Bathini_2022_IOP_Conf._Ser.__Earth_Environ._Sci._982_012047.pdf

IOP Conference Series: Earth and
Environmental Science
PAPER • OPEN ACCESS
Performance of Soil Nailing for Slope Stabilization-
A Review
To cite this article: Divya Jyothi Bathini and V Ramya Krishna 2022 IOP Conf. Ser.: Earth Environ.
Sci. 982 012047
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ISTCE 2021
IOP Conf. Series: Earth and Environmental Science 982 (2022) 012047
IOP Publishing
doi:10.1088/1755-1315/982/1/012047
1
Performance of Soil Nailing for Slope Stabilization- A Review
Divya Jyothi Bathini1
and V Ramya Krishna2*
1
Research Scholar and 2
Assistant Professor
1,2
Department of Civil Engineering, VNR Vignana Jyothi Institute of Engineering and
Technology, Hyderabad-500090
*ramya.k299@gmail.com
Abstract. A landslide is a geological event involving a wide range of ground motions that leads
to the collapse of soil slope. The stabilization of these soil slopes is done by constructing
retaining walls to withstand lateral soil pressure. These retaining walls are costly as well as it is
difficult to construct as they require wide excavation for the base or bottom slab. One of the
many new solutions to slope stabilization is the soil nailing built by strengthening the steep slope
by driving reinforcement into the soil. In this study, a review of the origin and mechanism of soil
nailing, the construction process of soil nailed retaining walls were discussed. The failure pattern
of soil nails is an important factor to be noticed which influence the stability of soil slope was
discussed. Numerical studies were given, which are used to determine the adverse effect of
orientation and inclination of nails on the stability of soil nailed walls. A couple of case studies
were discussed to evaluate the significance of soil nailing on the stability of the slope and to
retain the vertical cut. A Laboratory study was considered to estimate the effect of nail inclination
and different nail arrangements on settlement of soil slope. A sequential literature review
investigates the application, advantages and disadvantages of soil nailing. This study shall help
in understanding the various applications of soil nailing in the civil engineering sector.
Keywords: Helical plates, Inclination of nail, Landslide, Stability, Tensile capacity
1. Introduction
Landslide is a movement of a soil mass due to instability of the soil slope under gravitational force, and
soil slope needs careful field investigation [1]. The stability of soil slope is necessary in order to reduce
its effect on people’s life and property. In order to assess the stability of the slope, the Factor of Safety
(FOS) is the important criteria to be checked. The slope is said to be stable when FOS is greater than 1
and unstable when FOS is less than 1. The slope is said to be close to failure when FOS is nearly equal
to 1 [2]. Soil slopes may fail due to the erosion of materials present in the slope. This leads to the
variation in the geometry of the slope, causing instability. Failure of slope can also be due to the rainfall
in which rainwater enters into the existing cracks leads to the weakening of the slope [3]. Slope can also
fail due to the vibration generated by suddenly caused earthquakes in which stiffness and shear strength
of soil gets reduced. These problems can be rectified to a maximum extent by constructing the walls
which can retain or resist the lateral earth pressure of backfill known as Retaining walls.
Conventional retaining walls such as gravity walls, semi-gravity walls, cantilever walls, counterfort
walls, and buttress walls are costly and difficult to construct in hilly terrains as it requires large wide
excavation for the base, as shown in figure 1. Such large excavation with a steep slope may cause slope
instability. These walls require more quantity of materials such as concrete or bricks for the construction;
as a result, the self-weight of the retaining wall itself increases. In conventional retaining walls, there
will be less interaction between the wall and backfill soil as there will not be any medium to contact.

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Conventional holding walls are cumbersome to construct in hilly areas. Soil nailing technique requires
very much less area or space and material to assemble than conventional retaining walls [4]. Soil nailing
is a process of installation of closely spaced bars into a slope or excavation from top to bottom. It is an
in-situ reinforcement technique to reduce tensile forces and increases the resistance. The soil nailing
purpose is to reinforce and stabilize the current steep slopes and excavations as construction progresses
from top to bottom, as shown in figure 2 [5, 6].
Figure 1. Conventional retaining wall
Figure 2. Soil Nailed wall
The grout is adopted to protect the steel bars from corrosion which are inserted into the soil slope,
and shotcrete is provided on the facing, which acts as a support between the soil nails [7]. The soil
nailing technique is mostly used to stabilize the excavations or vertical cuts, the slope of the reservoir
and underpass [8]. Numerical modelling was conducted on soil slope using PLAXIS-2D software and
concluded that up to 60% of the construction of a soil-nailed wall, the lateral displacement of wall more
predicted by the Mohr-Coulomb material model [9]. Soil nailing is an innovative technique that can be
adopted to strengthen the facing of the tunnel [10]. The safety factor of slope increases by inserting soil
nails, and the optimum diameter of soil nails was between 0.08 and 0.12 m for a given slope and
optimum nail length is 0.7 and 1.1 times the height of the slope [11]. Finite element modelling was
conducted in PLAXIS software on soil nail cut and concluded that soil’s cohesion reduces the
displacement of the soil-nailed wall, and as the surcharge load increases, the axial force on the soil-
nailed wall gets increased [12].
The factor of safety increases with increase in inclination of nail found the optimal inclination is 300,
and after reaching the maximum value of inclination, the factor of safety decreases [2]. The safety factor

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was decreased by increasing the height of the soil nailed wall, and stability of the wall decreases as
horizontal acceleration coefficient values increases [13]. The stability of the slope decreased by
increasing the spacing between the soil nails and increased by the inclination of the nail [14]. Soil nailing
could be used for both weathered rock mass & intact soil mass and given that the cost of soil nailed wall
is less compared to conventional walls [4]. Soil nailing is the most preferred technique in order to resist
the soil pressure of slope, leads to the protection of many lives and found that soil nailing inclination
should be 600
, 500
and 400
for slope inclination of 300
, 450
and 600
respectively [15]. The largest force
was observed in the bottom nail when soil slope is subjected to earthquake [16]. The spacing of nails in
a slope is an important parameter to be checked as the stability of the slope depends much on it [17].
2. Origin of Soil Nailing
Soil Nailing emerged in 1964 for the development of excavation for support of road known as New
Austrian Tunnelling technology [18-20]. In this method, reinforcement is inserted into the ground and
thereby grouting the reinforcement combined with the shotcrete facing, which provides support for the
excavation. In 1971, this process extended to the stabilization of rock slope in which steel reinforcement
or rock bolts and shotcrete is combined. This process was further extended for the stabilization of
excavations and soil slopes [21].
In 1972, the soil nailing technique was used in Versailles, France, to stabilize the high-cut sand slope
of 60 ft height in order to widen the railroad, and this technique was proved to be faster and cost-effective
in comparison with conventional retaining walls [21]. In Germany, the first use of the soil nailing
technique was in 1975, in which lots of full-scale testing, field testing, numerical modelling and
monitoring was involved. In the United States, this application was first used in 1976 for the support of
deep excavation in dense, lacustrine and silty sands, which is of 45 ft height [22]. Utilization and
construction of soil nailed walls for road projects have increased rapidly in the U.S. As a result; the soil
nailing technique became most popular as it is cost-effective and requires less space for construction.
3. Mechanism of Nailing
Soil is strong in compression, and weak in tension leads to the destabilization of soil slopes. The purpose
of soil nailing is to increase the stability of slope by reinforcing in which interaction is developed
between the soil and nail leads to the tensile force development. This technique is followed to stabilize
the steep slopes and excavations as the process starts from the bottom [5]. The active force of the earth
present in the slope increases due to the various geological actions as a result of soil slope collapse. This
problem can be rectified by increasing passive force developed by nails or reinforcement inserted into
the slope. The passive force in reinforcement increases the shearing resistance of soil [23].
Figure 3. Behaviour of soil nails
In this technique, nails are inserted into the slope horizontally, or with a gentle slope against the tensile
strain, direction leads to the maximum development of force of tension [24]. The soil nailing method
involves active and passive zone or resistant zone, as shown in figure 3. During the failure of soil slope,

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the active zone starts to deform leads to the displacement of nails that are accommodated across the
failure surface. The displacement of nails results in the formation of tensile forces in the resistant zone
leads to the resistance of active zone deformation. The length of nails to be provided in the soil slope
depends upon the active and resistant zones [22]. Mostly the width of the active zone could be 0.3 to
0.35 times the height of the slope.
4. Construction process of Soil Nailed Wall
4.1. Construction process of the soil-nailed wall [21]
Step-1: Initially, excavation is made for cuts up to a depth of 3 to 5 ft, and a platform is created, as
shown in figure 4(a). For existing soil slopes, the upper layers of soil or weathered soil is trimmed off
up to the required depth. The excavation process is laborious and critical as the cut will not be stable
until the nails are installed.
Step-2: Holes are drilled into the cut or slopes up to the required length with specified diameter using
the specialized drilling machines, as shown in figure 4(b). The tensile capacity of nails is an important
criterion to be selected before construction. The stability of the slope or cut mostly depends on the tensile
capacity of the tendon or nail. The selection of tensile capacity of the nail to be designed depends on the
type of soil present in the slope or vertical cut [25].
Step-3: Nails or tendons are coated with epoxy resin to prevent corrosion. Next, tendons are placed into
the holes drilled previously, and grout prepared with the required water-cement ratio is injected into the
sides of the tendon. In this stage, drainage strips like geotextiles are placed vertically on the facing of
the slope from top to the down of the excavation, as shown in figure 4(c). Different types of nails include
self-drilling nails, grouted nails and driven nails etc.
Step-4: On the top of the drainage strip, welded wire mesh is placed, and shotcrete is pumped, as shown
in figure 4(d). Next, the nail end or nail head is pulled to accommodate into the mesh, and the bearing
plate is fixed and pushed little into the fresh concrete [26]. Washers and Nuts are placed against the nail
head on the bearing plate to provide anchorage. Anchorage provides sufficient strength by transferring
loads from one element to another.
(a) Initial excavation (b) Drilling of holes
(c) Installation and Grouting of nails (d) Placing Initial facing

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(e) Construction of all levels (f) Construction of final facing
Figure 4. The construction process of the soil-nailed wall
Step-5: 1 to 4 steps are repeated, and the subsequent levels are constructed, as shown in figure 4(e).
Step-6: After the construction of all levels, the final facing is constructed, as shown in figure 4(f). Final
facing involves reinforced concrete, prefabricated facia elements or panels or reinforced shotcrete.
Different facing elements includes Gabions, Modular blocks and square or hexagonal panels.
5. Failure of Soil Nails
The failure of soil nails can be divided into four types. Such as Tensile failure, Pull-out failure, Shear
failure and structural failure [25], [27]. Tensile failure may cause the insufficient tensile capacity of the
nail and improper materials used for the construction of the facing. In this case, the facing of the soil
nailed wall may deform or move from its position and breakage is observed in the nail, as shown in
figure 5(a). This failure can be avoided by adopting nails of sufficient tensile capacity. Pull-out failure
of nails may cause when the strength of the facing is higher than the strength of the grout material and
tensile capacity of the nails. In this case, nails inserted into the slope may move along with the facing
away from the slope, as shown in figure 5(b).
(a) Tensile Failure (b) Pull-out Failure
(c) Bending or shear Failure (d) Structural Failure
Figure 5. Types of soil-nail failure

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The pull-out failure can be avoided by adopting sufficient strength of grout and tensile capacity of
nails. Another type of nail failure is a shear failure, in which the heavy earth pressure of the soil induced
on the nail causes bending of the nail, as shown in figure 5(c). This failure may lead to the shearing or
brittle failure of a nail in the presence of rocky strata. This can be avoided by adopting a sufficient
bonding length of the nail. Structural failure may be due to the insufficient strength of nails, nuts and
bearing plate, as shown in figure 5(d). This failure may also be due to the improper connection between
the facing and nail head.
6. Numerical Modelling
6.1. Effect of nail orientation on the stability of soil slope
Soil nails are basically designed with proper uniform spacing and length by taking all the safety
requirements into account. The main parameters that affect the slope stability are slope geometry and
soil parameters. In addition to these, there are several other factors like the orientation of nails, property
of nails, nail length, and the spacing of nails. In order to find out the optimal layout of nails, numerical
modelling was carried out using PLAXIS-2D software. In this study, the height of the slope is taken as
10 m, Slope angle (β) and Back slope angle (α) were varied to find out their influence on soil nailed
slope. The soil in the slope was modelled using the Mohr-Coulomb material model using six-node
triangular elements. Nails were modelled as elastic-perfectly plastic material, and the interface material
was used on both sides of the nails. The nail used in this study is 29 mm, and it is surrounded by cement
mortar [28].
Table 1. Orientation of nail with various geometric conditions
Slope angle
(Degrees)
Backslope
angle=0
(degrees)
Backslope
angle=10
(degrees)
Backslope
angle=20
(degrees)
40 40 50 65
50 30 40 58
60 26 30 47
70 16 20 30
80 8 10 20
90 0 0 10
From Table 1, it was observed that the optimal orientation of the nail for slope angles of 400
, 500
, 600
,
700
, 800
, and 900
are 400
, 300
, 230
, 160
, 80
, and 00,
respectively, if the backslope angle is 00
. The optimal
orientation of the nail for slope angles of 400
, 500
, 600
, 700
, 800
, and 900
are 500
, 400
, 300
, 200
, 100
, and
00,
. The optimal orientation of the nail for slope angles of 400
,
500
, 600
, 700
, 800
, and 900
are 650
, 580
, 470
, 300
, 200
, and 100,
.
Stability analysis was carried out using PLAXIS finite element program and found that the FOS gets
increased by decreasing the inclination of the slope. For the slope angle of 400
, the FOS increases by the
increase in the orientation of the nail and for the slope angle of 900
, the FOS decreases by an increase in
the orientation of the nail.
6.2. Effect of the nail on the stability of slope under the static and seismic condition
In hilly regions and zones of heavy rainfall, sliding or falling of soil mass may occur due to several
environmental changes. This could be countered by providing proper techniques such as soil nailing
[29]. It is a recent and developing technique to retain the soil mass from sliding. The slope stability is
an important criterion to be checked for any retaining wall. In this study, finite element modelling was
carried out to simulate the behaviour of slope which is reinforced with nails under static and seismic
conditions using OPTUMG2 software. The safety factor of slope under static and seismic acceleration
was resolved by keeping constant nail diameter and varying the inclination of nail and spacing between
the nails [30].

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Mohr-Coulomb material model was used to simulate the behaviour of soil present in slope. The
bottom of the slope geometry was fixed in both x and y-directions, and the sides were fixed in the x-
direction and kept free in the y-direction. High yield strength deformed bars were used to reinforce the
soil slope, and nail inclination of 100
, 200
, 300
, 400
were taken with nail spacing of 0.5 m,1 m, 1.5 m. In
the seismic case, a seismic coefficient of 0.12 g was used. It was found that as the angle of slope
increases, the factor of safety decreases in both static and seismic conditions. When seismic forces were
induced in the slope, the factor of safety decreased compared to the static case, as shown in figure 6.
Figure 6. FOS with the variation of slope angle
Further analysis was carried by varying spacing and inclination of nails. At 0.5 m spacing, with an
increase in the inclination of the slope of 300
, 400
the FOS increases, and for 500
slopes, FOS remains
constant. In case of spacing 1 m, FOS increases for the soil slope of 300
and for soil slope of 400
the
FOS increase up to 300
nail inclination & reduces at 400
nail inclinations; for 500
soil slope, FOS decrease
with an increase in nail inclination up to 300
and further it decreases. It was found that the factor of
safety is higher for a slope inclination of 300
compared to 100
, 200
, 400
at a spacing of 0.5 m under a
seismic coefficient in horizontal direction of 0.12 g. It was concluded that there is 39.5% increase in the
factor of safety when the slope is reinforced with soil nails.
6.3. Effect of soil nail inclination on the stability of a slope
The main purpose of soil nailing is to stabilize the slope for excavations, roadway cuts, embankments,
landfills etc. The reinforcing mechanism provides interaction between the nail and the ground, thus
results in higher stability. The main function of soil nailing is to enhance the slope by increasing shear
forces along the failure surface and reduces the driving forces both in cohesive and cohesionless soil
[15]. In this study, the effect of the inclination of soil nail on the stability of slope was determined using
the SLOPE/W module of GEOSTUDIO 2012 software.
Figure 7. FOS for different slope angles
0
0.5
1
1.5
25 35 45 55
Factor
of
safety
Slope of soil with horizontal (degrees)
Kh=0
Kh=0.12g
0
0.5
1
1.5
2
2.5
10 20 30 40 50 60 70 80 90
Factor
of
safety
Inclination of soil nail (degrees)
Slope angle=30
Slope angle=45
Slope angle=60

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For the analysis, the Morgenstern-Price method is used to evaluate the factor of safety for critical failure
surfaces. The factor of safety is nearly 0.6, 0.8, 1.3 for the soil slope inclination of 600
, 450
, 300
without
the inclusion of nail into the soil slope. The maximum FOS was 400
, 500
and 600
for the soil slopes of
600
, 450
and 300,
respectively, as shown in figure 7. It was observed that FOS has increased by inserting
soil nails into the slope. FOS increases uniformly with an increase in wall inclination up to 200
but
beyond that, FOS increases highly [31]. The factor of safety is more in the case of the nail, which is
grouted with cement concrete compared to driven nails. Numerical modelling was performed using
FLAC-2D software with and without soil nails in the slope and estimated that the FOS gets increases as
the slope angle increases and the installation angle of the nail rises [32]. FOS got reduced as the length
of the nail increases, and as the nail inclination decreases, the FOS increases [33], [34].
6.4. Effect of helical plates on pull-out resistance of soil nail
Soil nails may fail due to the less interaction between the nail and surrounding soil. Nails may also fail
due to less pull-out resistance or less bond strength. Interaction between nails and soil can be achieved
by using rough surfaced nails or anchors. The interaction between soil and the nail was studied based
on the pull-out resistance of soil nail [35], [36]. In this study, nail with helical plates at different levels
was used as shown in figure 8. Numerical modelling was carried out to estimate the pull-out resistance
of soil nail by varying number of helical plates using PLAXIS-2D. For the analysis, nail with helical
plates was modelled in a circular tank using axisymmetric model. Well graded sand was used in a
circular tank which is modelled as a hardening soil material model [37]. Sand with a lower cohesion
value of 1.73 kPa and an angle of shearing resistance of 300
was taken. Soil nail and helical plates along
the shaft of nail were modelled as an elastoplastic material model. Bending stiffness (EI) and axial
stiffness (EA) of the helical soil nail were taken as 0.64 (kN m2
)/m and 28,355 kN/m, respectively with
a Poisson’s ratio of 0.2. An interface material was used between nail and the surrounding soil with Rinter
value as 0.67.
Figure 8. Soil nail with helical plates
The pull-out force of soil nail with helical plates was calculated for the increment of displacement of
the nail from its position by varying number of helical plates. The pull-out force of soil nail was
increased by an increase in displacement of the nail from its place. When one helical plate was used
along the shaft of the nail, the pull-out force was less but when the number of helical plates was increased
the pull-out force also gets increased. It was estimated that the pull-out capacity of nail improves to a
sufficient extent as the count of helical plates increases from 1 to 2 and then to 3. Once the helical plate
was announced along the shaft of nail, the bearing area has increased as a result, compaction of soil
between helical plates occurs easily [38]. Numerical modelling was conducted on decomposed granite
fill with nail using ABAQUS software to calculate the pull-out resistance of nail. It was observed that
as the dilation angle of fill increases, the pull-out resistance increases, and as the overburden pressure
increases, pull-out shear stress increases [39]. The combination of grouting and soil nails known as
Geonail increases pull-out capacity effectively in soft clay [40]. Finite element modelling was conduced
using PLAXIS-2D and concluded that as the displacement of the nail increased, the pull-out force was
increased. The lower nail in the soil slope exerts a higher pull-out force than the middle and upper nail
[41].

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7. Field Investigation
7.1. Stabilization of failed slope in hilly terrain
In this study, the field is located at the iron ore mines area which is situated at the eastern part of India.
The 33 kV power line existed on the slope top consists of lateritic soil clubbed with iron ore rubbles.
The contractor established 3 m height gabion wall to prevent the failure of slope. After 1 year of period,
during a significant amount of rainfall, they have noticed the shallow failure lines in the gabion wall.
There is a bulging at the bottom of the gabion wall. Stepped random stone masonry wall was constructed
as a means of protective measure. But after heavy rainfall, they have observed the failure of slope for
30 m which adversely affects the transmission tower. For the stabilization of failed slope, they have
carried out a geotechnical investigation of soil and carried out laboratory tests to determine the various
properties of soil. Soil nailing was adopted as a part of the stabilization technique for the existing slope
[42].
Soil nail of Fe500 grade was taken, and stability of slope was carried out using GEOSTUDIO 2007
software. The factor of safety was evaluated for the critical failure surface using Fellinious, Bishop,
Janbu and Spencer methods modelled in the SLOPE/W module of the software. The FOS was observed
as 1.57, 1.65, 1.61 and 1.64 for Fellinious, Bishop, Janbu and Spencer methods, respectively, when 8
rows of soil nails are used in the slope without 1 m height RCC wall at toe. After placing the 8 rows of
soil nails and 1 m height RCC toe wall, the FOS was observed as 1.72, 1.84, 1.82, 1.84 for Fellinious,
Bishop, Janbu and Spencer methods. After placing soil nails, shotcrete was done on the exposed surface
of the soil slope. It was concluded that soil nailing makes the rehabilitation process easier and provides
better stabilization techniques at the site [43]. From field investigation, it was concluded that the
combination of nail and geosyntheics as a reinforcement element densifies the soil and controls the
erosion of soil [44].
7.2. Protection of historical structures
Soil nailing can be used to protect or stabilize the slopes existing beneath old buildings and masonry
structures like retaining walls and abutments. Various historical buildings get collapsed or destroyed
due to the long-time foundation, and these foundations can be preserved by stabilizing using soil nailing
technique. The various preservation techniques include adopting timber foundation, gothic arch
foundation, underpinning [45]. The reinforced soil concept was used from the 1960s in which sticks or
branches of trees are used as a reinforcing element for soil. It is considered as a massive ground
reinforcing system, and then soil nailing came into existence. This nailing technique includes the
insertion of steel bars into the soil and finishing the facing with shotcrete. The repairing of old gravity
walls present in the vicinity of the river using soil nailing technique as shown in figure 9. Initially, cracks
were observed on the facing of stone. The stone facing was first dismantled, and small size light mesh
was kept on the facing of slope and shotcrete was sprayed. Then, holes were drilled into the soil slope,
and high yield strength nails of 5 m long and 16 mm diameter were inserted into the soil with a spacing
of 1.3 m in horizontal and vertical ways. Next, spacing around the nail was grouted or filled with cement
concrete, and then stones have placed a facing [46].
Figure 9. Stabilization of old gravity wall using
soil nailing

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8. Laboratory Study
Soil nailing is a remedial measure in order to stabilize the unstable natural and artificial soil slopes,
vertical cuts, excavations and embankments. Main elements such as nails or steel bars are used to
reinforce the slope. Proper selection and design of soil nails is a fundamental task to stabilize the slope
and decrease the settlement of soil slope. In this study, experiments were conducted on unreinforced &
soil nail reinforced slopes and settlement of soil slopes were determined. For this analysis, a rectangular
box of dimension 0.60 m x 0.40 m x 0.30 m was fabricated using plywood. Hollow aluminium tubes of
diameter 10 mm and length 16 cm was used for reinforcing the soil slope. Strain produced in the soil
and reinforcing elements was evaluated by providing a strain gauge of length 3 mm and resistance 120
ohms. A bearing plate made with mild steel of size 0.16 x 0.08 x 0.035 m was used to distribute the load
on the top of the soil slope. Dial gauge was used to estimate the settlement of soil slope. Poorly graded
sand of angle of shearing resistance 310
is used as backfill material in slope. Initially, soil slope without
reinforcement was analyzed, and settlement against failure load was determined. Next, soil slope with
nail inclination of 00
, 150
and 300
was made, and settlement against failure load was found out using dial
gauge [47]. It was observed that without reinforcement, the final settlement was 6.75 mm at the failure
load of 1020 N. Once the nail has inserted into the soil slope, the final settlement got decreased by taking
a large load compared to the unreinforced soil slope. As the inclination of the nail increases, the
settlement also gets increased, and the load-carrying capacity of the slope gets reduced. The load carried
by soil slope without reinforcement was less, and the final settlement was more. At a nail inclination of
00
, 150
and 300
, the final settlement of soil slope was found to be 5.19 mm, 5.75 mm and 6.08 mm at a
failure load of 1560 N, 1500 N, 1460 N, respectively.
Figure 10. Different nail patterns
The Next attempt was made to find out the settlement of slope by placing nails in different arrangements
such as square, diamond and triangular patterns, as shown in figure 10. The settlement of soil was
estimated by increasing the load for different arrangements of nails. The settlement was less in the case
of staggered patterns than the square and diamond patterns, as shown in figure 11. The final settlement
was observed to be 6.75 mm at the failure load of 1020 N for an unreinforced case. The final settlement
was found to be 5.19 mm, 6.05 mm and 4.75 mm against the failure load 1560 N, 1420 N and 1600 N
for square, diamond and staggered patterns, respectively as shown in figure 11.
Figure 11. Load Vs Settlement for a different arrangement of nails
0
2
4
6
8
0 500 1000 1500 2000
Settlement
(mm)
Load (N)
Unreinforced slope
Square pattern
Diamond pattern
Staggered pattern

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Laboratory tests were conducted on soil slope with different slope angles to study the stability of
slope with an increase in surcharge load. In this study, soil slope is prepared in a Perspex Sheet box of
size 750 mm × 300 mm × 400 mm with sidewalls of 10 mm thick. Yamuna sand was used to make the
soil slope with an angle of shearing resistance of sand as 370
. 45 mm thick sand layer was placed in a
box, and then 5 mm thick red coloured Yamuna sand was placed between 45 mm sand layers. Likewise,
400 mm height of sand slope was achieved, and the model box was mounted on Hounsfield
Tension/Compression Machine. This machine was connected to a computer with the QMAT Pro
software for automatic data acquisition. The load was applied on top of the crest through a Perspex sheet
of size 16 cm × 29 cm and 2.5 cm inch thick. Load Vs settlement graph was automatically drawn by
QMAT Pro software for different slope angles such as 300
, 450
and 600
. From Table 2, it can be observed
that the displacement got reduced as the angle of the slope increased [48].
Table 2. Load Vs displacement values for different
slope angles
Angle of slope
(Degrees)
Load (N)
Settlement
(mm)
30 6960 13.7
45 4282 11.4
60 2688 8.17
9. Applications, Advantages and Disadvantages of Soil Nailing
9.1 Applications
Soil nailing can be used in the following ways [21], [49]
1. Soil nailing technique is used in roadway cuts in order to avoid the limited excavation and
provides sufficient right-of-way for passengers.
2. It is used for widening roads present under the abutments of a bridge in which traffic flow will
not be interrupted as it requires less space.
3. It is used for the stabilization of a tunnel roof from spalling.
4. It is used for the repair and reconstruction of mechanically stabilized earth retaining walls in
which backfill is resisted from deformation.
5. It is used for the stabilization of steep slopes and vertical cuts.
6. It is used for the stabilization of weak grounds.
9.2 Advantages
The advantages of soil nailing are as follows [21]
1) Construction of soil nailed walls is easy as it requires less space.
2) Installation of soil nails or tendons into the slope will be relatively faster.
3) Soil nailed walls are more economical than the conventional retaining walls taller than 12 ft to
15 ft.
4) These walls are flexible and accommodate higher movements.
5) Soil nailing can be used for the protection of movement of adjacent structures or underpinning.
6) Soil nailed walls are proved to be economical under seismic conditions.
7) Soil nailed walls are most effective than anchored walls as there is great number of reinforcing
elements per unit area.
8) Soil nails typically require smaller holes or rows than conventional walls.
9) These walls improve the stability of slopes by increasing resisting forces.
9.3 Disadvantages
The disadvantages of soil nailing are given [21]
1) Permanent soil nail walls require permanent underground supports.

ISTCE 2021
IOP Publishing
doi:10.1088/1755-1315/982/1/012047
12
2) Soil nailed walls may interfere or come in contact with the electrical cables passing adjacent to
nailed walls.
3) Soil nailing can be adopted only above groundwater level.
4) These are less suitable for coarse-grained soils as they require permanent supports.
10. Conclusions
The present study discusses the different characteristics of soil nailing like laboratory study, numerical
modelling, field investigation. This paper also discusses the construction process of the soil-nailed wall,
its application, advantages & disadvantages, different failure mechanisms of soil nails. It is concluded
that the soil nailing makes the construction manner very easier and also requires very much less space
to assemble the material than conventional retaining walls. Stability of soil nailing slope decreases by
an increase in the spacing between the soil nails and increased by the inclination of nail. It was observed
that this technique could be used in various applications like retaining walls, widening of roads,
stabilization of vertical cuts or excavations, protection of historical buildings etc. The staggered
arrangement of nails in the slope was found to have lesser settlement and higher load-carrying capacity.
Nails may also fail because of the less pull-out resistance due to less interaction between soil and nail.
It was observed that the pull-out capacity of the nail increases by introducing helical plates along the
shaft of the nail. From the field studies, it is proved that the soil nailing can be used for both weathered
rock mass & intact soil mass, and the cost of soil nailed wall is less compared to conventional walls.
Soil nailing can be used to protect or stabilize the slopes existing beneath old buildings and masonry
structures like retaining walls and abutments as well as monuments. The different types of nail failures
can be avoided by adopting nails of sufficient tensile capacity and sufficient strength of grout.
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