Foundation Repair at Idaho FedEx Facility

The Challenge

A 2,500 square feet slab had settled 5 inches at FedEx Ground Distribution Center.

At the FedEx Ground Distribution Center located in Southern Pocatello, Idaho, the foundation beneath approximately 2,500 square feet of the facility’s front office area was on the move. In 2015, the slab had dropped more than five inches at its lowest point, and at that time it was believed that the soils below the building had settled all they would. A contractor hoped to address shallow voids and injected polymer grout just below the concrete slab, lifting it to roughly three inches at the lowest point. However, the slab continued to drop and by mid-2019 the interior slab had settled by more than seven inches, requiring additional geotechnical exploration at greater depths. Following these studies, Groundworks was contacted to densify the soils and raise the sunken slab.

Onsite geotechnical exploration revealed undocumented fill present beneath the structure at depths between 19 and 25 feet below grade. The fill appeared to consist of superficial, very dense, and poorly graded sand with silt and gravel that may have been placed as structural fill. The remaining fill was said to consist of loose to very dense silty sand and sandy clay mixed with construction debris such as brick, concrete, asphalt, wood, and plastic. The fill appeared to be underlain by native lean clay with gravel and by weathered basalt bedrock at approximately 22 to 28 feet below grade. It is believed that the undocumented fill and construction debris were not properly compacted and included voids during placement. The resulting settlement loosened the upper layers of structural fill and affected the interior slab more than typical settlement found within similar structures would.

Key Facts

The Solution

Crews injected a lightweight polyurethane grout to depths of 24′ below grade, effectively filling the targeted voids and densifying the surrounding soils.

Geotechnical studies confirmed that the facility’s exterior bearing foundation walls had not dropped in elevation and that the Helical Piers installed during initial construction had not failed. As such, it was agreed that the polyurethane injections process would provide an ideal solution for the ongoing soil failure issues underneath the main building foundation. Injection locations were pre-determined to ensure densification of the affected areas. Because of the variety of depths and the inconsistency of the fill below, pilot holes were pre-drilled to target depths and grout injection tubes were installed. Crews injected a lightweight polyurethane grout to depths of 24 feet below grade, effectively filling the targeted voids and densifying the surrounding soils. Laser levels determined the extent of injection required, with crews closely monitoring any slab movement to avoid internal structural repairs for the client.

The Impact

Groundworks successfully densified the soils to the 24′ depth without any removal of the interior slab.

A tent was installed to reduce dust within the facility while crews drilled holes in the slab. FedEx requested after-hours and weekend work scheduling to avoid interruptions to their normal operations. (Groundworks also worked around FedEx’s Christmas Holiday and end-of-the-year rush.) Although pre-drilling in-creased the installation time, Groundworks completed the project successfully and densified the soils to the 24-foot depth without any removal of the interior slab. FedEx was able to stay open with no shutdowns or costly business delays.