Definition

A secant pile wall is a type of retaining wall constructed by installing a series of overlapping concrete piles. The term “secant” refers to the way in which the piles intersect each other, creating a continuous, interlocked wall. Secant pile walls are used to provide lateral support for deep excavations and to retain soil or water in various geotechnical applications. This construction method is particularly effective in situations where groundwater control or minimal ground movement is critical.

Construction

The construction of a secant pile wall involves several key steps:

• Site Preparation: The construction site is prepared by clearing and leveling the area and setting up drilling equipment.
• Primary Piles Installation: The first step involves drilling and installing primary piles, which are usually unreinforced or lightly reinforced with concrete. These piles are spaced so that there will be overlap with the subsequent piles.
• Secondary Piles Installation: Secondary piles are drilled and installed between the primary piles, cutting into them to create an overlapping, interlocking structure. These secondary piles are typically reinforced with steel and are made of higher-strength concrete.
• Completion: Once all the piles are installed, the wall forms a continuous barrier that can effectively retain soil and control groundwater flow.

Context of Use

Secant pile walls are widely used in various geotechnical engineering applications, including:

• Deep Excavations: Secant pile walls provide robust lateral support for deep excavations, preventing soil movement and ensuring the stability of surrounding structures.
• Water Control: These walls are effective in controlling groundwater ingress, making them suitable for use in below-ground construction, such as basements and tunnels.
• Urban Construction: Secant pile walls are often used in urban areas where space is limited and construction must minimize disruption to nearby structures.
• Temporary or Permanent Structures: Secant pile walls can serve as both temporary excavation support and permanent retaining structures, depending on project requirements.

Advantages

• Effective Groundwater Control: The overlapping nature of secant piles creates a nearly watertight barrier, effectively controlling groundwater and minimizing seepage.
• Strong Structural Integrity: The interlocking design provides significant structural strength, making secant pile walls suitable for deep and challenging excavations.
• Adaptability: Secant pile walls can be constructed in a wide range of soil conditions and can be designed to meet specific project requirements, including load-bearing capacity and groundwater control.

Limitations

• Cost: Secant pile walls are generally more expensive than other types of retaining walls due to the complex construction process and the need for precise equipment and materials.
• Construction Time: The installation of secant pile walls can be time-consuming, especially when precise alignment and overlap of the piles are required.
• Potential for Structural Complexity: The need to overlap and cut into adjacent piles can complicate the construction process, requiring skilled labor and advanced equipment.

Summary

Secant pile walls are a highly effective solution for retaining soil and controlling groundwater in deep excavations and other geotechnical applications. By installing a series of overlapping piles, these walls provide strong lateral support and create a nearly watertight barrier, making them ideal for use in challenging environments, such as urban construction sites and below-ground structures. While secant pile walls offer significant advantages in terms of strength and adaptability, they also come with higher costs and construction complexity, requiring careful planning and execution.