Understanding Pier Underpinning Systems

Underpinning is a term that refers to the practice of shoring up a building's foundation through the installation of underlying structural elements. These elements protect against such common issues as foundation or basement cracks, tilting, and sinking. Traditional underpinning methods involve the addition of concrete structures to the underside of the foundation. While effective, this laborious method is not appropriate for all basement construction problems. If you would like to learn more about alternatives to traditional concrete-based underpinning systems, read on. This article will discuss the two main types of pier underpinning: push piers and helical piers.

Push Piers

A push pier system—also commonly referred to as a resistance pier system—bolsters your foundation through the installation of galvanized steel tubes, or piers. These piers are utilized in conjunction with heavy-duty metal brackets, which act to hold them in place. First the bracket is fitted into place, and then the pier is driven down into the ground by a hydraulic press. This method of installation is what gives push piers their name, since they are literally pushed down through the soil and into place. Multiple sets of brackets and tubes will be utilized to help distribute the foundation's weight evenly and safely.

There is no pre-set length for the steel piers. Rather they will be pressed down through the earth until they reach a relatively stable base. For this reason, push pier systems are best used when it is known that a stone or rock sublayer exists deep beneath the building. The principal advantage of push piers is their relatively simple installation, which requires very little in terms of excavation. 

Helical Piers

Helical piers differ from push piers in two significant ways. First of all, the steel piers at the heart of the system are fitted with a series of helical plates. This makes the pier look more like a screw. For this reason, helical piers are also commonly referred to as screwpiles. These plates help to anchor the pier, thus protecting against the heaving and shifting that naturally accompanies moisture changes deep in the soil. This is especially true in areas with expansive soils—in other words, those that contain a high percentage of water-absorbent clay.

The second difference between push piers and helical piers has to do with the method of installation. As you can imagine, a helical pier cannot simply be pushed into the ground. Rather it must be rotated while it is pushed, driving it downward much as if it actually were a screw.

For more information, contact local professionals like Hanover Concrete Company.