When it comes to deep foundation solutions, choosing the right retaining structure is critical for ensuring the safety, stability, and longevity of a construction project. Two of the most commonly used methods for deep excavations are diaphragm walls and sheet pile walls. Both systems have unique strengths and weaknesses, making them suitable for different project requirements, soil conditions, and environmental constraints.
In this comprehensive guide, we’ll explore the intricacies of diaphragm walls vs sheet pile walls, delve into their applications, advantages, and challenges, and highlight relevant case studies, including examples from Nepal. Additionally, we’ll provide actionable insights to help you make informed decisions for your next deep foundation project.
What Are Diaphragm Walls?
Diaphragm walls, also known as slurry walls, are reinforced concrete structures constructed in situ below ground level to provide robust lateral support and act as retaining walls in deep excavations. These walls are typically built by excavating a narrow trench, which is kept stable using a support fluid like bentonite slurry.
Once the trench is excavated, a reinforcement cage is inserted, and concrete is poured to form a continuous, watertight barrier. Diaphragm walls are highly versatile and can be used for permanent or temporary retaining structures, deep foundations, or cut-off walls to control groundwater.
Key Features of Diaphragm Walls
- Depth Capability: Can reach depths exceeding 100 meters, ideal for deep basements and metro stations.
- Thickness: Typically ranges from 0.5 to 1.8 meters.
- Construction Method: Involves panel-by-panel construction with interlocking joints for structural stability and water tightness.
- Applications: Deep basements, metro stations, tunnels, dams, and underground car parks.
What Are Sheet Pile Walls?
Sheet pile walls are constructed by driving interlocking steel, vinyl, or concrete sheets into the ground to form a continuous barrier. They are primarily used for temporary or permanent retaining walls, particularly in projects involving shallow to moderate excavations. Sheet piling is a faster and more cost-effective method compared to diaphragm walls, but it has limitations in terms of depth, strength, and water tightness.
Key Features of Sheet Pile Walls
- Depth Capability: Generally suitable for excavations up to 5–15 meters, though deeper applications are possible with additional support.
- Material: Commonly steel, but vinyl and concrete are also used in specific cases.
- Construction Method: Sheets are driven into the ground using vibratory or hydraulic hammers.
- Applications: Temporary retaining walls, coastal protection, riverbank reinforcement, and shallow excavations.
Diaphragm Wall Vs Sheet Pile Wall: Deep Foundation Solutions
When planning deep foundation projects, choosing between diaphragm walls and sheet pile walls is a critical decision that impacts stability, cost, and project timelines. Both systems serve as retaining structures but differ significantly in construction, applications, and performance.
1. Structural Strength and Stability
Diaphragm Walls
Diaphragm walls, constructed from reinforced concrete, offer exceptional structural strength and stability, making them ideal for deep excavations and high-load environments. These walls can withstand significant lateral earth pressures and seismic forces, which is crucial in regions like Nepal, prone to earthquakes. For example, in the Kathmandu Metro Project, diaphragm walls were used for a 20-meter-deep excavation at Durbar Marg station, ensuring minimal settlement and protecting nearby heritage structures. Their robust design allows them to serve as permanent structural elements, such as basement walls, enhancing long-term durability.
Sheet Pile Walls
In contrast, sheet pile walls, typically made of steel, provide moderate structural strength suitable for lighter loads and shallower excavations. They are less effective in high-pressure or seismic conditions due to potential deformation. In Nepal’s Bagmati River Improvement Project, steel sheet piles were driven to a depth of 8 meters to reinforce riverbanks against erosion. While effective for temporary support, their lower strength limits their use in deep or permanent applications. Consequently, sheet piles are better suited for projects with less demanding structural requirements.
2. Water Tightness
Diaphragm Walls
Diaphragm walls excel in water-tightness, making them a top choice for projects in high water table areas or near water bodies. The continuous concrete panels, interlocked with watertight joints, prevent groundwater ingress effectively. In the Kathmandu Metro Project, diaphragm walls ensured a dry excavation environment in the silty, waterlogged soils of the Kathmandu Valley, reducing the need for extensive dewatering systems. This makes them indispensable for metro stations, tunnels, and dams where water control is critical.
Sheet Pile Walls
Sheet pile walls, however, offer only moderate water-tightness due to potential gaps at interlocking joints, especially in steel piles. In the Bagmati River project, sheet piles required additional sealing measures to manage groundwater seepage, increasing costs slightly. While effective for temporary water barriers, they are less reliable for long-term waterproofing. For projects requiring robust water control, sheet piles often need supplementary solutions like grouting or dewatering.
3. Construction Process and Speed
Diaphragm Walls
The construction of diaphragm walls is a complex, multi-step process that involves excavating a trench withstrued into the ground to form a continuous, watertight barrier. This process requires specialized equipment like hydraulic grabs and bentonite slurry for trench stability, followed by reinforcement placement and concrete pouring. Due to its complexity, the process is time-consuming. For instance, in the Kathmandu Metro Project, diaphragm wall construction for a single station took several months due to the panel-by-panel approach and quality control measures like sonic integrity checks.
Sheet Pile Walls
Sheet pile wall construction is simpler and faster, involving driving interlocking sheets into the ground using vibratory or hydraulic hammers. This method allows rapid installation, often completed in days or weeks. In the Bagmati River project, sheet piles were installed in just a few weeks, enabling quick riverbank stabilization. The speed of sheet piling makes it ideal for projects with tight timelines or temporary needs, though additional supports like waling beams may be required for stability.
4. Depth Capability
Diaphragm Walls
Diaphragm walls are designed for deep excavations, capable of reaching depths exceeding 100 meters. Their ability to penetrate hard strata and maintain stability makes them suitable for large-scale infrastructure projects. In Nepal’s Dharahara Tower Reconstruction, diaphragm walls were considered for deep foundation work to ensure stability in soft alluvial soils, showcasing their suitability for complex urban projects requiring deep excavations.
Sheet Pile Walls
Sheet pile walls are generally limited to shallow to moderate excavations, typically up to 15 meters, though deeper applications are possible with additional anchoring. In the Melamchi Water Supply Project in Nepal, sheet piles were used for temporary excavations up to 10 meters deep to support pipeline installation. Their limited depth capability makes them less viable for projects requiring significant vertical reach.
5. Environmental and Urban Impact
Diaphragm Walls
Diaphragm walls generate minimal noise and vibration during construction, making them ideal for urban environments with strict regulations. In Kathmandu’s densely populated areas, diaphragm walls minimized disruption to nearby residents and structures during metro construction. However, the use of bentonite slurry poses environmental challenges if not managed properly, requiring careful disposal to avoid contamination.
Sheet Pile Walls
Sheet pile installation produces significant noise and vibration due to pile driving, which can disturb urban communities and nearby structures. In the Bagmati River project, temporary sheet pile walls were chosen despite noise concerns due to their quick installation and reusability. Steel sheet piles are environmentally friendly in terms of material reuse, but their installation can face restrictions in noise-sensitive areas.
The following table summarizes additional details for diaphragm walls and sheet pile walls, focusing on cost, duration, and other key factors:
| Parameter | Diaphragm Wall | Sheet Pile Wall |
|---|---|---|
| Cost (NPR/m²) | 13,400–40,200 (High due to equipment and labor) | 6,700–20,100 (Cost-effective for temporary use) |
| Construction Duration | 1–3 months for a typical project | 1–4 weeks for a typical project |
| Durability | Long-term, corrosion-resistant | Moderate, steel prone to corrosion |
| Reusability | Non-reusable, permanent structure | Reusable, especially steel piles |
| Seismic Resistance | Excellent, ideal for seismic zones like Nepal | Moderate, may deform under dynamic loads |
Applications and Case Studies
Diaphragm Walls
Diaphragm walls are widely used in permanent, high-stakes projects like metro systems, deep basements, and dams. Globally, the Marina Bay Sands in Singapore utilized diaphragm walls up to 50 meters deep to support underground parking in a high-water-table area, showcasing their strength and water-tightness. In Nepal, the Kathmandu Metro’s use of diaphragm walls highlights their effectiveness in soft soils and seismic zones.
Sheet Pile Walls
Sheet pile walls are common in temporary applications, such as riverbank protection, cofferdams, and shallow excavations. In Nepal, the Bagmati River project demonstrated their utility in erosion control, while globally, sheet piles are used in coastal protection projects like the New Orleans Levee System post-Hurricane Katrina. Their versatility makes them a go-to for cost-conscious, short-term projects.
Why Choose Eurasian Infra for Diaphragm Wall and Piling Solutions?
When it comes to executing diaphragm wall projects, Eurasian Infra stands out as a trusted partner, delivering innovative and reliable solutions tailored to Nepal’s unique geotechnical and seismic challenges. With years of experience in deep foundation projects, Eurasian Infra combines cutting-edge technology, such as advanced hydraulic grabs and vibratory hammers, with a skilled team to ensure precision and efficiency.
Our expertise in managing complex soil conditions, like Nepal’s soft alluvial soils, and adherence to environmental standards make them a top choice for projects like metro systems or riverbank stabilization. Eurasian Infra’s commitment to quality control and timely delivery ensures your project meets safety and durability standards.
Contact Eurasian Infra today to discuss your deep foundation needs and secure a robust solution for your next project.
Read More: How Groundbreaking Diaphragm Wall Machines Are Transforming Nepal’s Foundation Technology
