25,000 square feet of the industrial floor at a military facility settled up to 4 inches and was affected by sub-slab voids. The affected area also included 250 track feet of embedded rail, which was set in an independent, thickened slab section. The building had been used for warehousing but was being transitioned to light manufacturing/maintenance.
Plans called for a 4” thick overlay slab to be installed, with a vapor barrier, over the existing floor. Geotechnical investigation work determined there were extensive voids below the floor throughout the area affected by settlement.
The proposed repair method had to provide adequate bearing capacity for manufacturing and ensure complete void filling and stabilization.
Polyurethane grouting fills voids under the floor to stabilize against future settlement. Additionally, in areas that had settled, polyurethane grouting was proposed for correcting settlement.
Due to extensive compressive soil layers below the floor, polyurethane grouting was proposed as an alternative to the specified cementitious grout. The specified grout had an in-place density exceeding 115 pounds per cubic foot. The proposed polyurethane grout had a constrained density of 5.5PCF, yet a bearing capacity exceeding 12KSF.
CJGeo mobilized three polyurethane grouting crews to the facility, with a combined pumping capacity exceeding 5,000 pounds per hour. Nearly 2,000 dime-size injection holes were drilled through the slab, and 5,000 cubic feet of polyurethane grout was installed under the floor & section of embedded rail. The void filling was confirmed by visual inspection (material showing at adjacent drilled holes to injection locations), and slab lifting.
In areas that had not settled, 1/8 inches of the lift was used as the benchmark change in elevation to confirm complete void filling. Areas that had settled, including the embedded rail sections, were lifted up to 3 inches above the original elevations.