Soil Nailing: The MoDOT Experience

Soil nailing is a construction technique that is used to strengthen existing ground by installing grouted steel bars into the ground at closely spaced intervals. This increases the shear strength of the in-situ soil so that successive excavation lifts from top down can be made. The Missouri Department of Transportation (MoDOT) has overseen the construction of two temporary soil nail walls in the St. Louis metro area and one permanent wall in the Kansas City metro area. All three projects involved roadway widening under existing overpasses, which required the removal of the soil berm and construction of a soil nail wall next to the existing abutment. The ground conditions, construction methods and soil testing procedures for the projects varied widely from one another. These projects provided experience and valuable lessons in the design and construction of soil nail walls not only to MoDOT personnel, but also to the wall constructors and design firms involved in the projects