Discussion on Underpinning

Key Takeaways on Foundation Underpinning and Structural Stabilization

  • Foundation movement and settlement occur due to factors such as soil dehydration, excess moisture, inadequate pile design, water erosion, and construction issues.
  • Helical Screw Piles provide effective foundation stabilization, relying on end-bearing rather than soil friction, making them suitable for expansive soils where moisture levels fluctuate.
  • The screw pile installation process includes monitoring torque to confirm capacity, with the advantage of lifting structures back to level when used for underpinning.
  • High-quality helical piers require precise manufacturing standards, including stiffness in connections and adherence to load-bearing specifications.
  • Steel Pipe Push Piles use hydraulic jacking, offering benefits in constrained areas and ensuring reliable load testing for each pile.
  • Concrete Drilled Pile Caissons face challenges due to shallow installation depths and dependence on soil friction, making them less suitable for lifting and long-term stability in variable soils.
  • Expanding foam resin injection is generally not recommended for clay-based soils, as it lacks the mechanical lift capacity needed for sustained foundation stability.
  • A structured underpinning process by Abarent Construction involves engineered foundation design, soil data analysis, permit acquisition, and post-installation certification to ensure long-term foundation support.

Professional Assessment of Foundation Stabilization Methods

The following analysis covers various forms of underpinning and foundation stabilization techniques. Every situation requires a thorough structural analysis and investigation process to determine foundation movement causes, remediation priorities, and required processes.

Foundation movement and structural settlement occur in varying degrees. A qualified foundation specialist should assess the movement to determine its severity and provide appropriate remediation solutions. Abarent Construction specializes in foundation assessment and repair. We encourage you to inquire about our qualifications, experience, and technical resources relevant to your project.

Understanding the Causes of Foundation Movement and Settlement

To fully appreciate how foundation movement can be remediated through proper soil mechanics, one must understand the underlying causes. Foundation settlement and movement typically result from one or more of the following factors:

  1. Soil dehydration creating shrinkage of the soils and causing foundation settlement
  2. Soil expansion due to excessive moisture or frost action causing foundation uplift
  3. Existing pile failure due to improper design or installation affecting load-bearing capacity
  4. “Wash Out” of bearing soil due to water erosion and utility line issues
  5. Poor construction with weakened structural components unable to handle required loads
  6. Foundation components bearing on inadequate soil compression strength

While other causes of foundation movement exist, these represent the most common issues in ground stabilization. It is crucial that all relevant geotechnical investigation data be analyzed by an experienced foundation specialist to determine the root cause. Only then can an effective foundation repair plan be developed.

Underpinning Foundations to Stabilize Against Active Soil Layers

A primary solution for foundation stabilization involves underpinning the foundation onto more stable soil layers. The chosen soil layer must provide adequate bearing capacity and structural support for the imposed loads. This layer should lie below the “active soil layer”. The “Active Soil Layer” comprises the soil affected by seasonal moisture variations, typically within the top 20 feet. Drought periods or high precipitation can significantly impact expansive clay or sensitive soils.

Underpinning typically involves installing foundation piles beneath the existing structure. Several pile types offer different approaches to foundation repair. Here are the main underpinning methods used in foundation restoration:

Helical Piers and Screw Pile Systems

Helical piers or screw piles utilize a simple yet effective design. They consist of a steel shaft with an attached helix plate, similar to a single rotation of a screw. Alexander Mitchell invented and patented these foundation reinforcement systems in England around 1830. Analysis of original installations from that era shows maintained structural integrity over time.

Installation Process and Advantages of Screw Piles in Foundation Underpinning

Screw piles are installed using lateral support equipment at low RPM with increasing torque during the foundation reinforcement process. Crews add sections as they drive the pier into the ground. Upon reaching the predetermined depth and installation torques, they cut off the pile and attach a load-bearing plate or bracket. For underpinning applications, this bracket enables foundation leveling through structural support. This lifting capability provides a significant advantage over alternative underpinning systems. Installation requires equipment ranging from portable units to larger machinery like backhoes or skid steers. During installation, technicians monitor hydraulic motor pressure to calculate torque measurements. These measurements correlate directly to installed pile capacity. Reputable companies use installation torque only to confirm engineered pile designs based on comprehensive soil testing.

Key Advantages of Helical Screw Piles: Uplift Resistance and End-Bearing Design

Helical screw piles offer minimal vibration and soil disturbance while providing superior uplift resistance. This resistance proves especially valuable in expansive soil conditions. The helix anchors into competent load-bearing soil, where end-bearing force significantly outweighs shaft friction. The most significant advantage of helical screw piles lies in their design as true end-bearing piles. The system’s load capacity depends on the helix plate rather than unreliable skin friction along the pile shaft. This design creates confidence in foundation stability even when soil moisture levels fluctuate.

Importance of Manufacturing Quality in Helical Pier Systems

Helical pier manufacturers vary in quality standards and specifications. Connection stiffness, pile design, and manufacturing process adherence play crucial roles in structural integrity. Helical Pier Systems (HPS), our manufacturing partner, maintains rigorous quality control in their research and production processes. Since 1977, HPS has provided engineering, manufacturing, equipment design, and distribution services for helical piling products.

Steel Pipe Push Pile Systems

Steel pipe push piles utilize hydraulic jacking systems that drive steel pipes into the ground using the existing foundation as a reaction force. The soil-pipe friction accumulates until it exceeds the applied load capacity. These foundation repair methods excel in confined spaces where individual load testing ensures reliability.

Advantages of Abarent Construction’s Proprietary Push Pile System

Abarent Construction has developed an advanced push pile system that exceeds industry requirements. Our system offers these key benefits:

  • Installation of concentric push piers with preloaded design loads prevents eccentric loading of compromised foundations
  • Specialized pier brackets bridge foundation discontinuities
  • Site-specific proof load calibration ensures proper installation verification
  • Local design optimization for Edmonton’s unique geological conditions
  • Compliance with Alberta Building Code specifications including minimum shaft diameter requirements
  • Enhanced corrosion control through stainless steel components and grout encasement
  • Installation without on-site welding eliminates fire risks and toxic emissions
  • Complete engineering oversight by an APEGA Permitted Firm with comprehensive quality control

Concrete Drilled Pile Caissons

Concrete drilled pile caissons represent a deep foundation system utilizing fresh concrete and reinforcing steel in drilled shafts. Installation involves drilling, reinforcement cage placement, and concrete pouring. In underpinning applications, crews typically employ a fabricated A-Frame against the structure to hydraulically drill holes using specialized augers.

Critical Limitations of Concrete Drilled Pile Systems

  1. Drilling constraints typically limit depths to 25 feet, often insufficient for addressing underlying soil issues
  2. System reliability depends on soil friction along the pile surface, problematic in moisture-variable conditions
  3. Limited lifting capability restricts remediation options
  4. Challenges in load testing increase uncertainty in performance predictions
  5. Eccentric installation may exacerbate vertical displacement issues

Expanding Foam Resin Limitations

Some companies offer proprietary foam resin injection for foundation stabilization and lifting. However, mechanical lifting methods remain necessary for effective elevation adjustment. In expansive clay environments where dehydration causes settlement, soil densification through injection may not prevent further movement. While this method might suit granular soils or permafrost conditions, our experience shows limited success in typical foundation applications.

Abarent Construction’s Comprehensive Underpinning Process

After extensive research into various piling systems, Abarent Construction selected helical screw piles as optimal for our climate and soil conditions. Our structured approach includes:

1. Comprehensive structural analysis and engineered design encompassing:

  • Detailed crack pattern analysis for underpinning projects
  • Strategic pile type selection
  • Structural load calculations and distribution analysis
  • Pile spacing optimization based on foundation specifications
  • Geotechnical investigation through soil boring analysis
  • Engineer-designed pile specifications based on load requirements
  • Professional engineered project plans

Important Information about Foundation Underpinning
  1. A typical foundation underpinning project takes between 5 to 10 working days, depending on the project’s scope and complexity.
  2. Regular foundation inspections should occur every 3-5 years for preventive maintenance.
  3. Foundation underpinning can be performed in winter conditions, though additional preparations and precautions are necessary.
  4. Most foundation repairs carry a warranty period of 25-30 years when properly installed by certified professionals.
  5. Foundation movement exceeding 1 inch over 50 feet requires professional evaluation.
  6. Standard homeowner’s insurance typically covers foundation repairs only if damage results from covered perils.
  7. Professional foundation stabilization typically requires one support point every 6-8 feet along the foundation’s length.
  8. Properly installed foundation underpinning solutions can last over 75 years.
  9. Approximately 80% of foundation problems stem from soil-related issues.
  10. Foundation stabilization typically requires 1.5 to 2 load-bearing points per linear foot of affected foundation.

Key Takeaways for Understanding Foundation Stabilization Methods

  • Foundation movement requires immediate professional assessment to prevent further structural damage.
  • Helical screw piles provide superior stability in Edmonton’s variable soil conditions.
  • Proper installation monitoring and torque measurements ensure optimal foundation support.
  • Abarent Construction specializes in engineered foundation solutions with documented results.
  • Regular foundation inspections help prevent costly structural repairs.
  • Professional installation certification guarantees long-term foundation stability.
  • Abarent’s comprehensive approach ensures lasting foundation repair solutions.

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