Chemical Grouting for Soil Modification, Jacksonville, NC
Thomas V. Admay, P.E., Engineered Foundation Solutions, Durham, NC
Slab foundation of house settled, causing extensive racking of interior doors, and cracks in walls and floors, all of which are telltale signs of foundation problems. Soil borings indicated that up to 4 feet of uncontrolled fill material was placed below the floor slab during construction of the home. The soil study confirmed that the underlying virgin soil was of adequate strength, however the fill material placed to level the building pad (the lot had approximately 4 feet of fall across the width of the house) was improperly compacted. Construction debris was also encountered in the soil samples, indicating potential interference with helical slab pier installation.
Soil stabilization had to sufficiently increase the bearing capacity of treated columns to transfer the weight of the static and dynamic loads to the underlying virgin soil. Installation needed to be fast and efficient and allow for near-immediate treatment of voids and floor settlement with foam jacking.
Permeation grouting using chemical grout. The loose sand characteristics of the uncontrolled fill are ideal for treatment using a resin chemical grout. Using a grid pattern similar to which would be used for helical slab pier installation, given the existing soil conditions, chemical grout was a much more economical solution still capable of adequate load transfer.
Concrete Jack chemical grouting crew installed polyurethane resin chemical grout at 25 locations to treat columns at heights of 3 to 7 feet below finish floor elevation. Immediately after chemical grout installation was completed, foam jacking was used to fill voids and lift the floor back into position.