Strength Through Soil Nailing or Wire Mesh for Retaining Walls
The basic notion of soil nailing was introduced to reinforce and fortify the existing ground. This was achieved by installing closely spaced steel or iron bars called “nails,” onto a slope or quarry as construction moves from the top to the bottom. Soil nailing is an inexpensive means of creating shoring systems and retaining walls.
Often, nailing is less disruptive than other means of constructing retaining systems. What this process results in is a reinforced section that is stable in itself, and is also thereby capable of retaining the ground behind it. The nails themselves are passive in nature, but how they work is by developing their reinforcing action through nail ground interactions, as the ground deforms both during and subsequent to the construction activity.
Nails work predominantly in tension, but some say that they also work in bending under certain circumstances. Generally speaking, the soil nails significantly increase the perceptible cohesion of the soil through their ability to carry huge tensile loads. A construction facing, typically shotcrete armored with welded wire mesh is also usually required. For permanent walls, the shotcrete construction facing is typically covered in cast-in-place concrete (or similar material) facing.
Soil nailing appears similar to the age-old concept of the reinforced fill. Though there are some differences in the construction of the two, especially since the nails are inserted directly into an existing accumulation of earth, rather than being installed with the fill.
Two common applications for soil nailing are the construction of new slopes in cuttings, and also corrective works for otherwise unstable slopes. Soil nailing may be used in any natural ground, but, like most processes, some ground conditions are more suitable than others.
This is how the process typically occurs:
The shoring requires drilling through the active zone into the ground’s passive zone. A five-foot cut is prepared to begin initial stage of the nailing process. Holes are then drilled in to cut bank on about five foot centers. Next, threaded bars with centralizers are placed in the shoring holes. The threaded bars are grouted in place from bottom upwards. The wire screen is attached to rebar reinforcement installed over the soil’s cut face. First coating of the shotcrete is applied to cover protruding threaded bar. The plates, washers, nuts positioned on shoring bars are then locked down. Lastly, the second coat of shotcrete is applied over the soil and plates.
Like everything, soil nailing construction also has its drawbacks and pitfalls:
The method cannot be used at those sites where groundwater is a problem.
It is not appropriate for sites with soils having very low shear strength, or in sand and gravels that lack cohesion, and on those sites with other unsuitable soils.
The soil must be able to stand unsupported while it is in the process of being nailed and before shotcrete application.
Good drainage is essential, especially for permanent structures and in places susceptible to freeze-thaw cycles.
Finally, it is essential that projects be planned, constructed, and monitored by specialists with knowledge in soil nailing.
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