What are helical piers?
Helical piers may also be known as screw piles. As both “helical” and “screw” imply, this method employs a spiral-shaped head that is literally screwed into the ground using a high-torque hydraulic motor. The screw provides a bearing surface that transfers the load from the structure to the underlying soil or rock bearing strata. The piers are screwed into the ground as needed to provide structural remediation.
How are helical piers used in the Front Range?
Helical piers have a variety of uses, including slope stabilization and structural underpinning. In slope stabilization, the helical pier may be screwed into the slope past the poor soils and attached to a suitable retaining wall to maintain slope stability. In structural underpinning, the failed footings are exposed and helical piers are placed underneath the failed footings, which are raised to the desired elevation. Footings, building and piers are secured together using a bracket and the foundation is covered. Helical piers are also frequently used in place of a footing or drilled caisson for the construction of a new foundation or even structural slabs.
In many areas on the Front Range, soils near the surface can be suspect: either with poor bearing capacity or high swell/shrink potential when wetted/dried. These types of soil are not suitable for building a conventional “footing” type of foundation. Drilled concrete caissons have been used extensively in the past to drill through these layers of soil. This method has had success, but requires very large machinery to drill the caissons, can require casing of the drilled hole, pumping of groundwater and removal of the large amount of soil displaced from drilling the hole, “spoils’ that must be removed using a loader. For additions, pop-tops, decks and many mountain sites, access issues make it very difficult to use drilled caissons. Due to these reasons drilling caissons can be an expensive, messy and damaging part of building a new foundation.
The same, or greater strength and stability can be achieved by using helical piers, but it is done with equipment capable of accessing much smaller spaces, creates no drilling ‘spoils’ and causes much less impact on landscaping. In most cases, we install our piers with a skid-steer or small rubber-tracked excavator. If conditions are too tight for that, a smaller, portable rig can be used to install piers in even smaller spaces. Helical piers also are ready to bear weight as soon as they are installed. The top of the pier is tied into the foundation using one of many ICC Certified connections, transferring the load of the structure and the foundation wall through suspect/unsuitable soil layers down to competent, dense soils or bedrock. Another benefit of helical piers is the need to only coordinate one subcontractor: no more coordinating the caisson truck, pump-truck, concrete truck, and soils engineer.
To sum up: The helical pier foundation is preferred over driven piles, drilled shafts, grouted tendons, auger-cast piles, belled piers and other deep foundation systems for a number of compelling reasons:
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