Soil nailing is a construction technique which is usually exploited as a remedial technique to treat unstable natural soil slopes or as a construction technique that paves way for safe over-steeping of new or existing soil slopes.
Advantages of Soil Nailing
Soil nailing technique exhibits various advantages compared to other techniques, such as alternative top-down and ground-anchor construction. They include (Johnson Card and Darley 41-45):
- It provides a less congested work place, particularly when compared to other techniques, for instance, braced excavations.
- The technique is less disruptive to traffic and leads to less environmental impacts as compared to other construction techniques.
- Nail location , lengths and inclinations can be easy manipulated and adjusted when obstructions are encountered: boulders, piles or underground utilities. It is not easy to adjust the horizontal position covered by ground anchors, making field adjustments costly.
- Soil nails do not require the installation of soldier beams, in the case of a construction under a bridge. This minimizes the requirements of overhead construction compared to the requirements of ground anchors.
- Soil nail walls are fairly flexible and can accommodate comparatively huge differential and total settlements.
- The total deflection recorded in soil nail walls is normally within bearable limits. This renders soil nailing technique more efficient compared to other construction routines.
- Typically, building soil nail walls is less costly than the cost incurred in other construction methods. This is realized when unadventurous soil nailing construction procedures are respected.
- Soil nailing uses smaller equipment and, hence, more advantageous for use in remote sites.
Disadvantages of Soil Nailing
The soil nailing process has a numbers of shortcomings just like any other construction technique:
- Soil nailing technique cannot be suitable in situations where stringent deformation control is necessary for utilities and structures behind the proposed wall. This is because the constructed system will need to mobilize resistance, which is possible through actions meant to facilitate soil deformation.
- Soil nail walls are less applicable and incompatible in locations where a lot of ground water enters the excavation. This primary reason behind this is the method has to maintain a short-term excavation face that is not supported.
- In order to construct and maintain permanent soil nail walls, it is a requirement to have permanent underground basements.
- The construction of soil nail walls and the whole soil nailing construction routine requires specialized and experienced contractors.
- The existing structures and utilities may have restrictions on the soil nails’ length, location, and inclination. This limits the construction and renders it expensive where the construction is to be designed as not to impose any damages to the existing utilities (Byrne et al, 23).
Soil nailing is a technical process and requires extensive exploitation of equipments and machinery. The machinery used includes (Hartman & Rudy 32-36):
- Drilling equipments: Rotary air-flushed and water flushed, down-the-hole hammer, and tri-cone bit.
- Grout Mixing Equipment: sheer colloidal mixer and grout pump.
- Shotcreting Equipment: a valve at the nozzle outlet and measuring pin installed at fixed vertical and horizontal intervals in order to guide the nozzle man
- Compressor: it should have a minimum capacity to deliver concrete at a minimum rate of 9m3/min.
The failure of soil nailing as a construction technique was experienced in Malaysia; the failure of five berms soil nailed slope and seven berms cut slope. Before the soil nailing procedures are applied on any ground, it is of utmost importance that sub-surface investigations are carried out to determine the subsoil profile and any other relevant engineering parameters. The case history consisted of seven upper berms of 1V:1H and five berms of 4V:1H. The two cases failed due to Limited Equilibrium method and Finite Equilibrium method. The inappropriateness of these methods initiated the progressive failure (Shaw-Shong and Cheew-How 5).
Byrne. R. J, et al. Manual for Design and Construction Monituring of Soil Nail Wall. Federal Highway Administration of US, 1998. Print.
Hartman, Burt, & Rudy Hartmann. Soil Nailing Construction. Grand Junction, Colorado: Hartmann Engineering Inc, 2005. Print.
Johnson, P E, G B. Card, and P Darley. Soil Nailing for Slopes. Crowthrone, Berkshire, England: Transport Research Laboratory, 2002. Print.
Shaw-Shong, Liew and Cheew-How, Liong. Two Case Studies on Soil Nailed Slope Failures. N.p. Web. 26 Mar. 2016.