Secant piles are a type of deep foundation element used in civil engineering and construction. They are formed by constructing overlapping reinforced concrete piles, creating a continuous wall. The term “secant” refers to the fact that each pile is constructed to intersect with or partially overlap its neighboring piles. This design creates a continuous barrier that is particularly useful in deep excavation projects, providing structural support and preventing soil or water ingress.
Here are key features and uses of secant piles:
Construction Process:
- Alternate Construction: In a secant pile wall, the primary piles (female piles) are constructed first, leaving gaps or voids. Subsequently, secondary piles (male piles) are constructed in the voids, overlapping with the primary piles.
- Reinforcement: Both primary and secondary piles are typically reinforced with steel to enhance their structural strength and integrity.
- Grout or Concrete Filling: After construction, the voids between the primary and secondary piles may be filled with grout or concrete to increase the wall’s overall impermeability.
Key Components and Design:
- Overlap: The degree of overlap between adjacent piles can be adjusted based on design requirements and subsurface conditions. The overlap is chosen to ensure sufficient structural integrity and to control soil or water infiltration.
- Diameter and Spacing: The diameter and spacing of the piles are also design considerations and depend on factors such as soil conditions, the depth of excavation, and the structural requirements of the wall.
Advantages and Uses:
- Excavation Support: Secant pile walls are commonly used for deep excavations in urban areas, providing lateral support to prevent soil collapse.
- Waterproofing: The construction of secant piles with grout or concrete filling between the overlapping piles enhances the wall’s impermeability, making it suitable for preventing water ingress in below-grade structures.
- Adjacent Structures: Secant piles are often used in close proximity to existing structures where minimal ground movement is critical.
- Tunneling: They can be employed in tunneling projects to provide structural support and control ground movement.
Applications:
- Basement Construction: Secant pile walls are commonly used in the construction of deep basements for buildings.
- Deep Excavations: They are employed in projects where deep excavations are necessary, such as for underground parking structures or subway stations.
- Retaining Walls: Secant pile walls can act as retaining walls in situations where the terrain requires additional structural support.
In summary, secant piles are a versatile solution for providing structural support and stability in deep excavation projects. Their ability to create continuous walls with controlled overlap makes them effective in preventing soil or water ingress, and their use is often favored in urban environments with limited space and proximity to existing structures.