Support of Excavation Utilizing Helical Soil Nails with High Tensile Wire Mesh

Common technologies for temporary and permanent support of excavations (SOE) include soldier piles and lagging, secant/tangent piles, slurry walls, and tie-back walls. This paper discusses an innovative technology consisting of helical soil nails with high tensile wire mesh facing. This novel technology has been used on a number of SOE projects in recent years saving both time and money as well as providing a number of other benefits. Case histories including Denver Bronco’s training facility, Pulliam Theater, a bridge abutment, and a train platform are presented. This SOE technology is highly sustainable as both the mesh and soil nails can be removed and re-used, if desired. The system avoids the need for concrete or grout, so it eliminates curing times and problems associated with field quality assurance and inclement weather placement. Helical soil nails consist of central pipe or solid steel shafts with small diameter helices spaced over the entire length. The length of the nails is typically on the order of the height of the excavation. The nails are spaced relatively close together in rows to reinforce the earth. The face of the excavation is held back using high tensile strength steel wire mesh over geo-fabric. The mesh is stretched between the helical soil nails and fastened down using spike plates on the helical nail caps. Both hand calculation and computer methods for design of this concrete-less alternative to the traditional SOE will be covered. The SNAP 2.0 computer program is used to determine factors of safety with regards to overturning, sliding, and bearing, among other checks. Through practical applications and real-world calculations, this paper educates the reader on the proper design and application of the helical soil nail and high tensile mesh SOE system. AutoCAD details and example plans are provided.