Spread Footings vs. Aggregate Piers vs. Deep Foundations
A Practical Guide for General Contractors
Choosing the right foundation system comes down to one core question: How good is the soil, and how much load does the building put on it? The answer typically leads to one of three solutions—spread footings, aggregate piers, or deep foundations.
1. Spread Footings: The Simplest Option
Spread footings are the most straightforward and cost-effective foundation type.
- Concrete footings bear directly on near-surface soils
- No specialty equipment required
- Fast and economical
Best fit:
- Competent soils
- Low to moderate loads
The catch:
- If soils are soft or variable, settlement becomes a problem
- You may see cracking, floor movement, callbacks, or worse.
2. Aggregate Piers: The Middle Ground
Aggregate piers improve the soil so spread footings can still be used.
- Columns of compacted stone installed into the ground
- Increase the stiffness of the soil mass
- Reduce total and differential settlement
Key idea:
You are fixing the soil, not bypassing it.
Best fit:
- Soft to moderately weak soils (not terrible, but not great)
- Projects where settlement—not bearing capacity—is the issue
- Typical commercial buildings and parking garages – often in the 3 to 5 story range
Why contractors like them:
- Lower cost than deep foundations
- Often faster than deep foundations
- Keeps a shallow foundation system (simpler forming and layout)
3. Deep Foundations: When You Have to Go Down
Deep foundations transfer load to stronger soils or rock at depth.
- Auger Cast Piles
- Driven piles
- Drilled Shafts
- Micropiles
Best fit:
- Soft soil conditions
- Heavy structural loads
- Tight settlement tolerances
Tradeoffs:
- Higher cost
- Slower production
- More coordination (reinforcing, testing, inspections)
How to Know When Aggregate Piers Make Sense
Think of aggregate piers as the “in-between” solution.
They may be the right choice when:
- A geotech report shows soft clays or loose sands
- Spread footings alone would lead to too much settlement
- Deep foundations feel like overkill for the loads involved
A simple rule of thumb:
- Good soils → Spread footings
- Very poor soils and/or heavy loads → Deep foundations
- Everything in between → Aggregate piers
Real-World Example
- The building pad has 8–15 feet of soft soil
- Loads are typical for a 3 to 5 story commercial building or parking garage
- Spread footings alone = excessive settlement
- Deep foundations = technically works, but expensive
Aggregate piers step in to:
- Stiffen the ground
- Control settlement
- Allow use of standard spread footings
Where Aggregate Piers Don’t Work Well
Be cautious when:
- Soils are extremely soft or organic
- Loads are very high or highly concentrated
- The structure cannot tolerate much settlement at all
In those cases, deep foundations are usually the safer route.
Bottom Line for GCs
- Spread footings are cheapest—but only if soils cooperate
- Deep foundations solve tough problems—but at a cost
- Aggregate piers may hit the best balance of cost, speed, and performance
Need a ground improvement solution tailored to your site?
Contact us to speak with our engineering team and explore how aggregate piers can support your building or parking garage.