Challenge

Within the first six months of construction, the northwest corner of a 1,600 square-foot winery settled approximately 3.5 inches. The area of settlement included a basement with foundation walls extending eight feet below grade. A geotechnical exploration was not performed; however, the contractor anticipated weak clay and sand soils to extend to the underlying bedrock at approximately 20 feet. The owner wanted the building stabilized with a deep foundation system that could also lift the structure back toward its original elevation.

Solution

A system of hydraulically-driven push piers was chosen as the most economical method to lift and stabilize the structure. A total of sixteen (16) Model 288 (2.875-inch O.D. by 0.165-inch wall) push piers were installed at a three-foot maximum center-to-center spacing. The continuous wall footings were notched to allow the side-load retrofit brackets to extend beneath the foundation wall. During installation, the bedrock was encountered deeper than originally anticipated and the piers were driven 34 to 49 feet below the bottoms of the basement footings to achieve driving pressures of at least 4,000 psi (drive load ≥ 38.4 kips). After the piers were each driven individually, the piers were connected in series with hydraulic lift cylinders and simultaneously loaded to lift the structure approximately 3.5 inches to its original elevation. Hydraulic pressures as much as 2,200 psi, which correspond to working loads up to 21 kips, were required to lift the structure. On average, the push piers were installed to a factor of safety greater than or equal to 1.8 (FOS = driving pressure/lift pressure). Installation of the push piers and lifting of the structure were completed in just two days.

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Project Summary

General Contractor: Vanderhaar Construction

Certified Pier Installer: MidAmerica Basement Systems

Products Installed: (16) Foundation Supportworks® PP288 Push Piers, Installed to Depths From 34 to 49 feet Below the Bottom of the Basement Footing