Secant pile walls are a widely used geotechnical solution for excavation support, groundwater control, and slope stabilization. They provide a structurally robust and watertight retaining system, making them ideal for deep excavations in challenging soil conditions and urban environments where space constraints limit traditional shoring methods.
This article delves into the design principles, construction methodologies, advantages, and key considerations associated with secant pile walls. It is intended for specialized civil engineers, construction companies, and geologists looking to enhance their understanding of this important technology.
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Design of Secant Pile Walls
The design of secant pile walls involves several essential factors to ensure their efficiency and structural integrity. These include pile arrangement, reinforcement, pile spacing, diameter, and verticality control.
Pile Arrangement:
Secant pile walls consist of alternating primary (unreinforced) and secondary (reinforced) piles that overlap to form a continuous barrier. The typical overlap is around 75–150 mm (3–6 inches) to ensure stability and water tightness.
Primary piles: Usually made of unreinforced concrete or a weak cement-bentonite mix.
Secondary piles: Constructed between primary piles, cutting into their edges and reinforced with steel rebars or steel I-beams for structural strength.
Reinforcement Considerations:
In North America, steel I-beams are commonly used.
In Europe and South America, reinforced concrete secant piles are the preferred option.
Reinforcement depends on structural loads, lateral earth pressure, and depth of excavation.
Pile Spacing and Diameter
Typical pile diameters: Range from 600 mm to 1200 mm (24 to 48 inches).
Pile spacing is designed to ensure adequate overlap, preventing water seepage and maintaining rigidity.
Secant pile walls offer higher stiffness and deformation control than traditional sheet piling.
Verticality and Alignment:
Achieving and maintaining precise verticality is crucial to preventing structural gaps. Deviation should be kept within 0.5% of pile depth to maintain integrity. Advanced drilling techniques, CFA (Continuous Flight Auger) or rotary drilling, and real-time monitoring ensure proper alignment.
Construction Methodology of secant pile walls
The construction of secant pile walls follows a step-by-step process to ensure quality and performance.
Site Investigation and Planning:
A comprehensive geotechnical study is conducted to assess:
Soil conditions
Groundwater levels
Adjacent structures’ influence
Guide Walls
Temporary guide walls are constructed to maintain pile alignment and verticality.
Drilling and Pile Installation
Drill primary piles and fill them with unreinforced concrete or a cement-bentonite mix.
Allow the primary piles to harden sufficiently.
Drill secondary piles, cutting into primary piles to ensure overlap.
Place reinforcement (steel beams or rebars) into the secondary piles.
Concrete placement using tremie pipes to prevent segregation and voids.
Quality Control and Monitoring
Non-destructive testing (ultrasonic or sonic logging) verifies concrete integrity.
Real-time verticality monitoring ensures precision.
Water-tightness tests help confirm seepage control effectiveness.
Advantages of Secant Pile Walls
Secant pile walls offer several key benefits:
Structural and Design Flexibility
Can be adapted to various complex geometries.
Suitable for deep excavations in constrained urban spaces.
High Stiffness and Strength
Provides greater resistance to lateral loads compared to sheet piles.
Reduces ground movement and adjacent structure settlement risks.
Suitability for Challenging Ground Conditions
Effective in soft soils, mixed ground, and high groundwater tables.
Can be installed in hard soils with cobbles and boulders.
Groundwater Control
Overlapping piles form a semi-permeable or fully waterproof barrier.
Reduces dewatering needs in deep excavations.
Noise and Vibration Reduction
Less noise and vibration compared to driven pile walls, making it suitable for urban settings.
Challenges and Considerations
While secant pile walls offer many advantages, they also present challenges that must be carefully addressed in design and construction.
Verticality Tolerance Issues
Achieving precise verticality is difficult, especially for deep piles.
Advanced equipment and monitoring systems mitigate risks.
Water Tightness Limitations
Full waterproofing is difficult at pile joints.
Additional sealing techniques (such as grouting or membrane barriers) may be required.
Cost Considerations
More expensive than sheet pile walls due to material and installation complexity.
Requires highly skilled labor and specialized equipment.
Applications of Secant Pile Walls
Secant pile walls are widely used in civil and geotechnical engineering projects, including:
Excavation Support
Retaining systems for deep basements, metro stations, and tunnels.
Slope Stabilization
Used in steep slopes or areas prone to landslides and soil erosion.
Groundwater Cutoff Walls
Installed to prevent groundwater infiltration in underground structures.
Urban Construction Projects
Frequently used in dense urban areas where excavation affects adjacent structures.
Processing
Once secant piles are installed, their pile heads must be treated to prepare them for the next phase of construction. This process, known as pile breaking or pile head treatment, involves:
Removing excess concrete above the cut-off level.
Ensuring a flat, level surface for structural load transfer.
Avoiding damage to reinforcement bars.
Pile head treatment is a crucial step in foundation works and must be executed efficiently to maintain the structural integrity of secant pile walls.
Secant pile walls are a versatile, strong, and reliable solution for excavation support, groundwater control, and slope stabilization. Their design and construction require precision, advanced techniques, and careful planning. Understanding their benefits, challenges, and applications enables civil engineers and construction companies to implement efficient and structurally sound retaining solutions.
With secant pile walls installed, the next critical phase is pile head treatment and breaking, ensuring proper foundation readiness for superstructure construction.
Pile breaking of secant pile walls
Brextor® is an efficient, safe and high-quality method for breaking piles. With this method, not only single piles, but also all types of pile walls (tangent, secant or contiguous) are processed gently by machine. The work is done by one person and one machine. The weather conditions have no influence here.
Brextor® offers the following advantages:
🏗 Increased construction quality
Perfect pile breaking without cracks in the pile body or spalling on the pile outer skin, no bent or torn reinforcements and a height accuracy of +/- 1cm.
💵 Reduced construction costs
The demolition material consists of 80% gravel 0-30mm and can therefore be reused directly on the construction site. In addition, Brextor® requires less working space than conventional mining methods. This means that not only expenses for transportation and disposal incl. fees are saved, but the purchase and supply of replacement material is also eliminated. Furthermore, the preparatory work eliminates the need for a separating diamand cut at the final extraction level and the cleaning effort is massively lower than with conventional extraction methods.
⏱ Shortened processing time
For example, a pile with a diameter of 1 m and a height of 1 m can be processed within 40 minutes. A daily output of up to 16 piles is possible. In addition, Brextor® provides reliable performance and therefore increased planning security.
♻️ Environmentally friendly
With Brextor®, the demolition material (80% gravel 0-30mm) can be reused directly on the construction site. Brextor® also requires less working space. This saves excavation and replacement material. By reusing the demolition material directly on the construction site and saving on excavation and replacement material, transportation can be saved. In addition, landfills are less polluted.
👷 Increased health & safety at work
No heavy physical labor is required for pile processing, which massively reduces the risk of health hazards such as HAVS syndrome. Brextor® also avoids working in danger zones.
Find out more about Brextor® here:
Contact us for more information and find out how you can benefit from this revolutionary pile breaking method.
Call us on +41 41 495 05 20 or send an e-mail to info@brc.swiss. We look forward to working with you and taking your projects to the next level.The diameter of a bored pile is a key feature that significantly influences the load transfer of structures. A larger diameter can significantly improve the load-bearing capacity of the foundation soil, as it provides a larger bearing surface and distributes the loads more efficiently to deeper, more stable soil layers.
The diameter is determined depending on the structural requirements and the ground conditions. Once the shaft has been drilled, it is backfilled with concrete or reinforced concrete, often with reinforcement to ensure additional stability