What Are Secant Walls? Key Facts You Should Know

If you’ve ever faced challenges with stabilizing soil or controlling groundwater during excavation, secant walls offer a reliable solution. But what are secant walls exactly? 

They’re retaining walls made from intersecting reinforced concrete piles, where primary piles and secondary piles overlap to form a strong, water-resistant barrier. Known for their increased wall stiffness compared to sheet piles, these walls are ideal for tackling difficult ground conditions, including areas with cobbles and boulders.

With advanced tools like the Rockwheel, secant pile walls are constructed efficiently, even in confined urban spaces. Their combination of steel rebar, structural concrete, and strategic pile overlap creates walls that are more durable than traditional sheet pile walls.

From their construction process to the advantages they offer in excavation, groundwater control, and urban projects, secant walls are setting the standard for innovative engineering solutions. Let’s break down what makes them a cornerstone of modern construction.

Key Takeaways

• Secant pile walls are the go-to solution for stabilizing soil and managing groundwater in tough construction conditions.
• With overlapping primary and secondary piles, secant walls deliver strength, durability, and water resistance.
• Tools like Rockwheels make secant wall construction precise, efficient, and ready for any challenge.

Secant Walls 101: What Are They?

Secant pile walls are retaining structures made by constructing alternating primary and secondary piles that intentionally overlap. This overlapping design creates a strong, water-resistant barrier, making them ideal for stabilizing soil and controlling groundwater in challenging conditions.

Engineered for versatility, secant walls are widely used in basement construction, underground parking garages, tunnel approaches, and waterfront structures. Their ability to perform in difficult ground with cobbles and boulders is enhanced by the use of reinforced materials like steel beams and steel rebar.

Unlike tangent pile walls, which don’t overlap, the overlapping feature of secant walls is crucial for their strength and water resistance. Designed to support deep piles and withstand pressure, secant walls are a cornerstone of modern construction in tight urban spaces and beyond.

How Secant Walls Are Constructed: A Step-by-Step Guide

The construction of secant pile walls is a carefully coordinated process that delivers strong, water-resistant pile walls. From site preparation to reinforcing the structure, each step plays a vital role in the wall's stability and durability.

Step 1: Constructing the guide wall

The process begins with the creation of a guide wall at the surface. This temporary structure ensures precise alignment and consistent spacing between primary and secondary piles. It serves as a critical starting point for achieving the wall’s overlapping design.

Step 2: Drilling and casting primary piles

Primary piles (female piles) are installed first using low-strength concrete. Techniques like Continuous Flight Auger (CFA) drilling or rotary drilling are employed, depending on the project. 

These piles lay the groundwork for the wall and are particularly effective in difficult ground, such as areas with cobbles and boulders.

Step 3: Drilling and casting secondary piles

Once the primary piles are in place, the secondary piles (male piles) are constructed between them. Reinforced with either steel rebar or steel beams, these piles partially overlap the primary piles, creating a solid, interconnected structure that resists soil pressure and groundwater.

Advanced techniques: Hard/soft, hard/firm, and hard/hard

Different methods are used based on project needs:

• Hard/soft: Primary piles use a cement-bentonite mix with reinforced concrete for secondary piles.
• Hard/firm: Low-strength concrete for primary piles and reinforced concrete for secondary piles.
• Hard/fard: Both primary and secondary piles use structural concrete for maximum strength.

Tools & technology

Modern tools are essential for efficient construction. Equipment like rotary piling rigs and low-noisy construction tools streamline the process. 

The Rockwheel, for example, is highly effective for cutting through difficult ground, including cobbles and boulders. Its precision and power make it an invaluable asset for creating the overlapping design of secant walls.

Applications of Secant Walls: Where They Make a Difference

Secant pile walls are a versatile solution for projects requiring soil stabilization and water control. Their overlapping design, reinforced with materials like steel beams or steel rebar, makes them invaluable in various challenging scenarios. Here’s where they shine:

• Excavation support: Secant walls stabilize deep excavations for basements, tunnels, and underground garages by preventing soil collapse. Their interlocking secondary piles are partially cut into primary piles to create a strong, reliable barrier.
• Water control: In high-water-table areas or near bodies of water, secant walls act as a shield against groundwater flow, which keeps excavation sites dry and stable.
• Slope stabilization: On unstable slopes, secant pile walls constructed with reinforced pile walls prevent erosion and landslides, safeguarding nearby structures and infrastructure.
• Urban construction: Secant walls are ideal for urban environments with limited space, offering strong support for deep foundations while protecting adjacent buildings.

Secant Walls vs. Alternatives: Why Choose Secant?

When it comes to retaining structures, secant pile walls stand out for their strength and adaptability. But how do they compare to other options like sheet pile walls or diaphragm walls? Here's a closer look:

Advantages over sheet pile walls

• Increased stiffness: The overlapping design of secant piles provides better stiffness and load-bearing capacity compared to sheet piles.
• Handling difficult ground: Secant pile walls constructed with reinforced pile walls perform exceptionally well in difficult ground conditions, including areas filled with cobbles and boulders.
• Quieter construction: They involve less vibration and noise, making them ideal for urban environments or sensitive areas.

Comparison with diaphragm walls

• Flexible shapes: Secant walls can be formed into various shapes, making them more versatile for complex projects.
• Faster construction: Secant piles are often quicker to install than diaphragm walls, particularly in urban areas where speed is critical.

Limitations to consider

• Cost: Secant walls are generally more expensive than sheet pile walls, which may not be suitable for budget-sensitive projects.
• Precision in deep piles: Achieving perfect verticality in deep piles can be technically challenging, requiring skilled operators and advanced equipment.

Why RockZone Americas Is Your Go-To for Secant Wall Solutions

Facing challenges with cutting accuracy, noise, or vibration in secant pile wall construction? These common obstacles can complicate even the most well-planned projects, but RockZone Americas is here to help.

For over 50 years, we’ve provided innovative solutions with tools like Rockwheels. Designed for precision and efficiency, these drum cutters excel in cutting secondary piles partially cut into primary piles, even in difficult ground cobble boulders. They minimize disruption while maintaining the integrity of your pile walls.

Our product lineup also includes Rockcrushers, Soil Mixers, Rockscreeners, and Cutter Buckets, giving you versatile tools for excavation, trenching, demolition, and more.

Let us help you get the results you need. Call RockZone Americas today or reach out online to learn how our innovative tools can streamline your project.

Conclusion

Innovation in construction is often defined by the ability to solve complex challenges, and secant pile walls exemplify this perfectly. 

Created by constructing overlapping primary and secondary piles, these pile walls manage groundwater, stabilize soil, and perform exceptionally well in difficult ground cobble boulders. Their versatility makes them essential for urban excavations, tunnel approaches, and projects requiring precise foundations.

With tools like Rockwheels from RockZone Americas, contractors can work efficiently while maintaining the strength and integrity of these structures. Precision cutting, reduced noise, and adaptability in challenging conditions make them a perfect match for the demands of secant pile walls constructed in modern environments.

As foundational elements in construction, secant walls are a demonstration of how technology and engineering continue to redefine what’s possible.

Frequently Asked Questions

What is a secant wall?

A secant wall is a type of retaining wall formed by constructing overlapping primary and secondary piles. This design creates a strong, water-resistant barrier that stabilizes soil and manages groundwater, making it essential for excavation and foundation projects in difficult ground conditions.

When to use a secant pile wall?

Secant pile walls are ideal for projects requiring soil stabilization, groundwater control, or support in tight urban spaces. They’re commonly used for deep excavations, tunnels, basements, and areas with high water tables or difficult ground cobbles boulders.

What is the difference between contiguous and secant pile walls?

While both are formed by constructing a series of piles, contiguous pile walls have gaps between piles, providing minimal water resistance. 

Secant pile walls overlap their primary and secondary piles, creating a watertight, stronger structure suited for high-pressure and water-sensitive environments.

What is the difference between a secant wall and a tangent wall?

The key difference is overlap. Secant walls have overlapping primary and secondary piles, forming a continuous barrier. 

Tangent walls, on the other hand, are built with piles that touch but don’t overlap. This makes them less suitable for groundwater control or high-pressure applications.

Is secant piling expensive?

Secant piling can be more expensive than alternatives like contiguous or sheet pile walls due to the materials, precision, and equipment involved. However, its ability to perform in challenging conditions and provide long-term stability often justifies the cost for complex projects.

What is an example of a secant?

In geometry, a secant is a line that intersects a curve at two distinct points. For example, in a circle, a line passing through the circle and cutting it at two points is a secant. 

Similarly, in construction, secant pile walls involve overlapping primary and secondary piles, creating "intersections" to form a continuous, reinforced barrier.