Soil Nails / Rock Bolts

Soil Nailing is an in-situ technique used to reinforce and strengthen an existing embankment. Applications include stabilisation of cut slopes, ground retention systems in urban areas for high-rise building and underground facilities, tunnel portals in steep and unstable stratified slopes, construction and retrofitting of bridge abutments.

The fundamental concept is that soil can be effectively reinforced by installing closely spaced grouted steel bars, or “nails”, into a slope or excavation as construction proceeds from the top down. The nail bars are not pre-tensioned when they are installed (passive anchorage) and require very small deformations to mobilise frictional resistance. Soil nails transfer their load over the fully grouted length and increase the shear strength of the overall soil mass and limit displacement during and after excavation.

In soil nailing, similarly to ground anchors, the load transfer mechanism and the ultimate pull-out resistance of the nails depends primarily upon soil type and strength characteristics, installation technique, drilling method, size and shape of the drilled hole, as well as grouting method and pressure used. Hence, as with ground anchors, site specific geotechnical investigations are essential. In addition, the design of a soil nail requires that the ground is competent enough to be self supporting during drilling so that the necessary skin friction can be mobilized along the entire bonded length and the use of temporary casing or an overburden casing system will effectively smear the drill hole and potentially reduce the achievable bond stress. Should casing be required, this needs to be considered by the designer.