Introduction
Urban construction projects often involve deep excavations, confined working spaces, and the need to protect adjacent infrastructure. In such conditions, contiguous pile walls are a popular choice for retaining and foundation support. They provide stability during excavation, minimize settlement, and integrate effectively with permanent basement and foundation systems. The following case studies highlight the practical applications and benefits of contiguous piles in urban settings.
1. High-Rise Basement Construction – London, UK
- Project Scope: Construction of a multi-story office tower with a three-level basement in central London.
- Challenge: Excavation depth of 12 m within a congested site surrounded by historic buildings.
- Solution:
- A contiguous pile wall with 600 mm diameter piles spaced at 900 mm center-to-center.
- Temporary anchors and struts were used during staged excavation.
- Pile heads were later integrated with the basement raft foundation.
- Outcome:
- Minimal settlement (<15 mm) recorded on adjacent structures.
- The contiguous pile wall served as both temporary shoring and permanent basement wall.
2. Metro Station Development – Mumbai, India
- Project Scope: Underground metro station requiring deep excavation in a dense urban area.
- Challenge: Loose sandy soil, high groundwater table, and proximity to traffic-heavy roads.
- Solution:
- Installation of contiguous piles of 750 mm diameter with depths up to 25 m.
- Additional grouting between piles reduced groundwater seepage.
- Real-time monitoring using inclinometers and piezometers.
- Outcome:
- Safe excavation with controlled groundwater inflow.
- Traffic above ground continued without disruption.
- Permanent integration with station diaphragm walls.
3. Underground Parking Facility – Sydney, Australia
- Project Scope: Two-level underground parking lot in a densely built commercial area.
- Challenge: Confined site with restricted access for heavy machinery.
- Solution:
- Use of contiguous bored piles of 450 mm diameter with small spacing.
- Compact drilling rigs enabled work in restricted access areas.
- Basement slabs tied directly into pile heads, reducing the need for extra retaining walls.
- Outcome:
- Faster construction time due to integration of temporary and permanent support.
- Reduced project costs by eliminating separate retaining systems.
4. Mixed-Use Development – Singapore
- Project Scope: Multi-tower mixed-use complex with deep basement retail and service facilities.
- Challenge: Excavation depth of 18 m in soft clay with nearby high-rise structures.
- Solution:
- Contiguous pile walls combined with tieback anchors for additional lateral resistance.
- Waterproof membranes applied to improve long-term durability.
- Advanced 3D finite element modeling guided excavation sequencing.
- Outcome:
- Settlement limited to <10 mm on adjacent high-rises.
- Effective integration of contiguous piles with raft foundation and pile caps.
5. Lessons Learned from Case Studies
- Urban Suitability: Contiguous piles are highly adaptable in restricted spaces with minimal disturbance.
- Dual Functionality: Serve as both temporary excavation support and permanent foundation wall.
- Groundwater Management: Gaps require additional grouting or waterproofing in high-water-table conditions.
- Monitoring is Crucial: Real-time monitoring ensures control of lateral movement and settlement.
- Integration with Structural Systems: Tying piles with basement slabs or raft foundations enhances long-term stability.
Conclusion
Case studies across London, Mumbai, Sydney, and Singapore demonstrate that contiguous piles are a reliable and cost-effective solution in urban construction projects. They provide excavation stability, protect surrounding infrastructure, and integrate seamlessly with deep foundations. With proper design, monitoring, and construction sequencing, contiguous piles ensure safe and durable foundation support in complex metropolitan environments.
