Definition

A diaphragm wall is a type of deep, cast-in-place retaining wall made of reinforced concrete. It is constructed in situ and is used to provide lateral earth support for deep excavations, as well as to create permanent underground structures such as basements, tunnels, and shafts. Diaphragm walls are particularly effective in urban environments where space is limited, and noise and vibration must be minimized during construction. They are also used in areas with high groundwater levels due to their ability to form a nearly watertight barrier.

Construction

The construction of a diaphragm wall involves several key steps:

• Site Preparation: The construction site is prepared by clearing and leveling the area, followed by the installation of guide walls to ensure alignment.
• Trench Excavation: A narrow trench is excavated to the desired depth using specialized equipment such as clamshells or hydraulic grabs. The trench is typically supported by a bentonite or polymer slurry to prevent collapse.
• Reinforcement Installation: Steel reinforcement cages are lowered into the trench to provide the necessary structural strength for the wall.
• Concrete Pouring: The trench is filled with concrete from the bottom up, displacing the supporting slurry. The concrete forms a continuous, reinforced concrete wall as it cures.
• Joint Formation: Diaphragm walls are typically constructed in panels, with joints between the panels to accommodate movement and prevent cracking. These joints may be sealed to enhance watertightness.

Context of Use

Diaphragm walls are commonly used in various geotechnical and structural engineering applications, including:

• Deep Excavations: Diaphragm walls provide robust lateral support for deep excavations, ensuring the stability of the surrounding structures and preventing soil movement.
• Underground Structures: These walls are used to form the permanent walls of underground structures such as basements, tunnels, and underground parking facilities.
• Water Control: Diaphragm walls are effective in controlling groundwater, making them ideal for use in projects where water ingress must be minimized.
• Urban Construction: Due to their low noise and vibration during construction, diaphragm walls are suitable for urban environments where disturbance to nearby structures must be minimized.

Advantages

• High Structural Strength: Diaphragm walls provide significant structural strength, making them suitable for supporting large loads and deep excavations.
• Effective Groundwater Control: These walls form a nearly watertight barrier, making them ideal for projects with high groundwater levels or where water ingress is a concern.
• Minimal Disruption: The construction process generates minimal noise and vibration, making diaphragm walls well-suited for use in densely populated urban areas.
• Permanent Solution: Diaphragm walls can serve as both temporary excavation support and permanent structural walls, reducing the need for additional construction phases.

Limitations

• High Cost: Diaphragm walls can be expensive to construct due to the specialized equipment and materials required, as well as the complexity of the construction process.
• Longer Construction Time: The construction of diaphragm walls is time-consuming, particularly due to the need for careful excavation, reinforcement installation, and concrete curing.
• Complexity: The construction process is complex and requires skilled labor and advanced engineering techniques, making diaphragm walls less suitable for small or straightforward projects.

Summary

Diaphragm walls are a highly effective and versatile solution for providing lateral earth support and forming permanent underground structures in challenging environments. Constructed from reinforced concrete, these walls offer significant structural strength and watertightness, making them ideal for deep excavations and projects in areas with high groundwater levels. While diaphragm walls offer many advantages, including minimal disruption during construction and the ability to serve as permanent structures, they also come with higher costs and construction complexity, requiring careful planning and skilled execution.