Equipment Building Stabilization

Tuesday, October 7th, 2014 by Josh Kaiser

Challenge

A 20-foot by 45-foot, slab-on-grade, single-story equipment building had settled differentially at one end. Building construction consisted of shallow continuous wall footings, poured foundation walls, and CMU block walls above. The shallow foundations were reportedly bearing on ash fill. Cracks were observed through the mortar joints and through individual CMU blocks. Deep foundations would be needed to extend support beyond the fill and underpin the existing wall footings, and, if possible, attempt to lift the settled end of the structure.

Solution

A system of hydraulically-driven push piers was selected as the most economical method to stabilize the building. A total of ten (10) Model 288 (2.875-inch OD by 0.165-inch wall) push piers were installed at a five-foot maximum center-to-center spacing. The piers were spaced along the end wall and around the adjoining corners. The footing was prepared at each footing location by removing excess concrete that extended beyond the plane of the vertical face of the poured foundation wall. The underside of the footing was also trimmed smooth for uniform bearing on the retrofit bracket. Electrical equipment and other obstructions prevented exterior installation at several of the proposed push pier locations. Four piers were installed within the building. The floor elevation inside the building was approximately three feet above exterior grade; therefore, the excavations made to install the interior piers were nearly six feet deep.

The push piers were advanced to an average depth of 52 feet below the bottom of the footings, achieving hydraulic fluid pressures of at least 5,000 psi, corresponding to at least 48.1 kips of drive force. Driving of individual piers was discontinued when the structure began to mobilize. Hydraulic lift cylinders were then fitted to the installed pier assemblies and connected in series to attempt a uniform lift of the settled portion of the structure. Approximately 3/8-inch of lift was achieved. The piers were locked-off to stabilize the building and prevent further settlement. The pier installation and lift were completed in just two days.

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