Secant Pile Walls
Secant pile walls are interlocking drilled concrete piles that create continuous structural walls with groundwater cutoff capability for deep excavations in saturated soils and urban environments.
Understanding Secant Pile Walls
Secant pile walls consist of overlapping drilled shafts that interlock to form a continuous underground wall. Primary (female) piles are installed first at wider spacing, then secondary (male) piles are drilled between them, cutting into the still-curing primary piles to create a watertight structural barrier.
This construction sequence creates walls that simultaneously provide structural earth retention and groundwater cutoff—critical for deep excavations below the water table. Secant walls can be designed as temporary shoring or integrated into permanent building foundations, making them cost-effective for projects where the wall becomes part of the final structure.
This technique is used in our services for:
Drilling 
Shoring & Excavation Support Typical Applications
How It Works
Our proven methodology ensures consistent, high-quality results for every installation.
Survey and Guide Wall Construction
Survey pile locations precisely—secant walls require tight tolerances. Construct concrete guide walls (typically 12-18 inches deep) to align drilling equipment and maintain pile spacing accuracy throughout installation.
Primary Pile Drilling
Drill primary (female) piles at every other location using casing or slurry to maintain hole stability. Primary pile spacing equals the design overlap plus secondary pile diameter. Install reinforcement if specified.
Primary Pile Concrete
Place concrete in primary piles using tremie method if below water table. For soft secant walls, use low-strength concrete (1,000-2,000 psi) in primaries to facilitate cutting. For hard secant walls, use structural concrete throughout.
Secondary Pile Drilling
After primary pile concrete reaches design strength for cutting (typically 12-48 hours), drill secondary (male) piles overlapping into both adjacent primaries. The drill cuts through the primary pile concrete to create the interlock.
Secondary Pile Reinforcement and Concrete
Install steel reinforcement cages in secondary piles. Place structural concrete. Secondary piles carry the structural loads while overlaps provide continuity and water cutoff.
Wall Completion and Excavation
Allow secondary piles to cure. Begin excavation in controlled lifts, installing tiebacks or bracing at design elevations. Expose and clean wall face. Apply waterproofing or architectural finish if required.
Key Advantages
Watertight Excavation Support
Secant pile walls create continuous barriers that cut off groundwater flow. Excavate below the water table without extensive dewatering—critical for deep basements, tunnels, and waterfront construction.
Permanent Foundation Integration
Unlike temporary shoring, secant walls can serve as permanent basement walls. The structural concrete and reinforcement become part of the building, eliminating the cost of separate foundation walls.
Difficult Ground Capability
Drilling handles conditions that stop sheet pile driving: cobbles, boulders, buried debris, and variable soil layers. Secant piles install successfully where other wall systems fail.
Low Vibration and Noise
Rotary drilling creates minimal vibration compared to pile driving or vibratory sheet pile installation. Essential for urban sites near sensitive structures, hospitals, and historic buildings.
Deep Wall Capability
Secant walls can extend 100+ feet deep with appropriate equipment. For the deepest excavations—metro stations, high-rise basements, tunnels—secant walls provide both depth and structural capacity.
Technical Considerations
Soil/Rock Conditions
Secant walls work in nearly all soil conditions including cohesionless sands, soft clays, and grounds with obstructions. Hard secant walls (structural concrete in all piles) handle the most demanding conditions. Rock socketing extends capacity into bedrock.
Groundwater
Primary application is groundwater cutoff. Proper overlap and concrete quality ensure watertight construction. Minor seepage at joints can be addressed with post-construction grouting. Combine with dewatering only for exceptional inflows.
Load Capacity
Wall structural capacity depends on pile diameter, reinforcement, and concrete strength. Secondary piles carry primary structural loads. Tiebacks or bracing required for walls over 20-25 feet depending on soil conditions and surcharge.
Spacing
Pile spacing equals secondary pile diameter minus overlap. Typical 36-inch piles at 33-inch centers create 3-inch overlaps. Closer spacing (more overlap) increases waterproofing reliability; wider spacing reduces cost.
Installation Method
Kelly bar drilling with casing in unstable ground, or slurry-supported drilling in stable conditions. Secondary pile drilling uses rock augers or core barrels to cut through primary pile concrete. Guide walls are critical for tolerance control.
Equipment Used
- Large-diameter drill rigs (rotary drilling)
- Kelly bar systems with casing
- Rock augers and core barrels
- Concrete tremie equipment
- Reinforcement cages and handling equipment
- Guide wall formwork systems
Limitations
- Requires large drill rig access (significant overhead clearance)
- Higher cost than soldier pile walls in simple conditions
- Verticality tolerance critical—deviations compromise interlock
- Concrete timing coordination between primary and secondary piles
- Limited curve radius capability
Technical Specifications
System Variations
Soft Secant Wall
Primary piles use low-strength concrete (1,000-2,000 psi) that is easily cut by secondary pile drilling. Most economical for temporary excavation support where permanent wall integration is not required.
Best For:
- Temporary construction excavations
- Sites with no permanent wall requirement
- Cost-sensitive projects
Hard Secant Wall
Both primary and secondary piles use structural concrete (4,000+ psi). Primary piles are reinforced. Creates the strongest wall for permanent applications and high structural demands.
Best For:
- Permanent basement walls
- High-load applications
- Deep excavations with significant surcharge
Firm Secant Wall
Primary piles use medium-strength concrete (2,500-3,500 psi) without reinforcement. Intermediate option balancing drilling ease with improved structural performance.
Best For:
- Moderate-depth basements
- Permanent walls with lower load demands
- Balanced cost-performance requirements
Secant Tangent Hybrid
Secant configuration (overlapping) at the water table with tangent (touching but not overlapping) configuration above. Reduces cost while maintaining groundwater cutoff where needed.
Best For:
- Sites with shallow water table
- Cost optimization on deep walls
- Conditions where full-depth waterproofing not required
Integration With Other Systems
Tieback Anchors
Tieback anchors provide lateral support for deep secant walls. Anchors are installed through secondary piles or between pile pairs at design elevations as excavation progresses.
Learn More
Micropiles
Micropiles underpin adjacent structures before secant wall construction and excavation. Combined systems protect existing foundations during deep urban excavations.
Learn More
Pressure Grouting
Post-construction grouting seals minor joint seepage in secant walls. Permeation grouting can also improve soil behind walls in loose ground conditions.
Learn More Pressure Grouting
Grout columns can supplement secant walls at corners, connections, or areas where drilling access is limited. Combined systems address complex site geometries.
Learn MoreExample Project Types
- High-rise building foundations
- Underground parking structures
- Metro and transit stations
- Tunnel shafts and portals
- Waterfront development
- Industrial facility basements
- Hospital and institutional construction
- Contaminated site containment
Our Work in Action
Why Choose Rock Supremacy for Secant Pile Walls
Large-Diameter Drilling Expertise
Our drilling teams operate the equipment and possess the skills needed for precision large-diameter pile installation. Tight tolerances and proper sequencing are essential for successful secant walls.
Integrated Wall Systems
We provide complete secant wall construction including drilling, reinforcement, concrete placement, and tieback installation. One team delivers the entire wall system.
Difficult Ground Experience
Our crews have installed secant walls through cobbles, boulders, and variable conditions that stop other contractors. When ground conditions are challenging, experience matters.
Quality Control
Secant wall performance depends on execution quality. We monitor verticality, concrete placement, and timing to ensure the watertight, structural walls your project requires.
Urban Construction Capability
Low-vibration drilling and professional site management make us effective partners for sensitive urban projects near existing structures and active facilities.
Our Work
See how we've applied this technique and others to solve real-world geotechnical challenges.
Bingham Canyon Mine Support
Highwall stabilization in one of the world's largest open-pit mines to ensure safe ongoing extraction.
I-70 Corridor Stabilization
Installed 50,000 sq ft of high-tensile mesh and performed extensive scaling after a major weather event.
Lava Hot Springs Slope Stabilization
Multi-phase slope stabilization project protecting the historic hot springs resort and Highway 30 from an active landslide.
Secant Pile Walls FAQ
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Related Techniques
Explore other engineering methods we use to deliver comprehensive geotechnical solutions.
H-Pile Walls
H-pile walls use driven or drilled steel H-beams with lagging between flanges to create robust earth retention systems for deep excavations, bridge abutments, and permanent retaining structures.
Micropiles
Micropiles are small-diameter, high-strength deep foundation elements used to transfer loads into competent ground. Their versatility makes them ideal for underpinning, slope stabilization, and situations with limited access or difficult geology.
Pressure Grouting
Pressure grouting strengthens ground, fills voids, and reduces water infiltration by injecting grout into soil, fractured rock, or void spaces. This technique supports slope stabilization, foundation improvement, landslide remediation, and structural repairs.
Soldier Pile Walls
Soldier pile walls are proven earth retention systems for stabilizing deep excavations and steep slopes. Steel beams installed at intervals with lagging placed between them provide flexible, economical support that adapts to site constraints.