Practical aspects of soil nailing
The objective of soil nailing is to improve the stability of the soil in cases where the stability conditions are adverse. The stability is achieved by inserting soil nails, consisting of reinforcing bars, into the soil. Soil nailing is generally applied in connection with excavations, slopes and occasionally tunnelling, as shown in Figures A.1 and A.2, and for improvement of soil stability. The soil nails mobilise frictional forces along their entire length, which contributes to increasing the stability condition. The amount of nails and the length of installation of the nails have to be adjusted in relation to the stability conditions, encountered during the ongoing activities. Protection against corrosion in case of long-term stability problems is required in aggressive soil conditions.
|a) Vertical walls||b) Slopes|
- 1 ground surface
- 2 soil nails
- 3 tunnel advances
In the case of excavations, the sequence of excavation and soil nailing has to be adjusted in order not to comprise the stability conditions of the site. Typical methods of excavation in combination with soil nailing operations are illustrated in Figures A.3 and A.4.
- 1 excavation
- 2 installing the nails
- 3 reinforced shotcrete (or prefabricated facing panels)
- 4 next excavation
- 1 bulk excavation to proposed formation
- 2 berm
- 3 installed nails
- 4 existing ground
- 5 local trimming of face required to achieve agreed tolerances prior to nail installation of nail row "N"
- N Nth row
A.2 Examples of soil nail systems
The soil nail systems include reinforcement bars, usually steel bars, inserted into and bonded with the ground to the depth required with regard to safety conditions, and often provided with a head plate and a facing system to ensure stability between the nails and also to avoid erosion problems. There is a number of different soil nailing systems. Typical examples are given in Figure A.5.
|a) Pre-bored and grouted||b) Self-boring|
|1 facing||6 coupler|
|2 head plate||7 inner spacer|
|3 locking nut||8 grout annulus|
|4 outer spacer||9 reinforcing element|
|5 duct||10 drill bit|
NOTE Other systems may not use grout/duct/couplers/facing/spacers.