Challenge

The Eastbay headquarters building in Wausau, Wisconsin had been experiencing differential settlement for many years. An area of particular concern was the northwest end of the building which had measured settlement on the order of 2-3/4 inches along an exterior wall and 3-1/2 inches at an interior column pad and grade beam. The interior grade beam supported an upper mezzanine level with a Spancrete precast concrete floor. With signs of distress becoming more and more evident, the owner had concerns that further settlement could potentially lead to collapse of the mezzanine. A geotechnical investigation included seven interior hand auger borings and three exterior borings completed with a truck-mounted drill rig. The borings identified seven to eight feet of uncontrolled fill over dense sand over weathered bedrock at 9.5 feet to 17 feet. Original building details from 1965 showed the tops of both the interior and exterior footings to be seven feet below the floor slab elevation. These footing depths correlated well with the depths of uncontrolled fill. Helical piers were initially considered to stabilize the settled foundations. However, due to the anticipated deep excavations and difficult equipment access, hydraulically-driven push piers were ultimately selected.

Solution

The piers were spaced no more than 4.5 feet apart to support a design working load of 23.4 kips per pier. Soil at the pier locations was removed by hydro-excavation to the top of the footing. Flush mount pier brackets were set against the foundation wall with adhesive anchors after a five-inch diameter core hole was made through the footing. The Model 288 (2.875-inch OD by 0.165-inch wall) piers were driven to an average depth of 17 feet below floor slab elevation. After the piers were driven individually, they were connected in series and uniformly reloaded to stabilize the building. The foundation supporting the mezzanine was lifted about ¾-inch to partially close cracks and separations in the walls. The excavations were backfilled and the soil compacted with a pneumatic hand tamper. With all phone orders from Footlocker.com and Eastbay catalogs taken at this facility, all work had to be performed after hours between 5 P.M. and 7 A.M. The 21 piers were installed in stages over a two week period. Hydraulically-driven slab piers and PolyLEVEL™ polyurethane foam injection were also utilized in this and other areas of the building to support and relevel settled floor slabs.

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Project Summary

Structural Engineer: EDC Management Corporation

Geotechnical Engineer: American Engineering Testing, Inc.

General Contractor: Miron Construction

Certified Pier Installer: Foundation Supportworks® of Wisconsin

Products Installed: (21) Foundation Supportworks® Model 288 Push Piers with Flush Mount Brackets; Average Depth of 17 feet Below Floor Slab Elevation