FRAC Grouting—A Case History

The United States Postal Service's (USPS) Eastpointe Facility in Clarksburg, West Virginia is located at the site of a former strip mine. Reclamation activities prior to construction were accomplished by backfilling the stripped area with the excavated materials after the coal seam had been removed. Subsurface investigations performed for the design of the facility identified settlement concerns due to loose fill and the existence of nested cobbles and boulders. To address this concern the site was reportedly over excavated and replaced with a controlled engineered fill. Placement and compaction methods utilized during placement of this controlled fill are unknown. Constructed in 1989, the 9,300 m² single story steel frame structure is supported by columns founded on spread footings. The floor of the building is a grade supported concrete slab isolated from the primary foundation system. Differential settlement of up to 150 mm has occurred causing structural damage and serviceability problems. This paper details, from a construction perspective, the applied grouting technology utilized to stabilize the structure, along with an analysis of the performance achieved. The work was substantially completed in the fall of 2001.