Soil nailing involves the employment of man made reinforcement to enhance stability when construction occurs on natural sloping surfaces. The stability of the steepened soil is accomplished in a number of ways. In most cases, this involves the reinforcement of potentially unstable soil with the insertion of rather slender solid rods known as rebar. These solid bars are inserted into pre-drilled holes and held in place by pumping grout from a separate line. Hollow rods can also be utilized which involve the use of a sacrificial drill bit and the shooting of grout within the rods themselves during the drilling process. The use of a kinetic process is also now possible. When using shorter bars, they are usually inserted fully grouted at a slight incline at set intervals across the slope face. Pnuematic applications of concrete, commonly known as shotcrete, provide a rigid facing, as does the use of isolated steel nail headplates. An alternative is the use of a flexible soil mesh which holds in place the soil beneath the headplates. Rabbit proof wire mesh is a potential solution to environmental erosion as are other fabrics used in conjunction with flexible mesh facing when certain conditions demand innovative solutions. Soil nailing components are also used in stabilizing retaining walls and fills made of natural material such as embankments or levees.
Once all design is complete the project is ready for construction. The use of soil nail wall construction follows a specific set of procedures. First, the initial cuts are excavated with temporary bracing employed as needed. This is accomplished with the use of earth moving equipment and pneumatic drills. Holes are then drilled for the soil nails at predetermined points identified by the engineer. Choices of equipment to facilitate the insertion of the soil nails are determined by the stability wall conditions unique to each project. Rotary or rotary percussive methods using air flush or dry uger are used when there are stable ground conditions. Unstable soils require single tube or duplex rotary methods with air or water flush and hollow stem auger use. Once the holes have been drilled the nails must be grouted and inserted. Upon completion of soil nail placement a drainage system is established. Vertically placed synthetic draining is placed between the nail heads. This system extends all the way down to the base of the wall where it is usually connected to a footing drain. A layer of shotcrete is applied and bearing plating is installed before a final facing is put on the soil nail wall. During some projects variations on this methodology is employed as each individual situation dictates.