When a building’s foundation begins to shift, settle, or fail, one of the most effective solutions is underpinning—a technique used to strengthen or deepen the existing foundation. This process is critical in both residential and commercial construction, especially in cases of unstable soil, structural upgrades, or changes in load-bearing requirements.
Selecting the right underpinning method requires technical expertise. Specialists like NadeauSDM underpinning engineers evaluate structural conditions, soil profiles, and project objectives to recommend the safest and most cost-effective solutions. But what types of underpinning are commonly used, and why?
1. Mass Concrete Underpinning (Traditional Underpinning)
Overview:
This is the oldest and simplest method, dating back over a century. It involves digging sections beneath the existing foundation and filling them with concrete in stages.
Best For:
- Shallow foundations
- Stable soil conditions
- Low-cost residential repairs
Advantages:
- Simple and proven
- No special equipment needed
- Suitable for small structures
Limitations:
- Labor-intensive and slow
- Disruptive to property use during work
2. Beam and Base Underpinning
Overview:
This technique improves upon mass concrete underpinning by introducing reinforced concrete beams below or in place of the existing foundation. These beams then distribute the load to a series of concrete bases.
Best For:
- Buildings with heavy or uneven loads
- Areas requiring minimal excavation
Advantages:
- Stronger structural support
- More flexible design for complex layouts
- Can be tailored for different soil conditions
Limitations:
- Requires detailed engineering and structural design
- More expensive than mass concrete
3. Mini-Piled Underpinning (Micropiles)
Overview:
This method uses small-diameter piles (typically 100–300 mm) drilled deep into the ground to reach more stable strata. These piles then support a new reinforced concrete foundation.
Best For:
- Sites with variable or poor soil
- Locations with access limitations
- High-rise or sensitive buildings
Advantages:
- Minimal vibration—ideal for historic structures
- High load capacity
- Applicable in restricted spaces
Limitations:
- Requires specialized equipment
- Higher upfront costs
4. Screw Pile Underpinning
Overview:
Helical screw piles are mechanically screwed into the soil and then attached to the building’s foundation. These are particularly popular for lightweight structures or areas with expansive soils.
Best For:
- Fast-track construction
- Buildings in clay-rich soils
- Temporary or modular structures
Advantages:
- Quick installation
- Immediate load-bearing capability
- Minimal soil displacement
Limitations:
- Not ideal for very dense or rocky soils
- Limited load-bearing in some cases
5. Jet Grouting
Overview:
Jet grouting involves injecting high-pressure grout into the soil to form a solid column beneath or around the foundation. This reinforces weak soils and adds stability.
Best For:
- Sites with loose, saturated, or contaminated soil
- Urban locations with adjacent sensitive structures
Advantages:
- High precision
- Strong ground improvement
- Works in almost all soil types
Limitations:
- Technically complex
- Expensive and equipment-heavy
6. Soil Injection (Pressure Grouting)
Overview:
Cementitious or chemical grout is injected under low pressure to fill voids, increase soil density, and lift the foundation.
Best For:
- Minor settlement correction
- Restoring level surfaces
- Stabilizing weak spots
Advantages:
- Non-invasive
- Fast results
- Cost-effective for smaller issues
Limitations:
- Not suitable for extensive damage
- Temporary in some soil conditions
Conclusion
There is no one-size-fits-all approach to underpinning. The optimal method depends on several factors including building design, soil type, load requirements, access limitations, and budget. Expert firms like NadeauSDM underpinning engineers play a crucial role in diagnosing foundation problems and recommending tailored, technically sound solutions.