Soil nailing is a construction technique that we use to reinforce soil to make it more stable. We use this technique for slopes, excavations, retaining walls etc. to make it more stable.
In this technique, soil is reinforced with slender elements such as reinforcing bars which are called as nails. These reinforcing bars are installed into pre-drilled holes and then grouted.
These nails are installed at an inclination of 10 to 20 degrees with vertical.
Soil nailing is used to stabilize the slopes or excavations where required slopes for excavation cannot be provided due to space constraints and construction of retaining wall is not feasible. It is just an alternate to retaining wall structures.
As the excavation proceeds, the shotcrete, concrete or other grouting materials are applied on the excavation face to grout the reinforcing steel or nails. These provide stability to the steep soil slope.
Types of Soil Nailing:
There are various types of soil nailing techniques:
- Grouted Soil Nailing:
In this type of soil nailing, the holes are drilled in walls or slope face and then nails are inserted in the pre-drilled holes. Then the hole is filled with grouting materials such as concrete, shotcrete etc.
- Driven Nails:
Driven nailing is used for temporary stabilization of soil slopes. In this method, the nails are driven in the slope face during excavation. This method is very fast, but does not provide corrosion protection to the reinforcement steel or nails.
- Self drilling Soil Nail:
In this method, the hollow bars are used. Hollow bars are drilled into the slope surface and grout is injected simultaneously during the drilling process. This method of soil nailing is faster than grouted nailing. This method provides more corrosion resistance to nails than driven nails.
- Jet Grouted Soil Nail:
In this method, jets are used for eroding the soil for creating holes in the slope surface. Steel bars are then installed in this hole and grouted with concrete. It provides good corrosion protection for the steel bars (nails).
- Launched Soil Nail:
In this method of soil nailing, the steel bars are forced into the soil with very high speed using compressed air mechanism. The installation of soil nails are fast, but control over length of bar penetrating the ground is difficult.
These points must be noted for installation of soil nails:
- Soil Nails must penetrate beyond the slip plane into the passive zone typically for 4 to 5m.
- The spacing of soil nails in horizontal or vertical direction must be related to strength of the soil. Extra soil nails should be installed at the edge of any surface being stabilized.
- Soil nailing should start immediately after excavation. Any delay may lead to collapse of soil slope.