In this article, we will discuss
What is a helical pile | How do helical pile Work | How to install helical Piles | How much do helical piles cost? | What are helical piles used for
What is a helical pile?
A helical pile is a deep foundation that can support light and heavy structures. They support compressive loads of less than 1kN (225 lb) or more than 5,000kN (1.125 million lb). This means they can be used for anything from small landings to 32-story towers. "Screw piles" is another name for helical piles.
A helical pile comprises a round steel shaft welded to one or more helical bearing blades. Several things affect how long, thick, and wide a shaft is, as well as how many, how thick, and how wide helical piles are. No matter the size, the helical's pitch (plane or angle) should be the same. This ensures that the design and installation methods are reliable and follow generally accepted engineering guidelines.
How do helical pile Work
Similar to how a corkscrew is twisted into a bottle of wine, helical piles are installed by twisting them into the soil. Additional extension segments are joined with bolted couplers and screwed into the soil as the shaft of each Pile descends below the surface, resulting in a single pile that can extend hundreds of feet underground.
The steel pile is frequently sufficient to meet the project's load requirements. Concrete, also referred to as grout can be used to create deeper foundation systems that are more durable. In a grouted column, the steel shaft is enclosed by a continuous flow of concrete that follows the displacement plate down the column's sides. Using this method, a reinforced pillar is created that can withstand the strongest lateral, compressive, and uplift forces.
A helical pile is used to help support structures of all shapes and sizes at their base. Like old-fashioned pile foundations, helical piles (also called screw piles, helical piers, helical anchors, etc.) are driven deep into the ground to spread out the huge weight that sits on top of them. Installing several piles makes a platform that can hold a building, a bridge, or any number of other big structures.
Due to an empirical relationship between installation torque and soil capacity, helical piles can be used to predict how well they will work. The relationship between installation torque and capacity is very reliable, but it is not a substitute for a geotechnical investigation when liability is high. A good comparison would be a driven pile, which is installed to withstand a certain amount of force, making it a reliable pile in terms of performance. Again, the installation force is not a replacement for geotechnical investigation. When capacities and liabilities are low, like on a residential deck, it's hard to justify the cost of a geotechnical investigation. Instead, an engineer might design helical piles based on the torque needed to install them.
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How to install helical Pile
Helical piles are installed today using a variety of hydraulic machinery. Light hydraulic torsion bars or towers, mini-skid steers, skid steers, mini excavators, midi excavators, and utility sector auger trucks are used to install light-capacity helical piles (Digger Derricks). Excavators of 15 tonnes or more are typically used to install high-capacity helical piles, but specialized machinery or drill rigs are used at other times.
The tool selected must be suitable for the anchor drive that will rotate the Pile in the ground. The installation of a helical pile must consider the swing resistance, auxiliary hydraulic flow and pressure, reach, break-out force, and downward axial force. High-capacity helical piles are typically installed to refusal; a machine like a skid steer lacks the downward axial force necessary for the helical Pile to penetrate soft till without the aid of a suitable machine.
A common image is installing a mid-capacity helical pile using a small machine like a skid steer or tracked loader. Although it's impressive that a pile can be installed using such small equipment, it's not always the best. Because skid steers are designed for lifting, they frequently lack the swing resistance and force needed to accurately and correctly install helical piles, which can lead to piles that are out of plumb and auger the soil during installation. A helical pile should ideally be installed so that it is within 2 degrees of the plumb and advances directly in relation to the pitch of the helical blade(s), disturbing the least amount of soil possible. Excavators are designed to dig and are much better equipped to use downward pressure to complete a professional installation. Hoyt and Clemence compared the performance of helical piles installed improperly to those installed properly and professionally in the same soil and at the same depth. There was a 50% difference in tension performance!
Additional on-site confirmatory load tests will boost confidence in the design and installation when liabilities are high. Based on the actual performance of the piles at the site where they are being load tested, the design may be more efficient.
The presence of a third-party engineer to oversee the installation is another step that we might see on project sites with higher liability. It is a very good idea to supervise the installation and ensure that the piles are not auguring the soil and that the installation torques necessary are being achieved if you are working with a helical pile contractor with whom you do not have a strong working relationship.
Regardless of the project type, a helical pile contractor should always complete a piling report with achieved depths, torques, and any observations that might relate to performance.
How much do helical piles cost?
Since businesses rarely charge per pier, this is kind of a trick question. They charge per pier location rather than per piece of steel used.
The average cost per location for a helical pier in Southern California and Arizona is between $2,000 and $3,000.
Due to the price of steel rise and the current transportation crisis brought on by COVID-19, these prices may even be higher depending on your state.
The $2,000 to $3,000 per pier location price so we will install the pier system to whatever depth is necessary to achieve the required pier capacity.
After 21 feet of installed material, there is an option to pay per pier with a depth restriction.
After the first 21 feet, we charge $35 per foot of installed material. That can quickly add up and become expensive (which is why we often do not offer this option).
Unless you are certain of the target depth from a geotechnical report, choosing to have a helical pier project with a depth clause is similar to gambling.
Yes, you can get a lower price upfront, which is great, but the cost will quickly rise as soon as the piers are longer than 21 feet.
We advise you to always choose the no-depth clause option to prevent stress and change orders.
The average cost of underpinning a helical pier is between $24,000 and $60,000.
Everything falls into this range:
Foundation repair inspection, engineering, permit, material, labour, warranty
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What are helical piles used for
- Efficient installation on a typical project site, taking 30 seconds per lineal foot of a pile
- Being able to load the piles immediately without curing or heating them during the winter
- They are clean; the Pile is simply turned into the ground without any predrilling or tailings, or waste
- simple removal, reuse, or recycling of helical piles for project site remediation;
- The installation's low noise and vibration levels won't disturb nearby residents or wildlife
- Savings on mobilization and easier accessibility of challenging project sites result from an installation using smaller, more manoeuvrable equipment than traditional piles
- Helical pile extension is quick and economical. Helical piles are proportionately more expensive, as opposed to potentially exponentially higher costs to go deeper
- the ability to easily traverse soil layers that are wet, sloppy, and sloughing
- can be galvanized, thickened, or added anode systems to extend the piles' lifespan by centuries
- a helical can be easily modified in the field to accommodate unforeseen site conditions (for instance, if soils are denser than anticipated, the diameter of the helical can be reduced)
- Helical piles can be installed underneath existing structures or in places with very limited access thanks to a variety of installation techniques and tools
- Lightweight and transportable
- For helical piles, a variety of pile caps and transitions can be engineered to support almost any beam or structural component
- being able to install through frost for effective building during the winter
- Predictable performance is implied by the empirical relationship between installation torque and capacity
- If you have the option to remove a pile, you can move a pile that runs into a boulder rather than abandoning it
- When many design elements can be changed, a value-engineered pile is frequently both efficient and effective
- installation on a batter to reduce high lateral forces or combine pile clusters in a small area