Repair for foundation settlement usually calls for installing piles that penetrate past softer soils, down to hard soil or rock that will stabilize and support the structure in the future. These piles are typically driven to refusal and lock up in what geotechnical engineers describe in borings as 40-50 blow count soils. This is technical jargon for “pretty hard soil”. Basically, enough to support the structure above.
Make sure the Foundation Repair Contractor you select has the tools, equipment & skillset to complete your project.
As you might imagine, soil layers are not always deposited in uniform layers from soft at the surface to hard at the bottom…. although in general this is mostly correct because the deeper you go, more weight of soil is on top of it is squishing it down and compressing it to a harder condition. However, this is not always the case as the various layers have different make ups with various densities, reactions to water, and geologic properties during the time of deposition.
The problem then becomes, what happens if a stiffer layer is on top of a softer layer? It could be hard enough to stop a pile that is being driven to refusal, yet still the soil below it may be soft enough to cause problems of the soil above it.
We have run into this problem before. See blog 'Mistakes we have made part 7': https://www.foundationaz.com/blog/mistakes-lifes-opportunity-grow-learn-part-7. We have also discussed this in previous blogs https://www.foundationaz.com/blog/reaching-sufficient-depth-to-give-a-permanent-solution .
Although it is great to have the technology to drill deeper with expensive drilling equipment, mobilizing that equipment to a site is expensive and not a fun surprise to the homeowner. Many times the problem is not thoroughly examined because the alternative is so expensive and contentious that many times it is just fudged as “being good enough”.
Repair for foundation settlement usually calls for installing piles that penetrate past softer soils, down to hard soil or rock that will stabilize and support the structure in the future.
I have thought about this a lot and have searched for a better solution. We have equipped each of our rigs with a high powered air compressor. One typically powerful enough to run a jack hammer. But instead of running a jack hammer, we use it to power a rock drill and extension bits long enough to reach 9 feet below the surface…. which geotechnical engineers have determined is deep enough to avoid the problem. It is called minimum pile depth.
What happens if the foundation repair contractor that you hire does not have the needed equipment with them on the job? Well I am not sure, however the various alternatives likely include:
1) ignoring the problem and not getting deep enough, or
2) to having a very expensive change order that increases the cost by more than double in order to mobilize expensive drilling equipment.
Perhaps a few great questions to ask a foundation repair contractor who is proposing work at your home:
- What is your minimum depth?
- What is your plan if you don’t reach it?
- Does your required special inspector check and report on this?
If the answer to these questions is anything short of a well-defined plan that controls costs for you, you should keep looking for a foundation repair contractor that can deliver that.
