This document discusses soil nailing and compares glass fiber reinforced polymer (GFRP) soil nails to traditional steel bar soil nails. It provides details on the components and construction sequence of a typical soil nail wall. It outlines several advantages of GFRP soil nails over steel bars, including corrosion resistance, lighter weight, and similar tensile strength. Applications of GFRP soil nails include stabilizing cut slopes, excavations, tunnels, bridges, and existing structures. The document explains that GFRP soil nails provide a more durable and cost-effective alternative to steel due to eliminating corrosion protection needs.

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CHAPTER 1
INTRODUCTION
Soil nailing is a construction technique that can be used as a remedial measure to
treat unstable natural soil slopes or as a construction technique that allows the safe over-
steepening of new or existing soil slopes.
The procedure involves the insertion of relatively slender reinforcing elements
into the slope, often general purpose reinforcing bars(rebar) ,although proprietary solid or
hollow system bars are also available. Solid bars are usually installed into pre-drilled holes
and then grouted into place using a separate grout line, whereas hollow bars may be drilled
and grouted simultaneously by the use of a sacrificial drill bit and by pumping grout down
the hollow bar as drilling progresses.in a soil nailed retaining wall.
The properties and material behavior of three components-the native soil,the
reinforcement (nails) and the facing element-and their mutual interaction significantly
affect the performance of the structure.
A rigid facing (often pneumatically applied concrete, otherwise known
as shotcrete) or isolated soil nail head plates may be used at the surface. Alternatively a
flexible reinforcing mesh may be held against the soil face beneath the head plates.
1.1 ORGIN AND DEVELOPMENT
The origin of soil nailing can be traced to a support system for underground
excavations in rock referred to as the New Austrian Tunneling Method (Rabcewicz, 1964a,
1964b, 1965). This tunneling method consists of the installation of passive steel
reinforcement in the rock (e.g., rockbolts) followed by the application of reinforced
shotcrete.

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One of the first applications of soil nailing was in 1972 for a railroad widening project near
Versailles, France, where an 18 m (59 ft) high cut-slope in sand was stabilized using soil
nails (Rabejac and Toudic 1974). Clouterre research program, (Schlosser 1983; Clouterre
1993) is another step.
In Germany, the first use of a soil nail wall was in 1975. The first major research program
on soil nail walls was undertaken in Germany from 1975 through 1981 by the University of
Karlsruhe and the construction company Bauer. (Gassler and Gudehus 1981; Schlosser and
Unterreiner 1991).
In US, the first FHWA document on soil nailing was issued through FHWA’s Office of
Research and Development (Elias and Juran 1991). Updated version of above FHWA soil
nailing manual was made public in 2003 .
In India use of soil nailing technology is gradually increasing and guidelines have been
made by IRC with the help of Indian Institute of Science, Bangalore.
1.2 FAVOURABLE GROUND CONDITION FOR SOIL NAILING
Soil nails can be used for wide range of soil types and conditions .Experience
have shown that certain favourable ground condition make soil nailing cost effective over
other techniques.
Soil nailing has proven economically attractive and technically feasible when:
• Soil in which the excavation is constructed should able to stand unsupported in a
1m – 2m (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 the soil nails are below the groundwater table, 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).

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• It is advantageous that ground condition allow drill holes to be advanced without
use of drill casing and for the drill holes to be unsupported for few hours until nail
bars are installed and drill hole is grouted.
The result from standard penetration test provides the SPT values
which can be used preliminary identify the favourable soil condition for soil
nailing.Following ground condition are well suited for soil nail application
✓ Stiff to hard fine –grained soils: Fine grained or cohesive soils may include stiff to
hard clay,clayey silts, sandy silts and combination there of.these types of soils have
the spt value N around 9 blows/300mm.fine grained soil should have already
relatively low plasticity
✓ Dense to very dense granular soil: These soil include sand and gravel with SPT
value n greater than 30 and some fine with 10to 20% and with weak natural
cementation that provide cohesion.
✓ Weathered rock with no weaknes planes: Weathered rock may provide suitable
supporting material for soil nails as long as the weakness plane occurring
unfavourable orientation are not prevalent.
✓ Glacial soils: Glacial outwash and glacial till materials are typically suitable for soil
nail application as these soils are typically dense, well graded granular material with
a limited amount of fines.
In addition to above conditions certain other factors to be considered for soil nail structure
is that prolonged exposure to ambient freezing temperature may cause frost action in
saturated ,granular soils,as a result increased pressure will be applied on the temporary and
permanent facing. Repeated freeze and thaw cycle may reduce the bond strength.a suitable
protection against frost penetration and appropriate concrete mix must be provided.
Granular soils that are very loose (N<=4),loose (4<N<10) may undergo excessive
settlement due to vibration caused by construction equipment and traffic.

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CHAPTER 2
COMPONENTS OF A SOIL NAIL WALL
Fig 2. 1 Components Of Soil Nail Wall(Ravindra Budania, Dr. R.P Arora,2016)
Nail bars: Steel reinforcing bars used for soil nail are commonly threaded and may be
either solid or hollow .Bars with lower grade are preffered because they are more ductile ,
less suceptable to corrosion and are readily available.bars generally have a nominal strength
of 420 MPa for grade 60 or 520MPa for grade 75.

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Fig 2. 2 Soil nails reinforcement Bars(Ravindra Budania, Dr. R.P Arora,2016)
Nail head: This has two main components, bearing plate, hexnut and washers and the
headed stud.the purpose of bearing plate is to distribute the force at nail end to the
temporary shotcrete facing and the ground behind the facing.
Grout: Grout for soil nails is commonly neat cement grout ,which fills the annular space
between the nail bar and the surrounding ground.the water-cement ratio generally used
ranges from 0.4 to 0.5.
Fig 2.3 Grouting(Ravindra Budania, Dr. R.P Arora,2016)

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Centralizers: These are the device made up of PVC or other synthetic material that are
installed at various location along the length to ensure that minimum thickness of grout
completely covers the nail bar.
Fig 2.4 Centralizer(Ravindra Budania, Dr. R.P Arora,2016)
Drainage system: To prevent water pressure from developing behind the wall
facing,vertical geo composite strip drains are installed between the temporary facing and
the excavation.
Fig 2.5 Drainage system(Ravindra Budania, Dr. R.P Arora,2016)

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2.1 CONSTRUCTION SEQUENCE
• Excavation
• Drilling of nail holes
• Installation and grouting nails
• Construction of temporary shotcrete facing
• Construction of subsequent level
• Construction of final permanent facing
Fig 2.6 Construction Sequence(Piyush Sharma,2015)

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CHAPTER 3
GFRP SOIL NAIL TO STEEL BAR SOIL NAIL
3.1 ADVANTAGES
• The GFRP soil nail is highly corrosion resistant , durable and light weight.
• The tedious corrosion protection procedure for steel soil nails can thus be eliminated,
resulting in considerable savings in fabrication and field installation of soil nails.
• Posses high axial tensile strength comparable or superior to that of steel,which can
be controlled easily by the use of different resin.
• GFRP bars of similar diameters may replace steel bars for a required tensile force
without any modification of the drillhole dimensions and grouting equipments
• The transportation, handling, and installation of GFRP soil nails are convenient and
efficient, which is especially important for slope stabilization projects where site
accessibility is always limited.
• Thermal stress induced is significantly decreased by the reduction of the Young’s
modulus of GFRP (normally 25–30% of that of steel) when temperature suddenly
changes, as the coefficients of thermal expansion of GFRP and steel are similar.
• High adaptability of GFRP materials to fiber optic sensors.
• Hollow sections can increase the bending capacity of the slender member , allowing
for more tolerance on nonlinearity of installed nails.
• The GFRP pipes manufactured using pultrusion process has the ability to form
composites of various shapes suitable for different enginnering applications.
• Pressure grouting is adapted in GFRP soil nail,where this is not possible in
conventional method.
• The double grouting method has led to the improvement and increase in shear
strength of weak soil slopes, to reinforce cut slopes, to construct seepage cut off to
stabilize fault zones or any other discontinuities in rock masses.

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3.2 APPLICATIONS
• Stabilisation of railroad and highway cut slopes
• Excavation retaining structure in urban areas for high – rise building and
underground facilities
• Tunnel portal in steep and unstable stratified slope
• Construction and retrofitting of bridge abutments with complex boundaries
involving wall support under piled foundation
• Stabilizing steep cuttings to maximize development space
• The stabilizing of existing over steep embankments
• Soil nailing through existing concrete or masonry structures such as retaining walls
and bridge abutments to provide long term stability without demolition and rebuilt
cost
• Temporary support can be provided to excavation without the need for bulky and
intrusive scaffold type temporary work solution.
3.3 WHY GLASS FIBER REINFORCED POLYMER?
The current method of steel soil nail construction is both labour intensive as well
as expensive. As construced soil nails are always buried in the ground, they cannot be
inspected or maintained routinely. Therefore, corrosion protection is of paramount
importance to the longevity of steel soil nails installed in slopes.Many engineers are
considering use of new soil nail materials.an innovative soil nail is constructed by light
weight high strength glass fiber reinforced plastic pipe. It was a comparatively new
composition material, as a replacement of traditional steel rebar. In the 1960s, glass fiber-
reinforced polymer (GFRP) material was first used in structural reinforcement engineering
because of the typical advantages such as high corrosion resistance and light weight. As the
properties of GFRP material have been examined and understood for years, this
composition material became more and more popular in geotechnical engineering
projects.The main advantages of GFRP over conventional method is that it is corrosion
resistant ,light weight,high strength to weight ratio etc.the adaptability of grpf can be still
improved by pultrusion methods and double groting methods which is widely used in hong
kong and korea.

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Experiments have shown that the mechanical properties of GFRP differ from those
of steel, the bonding strength and failure mechanism of the GFRP soil nail are to be
investigated. The pullout resistance is a critical parameter in the design of soil nails and is
affected by a number of factors, including construction methods and process, properties of
soil and cement grout, roughness of soil-grout interface, and geometry of slope and
drillholes.In Hong Kong, field pullout tests are routinely performed on sacrificial soil nails
to verify the design bond strength between in situ soil and cement grout inside drillholes.

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CHAPTER 4
CASE STUDY
The total area of Hong Kong is approximately 1,103km2 , accommodating a
population of 6.8 million. The terrain of Hong Kong is hilly. To accommodate the
population and economic development, many slopes are formed for land development to
cope with the rapid development of Hong Kong. Natural hillsides have been transformed
into residential and commercial areas and used for infrastructural development. Hong
Kong’s steeply hilly terrain, heavy rain, and dense development make it prone to the risk of
landslides.
Currently, high yield steel bars are used as soil nails to stabilize slopes in Hong Kong and
many other countries. . In Hong Kong, higher factors of safety are required as many
buildings are constructed adjacent to slopes. The performance (tensile capacity) of a soil
nail is governed by the minimum of:
(1) tensile strength of the soil nail controlled by the yield stress of steel and the cross-
sectional area of the steel bar.
(2) bond resistance between the steel bar and cement grout, which is controlled by the
chemical and mechanical interlock at the nail-grout interface.
(3) stress transfer between cement grout and the soil which is controlled by the bond at the
soil-grout interface.
But in steel soil nail bars corrosion protection is of paramount importance to the
durability in slopes.Usually, no pressure is applied during grouting of conventional soil nail
(gravity flow of grout) as application of pressure with the current soil nail system is
difficult to carry out.
In view of the various problems associated with the use of steel bars as soil nails,
there are many research programs being carried out in Hong Kong, China and many other
countries. The features that would be desired for soil nails in Hong Kong include the
following:

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1. Light weight and high strength;
2. Application of pressure to control the grouting zone, quality of grouting, and bond strength;
3. Address corrosion problems;
4. Acceptable cost; and
5. Ease of construction—handling, joining, and cutting.
The authors have carried out research works on the use of GFRP bars as soil nails for a
project at Sanatarium Hospital in Hong Kong. From a pilot study by the authors, it was
concluded that the limitations of GFRP bar for soil nails are as follows:
(1) pressure grouting is complex
(2) joining of bars is not easy
(3) low shear strength.
For the present system, GFRP pipes of 37mm internal diameter and 5mm are utilized. The
pipes are fabricated by pultrusion process,where it serves as the structural member as well
as the grout pipe during construction. Pultrusion is a continuous molding process that
impregnates fiber reinforcement in a matrix of liquid thermosetting resins. Glass fiber is
drawn from spools through a resin bath where the reinforcement is impregnated with the
resin . The impregnated fibers are woven into the designed pattern and pulled by the
pultrusion machine at a constant rate through a steel die heated to a precisely controlled
temperature to cure resin.
Fig4.1 Spools of Glass Fiber(Alfred et al,2009)

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Fig4.2 Drawing of Glass Fiber and Impregnation With Liquid Thermosetting resin(Alfred
et al,2009)
Fig4.3 Weaving of the Impregnated Glass Fiber(Alfred et al,2009)
The composite is thus thermoset and molded to the pipe shape as shown in the figure. The
pultrusion process has the ability to form composites of different shapes suitable for
different engineering applications. The mechanical properties of the composite can be
easily controlled by the use of different combinations of resins and reinforcement fibers.
Moreover, suitable filler, catalysts, ultraviolet inhibitors and color pigments can be added to
the resin matrix to satisfy specific engineering, appearance and design requirements.

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Fig4.4 Pulling of Impregnated Glass fiber through Shaping Die(Alfred et al,2009)
Fig4.5 Thermoset and Molding of GFRP pipe to exact shape(Alfred et al,2009)
Fig4.6 Installation of Centralizers and Two additional Layers of Glass Fiber
Reinforcement(Alfred et al,2009)

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Fig4.7 Grout Holes In GFRP Pipe(Alfred et al,2009)
Fig4.8 Delivery of GFRP Pipes to Site(Alfred et al,2009)
Structural sections of GFRP pipe manufactured in this process possess the following
advantages:
• Strength—the strength is high and can be controlled easily by the use of different
fiber or resin. For example, urethane can greatly improve the strength of the FRP
products as compared with vinyl resin. Due to the size of the die, the internal
diameter of GFRP pipe is usually maintained constant and the tensile capacity of the
pipe is usually controlled by the thickness of the section.
• Lightweight—the unit weight is about 18–20% of steel.
• Corrosion resistance—can be controlled easily for various purposes and is much
better than structural steel.
• Electrical resistance—nonmagnetic and insulator to electric.
• Manufacturing process—small parts can be joined together to form large parts
easily by the pultrusion process.

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CHAPTER 6
CONCLUSION
• GFRP possesses a very high tensile strength which can be controlled easily by the
use of different resin.
• The shear strength of the material can be controlled by the addition of FRP layers
wrapped at 45° to the longitudinal direction and the actual lamination of the FRP as
produced from the pultrusion process .
• The use of hollow GFRP pipe has also effectively increased the second moment of
area as compared with the use of a bar section.
There is active research in the design of the innovative soil nail system in Hong Kong,
China, Korea, and many other countries. Through the present large scale study, it was
established that the use of light weight high strength GFRP can be utilized as an alternative
to the classical steel bar soil nail. While most researchers and engineers are working on the
use of FRP bars as soil nail, the present study has demonstrated that FRP pipe can be a
competitive solution for steep slope with limited working space.

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REFERENCE
• Albert T. Yeung, Y. M. Cheng ; L. G. Tham, Alfred S. K. Au, Sunny T. C. and Yong-
ki Choi(2007). “Field Evaluation of a Glass-Fiber Soil Reinforcement
System”.Journal of Performance of Constructed Facilities,Vol.21,No.1
• Alfred S. K. Au, W. B. Wei , J. Chen, Y. M. Cheng, Yong-ki Choi, Albert T. Yeung,
L. G. Tham, (2009).” New Soil Nail Material—Pilot Study of Grouted GFRP Pipe
Nails in Korea and Hong Kong” Journal of Materials in Civil Engineering,
Volume:21,Issue Number: 3
• Hong-Hu Zhu; Jian-Hua Yin, Albert T. Yeung, and Wei jin(2011). “Field Pullout
Testing and Performance Evaluation of GFRP Soil Nails”. Journal Of Geotechnical
And Geoenvironmental Engineering,
• Huafu Pei, Jianhua Yin ,Honghu Zhu, Chengyu Hong(2013).“Performance Monitoring
of a Glass Fiber-Reinforced Polymer Bar Soil Nail during Laboratory Pullout Test
Using FBG Sensing Technology”.
• Marek Kulczykowski, Jarosław Przewłócki, Bogusława Konarzewska(2017).
” Application of Soil Nailing Technique for Protection and Preservation Historical
Buildings”, IOP Conf. Ser.: Mater. Sci. Eng.
• Piyush Sharma(2015).” Theoretical Analysis Of Soil Nailing: Design, Performance
And Future Aspects” International Journal of Engineering Research and General
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• Ravindra Budania, Dr. R.P Arora(2016).” Soil Nailing for Slope Stabilization: An
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Cohesive And Cohesionless Soils”. Measurement,Volume:73