provide stability for vertical cuts in congested urban sites.
- Minimize ground settlement and protect adjacent structures, utilities, and roads.
(c) Groundwater Considerations
- Not completely watertight due to gaps between piles.
- Integration with grouting, shotcrete lining, or waterproof membranes improves groundwater control.
2. Integration with Deep Foundations
(a) Load Transfer
- Contiguous piles can serve as part of the foundation system, carrying axial loads from the superstructure.
- Pile caps or raft slabs integrate the piles with vertical and lateral load paths.
(b) Combined Systems
- Often combined with bored piles, secant piles, or diaphragm walls for deeper foundations.
- Hybrid systems improve load distribution and lateral stiffness.
(c) Settlement Control
- Piles reduce differential settlement by transferring loads to competent strata at greater depths.
- Essential in soft soil or reclaimed land projects.
3. Construction Strategies
(a) Excavation Sequencing
- Install contiguous piles before excavation begins.
- Excavation proceeds in stages, supported by struts, anchors, or braces as depth increases.
(b) Structural Connections
- Pile heads are connected using pile caps or basement slabs, ensuring integration with the permanent structure.
- Reinforcement continuity between piles and basement slabs enhances structural stability.
(c) Monitoring and Control
- Use of inclinometers, strain gauges, and settlement markers during excavation prevents overloading and structural distress.
- Real-time monitoring ensures safe progress in urban sites.
4. Advantages of Integration
- Space Efficiency: Allows basement construction in congested areas without large open cut slopes.
- Dual Functionality: Provides both excavation support and permanent foundation support.
- Cost Efficiency: Eliminates the need for separate retaining structures.
- Reduced Risk: Controls ground settlement and protects nearby buildings and utilities.
5. Case Applications
- Urban Basements: High-rise buildings with 2–5 level basements in dense cities use contiguous piles for both excavation shoring and foundation transfer.
- Transport Infrastructure: Subway stations and underground parking lots use contiguous piles for lateral support and long-term durability.
- Mixed-Use Developments: Integration with raft foundations reduces settlement and improves load-sharing.
Conclusion
The integration of contiguous piles with basement excavations and deep foundations provides a safe, cost-effective, and versatile solution for urban geotechnical projects. By serving as both retaining structures and foundation elements, contiguous piles minimize ground movement, support deep excavation, and enhance structural performance. When combined with proper design, sequencing, and monitoring, they ensure long-term safety and durability in challenging construction environments.
