A diaphragm wall is a reinforced concrete wall that is cast in situ (on-site) using a trench excavation technique. It is typically used as a structural element in underground construction projects, providing support and stability to deep excavations. Diaphragm walls are commonly employed in projects such as deep basements, underground structures, tunnels, and as retaining walls in areas with challenging soil or water conditions.
Here are key features and uses of diaphragm walls:
Construction Process:
- Trench Excavation: A trench is excavated to the desired depth and width using special equipment such as grabs or clamshells.
- Reinforcement Installation: Steel reinforcement cages are lowered into the trench. The reinforcement is usually in the form of vertical bars and sometimes includes horizontal reinforcement to enhance the structural integrity of the wall.
- Concrete Placement: High-strength concrete is poured into the trench, displacing the slurry (usually bentonite or polymer-based) that stabilizes the trench during excavation.
- Slurry Wall Technique: The use of a slurry during excavation helps support the walls of the trench, preventing collapses. The slurry is usually maintained until the concrete has set.
Key Components and Design:
- Thickness: The thickness of diaphragm walls can vary based on design requirements but is typically in the range of 0.6 to 1.5 meters.
- Reinforcement: Diaphragm walls incorporate reinforcement to provide additional strength and ductility. Reinforcement cages are designed based on the specific structural requirements of the wall.
Advantages and Uses:
- Deep Excavations: Diaphragm walls are particularly suitable for deep excavations where the lateral support of the soil is critical to prevent collapse.
- Waterproofing: Due to the construction process involving a slurry wall, diaphragm walls can be relatively impermeable, providing effective waterproofing for underground structures.
- Stability: Diaphragm walls offer high structural stability, making them suitable for retaining large volumes of soil or resisting lateral earth pressures.
- Adjacent Structures: They are used in urban areas where the proximity of existing structures makes traditional excavation methods challenging.
Applications:
- Basement Construction: Diaphragm walls are commonly used in the construction of deep basements for buildings.
- Tunneling: In tunnel construction, diaphragm walls may be used to provide structural support and control groundwater ingress.
- Underground Structures: They are used for the construction of underground structures such as subway stations, parking garages, and utility tunnels.
In summary, diaphragm walls are a versatile and effective solution for providing structural support in deep excavations, especially in urban areas where space constraints and the need for waterproofing make them a preferred choice. Their ability to resist lateral soil pressures and provide stability makes them a valuable element in various civil engineering and construction projects.