When structural engineers specify underpinning systems to stabilize settling homes in Olympia, Washington, they select between two proven commercial technologies: resistance steel push piers and helical screw piers. Both systems utilize heavy-duty galvanized steel to bypass unstable surface soils, but their installation mechanics and geotechnical applications differ substantially.
Resistance push piers—often referred to as hydraulically driven micro-piles—utilize the dead weight of the home itself as a reaction anchor. Heavy steel brackets are bolted directly to the underside of the concrete foundation footing. High-pressure hydraulic cylinders then drive hollow steel pipe sections downward through loose fill and saturated topsoils until reaching refusal on solid bedrock or dense Vashon glacial till. Push piers excel on heavy two-story homes, masonry structures, and full concrete basements where substantial downward weight is available to drive the piles deep.
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In contrast, helical piers feature welded screw flights (helixes) at the tip of the lead steel shaft. Instead of pushing against the building's weight, an industrial hydraulic torque motor screws the pier into the ground much like a giant wood screw. Installers monitor digital torque gauges during the entire driving process; because rotational torque correlates directly with soil shear strength, technicians verify the exact tonnage capacity of each pier before lifting the structure.
Helical piers are particularly advantageous for single-story ranch homes, lightweight additions, detached garages, decks, and timber pole barns that lack sufficient mass to drive push piers. Furthermore, in areas with deep unstable peat or loose sandy outwash along the Deschutes River basin, helical blades can be advanced dozens of feet into reliable bearing strata without shaking the house.