Foundation Repair With Helical Piers or Piles
As we mentioned before, piering or underpinning is the most cost-effective way to solve your foundation settlement problems in Missouri. On this page we will focus on Helical Piers and Piles.
Helical piers uses steel piers attached to the foundation based on the engineering requirements of the structure.
The steel piers (think 3-4 inch heavy duty pipe) are hydraulically driven to stable bedrock or or soil that will support the structure, and the weight of the structure is transferred to the steel brackets attached to the foundation. Instead of being driven (pushed) helical piers are screwed into the ground.
Then a foundation bracket is slid over the helical pier and fastened to the concrete footing. It s below the ground so nothing is exposed once the process is completed. (They bury it).
As they install each pier, it is load tested with a safety factor calculated to ensure a reliable permanent solution. What this means they "should" drive until the pressure reaches high enough to support 1.5 to 2 times the weight of the structure.
The structure weight is based on the normal construction practices and what structures weigh per foot that is on the footing. The pressure on helical piers is measured in tourque instead of foot pounds in compression like that of push piers. The helix or multiple helix blades on the pier actually develop load supporting capability as it gets driven into better soil.
As with other types of piers, they will position the piers out as wide as the capacity of the pier will support, or what the concrete is engineered to span - whichever is less. Normal pier spacing is every 6-8 feet. If you have an estimate with them spaced further apart than this - get another estimate. Engineering would say they concrete in Missouri most construction won't support piers spaced out further than that.
Pier spacing will greatly affect how much the foundation repair job will cost you as it will dictate how many have to be installed. Any reputable foundation repair company should be able to show or explain the capacities of their pier products and how they figured the spacing on your job.
Once all the piers have been installed according to the design plan, it is time to lift or stabilize the structure. They will hook up all the lifting devices to the piers and lift the building. Should they encounter problems lifting at this point they could be experiencing deflection of the helix blade (giving against the load). In which case they would need to drive deeper or install larger capacity helical piers.
On the majority of Missouri foundation lifting projects, windows and doors that used to stick will become functional, and cracks and other blemishes can be permanently repaired without concern for them reappearing.
Since push piers require the weight of the structure to push the pier downward to bedrock or better load supporting soil. Sometimes the structure may experience lift before the push piers get to depth. This is where helical piers come in. Helical piers don't require the weight of the structure to install since they are screwed in with a rotating drive motor.
Good applications for helical piers are:
- Metal Buildings
- Concrete Slabs
- Pre-Construction (where there currently is no building)
- Any other light structure.
Helical Pier Variations
Lifting Vs. Stabilize Foundations
So what's the difference between Lifting and Staiblizing my foundation? It works the same as Push Piers with Helical with a couple of exceptions.
Lifting With Helical Piers
Lifting a foundation (really means lift and stabilize) involves more work including a complete excavation of the foundation where it is affected. They will install the piers, connect them all together and lift the structure back to close to the original height. They will then pin it off so it stays there (that's the stabilize part). So on a basement they are digging down 7-9 feet deep to attach the pier brackets. On a craw space they can just dig square holes at each pier location so the excavation is a lot less (and cheaper).
Stabilizing With Helical Piers
Stabilizing a foundation simply means they will install piers to that engineered torque pressure and depth and lock things off without lifting the structure. There could be a couple of reasons to do this. One - it might be less damaging to the structure to just stabilize. Another reason might be that the structure has been moving up and down depending on the moisture content or seasons.
Plan on being there the day the lift is suppose to happen and monitor their progress.
Pier Depths (How Deep Will They Go?)
Most companies working in Missouri price piers at so much a piece with X number of feet installed per pier. The reason why they do this is because the steel pier pipe costs money and it takes so many minutes per section of pipe to install it. At some point if your piers need to go very deep - they will loose money.
We discussed this issue on push piers where depths could reach 70ft in Missouri to get to stable soil. Most helical piers will be specified to range anywhere from 15ft to 30 ft and priced accordingly. The difference is, on helical piers if they aren't getting the required torque readings, they can back a pier out and add helix bladed to increase the capacity of the helical pier without going deeper. This is a labor and material savings
So you may wonder - why not just go with helical piers to start with and don't consider push piers. Well for one they typically are a lot higher in cost and harder to install in tight areas. So they may not be cheaper. But also consider helical piers may be your only option depending on the structure.
Visit with the estimator about what could happen if they run into issues getting the proper torque.
How Much Will Foundation Repair Cost Me Using Helical Piers?
Again there are many factors in the costs of foundation repairs. They are:
1) Lift vs. Stabilize
2) Depth of Piers
3) Number of Piers Needed (Spacing)
4) Size of piers (capacity)
5) Basement or Crawl Space
6) Access to the Affected Areas
7) Cost of Steel
So here is a rough estimate to help you with the sticker shock when the estimates start rolling in.
Most designs will call for piering from crack to crack where the foundation is broken. Starting with a pier ON the cracks (2) and spaced no more than 6 feet apart. So if the two cracks are 24 feet apart, you would need 5 piers. One at each crack, one at 6 feet, one at 12 feet, and one at 16 feet. The estimator should provide you with a drawing of your structure showing the placement of the piers.
Pier prices will typically average between $1200 and $2400 each installed inclluding the excavation and repairing the dirt work. So in the above example you could expect to spend $6000-$12000 for the foundation repair.
Helical Pile World did a survey amoung installation contractors across the U.S. to see what everyone was charging. The results are interesting and can be found here at the article Average Installed Helical Pile Prices.