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Soil Nailing for Slope Stabilization: An Overview

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Research Article Volume 6 Issue No. 12

Soil Nailing for Slope Stabilization: An Overview

Ravindra Budania1, Dr. R.P Arora2
M. Tech Scholar, CE, CTAE, Udaipur, India1
Associate Professor, CE, CTAE, Udaipur, India2

Abstract:
Soil nailing is an in-situ reinforcement technique by passive bars which can withsand tensile forces, shearing forces and bending
moments. This technique is used for retaining walls and for slope stabilization. Its behaviour is typical of that of composite materials
and involves essentially two interaction mechanisms. The soil- reinforcement friction and the normal earth pressure on the
reinforcement. The mobilization of the lateral friction requires frictional properties for the soil, while the mobilization of the normal
earth pressure requires a relative rigidity of the inclusions. early 1960s was the premier prototype to use steel bars and
shotcrete to reinforce the ground. With the increasing use of the
Keywords: Stabilization, Nails, Centralizers technique, semi-empirical designs for soil nailing began to
evolve in the early 1970s. The first systematic research on soil
I. INTRODUCTION nailing, involving both model tests and full-scale field tests, was
carried out in Germany in the mid-1970s. Subsequent
A landslide (landslip) is a geological phenomenon that comprises development work was initiated in France and the United States
a wide range of ground movements, such as rock falls, deep in the early 1990s.
failure of slopes etc. Landslides can occur in offshore, coastal
and onshore environment. It can be controlled by the use of • Tunnelling Method in the 1960’s.One of the first
proper slope stabilization techniques. Soil stabilization is a term applications of soil nailing was in 1972 for a railroad
in which the natural soil is changed in order to meet the widening project near Versailles, France, where an 18 m
engineering purposes by means of physical, chemical, biological (59 ft) high.
and combined method of either two of them or all three. Weight • In Germany, the first use of a soil nail wall was in 1975.
bearing capacity and the performance of the in-situ soil and sand • The United States first used soil nailing in 1976 for the
can be increased by soil stabilization techniques (Sharma 2015). support of a 13.7 m deep foundation excavation in
Soil nailing is an advance technique of slope stabilization dense silty sands.
amongst other techniques. Soil nailing is the technique used in • In India use of soil nailing technology is gradually
slope stabilization and excavation with the use of passive increasing and guidelines have been made by IRC with
inclusions, usually steel bars, termed as soil nail. Soil nailing is the help of Indian Institute of Science, Bangalore.
typically used to stabilize existing slopes or excavations where
top-to-bottom construction is advantageous compared to other III.CONCEPT OF SOIL NAILING:-
retaining wall systems (Taib, 2010). Soil nails are structural
reinforcing elements installed to stabilize steep slopes and The function of soil nailing is to strengthen or stabilize the
vertical faces created during excavations. Commonly used soil existing steep slopes and excavations as construction proceeds
nails are made of steel bars covered with cement grout. The grout from the top to bottom. Soil nails develops their reinforcing
is applied to protect the steel bars from corrosion and to transfer action through soil-nail interaction due to the ground
the load efficiently to nearest stable ground. Some form of deformation which results in development of tensile forces in soil
support, usually wire mesh-reinforced shotcrete, is provided at nail. The major part of resistances comes from development of
the construction face to support the face between the nails and to axial force which is basically a tension force. Conventionally,
serve as a bearing surface for the nail plates (Palmeira et al., shear and bending have been assumed to provide little
2008). contribution in providing resistance (Dey, 2015). The effect of
soil nailing is to improve the stability of slope or excavation
II.ORIGIN OF THE SOIL NAILING TECHNIQUE through

The soil nailing technique was developed in the early 1960s, a) Increasing the normal force on shear plane and hence
partly from the techniques for rock bolting and multi-anchorage increase the shear resistance along slip plane in friction soil.
systems, and partly from reinforced fill technique (FHWA, b) Reducing the driving force along slip plane both in
1998). The New Austrian Tunneling Method introduced in the friction and cohesive soil.
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In soil nailing, the reinforcement is installed horizontally or results in increment of the normal force coming on slip plane and
gently inclined parallel to the direction of tensile strain so that it reduces the driving shear force. The soil nails are embedded in
develops maximum tensile force develops. Soil nails are passive passive region through which it resists the pull-out of nail from
inclusions, which improve shearing resistance of soil. The soil slope through friction between nails and soil. Based on the above
nail system can be divided into active and passive region as two mechanisms, the required amount of nail length should be
shown in Figure. During the slope failure, active region tends to placed in resistive zone. In addition, the combined effect of nail
deform which results in axial displacement along soil nails head strength and tension force generated in active zone must be
which are placed across the slip plane. This results in the adequate to provide the required nail tension at the slip surface
development of tensile forces in soil nail in the passive zone (Byrne et al. 1998).
which resists the deformation of active zone. This tension force
Figure.1. Conceptual soils nail behavior (Byrne et al., 1998) Figure.2. Soil nails reinforcement Bars

• Construction of soil nailing structures • 4.1.2. Centralizers- Centralizers are devices made of polyvinyl
Constructional elements • Constructional procedure chloride (PVC) or other synthetic materials that are installed at
various locations along the length of each nail bar to ensure that
4.1. Elements of nailed structure:- a minimum thickness of grout completely covers the nail bar.

Various components of a grouted soil nail are:-

4.1.1. Steel reinforcing bars – The solid or hollow steel

reinforcing bars (with minimum strength of 415 kPa) are the
main component of the soil nailing system. These elements are
placed in pre-drilled drill holes and grouted in place.

Figure.3. Typical Centralizers

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4.1.3. Grout – Shotcrete or grout can be continuous flow of
mortal or concrete mixes projected at high speed perpendicularly
onto the exposed ground surface. Grout is injected in the
predrilled borehole after the nail is placed to fill up the annular
space between the nail bar and the surrounding ground.
Generally, neat cement grout is used to avoid caving in drillhole;
however, sand-cement grout is also applied for open-hole drilling
(Shong, 2005).

Figure.5. Typical cross-section of a drilled soil nail wall

(Byrne et al., 1998) Constructional Procedure
Figure.4. Grout is being placed with the help of pipes
• Excavation
4.1.4. Nail head – The nail head is the threaded end of the soil
nail that protrudes from the wall facing. It is a square shape Prior to any excavation, surface water controls should be
concrete structure which includes the steel plate, steel nuts, and constructed to prevent surface water from flowing into the
soil nail head reinforcement. This part of structure provides the excavation, as this condition will adversely affect construction
soil nail bearing strength, and transfers bearing loads from the and potentially cause instability of the excavated face. Collector
soil mass to soil nail. trenches behind the limits of the excavation usually intercept and
divert surface water. Initial excavation is carried out to a depth
4.1.6. Temporary and permanent facing – Nails are connected for which the face of the excavation may remain unsupported for
to the excavation or slope surface by facing elements. Temporary a short period of time, e.g. 24 to 48 hours. The depth for each
facing is placed on the unsupported excavation prior to excavation reaches slightly below the elevation where nails will
advancement of the excavation grades. It provides support to the be installed. The width of the excavated platform or bench is
exposed soil, helps in corrosion protection and acts as bearing such that it can provide sufficient access to the installation
surface for the bearing plate. Permanent facing is placed over the equipment. The initial lift is typically taken as 1 to 1.2 m high.
temporary facing after the soil nails are installed. The excavated face profile should be reasonably smooth and not
too irregular to minimize excessive shotcrete quantities.
4.1.7. Drainage system – Vertical geo-composite strip drains are
used as drainage system media. These are placed prior to
application of the temporary facing for collection and
transmission of seepage water which may migrate to the
temporary facing.

Figure.6. Excavation of small cut (Byrne et al., 1998)

Drilling Nail Holes:-

There are two types of processes which can be carried out after
excavation for putting the nails. The nail can be directly pushed
into the soil using suitable equipment, in which the nail itself
makes its way forward. Alternatively, a hole can be drilled prior
to putting the nail by using some drilling equipment. Some of the
drilling equipments used for this method are listed below.

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 and admixtures are mixed in a batch plant and conveyed to the
• Drill bit machine nozzle by a hydraulic pump. Both shotcrete methods produce a
• Rope core drill mix suitable for wall facings. Dry mix and wet mix shotcrete use
• Air leg rock drill a water-cement ratio of about 0.4 and produce roughly the same
mix quality, although shotcrete obtained with the wet mix
• Horizontal drill machine
process yields a slightly greater flexural strength.

Figure.9. Construction of Temporary Shotcrete Facing

(Byrne et al., 1998)
Figure.7. Drilling Nail Holes (Byrne et al., 1998) Nail
Installation and Grouting:-
Construction of Subsequent Levels:-
The steps mentioned above are repeated for the remaining
Nail bars are placed in the pre-drilled holes. Centralizers are
excavation stages. At each excavation stage, the vertical drainage
placed around the nails prior the insertion of nails to maintain
strip is unrolled downward to the subsequent stage. A new panel
proper alignment within the hole and also to allow sufficient
of WWM is then placed overlapping at least one full mesh cell.
protective grout coverage over the nail bar. Grout pipe is also
The temporary shotcrete is continued with a cold joint with the
inserted in the drill hole at this stage. A grouting pipe is normally
previous shotcrete lift. At the bottom of the excavation, the
attached with the nail reinforcement while inserting the nail into
drainage strip is tied to a collecting toe drain.
the drilled hole. Sometimes additional correctional protection is
used by introducing corrugated plastic sheathing The normal
range of water/cement ratio of the typical grout mix is from 0.45
to 0.5. The grout is commonly placed under gravity or low
pressure. The grouting is from bottom up until fresh grout return
is observed from the hole.

Figure.10. Construction of Subsequent Levels (Byrne et al.,

1998)

Construction of Permanent Facing:-

The final facing is constructed after the bottom of the excavation

is reached and nails are installed. Final facing consists of cast-
inplace (CIP) reinforced concrete, reinforced shotcrete, or
prefabricated panels. Generally, conventional concrete bars or
Figure.8. Nail Installation and Grouting (Byrne et al., 1998) WWM is provided as reinforcement in permanent facing. When
CIP concrete and shotcrete are used for the permanent facing,
Construction of Temporary Shotcrete Facing horizontal joints between excavation stages are avoided to the
maximum extent possible.
The temporary shotcrete facing is placed to temporarily restrain
the exposed soil in cut face. It consists of 3-4 inches of shotcrete
reinforced with a single layer of welded wire mesh. Two types of
shotcrete methods are commonly used: dry mix and wet mix. In
the dry mix method, the aggregate and cement are blended in the
dry and fed into the shotcrete gun while the mix water is added at
the nozzle. In the wet mix method, the aggregate, cement, water,
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Figure.11. Construction of Permanent Facing (Byrne et al.,
1998)

• VARIOUS TYPES OF SOIL NAILING:-

Various types of soil nailing methods that are employed in the
field are listed below:
• Grouted Nail: After excavation, first holes are drilled
in the wall/slope face and then the nails are placed in
the predrilled holes. Finally, the drill hole is then filled
with cement grout.
• Driven Nail: In this type, nails are mechanically driven Figure. 12. Roadway Cuts (lazarte et al., 2015)
to the wall during excavation. Installation of this type
of soil nailing is very fast; however, it does not provide 6.2. Road Widening Under Existing Bridge Abutments Soil
a good corrosion protection. This is generally used as nail walls can be advantageous for underpass widening when
temporary nailing. the removal of an existing bridge abutment slope is necessary.
• Self-Drilling Soil Nail: Hollow bars are driven and While the cost of installing a soil nail wall under a bridge
grout is injected through the hollow bar simultaneously abutment may be comparable to that of other applicable
during the drilling. This method is faster than the systems, the advantage of soil nailing is that the size of the soil
grouted nailing and it exhibits more corrosion nail drill rig is relatively small.
protection than driven nail.
• Jet-Grouted Soil Nail: Jet grouting is used to erode the
ground and for creating the hole to install the steel
bars. The grout provides corrosion protection for the
nail.

• Applications
Soil nail can be used in the following applications: (lazarte
et al., 2015)
6.1. Roadway Cuts
Soil nailing is attractive in roadway cuts because a limited
excavation and reasonable right-of-way (ROW) and clearing
limits are required. These factors help to reduce the
environmental impacts along the transportation corridor. The
impact to traffic may also be reduced because the equipment for
installing soil nails is relatively small.

Figure.13. Road Widening under Existing

Bridge Abutments (lazarte et al., 2015)

Repair and Reconstruction of Existing Retaining Structures

Soil nails can be used to stabilize and/or strengthen failing or

distressed retaining structures. For example, some mechanically
stabilized earth (MSE) walls may exhibit excessive deformation
due to poor design, poor construction, or both. Soil nails can be
installed directly through the face of an MSE wall if the existing
face is sufficiently stable to resist drilling. The selection of an
appropriate bearing plate to support soil nails stabilizing MSE
and masonry walls is very important. The bearing plate must be
International Journal of Engineering Science and Computing, December 2016 3881 http://ijesc.org/
able to fully transfer loads without damage to the existing be
facing. appropri
ate for
• Advantage and Disadvantages of soil nailing applicat
ions
Advantages associated with soil nailing fall into three main where
categories: Construction, Performance, and Cost. (lazarte et al., very
2015) strict
deforma
Construction tion
control
• Soil nail walls require smaller rows than most other is
competing systems. This is also true for ground anchors as soil required
nails are typically shorter. for
• Soil nail walls are less disruptive to traffic and cause
less environmental impact compared to other construction
techniques such as drilled shafts or soldier pile walls, which
require relatively large equipment. • The installation of soil nail
walls is relatively fast.
• Soil nail wall installation is not as restricted by
overhead limitation as in the case of soldier pile installation. This
advantage is particularly important when construction occurs
under a bridge.
• Soil nailing may be more cost-effective at sites with
remote access because the smaller equipment is more readily
mobilized.
• Soil nails are installed using equipment that is
multipurpose and can be used for other substructure elements
such as underpinning or protection of adjacent, movement-
sensitive structures.
Performance

Soil nail walls are relatively flexible and can accommodate

comparatively large total and differential movements. • The
measured deflections of soil nail walls are usually within
tolerable limits in roadway projects when the construction is
properly controlled. • Soil nail walls have performed well during
seismic events. • Soil nail walls have more redundancy than
anchored walls because the number of reinforcing elements per
unit area of wall is larger than for anchored walls.

Cost

• Conventional soil nail walls tend to be more economical

than conventional concrete gravity walls taller than
approximately 12 to 15 ft.
• Soil nail walls are typically equivalent in cost or more
costeffective than ground anchor walls when conventional soil
nailing construction procedures are used.

• Soil nail disadvantages

Some of the potential disadvantages of soil nail walls are (Liew

Shaw-Shong, 2005):
• Soil nail
walls
may not
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 structures and utilities located behind the proposed
wall, as the system requires some soil deformation to
mobilize resistance. Deflections can be reduced by post
tensioning but at an increased cost.
• Existing utilities may place restrictions on the location, inclination,
and length of soil nails.
• Soil nail walls are not well suited where large amounts of
groundwater seep into the excavation because of the requirement to
maintain a temporary unsupported excavation face.
• Permanent soil nail walls require permanent, underground
easements.
• Less suitable for course grained soil and soft clayey soil, which have
short self-support time, and soils prone to creeping.
• Suitable only for excavation above groundwater.

IV. REFERENCES

[1]. Babu, GL Sivakumar, R. S. Rao, and S. M. Dasaka.

"Stabilisation of vertical cut supporting a retaining wall using
soil nailing: a case study." Proceedings of the Institution of Civil
Engineers-Ground Improvement 11.3 (2007): 157-162.

[2]. Byrne, R. J., Cotton, D., Porterfield, J., Wolschlag, C. and

Ueblacker, G. (1998) “Soil Manual for design and construction
monitoring of soil nail wall” Manual of the Federal Highway
Administration Division, (No. FHWA0-SA-96-069R.)

[3]. Lazarte, C. A., Robinson, H., Gómez, J. E., Baxter, A.,

Cadden, A., & Berg, R. (2015). Soil Nail Walls Reference Man
ual (No. FHWA-NH I-14-007).

[4]. Liew, S. S., & Liong, C. H. (2006). Two Case Studies on Soil
Nailed Slope Failures. In submitted) International Conference on
Slopes, Malaysia.

[5]. Palmeira, E. M., Tatsuoka, F., Bathurst, R. J., Stevenson, P.

E., & Zornberg, J. G. (2008). Advances in geosynthetics
materials and applications for soil reinforcement and
environmental protection works. Electron J Geotech Eng, Spec
Issue State of the Art in Geotech Eng, 13, 1-38.

[6]. Shaw-Shong, L. (2005). Soil nailing for slope strengthening.

Geotechnical Engineering, Gue & Partners Sdn Bhd, Kuala
Lumpur, Malaysia.

[7]. Taib, S. N. L. (2010). A Review of Soil Nailing Design

Approaches. UNIMAS E-Journal of Civil Engineering, 1(2).

[8]. Jewell, R. A. and Pedley, M. J. (1992) “Analysis for soil

reinforcement with bending stiffness” Journal of Geotechnical
Engineering, ASCE, Vol. 118, No. 10, pp. 1505-1528.

Journal of Engineering Science and Computing, December 2016 3883 http://ijesc.org/

[9]. Sharma, P. “Theoretical analysis of soil nailing: design,
performance and future aspects (2015)”. International Journal of
Engineering Research and General Science

International
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