---
title: "Deep Foundation Systems Piles Caissons | AVANORTH"
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"og:title": "Deep Foundation Systems Piles Caissons"
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AVANORTH Home
**Construction Tips**·April 21, 2026· 4 min read
# **Deep Foundation Systems: Piles and Caissons Explained**
When soil near the surface cannot support a structure, deep foundations transfer loads to competent bearing layers below. Understanding pile types, installation methods, and load testing ensures a reliable foundation.
**AVANORTH Team**
AVANORTH Construction
Shallow foundations (footings, mats) work when competent soil or rock exists near the surface. But in many sites across Ontario, the upper soil layers are too weak, too compressible, or too variable to support a structure with shallow foundations. In these conditions, deep foundations transfer the building loads through the weak upper layers to competent bearing material at depth. The two main categories are driven piles and drilled shafts (caissons).
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## When Are Deep Foundations Needed?
- **Soft or compressible soil:** Thick deposits of clay, silt, peat, or organic soil that would settle excessively under shallow foundation loads
- **High water table:** Where excavation for shallow foundations is impractical without extensive dewatering
- **Heavy structural loads:** High-rise buildings, bridges, and industrial structures that exceed shallow foundation bearing capacity
- **Scour conditions:** Bridge piers in rivers where soil around the foundation can be eroded by water flow
- **Seismic conditions:** Liquefiable soils where deep foundations provide stability during earthquake loading
- **Variable soil conditions:** Where the bearing layer depth varies significantly across the site
---
## Pile Types
| Pile Type | Material | Capacity Range | Maximum Length | Best For |
| --- | --- | --- | --- | --- |
| Steel H-pile | Structural steel (HP shapes) | 500-2,000 kN | 40+ m (spliced) | End bearing on rock, high capacity |
| Steel pipe pile | Steel pipe (open or closed end) | 500-5,000+ kN | 50+ m | Marine, heavy loads, battered piles |
| Precast concrete | Reinforced or prestressed concrete | 500-3,000 kN | 30 m | Friction piles in medium soils |
| Timber | Treated wood (Douglas fir, Southern pine) | 200-500 kN | 15-20 m | Light structures, temporary, marine |
| Helical (screw) pile | Steel shaft with helical plates | 100-1,500 kN | 25 m | Light to medium loads, fast install, no vibration |
| Micropile | Steel casing + grout | 300-2,000 kN | 30+ m | Limited access, underpinning, seismic retrofit |
---
## Driven Piles
### Installation Process
1. **Pile driving rig:** A crane-mounted or track-mounted hammer drives piles into the ground by repeated impact
2. **Hammer types:** Diesel hammer (most common), hydraulic hammer (quieter, more controllable), vibratory hammer (for steel sheet piles and pipe piles in granular soil)
3. **Driving criteria:** Piles are driven to a specified depth or a specified resistance (blows per 25 mm of penetration). The geotechnical engineer establishes the driving criteria based on the design capacity.
4. **Pile Dynamic Analysis (PDA):** Sensors on the pile head measure force and velocity during driving. Computer analysis (CAPWAP) calculates the actual capacity of the pile from the dynamic measurements.
### Advantages and Disadvantages
| Advantages | Disadvantages |
| --- | --- |
| Fast installation (10-30 piles per day) | Noise and vibration (may damage adjacent structures) |
| Capacity verified by driving resistance | Cannot penetrate boulders or very dense layers |
| Displaces soil (improves density for friction piles) | Limited to straight alignment (no belling) |
| No spoils to remove | Splicing required for long piles |
---
## Drilled Shafts (Caissons)
### Installation Process
1. **Drill rig:** A large rotary drill bores a hole into the ground. Temporary or permanent casing may be used to hold the hole open in unstable soil.
2. **Excavation:** Soil is removed by the auger and inspected. The engineer verifies that the bearing layer has been reached.
3. **Belling (optional):** At the bottom of the shaft, the drill can widen the base (bell) to increase bearing area. Used in cohesive soils.
4. **Reinforcing cage:** A pre-assembled rebar cage is lowered into the hole.
5. **Concrete placement:** Concrete is placed by tremie (a pipe that delivers concrete to the bottom, displacing water or slurry). Self-compacting concrete (SCC) is often used for drilled shafts.
### Advantages and Disadvantages
| Advantages | Disadvantages |
| --- | --- |
| Very high capacity (10,000+ kN for large diameters) | Slower installation than driven piles |
| Can penetrate boulders and rock | Spoils must be removed and disposed |
| Low noise and vibration | Quality depends on construction procedure (concrete placement) |
| Can be belled for increased base bearing | Groundwater management may be complex |
| Direct inspection of bearing soil | Higher cost per pile |
---
## Load Testing
| Test Type | Method | Purpose |
| --- | --- | --- |
| Static load test | Dead weight or reaction piles apply load to the pile head incrementally | Direct measurement of ultimate capacity |
| Dynamic load test (PDA) | High-strain impact with force/velocity sensors | Rapid capacity estimate during driving |
| Bi-directional (O-cell) test | Hydraulic jack built into the shaft expands against resistance | High-capacity drilled shaft testing |
| Integrity test (PIT) | Low-strain impact measures wave reflections | Detect defects (necking, inclusions) |
> **AVANORTH Practice:** Deep foundations are only as reliable as their design and installation. We work with experienced geotechnical engineers and pile contractors. Every deep foundation project on our sites includes driving records or shaft inspection logs, PDA testing on a representative sample of piles, and strict concrete placement procedures for drilled shafts. The foundation is the most critical element of any building, and we invest the effort to get it right.
#deep-foundation #piles #structural
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