In construction, the choice of retaining systems plays a pivotal role in ensuring the stability and longevity of a project. Among the most debated options are diaphragm walls and secant piles. Both techniques are used to create robust retaining structures in deep excavation and foundation works, but they differ significantly in their applications, cost, and technical considerations.
This blog delves into the key distinctions between both to help you choose the best retaining solution for your project.
What Are Diaphragm Walls?
They are deep, continuous reinforced concrete walls constructed using a slurry trenching method. They are particularly suited for urban construction projects, large-scale infrastructure, and areas requiring high water-tightness and load-bearing capabilities.
Applications:
- Deep basements
- Tunnels
- Underground parking structures
- High-water table zones
- Seismic-resistant structures
What Are Secant Piles?
Secant piles involve drilling overlapping concrete piles to form a retaining wall. These walls are often used for circular shafts, foundation pits, and temporary retaining works in confined spaces. The piles may be reinforced or unreinforced, depending on the project’s load requirements.
Applications of Secant Piles:
- Shaft construction
- Temporary retaining walls
- Confined or irregular-shaped excavation areas
Diaphragm Walls vs. Secant Piles: A Comparative Analysis
1. Structural Integrity
- Diaphragm Walls: Known for their superior load-bearing capacity and rigidity, diaphragm walls are ideal for projects requiring long-term structural stability.
- Secant Piles: While versatile, secant piles offer comparatively less structural integrity and are more prone to deformation under heavy loads.
2. Water-Tightness
- Diaphragm Walls: Constructed using slurry during excavation, diaphragm walls offer excellent water-tightness, making them a preferred choice in high-water table areas.
- Secant Piles: Water-tightness depends on the overlapping and composition of the piles. They are generally less effective than diaphragm walls in preventing water seepage.
3. Excavation Depth
- Diaphragm Walls: Suitable for very deep excavations, often exceeding 30 meters, without compromising stability.
- Secant Piles: Effective for medium-depth excavations but less practical for extremely deep projects.
4. Construction Speed
- Diaphragm Walls: Construction requires meticulous planning and is relatively time-intensive due to the trenching and reinforcement processes.
- Secant Piles: Faster to install, especially for smaller projects or temporary structures, making them a cost-effective choice for short timelines.
5. Cost
- Diaphragm Walls: Higher initial costs due to the complex construction process and the need for specialized equipment. However, they provide long-term savings through durability and minimal maintenance.
- Secant Piles: More economical for temporary or small-scale projects, but may require additional reinforcement or repairs over time.
6. Environmental Impact
- Diaphragm Walls: Produce less noise and vibration, making them suitable for urban areas with strict environmental regulations.
- Secant Piles: Drilling and pile-driving can generate significant noise and vibrations, potentially disrupting surrounding environments.
7. Design Flexibility
- Diaphragm Walls: Offer flexibility for integrating additional features such as drainage or monitoring systems, which are critical for complex infrastructure projects.
- Secant Piles: Better suited for irregular or confined shapes but offer limited options for additional features.
Factors to Consider When Choosing
- Project Type and Scale:
Large-scale, permanent structures such as underground parking lots or tunnels benefit more from the stability of diaphragm wall. For temporary or small-scale works, secant piles are a practical option. - Site Conditions:
Assess the soil type, water table levels, and environmental regulations. Diaphragm walls are often the go-to choice for challenging site conditions. - Budget:
While diaphragm wall may seem costlier initially, their durability often outweighs the long-term costs associated with secant piles. - Timeline:
If project deadlines are tight and the structural requirements are moderate, secant piles may offer faster construction.
Real-World Applications
Diaphragm Walls in Urban Metro Projects:
In cities like Singapore and Dubai, diaphragm walls are extensively used for metro systems and underground stations due to their high load-bearing capacity and water-tightness.
Secant Piles in Circular Shaft Construction:
Secant piles have been widely employed in projects requiring shaft construction for utilities or transportation, particularly in confined urban areas.
Innovations in Retaining Systems
Recent advancements in construction technology have blurred the lines between diaphragm wall and secant pile. Innovations such as:
- Polymer-based slurry for diaphragm walls improve excavation precision.
- High-strength concrete for secant piles enhances water-tightness and load capacity.
These developments allow engineers to customize retaining systems based on unique project needs.
Conclusion
Choosing between diaphragm walls and secant piles requires a thorough understanding of your project’s requirements, site conditions, and budget constraints. For large, permanent structures requiring high durability, diaphragm wall is often the superior choice. Conversely, for temporary works or small-scale projects, secant piles may provide a cost-effective solution.
Consult with structural engineers and consider long-term implications to ensure your retaining system aligns with your project’s goals.
