The three most common ways of underpinning a home foundation in need of repair are steel piers, pre-cast concrete cylinders (or push piers) and the drilled bell bottom piers. Each method has it’s pros and cons and affects the cost of foundation repair.
Steel piers can be shoved into the ground deeper than concrete cylinders because they have a smaller diameter. Using concrete cylinders provides more surface area for the “skin friction” concept of engineering. The drilled bell bottom piers is the oldest method of foundation repair and still widely used although this method takes the most time.
I’m watching TV the other day and here comes a commercial for the Olshan foundation company pitching a combination of steel and concrete cylinders for a foundation fix.
Here’s the claim:
- The steel segments provide added depth. The concrete sections offer greater bearing area which provides better support.
- The larger diameter concrete cylinder provides more surface area for better support. The smaller diameter steel segments penetrate deeper into soils not affected by weather.
- Cable Lock™ ST penetrates deeper into tough soil conditions. Once a foundation repair piling is driven past the weather affected zone, it provides better support.
- The combination of concrete and steel adds up to a repair that is deeper and stronger.
So basically steel piers are pushed into the ground first right at the edge of your concrete slab foundation. Then a transition segment is added to go between the steel and concrete cylinders. The cylinders are stacked upon each other until they almost reach the foundation, creating a piling. A pile cap is added to the top of the stack where two sets of spacers can be used to transfer the load of the foundation to the new piers. It’s kind of hard to describe, but you can see a diagram of it on the Olshan website.
If you choose the ST Plus system, a steel cable is strung through the entire pier. The cable is used to confirm the depth of the steel segments and align the concrete cylinders.
The structural engineer I hired to inspect my foundation is not a big fan of the concrete cylinder method of foundation repair. Why? He said there is no way of knowing for sure that one or more of the cylinders in the stack hasn’t broken, or is misaligned. No way to inspect for that possibility. He said 90 per cent of the time, it works OK, but he prefers to be sure. So I’m thinking the steel cable through the stack is a way of attacking that problem.
So is this really a better method of foundation support or a marketing gimmick? I’d love to hear from some foundation repair professionals about this hybrid underpinning method. Please leave a comment below. Thanks.