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What is soil nailing technique?Soil nailing technique used to reinforce soil to make it more stable. Added to that, it is used for slopes, excavations, retaining walls etc. to make it more stable. This article will shed light on soil nailing technique, its types and applications.
Soil nailing technique processIn this technique, soil is reinforced with slender elements such as reinforcing bars which are called as nails as illustrated in Fig.1. These reinforcing bars are installed into pre-drilled holes and then grouted. Moreover, these nails are installed at an inclination of 10 to 20 degrees with vertical. As the excavation proceeds, the shotcrete, concrete or other grouting materials are applied on the excavation face to grout the reinforcing steel or nails. Fig.2 to Fig.5 illustrate typical soil nailing process.
Types of Soil Nailing techniquesThe following sections present different types of soil nailing technique:
Drilled and grouted Soil Nailing method
- In this type of soil nailing methods, the holes are drilled in walls or slope face
- Then, nails are inserted in the pre-drilled holes.
- after that, the hole is filled with grouting materials such as concrete, shotcrete etc.
- Finally, diameter of nails ranges from 100-200mm with spacing of 1.5m.
Driven soil nailing method
- It is used for temporary stabilization of soil slopes.
- Driven soil nailing method is considerably fast.
- However, it does not provide corrosion protection to the reinforcement steel or nails.
- In driven soil nailing method, the nails are driven in the slope face during excavation.
- Diameter of the nail is around 19mm to 25mm which is comparatively small.
- Lastly, nail spacing is 1m to 1.2m.
Self drilling Soil Nailing method
- Hollow bars are used in self driven soil nailing method.
- Bars are drilled into the slope surface. Grout injected simultaneously during the drilling process.
- It is faster than drilled grouted nailing.
- Lastly, self-drilling soil nailing method provides more corrosion resistance to nails than driven nails.
Jet Grouted Soil Nailing method
- In jet grouted soil nailing method, jets are used for eroding the soil for creating holes in the slope surface.
- After that, steel bars are installed in this hole and grouted with concrete.
- Finally, jet grouted soil nailing provides good corrosion protection for the steel bars (nails).
Launched Soil Nail method
- In this method of soil nailing, the steel bars are forced into the soil with a single shot using compressed air mechanism.
- The installation of soil nails is fast, but controls over length of bar penetrating the ground is difficult.
- Utilized to reinforce an unstable or potentially unstable soil mass. capacity into the sliding soil.
- Finally, nail diameter is 38mm and its length is around 6m.
Applications of soil nailing
- Stabilization of existing retaining wall
- Excavating retaining structures in urban areas for high rise buildings and underground facilities.
- Landslide redemption
- Stabilization of highway and roadway embankments and cut slopes
- Tunnel portals in unstable and steep stratified slopes
- Construction and retrofitting bridge abutments
- Steep cutting stabilizations
- Stabilizing of over steep existing embankments
- Provide long term stability to existing concrete structures without demolition and rebuilding costs
- Lastly, temporary excavation shoring
Soil nail installation considerations
- 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.
- Finally, soil nailing should start immediately after excavation. Any delay may lead to collapse of soil slope.