Soil nailing is a ground stabilization technique that can be used on either natural or excavated slopes. It involves drilling holes for steel bars to be inserted into a slope face which are then grouted in place. Mesh or shotcrete is attached to the bar ends to hold the slope face in position.
Soil nailing is commonly used as a remedial measure to stabilize steep sloping embankments. Other applications for soil nailing include:
- Temporary excavation shoring
- Tunnel portals
- Roadway cuts
- Under bridge abutments
- Repair and reconstruction of existing retaining structures
- Landslide redemption
- Steep cut stabilization
- Long term stabilization to existing structures without the need for demolition
The main considerations for deciding whether soil nailing will be appropriate include; the ground conditions, the suitability of other systems to perform the same task (ground anchors), geosynthetic materials, and finally cost.
Soils which are particularly suited to soil nailing include clays, clayey silts, silty clays, sandy clays, sandy silts, sand, and gravels. Soil nailing can be used on weathered rock as long as the weathering is even throughout the rock.
Soils which are not well-suited to soil nailing include those with a high groundwater table, cohesion-less soils, soft fine-grained soils, loose granular soils, and ground exposed to repeated freeze-thaw action.
Some of the advantages of using soil nailing include:
- They are good for confined spaces with restricted access
- There is less environmental impact
- They are relatively quick and easy to install
- They use less materials and shoring
- They are flexible enough to be used on new construction, temporary structures, or on remodeling processes
- The height is not restricted
Limitations of using soil nailing include:
- They are not suitable for areas with a high water table
- They are not suitable for permanent use in sensitive and expansive soils
- Specific contractors are required.
- Extensive 3D modelling may be required.
Long-term performance monitoring is typically implemented to collect data to ensure adequate performance and refine future design practices. Parameters to be measured include vertical and horizontal movement of the wall face, local movements or deterioration of facing elements, drainage to the ground, loads, load distribution and load changes in the nails, temperature, and rainfall.
Soil nailing, in many cases, provides a cost-effective solution to steep slope erodibility problems throughout the construction process. It is an often forgotten about remedial practice that is both functional and environmentally friendly. Keep it in the back of your mind as a topic of discussion with your engineer the next time you’re between a rock and a hard place.