The horizontal installation of threaded steel bars into a cement grout filled hole.
Soil nails are used for stabilizing slopes and excavations. They find an efficient application in granular soils of medium to high density with sufficient internal friction, so that a good load transfer along the soil nail is possible, and only slight creep movements occur in the supported soil mass. The soil nails are installed as the excavation progresses from top to bottom. The surface of the cut is usually stabilized by shotcrete and rebar mats.
Since the soil nails are loaded only by ground movement, a certain outward deflection of the top of the stabilized wall must be expected. The theoretical pivot of the wall is at the bottom of the excavation. Calculations assume the maximum tensile force in the earth mass to occur at a distance from the wall equal to 1/3 to 1/2 of the wall height. There, parallel to the wall, the interface between the unstable soil and the retaining stable ground must be assumed. This location is also the area of the highest bending for the soil nails. The anchoring length of the soil nails must extend into stable ground.
DYWIDAG soil nails can be protected against corrosion in a variety of ways suitable for both temporary (= 24 months) and permanent (>24 months) applications.
Bare bar in cement grout
Cement grout alone can be used for corrosion protection of temporary soil nails and permanent nails in non-aggressive ground, provided the thickness of the grout cover exceeds 1-1/2" (38 mm).
The DYWI ® Drill bar system is ideally suited for temporary soil nails, particularly in non-cohesive soils.
Steel elements of the soil nail system can be oversized to allow for loss of cross sectional area due to corrosion. The rate of corrosion shall be based on historical data for ground conditions with the same or lower level of aggressiveness. Additional factors of safety are recommended.
Hot Dip Galvanizing
Permanent soil nails in non-aggressive ground can be protected against corrosion by hot dip galvanizing in accordance with ASTM A-153. Hot dip galvanizing of GR150 bars requires specialized procedures to avoid hydrogen embrittlement.
DYWIDAG soil nails in non aggressive ground and temporary nails in aggressive ground can be protected against corrosion by epoxy coating in accordance with ASTM A-934 or ASTM A-775. Although ASTM A-934 has shown better performance than A-775 coating, it is not available in all areas of North America. With the DYWIDAG system, it is possible to epoxy coat the entire length of the bar. Oversized hardware is available to thread over a coating up to 10 mils thick. ASTM A-934 is usually purple or gray in color while ASTM A-775 is green in color.
Epoxy coated bar with partial or full DCP
Partial Double Corrosion Protection (DCP) protection over epoxy-coated bar provides additional protection in areas considered most corrosive. A bar that is epoxy coated over its entire length with a pregrouted plastic sheathing is often referred to as a triple corrosion protected soil nail. This type of corrosion protection is used in extremely aggressive environments.
Double Corrosion Protection - DCP
The most reliable corrosion protection for soil nails in permanent applications or for nails used in critical structures is to pregrout the nail in corrugated PVC or HDPE sheathing. The sheathing provides a watertight barrier. Tests have proven that the deformations of the THREADBAR ® limit crack width to 0.1 mm (4mils).