Soil nails are a cost effective method for long or short term stabilisation of steep existing or proposed slopes. The stability of the slope is increased with the installation of steel or glass fibre threaded soil nails placed into pre-bored holes or simultaneous drilling and installation techniques. The end results along with the correct drainage significantly reduce the chances of a landslide or other ground movements. At Aarsleff, we take pride in being fully proactive with our clients to offer a one-stop design and build soil nail, ground anchor solution to enable our clients to rest easy in the knowledge that their contract is in safe hands.
Soil nails are typically used to stabilise existing slopes or excavations where top-to-bottom construction is advantageous compared to other retaining wall systems. For certain conditions, soil nails offers a viable alternative from the viewpoint of technical feasibility, construction costs, and construction duration when compared to ground anchor walls, which is another popular top-to-bottom retaining system.
Soil nail walls are particularly well suited to excavation applications for ground conditions that require vertical or near-vertical cuts and have been shown to be particularly well suited for the following temporary or permanent applications:
- Roadway cut excavations.
- Road widening under an existing bridge end.
- Repair and reconstruction of existing retaining structures.
- Temporary or permanent excavations in an urban environment.
Soil nails have proven economically attractive and technically feasible when:
- The soil in which the excavation is constructed is able to stand unsupported in a 1- to 2-m (3- to 6-ft) high vertical or nearly vertical cut for one to two days.
- All soil nails within a cross section are located above the groundwater table
- If soil nails are below the groundwater table, and the groundwater does not adversely affect the face of the excavation, the bond strength of the interface between the grout and the surrounding ground, or the long-term integrity of the soil nails (e.g., the chemical characteristics of the ground do not promote corrosion).
Soil nail advantages
Soil nail walls exhibit numerous advantages when compared to ground anchors and alternative top-down construction techniques. Some of these advantages are described below:
- Less disruptive to traffic and causes less environmental impact compared to other construction methods.
- Provide a less congested workplace, particularly when compared to bracedexcavations.
- There is no need to embed any structural element below the bottom of excavation as with soldier beams used in ground anchor walls.
- Soil nail installation is relatively rapid and uses typically less construction materials than ground anchor walls.
- Nail location, inclination, and lengths can be adjusted easily when obstructions (cobbles or boulders, piles or underground utilities) are encountered. On the other hand, the horizontal position of ground anchors is more difficult to modify almost making field adjustments costly.
- Since considerably more soil nails are used than ground anchors, adjustments to the design layout of the soil nails are more easily accomplished in the field without compromising the level of safety.
- Overhead construction requirements are smaller than those for ground anchor walls because soil nail walls do not require the installation of soldier beams (especially when construction occurs under a bridge).
- Soil nailing is advantageous at sites with remote access because smaller equipment is generally needed.
- Soil nail walls are relatively flexible and can accommodate relatively large total and differential settlements.
- Measured total deflections of soil nail walls are usually within tolerable limits.
- Soil nail walls have performed well during seismic events owing to overall system flexibility.
- Soil nail walls are more economical than conventional concrete gravity walls when conventional soil nailing construction procedures are used.
Soil nail walls are typically equivalent in cost or more cost-effective than ground anchor walls when conventional soil nailing construction procedures are used.