push piers vs. helical

[John Dirks Jr]

A close family member is about to have some foundation repair done. The problem is cracks and settling on a poured concrete foundation. The lot has significant slope to the rear. Significant enough that only the first floor is visible from the front but the rear is complete walkout basement.

There is an engineering report calling for a number of helical piers to be installed to support the footings on the rear and sides of the house. The contractor of choice has offered either helical or push piers for the same price and says he prefers push piers.

What are the pros and cons of both helical and push piers?

Can you think of a reason why the contractor would prefer push piers?

If you have any specific questions, ask and I'll try my best to answer them.

[Bill Kibbel]

I have limited experience with push piers. I was at a seminar that they were featured for historic building stabilization. Unlike helical piers, they need to go as deep as needed to hit bedrock.

I have some field experience with a specific helical piering system, used for both vertical piers and horizontal anchors. In my experience, the system has been quite effective at stabilizing some serious foundation problems in tight spaces.

[Marc]

If I'm not mistaken, push piers, what I refer to as pilings, depend primarily on the material at the bottom of the piling for support. Friction along the length of the piling is a smaller factor. Helical screw piers use the earth itself and don't need a solid surface to rest on. They gain load capacity along the length of the screw. Final load capacity is a function of the torque developed as it's driven into the earth. Contractor merely ask what load bearing you want then uses a load capacity vs torque chart with engineered values to tell him when he has the capacity you want. He monitors the torque via some hydraulic indicators. He actually tenders an engineering sheet for you to show the muni inspector. Some screws go deep, some shallow, depending on the composition of the soil.

Already, I'm suspicious about your contractor. Different concepts are invoked by pilings and helical screws. Your contractor should have told you about this, if he really knows his craft.

Marc

[inspector57]

Can you think of a reason why the contractor would prefer push piers?

Push Piers or Pressed Pilings likely are cheaper, just concrete. Why wouldn't he prefer to make more money?

Do it like the engineer said, unless he has a "too" close relationship to the contractor.

[Scottpat]

As noted by others, "Push" piers are used when bedrock is shallow, like less than a few feet is ideal..... Helical piers are better and used when bedrock is deep and you are dealing with just dirt..

The idea with a push pier is that it is driven down till it hits the bedrock.....

[philippeyergeau]

Helical piles definitively guaranty a much better load capacity for that type of application.

With helical piles, the load-bearing capacity relates to the amount of torque requires to screw the pile. A pressure gauge on the installation machine reads the torque as the pile is rotated into the ground. The helix is mainly what induce the torque during the installation. The size of the helix will vary based on soil conditions. Some helical piles company uses small hydraulic equipments that will have an easy access in your backyard and with leave a smaller footprint on the job site. Make sure the company you will select have appropriate engineering support and use primary steel.

Good luck for your project?

[mjr6550]

Concrete push piers are used in some areas like Texas, but not widely throughout the country. I am assuming that you are talking about steel push piers. The relatively cost is about the same as helical piers.

I have used both. Helical piers are a problem in rocky soil. On one job a contractor bent a 1/2" thick steel helix 90 degrees when he hit a rock. Sometimes installation is difficult or impossible. When they go in easy they are usually much faster to install. The load rating is related to installation torque. You can get false readings from rocks.

Push piers often can push through rocks (or push them out of the way). Since you are reacting against the foundation the load rating can be measured and is more certain.

I have usually relied upon the contractors preference. I would ask them why they would choice one over another for the given job.

[rmayo]

I agree with Scott, the decision to use push piers versus helical is a matter of economics. If bedrock is fairly shallow push piers are typically used, deeper soils require helical piers. Be skeptical if the engineer that designed them works for the foundation company or was referred by the company. Most of these foundations companies install way more piers than needed, remember the more they use the more they make. Most walkout basements are partially supported on fill dirt that was poorly compacted causing the back half to settle. So only the back half would typically need piers. If they want to pier the entire perimeter of the foundation, get a second opinion from an independent engineer. Around here those piers are about $1000 each, of if the engineer reduced the number of required piers by one you saved money. Also the typical spacing between piers is about 6 to 8 feet.