Installing Helical Underpinning Piles
Helical underpinning piles are one of our most essential items for our customers. As you can see in this photo, it’s a tilt panel building, and about 200 feet of panels have been shifting. There was an enormous void under the slab in the back right corner of the photograph. It was determined that the dirt wasn’t optimally compacted for the project, thus creating the shifting.
This next image is on the right side of the building. When we arrived on site, we started digging using mini-excavators. These mini-excavators are needed to get in and around buildings to do the most effective and efficient job possible. Typically our machinery isn’t big, but your capacity for helical piles can be different. Still, the mini-excavator is needed for your typical piles to get in and do the job.
We had plenty of room on this job to throw two or three crews at the problem. Which helped make it a much faster process. That’s one of the benefits we have with large crews; we can get in a knock the job out efficiently.
Typically, we have three people per crew, and each team can get about four piles daily with a project like this.
We open everything up by digging a two-by-three hole at each pile location. You can see the 7ft. steel extensions in the bottom right of the above photograph.
Here you will see our torque head that we attach to those 7ft pieces of steel extensions. That silver torque head at the top of the shaft is utilized to reach the load that the engineer has determined that it needs to be.
For this situation, each pier needs to hold 20,000 pounds. For the helical, they are spaced out, so they don’t auger the soil. Instead, the helical piers slice through the soil to keep the ground as intact as possible to provide support around that shaft.
When we install the helical piers, we measure what that torque is. For example, let’s say you put a screw into a piece of wood, use a screwdriver, and torque it instead of a gun. When turning that screw in, you recognize it takes more torque the deeper that screw goes into the wood. That’s what we are measuring with that torque head when installing helical piers.
We are the only company that has that on every one of our machines. We do because we recognize the importance of our customers recognizing what that torque reading is because that’s what tells you that you are meeting the engineer’s requirements.
Suppose you have a third party out there observing our work. In that case, we have a digital display in the excavator’s cab and on the reaction torque head, so we are getting a live-time feed of how much time it’s taking to turn this pier in the ground – and the more torque, the more resistant the soil is. The stiffer the earth, the more load it can handle.
Before we go on-site, we want everyone to know the magic number of the torque we are trying to hit. The primary and essential reason is that we are shooting to meet the engineer’s requirements, and the second reason is because of cost. Whenever we price a helical pile, if there’s soil data that we can use, we say that we can hit this torque at this depth. So, we price everything to that depth.
Keep in mind that if that torque number isn’t registering high enough and we have to go deeper, there are additional costs. That’s the reason we believe everyone must know what that number is upfront, so we know when that pier is where it needs to be to hold.
Our torque heads are calibrated yearly, and we have several in reserve, so we never have downtime costing the client money and time.
COMPLETED PILE INSTALL
The image above is what it looks like when it’s all in. That’s the bracket with the t-pipe on top of it. You see the shaft that was screwed in and the bracket that has been bolted to the footing. The goal is to get the helical and the bracket as close to the load as possible. It eliminates the footing wanting to roll.
And this is what it looks like when we are done with the site. When we put the dirt back in, we use a jumping jack tamper, so six months from the project completion, you won’t see divots every six feet from where the soil has drooped. You won’t see these piles because they are all below grade. We grade the soil away from the building, so the water flow is correct.
Written by John Adams, Technical Consultant, and Chief Estimator