A helical pier is a common footing option used when the ground is less than stable, or an option used to create the best base for a project such as a deck or home foundation. Manufactured from steel, a helical pier is a foundation pin that is driven into the ground at a depth that is below the frost line. A hydraulic machine is used to push the pin down below the frost line to ensure a proper and secure base. This type of pier is more commonly used during commercial construction but can also be a method used to create a deck, repairs to a foundation or other construction projects.
Helical Pier Sizing
A typical helical pier will have a seven-foot shaft and use a bearing plate that is welded to the end. The top will have a cap that will attach to the framing, depending on your project. Piers that are used in residential projects will be created with hot-dipped galvanized steel. Sacrificial anodes are added to the pier when the soil has issues and additional strength is needed. Diameter sizing of the pier will also be based on the condition of the soil. Rocky type soil will need a smaller helix while a larger helix will be used for soil consisting of clay or marshy areas.
Bearing Capacity of Helical Piers
A helical pier’s load bearing capacity will be dependent on the amount of torque used during installation. Along with the torque, the helix size and bearing capacity of the soil must also be considered. The installation machine will include a pressure gauge which will show the torque used as the helical pier is rotated and placed in the ground.
When the soil is weaker, the pier will have to be driven deeper to be able to reach a stronger soil base. Once the helix is placed below the frost line, the pressure gauge will reach a higher number that will be in correlation with the loading requirements of the structure you are creating.
When rocks are encountered, the process is a bit different. Rocks that are smaller can simply be powered through but larger rocks can affect the installation which will then affect the overall foundation of your project. With the helix, the installer has the option to steer around rocks but sometimes rocks are too large and there is nowhere to go. If a large rock is encountered during an installation, the pile will be placed on top of the rock and load-testing will need to occur. If the test is passed, then the pier can remain in place.
Load-testing the Pile
A helical pile will need to be load-tested for a variety of reasons, especially when encountering a rock as mentioned above. To do this, the height of the pile above grade will need to be measured and a cap put in place to protect the top. The cap is then slammed five times with a tool such as a sledgehammer with the height measured again. The measurement of how far down the pile moved will indicate the bearing capacity of the coil. This testing must be done to ensure the helical pier is going to be grounded and secure.