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MAULANA AZAD NATIONAL INSTITUTE OF TECHNOLOGY BHOPAL
A
SEMINAR REPORT
ON
“SLOPE STABILIZATION BY SOIL NAILING TECHNIQUE”
A seminar report submitted in partial fulfillment of the requirement of Master of
Technology in Geotechnical engineering course during the year 2018-2019
Submitted by
BHANU PRATAP SINGH
(Scholar Number 182111119)
Under the Guidance of
Asst. Prof. Dr. Rakesh Kumar
GEOTECTNICAL ENGINEERING
DEPARTMENT OF CIVIL ENGINEERING
2018-19
2
MAULANA AZAD NATIONAL INSTITUTE OF TECHNOLOGY BHOPAL
DEPARTMENT OF CIVIL ENGINEERING
DECLARATION
I Bhanu Pratap Singh, student of M. tech, Geotechnical Engineering, Department of Civil
Engineering, Maulana Azad National Institute of Technology, Bhopal, hereby declare that the work
presented in this seminar report is outcome of my own work, is Bonafide to the best of my knowledge
and this work has been carried out taking care of Engineering Ethics. The work presented does not
infringe any patented work and has not been submitted to any University for the award of any degree or
any professional diploma.
Bhanu Pratap Singh
Scholar no. 182111119
3
MAULANA AZAD NATIONAL INSTITUTE OF TECHNOLOGY
BHOPAL
DEPARTMENT OF CIVIL ENGINEERING
CERTIFICATE
October 2018
This is to certify that the seminar entitled “SLOPE STABILIZATION BY SOIL NAILING
TECHNIQUE” Submitted by Bhanu Pratap Singh (182111119) of M. tech 1st year, Geotechnical
Engineering (Department of Civil Engineering), Maulana Azad National Institute of Technology, Bhopal,
is a record of bonafide seminar carried out by him under my supervision and guidance.
To the best of my knowledge, the presented seminar report has not been submitted for the award
of any other diploma or degree certificate.
Dr. Rakesh Kumar
(Assistant Professor)
4
ACKNOWLEDGEMENT
I would like to express my gratitude to my mentor, Assistant Prof. Dr. Rakesh Kumar
for introducing me to the topic as well as for his useful comments, remarks and engagement
through the learning process of this project.
I am very thankful to Prof Dr. S.K. Katiyar, Head of Department (Civil Engineering) for his
kind support and cooperation.
This seminar report would never have been completed without the guidance and support
of Prof Dr. N. Dindorkar, Prof Dr. P.K. Jain, Associate Prof Dr.Suneet Kaur and
Assistant Prof. Dr. Kishan Dharavat. I owe a hearty gratitude towards them.
My thanks and appreciation also goes to my colleagues and people who have willingly
helped me out with their abilities.
5
ABSTRACT
Soil nailing is an in-situ reinforcement technique by passive bars which can withstand tensile
forces, shearing forces and bending moments.
This technique is used for retaining walls and for slope stabilization. Its behavior 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.
Taking into account these mechanisms, multi-criteria at failure design method is proposed. It
is derived from the slice methods used in slope stability analysis. The criteria lead to
a yielding curve in the shear – tensile forces plane and the consideration of the principle of the
maximum plastic work enables to calculate the shear and tensile forces mobilized at failure in
each inclusion.
Using a formulation determinate, the slope stability analysis take into account the passive
force of reinforcement.
6
CONTENTS
Page no.
1. INTRODUCTION 7
2. ORIGIN AND DEVELOPMENT 8
3. FAVOURABLE GROUND CONDITIONS FOR SOIL NAILING 9
4. COMPONENTS OF A SOIL NAIL WALL 11
5. TYPES OF NAILS USED 14
6. MACHINERIES USED IN SOIL NAILING 15
7. MATERIALS USED IN SOIL NAILING 17
8. DESIGN REQUIREMENTS 19
9. CONSTRUCTION SEQUENCES 24
10. APPLICATIONS AND ADVANTAGES 28
11. CONCLUSION 30
12. REFERENCES 31
7
CHAPTER 1
INTRODUCTION
Soil nailing consists of the passive reinforcement of existing ground by installing
closely spaced steel bars (i.e. nails), which may be subsequently encased in grout.
As construction proceeds from the top to bottom, shotcrete or concrete is also applied on
the excavation face to provide continuity. In a soil-nailed retaining wall, the properties
and material behavior of three components—the nail soil, the reinforcement (nails) and
the facing element—and their mutual interactions significantly affect the performance
of the structure.
Soil nailing is typically used to stabilize existing slopes or excavations where top-to-
bottom construction is advantageous compared to other retaining wall systems. For certain
conditions, soil nailing offers a viable alternative from the viewpoint of technical
feasibility, construction costs, and construction duration when compared to ground anchor
walls, which is another popular top-to bottom retaining system.
An alternative application of passive reinforcement in soil is sometimes used to stabilize
landslides. In this case, the reinforcement (sometimes also called “nails”) is installed
almost vertically and perpendicular to the base of the slide. In this alternative
application, nails are also passive, installed in a closely spaced pattern approximately
perpendicular to the nearly horizontal sliding surface, and subjected predominantly to shear
forces arising from the landslide movement.
8
CHAPTER 2
ORIGIN AND DEVELOPEMENT
The soil nailing technique was developed in the early 1960s, partly from the techniques for
rock bolting and multi-anchorage systems, and partly from reinforced fill technique (FHWA,
1998). The New Austrian Tunneling Method introduced in the early 1960s was the premier
prototype to use steel bars and shotcrete to reinforce the ground. With the increasing use of the
technique, semi-empirical designs for soil nailing began to evolve in the early 1970s. The first
systematic research on soil nailing, involving both model tests and full-scale field tests, was
carried out in Germany in the mid-1970s.
Subsequent development work was initiated in France and the United States in the early 1990s.
• Tunneling Method in the 1960’s.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.
• In Germany, the first use of a soil nail wall was in 1975.
• The United States first used soil nailing in 1976 for the support of a 13.7 m deep foundation
excavation in dense silty sands.
• 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.
.
9
CHAPTER 3
FAVOURABLE GROUND CONDITIONS FOR SOIL NAILING
Soil nail walls can be used for a wide range of soil types and conditions. Project experience
has shown that certain favorable ground conditions make soil nailing cost effective
over other techniques.
Soil nailing has proven economically attractive and technically feasible
when:
The soil in which the excavation is constructed should able to stand unsupported in a
1- to 2-m (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).
It is advantageous that the ground conditions allow drill holes to be advanced without
the use of drill casings and for the drill hole to be unsupported for a few hours until
the nail bars are installed and the drill hole is grouted.
The results from the Standard Penetration Test provides the SPT value
‘N’ which can be used to preliminary identify the favorable soil conditions for Soil
Nailing. Based on the general criteria for favorable conditions noted above, the
following ground types are generally considered well suited for soil
nailing applications
Stiff to Hard Fine -Grained Soils: Fine-grained (or cohesive) soils may include stiff
to hard clays, clayey silts, silt clays, sandy clays, sandy silts, and combinations
thereof. These types of soils have the SPT value (N) around 9 blows/300mm.Fine-
grained soils should have relatively low plasticity i.e. PI<15.
Dense to Very Dense Granular Soils : These soils include sand and gravel with SPT
N-values larger than 30 and with some fines about 10 to 15 percent and with weak
natural cementation that provide cohesion. To avoid excessive breakage of capillary
forces thereby reducing apparent cohesion the movement of water toward the
10
excavation face needs to be minimized by redirecting surface water away from the
excavation face.
Weathered Rock with no Weakness Planes: Weathered rock may provide a suitable
supporting material for soil nails as long as weakness planes occurring in
unfavorable orientations are not prevalent (e.g., weakness planes dipping into
the excavation).
Glacial Soils: Glacial outwash and glacial till materials are typically suitable for soil
nailing applications as these soils are typically dense, well-graded granular materials
with a limited amount of fines.
In addition to these above conditions certain other aspects Should be considered for
the construction of soil nailed structures:
The prolonged exposure to ambient freezing temperatures may cause frost action in
saturated, granular soils and silt; as a result, increased pressures will be applied to the
temporary and permanent facings.
Repeated freeze-and-thaw cycles in the soil may reduce the bond strength at the soil
nail grout-ground interface and the adhesion between the shotcrete and the soil.
A suitable protection against frost penetration and an appropriate concrete mix must be
provided.
Granular soils that are very loose (N ≤ 4) and loose (4 < N ≤ 10) may
undergo
excessive settlement due to vibrations caused by construction equipment and
traffic.
11
CHAPTER 4
COMPONENTS OF A SOIL NAIL WALL
Fig 4.1: Main Components of a Typical Soil Nail.
The components of a soil nailed wall are shown above in the (Fig 4.1) they are as
follows:
Nail Bars: Steel reinforcing bars used for soil nails are commonly threaded and may
be either solid or hollow. Bars generally have a nominal tensile strength of 420 MPa
(Grade 60) or 520 MPa (Grade 75). Bars with a tensile strength of 665 MPa (Grade
95) and as high as 1,035 MPa (Grade 150) may be considered for soil nailing, but
their use should be restrictive. Bars with lower grades are preferred because they are
more ductile, less susceptible to corrosion, and readily available. Grade 150bars
should not be used because they are more brittle under shear and more susceptible to
stress corrosion than steel at lower grades. Threaded bars applications are available in
19-, 22-, 25-, 29-, 32-, 36-, and 43-mm diameter (No. 6, 7, 8, 9, 10, 11, and 14 in
English units) up to approximately 18 m (59 ft) in
length.
12
Nail Head: The nail head comprises two main components, the bearing-plate,
hex nut, and washers; and the headed-stud. The bearing plate is made of Grade 250
MPa (Grade 36) steel and is typically square 200- to 250-mm (8- to 10-in.) side
dimension and 19-mm (¾-in.) thick. The purpose of the bearing plate is to distribute
the force at the nail end to the temporary shotcrete facing and the ground behind
the facing. Washers and nuts are steel with a grade consistent with that of the nail bar
commonly of 420 or 520 MPa (Grade 60 or 75).
Grout: Grout for soil nails is commonly a neat cement grout, which fills the annular
space between the nail bar and the surrounding ground. Sand-cement grout can also
be used in conjunction with open hole-drilling (i.e. for non-caving conditions)
for economic reasons. Cement Type I (normal) is recommended for most
applications. Cement Type III is grounded finer, hardens faster, and can be used when
target grout strength is required to be achieved faster than for typical project
conditions. Cement Type II hardens at a slower rate, produces less heat, and is
more resistant to the corrosive action of sulphates than Cement Type I. The
water/cement ratio for grout used in soil nailing applications typically ranges from
0.4 to 0.5.
Fig 4.2: Grout is being placed with the help of pipes
Ce ntralize rs: Centralizers are devices made of polyvinyl chloride (PVC) or
other synthetic materials that are installed at various locations along the length of each
nail bar to ensure that a minimum thickness of grout completely covers the nail bar
(Fig
4.3). They are installed at regular intervals, typically not exceeding 2.5 m (8 ft), along
the length of the nail and at a distance of about 0.5 m (1.5 ft) from each end of the
nail
.
13
Fig 4.3: Typical PVC centralizers
Co rrosion Prote ctio n Ele me nts: In addition to the cement grout, this provides
both physical and chemical protection to the nail bars. Protective sheathings
made of corrugated synthetic material [HDPE (High Density Polyethylene) or
PVC tube) surrounding the nail bar are usually used to provide additional
corrosion protection.
Wall Fac ing: Nails are connected at the excavation surface (or slope face) to a facing
system, which most commonly consists of a first-stage, temporary facing of shotcrete
during construction and, a second-stage, permanent facing of CIP concrete. The
purpose of the temporary facing is to support the soil exposed between the
nails during excavation, provide initial connection among nails, and provide
protection against erosion and sloughing of the soil at the excavation face. The
purpose of the permanent facing is to provide connection among nails, a more
resistant erosion protection, and an aesthetic finish. Temporary facing typically
consists of shotcrete and WWM and additional shorter reinforcement bars
(referred to as waler bars) around the nail heads. Permanent facing is commonly
constructed of CIP reinforced concrete and WWM-reinforced shotcrete.
Drainage Syste m: To prevent water pressure from developing behind the wall facing,
vertical geo-composite strip drains are usually installed between the temporary facing
and the excavation. The drainage system also includes a footing drain and weep holes
to convey collected drainage water away from the wall face.
14
CHAPTER 5
TYPES OF NAILS
The types of nails used in the construction of soil nailed walls are as follows:
Drilled and grouted soil nail
Driven soil nails
Self-drilling soil nails
Jet-grouted soil nails
Launched soil nails
These are explained as follows:
Drille d a nd gro ute d soil na il: These are approximately 100- and 200-mm (4- to
8- in.) diameter nail holes drilled in the foundation soils. These holes are
typically spaced about 1.5 m (5 ft) apart. Steel bars are placed and the holes
are grouted. Grouted soil nails are the most commonly used soil nails for FHWA
projects and they can be used as temporary and permanent applications, provided
that appropriate corrosion protection is in place.
Drive n soil na ils: These soil nails are relatively small in diameter [19 to 25 mm (¾ to
1 in.)] and are mechanically driven into the ground. They are usually spaced
approximately 1 to 1.2 m (3 to 4 ft) apart. The use of driven soil nails allows for a
faster installation as compared to drilled and grouted soil nails.
Se lf-drilling soil nails: These soil nails consist of hollow bars that can be drilled and
grouted in one operation. In this technique, the grout is injected through the hollow
bar simultaneously with the drilling. This soil nail type allows for a faster installation
than that for drilled grouted nails and, unlike, driven soil nails, some level of
corrosion protection with grout is provided.
Je t-gro ute d soil na ils: Jet grouting is performed to erode the ground and allow
the hole for the nail to be advanced to the final location. The grout provides
corrosion protection to the central bar. In a second step, the bars are typically
installed using vibro-percussion drilling methods.
La unche d soil na ils: In this method, bare bars are “launched” into the soil at very
high speeds using a firing mechanism involving compressed air. Bars are 19 to 25
mm (¾ to 1 in.) in diameter and up to 8 m (25 ft) in length. This technique allows for
a fast installation with little impact to project
site.
15
CHAPTER 6
MACHINERIES USED IN SOIL NAILING
The following tools or machineries are used for soil nailing:
Drilling Equipment’s
Grout Mixing Equipments
Shotcreting / Guniting Equipments
Compressor
They can be broadly explained further as follows:
Drilling Equipme nts: It’s a rotary air-flushed and water-flushed system. It consists
of a down the hole hammer with a tri-cone bit(Fig 6.1).It is important to procure
drilling equipment with sufficient power and rigid drill rods.
Grout M ixing Equipme nts: In order to produce uniform grout mix, high speed
shear colloidal mixer should be considered. Powerful grout pump is
essential for uninterrupted delivery of grout mix (Fig 6.2).If fine aggregate is
used as filler for economy, special grout pump shall be used.
Shotc re ting / Guniting Equipme nts: Dry mix method will require a valve at
the nozzle outlet to control the amount of water injecting into the high pressurized
flow of sand/cement mix (Fig 6.3).For controlling the thickness of the shotcrete,
measuring pin shall be installed at fixed vertical and horizontal intervals to guide
the nozzle man.
Co mpre ssor: The compressor shall have minimum capacity to delivered shotcrete at
the minimum rate of 9m3/min. Sometimes, the noise of compressor can be an issue if
the work is at close proximity to residential area, hospital and school.
Fig 6.1: Typical drilling equipment
16
Fig 6.2: Grout Mixing Instrument
Fig 6.3: Shotcreting is done with the help of a pipe with a nozzle
17
CHAPTER 7
MATERIALS USED IN SOIL NAILING
This presents information on construction materials used for the construction of a soil nailed
wall. They are:
Stee l Re info rce me nts: Steel reinforcements are used in the construction of soil
nailed walls. For corrosion protection; all steel component shall be galvanized. If
machine threading after galvanization is unavoidable, then proper zinc based coating
shall be applied onto the thread. For double corrosion protection, the PVC
corrugated pipe used shall be of good quality and adequate thickness.
Fig 7.1: Reinforcements used in Soil Nailing
Grout M ix: For conventional soil nail, the water cement ratio of the grout mix ranges
from 0.4 to 0.5.As most cementitious grout will experience some grout
shrinkage, non-shrink additive can be used to reduce breeding and grout
shrinkage. The resistance at grout-soil interface of nail will significantly reduced
when the grout
shrink.
18
Fig 7.2: Grout Mix is being formed in the Grout Mixing
Machine
Shotc re te /Gunite: Shotcrete or gunite can be continuous flow of mortal or
concrete mixes projected at high speed perpendicularly onto the exposed ground
surface by means of pneumatic air blowing for dry mix or spraying for wet mix.
Fig 7.3: Shotcreting is being done on the wire
mesh
19
CHAPTER 8
DESIGN REQUIREMENTS
The design of a soil nailed wall is organized to first introduce the technical concepts related to
the mechanisms underlying soil nail wall response to construction and operation.
Following this introduction, specific topics related to analysis and design are
introduced, starting with a presentation of the two specific limit states that must be
considered by the designer, namely, the strength limit states and service limit states.
This is followed by a description of potential failure modes for soil nail walls. Then it
introduces and compares calculations resulting from SNAIL and GOLDNAIL, two of the
most widely used computer programs in the United States.
8a) LOAD TRANSFER CONCEPT IN SOIL NAIL WALLS
Fig 8.1
20
Soil excavation is initiated from the ground surface and the Excavation Phase 1 is
completed (Figure 5.1). Because of the soil ability to stand unsupported, the upper
portion of the soil behind the excavation is stable (or at least marginally stable) before
the first row of nails (Nails 1) is installed.
As Nails 1 and the temporary facing are installed, some load derived from the
deformation of the upper soil is transferred to these nails through shear stresses along
the nails and translate into and axial forces. The top portion of Fig shows
schematically the axial force distribution in Nails 1 at the end of excavation Phase 1.
At this point, the temporary facing supports the excavation surface and provides
connectivity between adjacent nails in row of Nails 1.
As excavation proceeds to Excavation Phase 2, the uppermost and the unsupported
portions of the soil nail wall deforms laterally. At this point, another potential sliding
surface, one originated from base of Excavation Phase 2 is formed.
Nails 2 are then installed. Subsequently the temporary facing between the bottom of
excavation Phases 1 and 2 is installed and integrated to the facing constructed
in Phase 1. Movements of the soil above the Phase 2 depth will cause additional loads
to be transferred to Nails 1 and generate loads in Nails 2.
To provide global stability, the soil nails must extend beyond the potential
failure surface. As the depth of excavation increases, the size of the retained
soil mass increases, as shown in Fig.
As the size of the retained zone increases, the stresses at the soil/nail interface and the
axial forces in the nails increase.
The upper portion of Fig shows schematically that the axial force distribution for
Nails 1 at the end of the last excavation Phase N does not exhibit the largest
values.
As the critical failure surface becomes deeper and larger, the contribution of the upper
nails to the stabilization of this larger sliding mass diminishes.
8b) LIMIT STATES
The analysis and design of soil nail walls must consider two distinct limiting
conditions: Strength Limit States and the Service Limit States.
Stre ng th limit state s: These limit states refer to failure or collapse modes in which
the applied loads induce stresses that are greater than the strength of the whole system
21
or individual components, and the structure becomes unstable. Strength limit states
arise when one or more potential failure modes are realized.
Se rvice limit state s: These limit states refers to conditions that do not involve
collapse, but rather impair the normal and safe operation of the structure. The major
service limit state associated with soil nail walls is excessive wall deformation.
Othe r se rvice limit state s: These are beyond the scope of this document;
include
total or differential settlements, cracking of concrete facing, aesthetics, and fatigue
caused by repetitive loading.
Fig 8.2: Modes of Failure
22
DESIGN CONSIDERATIONS
. Vertical and Horizontal Spacing of Soil Nails
• Adopt SH = SV = 5 ft.
• Check: SH × SV ≤ 36 to 42 ft2
2. Vertical Spacing at the Top and Bottom of the Wall
• The spacing between the first row and the top of the wall (SV0) is
selected as:
SV0 ≤ 3.5ft.
• The spacing between the deepest row and the bottom of the wall (SVN)
is:
SVN ≤ 2 to 3 ft
3. Soil Nail Inclination
• between 10 to 20 degrees
4. Soil Nail Length
• L = 0.7 H ; generally in between 0.6H to 1.2H
5. Soil Nail Pattern
either square or staggered pattern
6.Tendon for soil nail
Solid Bar- Dia .86in. To 1.86in. ; Length- 60ft
Hollow Bar- Dia. Outer: 1-3in , Dia inner: .3-1in, Length- 10-20ft
7.Maximum tensile forces
• In upper two third
• In lower one third values reduces to 50% of above.
8. Tensile force at wall facing
Tmax = 0.50 Ka γs H SV SH to Tmax = 1.1 Ka γs H
SV SH.
To= Tmax[0.6+.057(Smax-3)])]
23
9. Pullout Resistance
q = nominal bond strength of the nail-grout-soil interface (force/unit area)
D = diameter of the drill hole
L = pullout development length
10.Nail Tensile Resistance
A = cross-sectional area of nail tendon
F = nominal yield resistance of nail tendon
 . Tmax = min of
Rp = πqDL
Rt = Af
• Tensile Resistance of Nail
• Pull out resistance
• Facing Resistance
24
CHAPTER9
CONSTRUCTION SEQUENCES
The sequence of construction for typical soil nail walls was described in and consisted of:
Excavation;
Drilling of nail holes;
Installation and grouting nails;
Construction of temporary shotcrete facing;
Construction of subsequent levels; and
Construction of a final, permanent facing.
Fig 9.1: Steps in constructing a soil nailed wall
25
Fig 9.2: Initial Excavation Lift and Nail
Installation
Fig 9.3: Typical Drilling of Soil Nails with Rotary
Method
26
Construction Sequence
The typical sequence of construction of a soil nail wall is described below and shown schematically
in Fig
Step 1. Excavation.
The depth of the initial excavation lift (unsupported cut) may range between 2.5 and 7 ft, but is
typically 3 to 5 ft and reaches slightly below the elevation where the first row of nails will be
installed. The feasibility of this step is critical because the excavation face must have the ability to
remain unsupported, until the nails and initial face are installed, typically one to two days. The type
of soil that is excavated may limit the depth of the excavation lift. The excavated platform must be
of sufficient width to provide safe access for the soil nail installation equipment.
Step 2. Drilling of Nail Holes.
Drill holes are advanced using specialized drilling equipment operated from the excavated platform.
The drill holes typically remain unsupported.
Step 3. A) Nail Installation and Grouting.
Tendons are placed in the drilled hole. A tremie grout pipe is inserted in the drill hole along with the
tendon; and the hole is filled with grout, placed under gravity or a nominal, low pressure (less than 5
to 10 psi). If hollow bars are used, the drilling and grouting take place in one operation.
B) Installation of Strip Drains.
Strip drains are installed on the excavation face, continuously from the top of the excavation to
slightly below the bottom of the excavation. The strip drains are placed between adjacent nails and
are unrolled down to the next excavation lift.
27
Step 4. Construction of Initial Shotcrete Facing. Before the next lift of soil is excavated, an
initial facing is applied to the unsupported cut. The initial facing typically consists of a lightly
reinforced 4-in. thick shotcrete layer. The reinforcement includes welded-wire mesh (WWM),
which is placed in the middle of the facing thickness (Figure 2.1). Horizontal and vertical bars
are also placed around the nail heads for bending resistance. As the shotcrete starts to cure, a
steel bearing plate is placed over the tendon that is protruding from the drill hole. The bearing
plate is lightly pressed into the fresh shotcrete. Hex nuts and washers are then installed to
engage the nail head against the bearing plate. The hex nut is wrench-tightened within 24 hours
of the placement of the initial shotcrete. Testing of some of the installed nails to proof-load their
capacity or to verify the load-specified criterion may be performed before proceeding with the
next excavation lift. The shotcrete should attain its minimum specified 3-day compressive
strength before proceeding with subsequent excavation lifts. For planning purposes, the curing
period of the shotcrete should be considered 72 hours.
Step 5. Construction of Subsequent Levels.
Steps 1 through 4 are repeated for the remaining excavation lifts. At each excavation lift, the
strip drain is unrolled downward to the subsequent lift. A new panel of WWM is then placed
overlapping at least one full mesh cell with the WWM panel above. The temporary shotcrete is
continued with the previous shotcrete lift.
Step 6. Construction of Final Facing.
After the bottom of the excavation is reached and nails are installed and tested, the final facing
is constructed. Final facing may consist of CIP reinforced concrete, reinforced shotcrete, or
prefabricated panels. Weep holes, a foot drain, and drainage ditches are then installed to
discharge water that may collect in the continuous strip drain.
Variations of the steps described above may be necessary to accommodate specific project
conditions. For example, shotcrete may be applied at each lift immediately after excavation and
before drilling of the holes and nail installation, particularly where stability of the excavation
face is a concern. Another variation may be grouting the drill hole before placement of the
tendon in the wet grout.
28
CHAPTER 10
APPLICATIONS AND ADVANTAGES
Stabilization of railroad and highway cut slopes
Excavation retaining structures in urban areas for high-rise building and underground
facilities
Tunnel portals in steep and unstable stratified slopes
Construction and retrofitting of bridge abutments with complex boundaries involving
wall support under piled foundations
Stabilizing steep cuttings to maximize development space.
The stabilizing of existing over-steep embankments.
Soil Nailing through existing concrete or masonry structures such as failing retaining
walls and bridge abutments to provide long term stability without demolition and
rebuild costs.
Temporary support can be provided to excavations without the need for bulky
and intrusive scaffold type temporary works solutions.
ADVANTAGES
Soil nail walls exhibit numerous advantages. Some of these advantages are described
below:
11a) CONSTRUCTION:
Requires smaller ROW than ground anchors as soil nails are typically shorter
Less disruptive to traffic and causes less environmental impact compared to
other construction techniques
Installation of soil nail walls is relatively rapid and uses typically less
construction materials
Soil nailing is advantageous at sites with remote access because smaller equipment is
generally needed
29
11b) PERFORM ANCE:
Soil nail walls are relatively flexible and can accommodate relatively large total and
differential settlements
Total deflections of soil nail walls are usually within tolerable limits
Have performed well during seismic events owing to overall system flexibility.
11c) COST:
Soil nail walls are more economical
Soil nail walls are typically equivalent in cost or more cost-effective than
ground anchor walls
Shotcrete facing is typically less costly
30
CONCLUSION
• Soil nailing has great advantages, thus there is a need to use this technique on large scale
in India in many infrastructure projects wherever applicable to realize the technical and
economic advantages associated with the technique.
• Soil nailing is being used in many geotechnical applications to improve stability of
excavated vertical cuts and existing slopes.
• The vertical cut stability/slope stability improved due to the reinforcing effect of nails. The
study illustrates that the technique is a viable technique to improve the stability of vertical
cuts and stability of existing slopes and its advantages need to be exploited on a large scale
in infrastructure projects.
REFERENCE
31
REFERENCES
• Soil Nail Walls Reference Manual, “AASHTO LRFD Bridge Design Specifications, 7th Edition. “ , U.S.
Department of Transportation Federal Highway Administration.
• Sivakumar Babu G.L., ”Professor, Department of Civil Engineering, Indian Institute of Science, Bangalore
“ , “Case Studies in Soil Nailing”, IGC 2009, Guntur, INDIA.
• Arora R.P,Associate Professer, CE, CTAE, Udaipur, India ‘’Soil Nailing for Slope Stabilization’’ ,
International Journal of Engineering Science and Computing, December 2016 .
• Dr. Purnanand P. Savoikar, Professor2Department of Civil Engineering, Goa Engineering College,
Farmagudi, Goa, “Study of soil nailing for highway retaining wall in Goa”, Indian Geotechnical
Conference IGC2016 15-17 December 2016, IIT Madras, Chennai, India.
• Sivakumar Babu G.L, ”Professor, Department of Civil Engineering, Indian Institute of Science, Bangalore
Ground improvement, “Ground reinforcement using soil nailing”, NPTEL Courses.

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Maulana azad national institute of technology

  • 1. 1 MAULANA AZAD NATIONAL INSTITUTE OF TECHNOLOGY BHOPAL A SEMINAR REPORT ON “SLOPE STABILIZATION BY SOIL NAILING TECHNIQUE” A seminar report submitted in partial fulfillment of the requirement of Master of Technology in Geotechnical engineering course during the year 2018-2019 Submitted by BHANU PRATAP SINGH (Scholar Number 182111119) Under the Guidance of Asst. Prof. Dr. Rakesh Kumar GEOTECTNICAL ENGINEERING DEPARTMENT OF CIVIL ENGINEERING 2018-19
  • 2. 2 MAULANA AZAD NATIONAL INSTITUTE OF TECHNOLOGY BHOPAL DEPARTMENT OF CIVIL ENGINEERING DECLARATION I Bhanu Pratap Singh, student of M. tech, Geotechnical Engineering, Department of Civil Engineering, Maulana Azad National Institute of Technology, Bhopal, hereby declare that the work presented in this seminar report is outcome of my own work, is Bonafide to the best of my knowledge and this work has been carried out taking care of Engineering Ethics. The work presented does not infringe any patented work and has not been submitted to any University for the award of any degree or any professional diploma. Bhanu Pratap Singh Scholar no. 182111119
  • 3. 3 MAULANA AZAD NATIONAL INSTITUTE OF TECHNOLOGY BHOPAL DEPARTMENT OF CIVIL ENGINEERING CERTIFICATE October 2018 This is to certify that the seminar entitled “SLOPE STABILIZATION BY SOIL NAILING TECHNIQUE” Submitted by Bhanu Pratap Singh (182111119) of M. tech 1st year, Geotechnical Engineering (Department of Civil Engineering), Maulana Azad National Institute of Technology, Bhopal, is a record of bonafide seminar carried out by him under my supervision and guidance. To the best of my knowledge, the presented seminar report has not been submitted for the award of any other diploma or degree certificate. Dr. Rakesh Kumar (Assistant Professor)
  • 4. 4 ACKNOWLEDGEMENT I would like to express my gratitude to my mentor, Assistant Prof. Dr. Rakesh Kumar for introducing me to the topic as well as for his useful comments, remarks and engagement through the learning process of this project. I am very thankful to Prof Dr. S.K. Katiyar, Head of Department (Civil Engineering) for his kind support and cooperation. This seminar report would never have been completed without the guidance and support of Prof Dr. N. Dindorkar, Prof Dr. P.K. Jain, Associate Prof Dr.Suneet Kaur and Assistant Prof. Dr. Kishan Dharavat. I owe a hearty gratitude towards them. My thanks and appreciation also goes to my colleagues and people who have willingly helped me out with their abilities.
  • 5. 5 ABSTRACT Soil nailing is an in-situ reinforcement technique by passive bars which can withstand tensile forces, shearing forces and bending moments. This technique is used for retaining walls and for slope stabilization. Its behavior 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. Taking into account these mechanisms, multi-criteria at failure design method is proposed. It is derived from the slice methods used in slope stability analysis. The criteria lead to a yielding curve in the shear – tensile forces plane and the consideration of the principle of the maximum plastic work enables to calculate the shear and tensile forces mobilized at failure in each inclusion. Using a formulation determinate, the slope stability analysis take into account the passive force of reinforcement.
  • 6. 6 CONTENTS Page no. 1. INTRODUCTION 7 2. ORIGIN AND DEVELOPMENT 8 3. FAVOURABLE GROUND CONDITIONS FOR SOIL NAILING 9 4. COMPONENTS OF A SOIL NAIL WALL 11 5. TYPES OF NAILS USED 14 6. MACHINERIES USED IN SOIL NAILING 15 7. MATERIALS USED IN SOIL NAILING 17 8. DESIGN REQUIREMENTS 19 9. CONSTRUCTION SEQUENCES 24 10. APPLICATIONS AND ADVANTAGES 28 11. CONCLUSION 30 12. REFERENCES 31
  • 7. 7 CHAPTER 1 INTRODUCTION Soil nailing consists of the passive reinforcement of existing ground by installing closely spaced steel bars (i.e. nails), which may be subsequently encased in grout. As construction proceeds from the top to bottom, shotcrete or concrete is also applied on the excavation face to provide continuity. In a soil-nailed retaining wall, the properties and material behavior of three components—the nail soil, the reinforcement (nails) and the facing element—and their mutual interactions significantly affect the performance of the structure. Soil nailing is typically used to stabilize existing slopes or excavations where top-to- bottom construction is advantageous compared to other retaining wall systems. For certain conditions, soil nailing offers a viable alternative from the viewpoint of technical feasibility, construction costs, and construction duration when compared to ground anchor walls, which is another popular top-to bottom retaining system. An alternative application of passive reinforcement in soil is sometimes used to stabilize landslides. In this case, the reinforcement (sometimes also called “nails”) is installed almost vertically and perpendicular to the base of the slide. In this alternative application, nails are also passive, installed in a closely spaced pattern approximately perpendicular to the nearly horizontal sliding surface, and subjected predominantly to shear forces arising from the landslide movement.
  • 8. 8 CHAPTER 2 ORIGIN AND DEVELOPEMENT The soil nailing technique was developed in the early 1960s, partly from the techniques for rock bolting and multi-anchorage systems, and partly from reinforced fill technique (FHWA, 1998). The New Austrian Tunneling Method introduced in the early 1960s was the premier prototype to use steel bars and shotcrete to reinforce the ground. With the increasing use of the technique, semi-empirical designs for soil nailing began to evolve in the early 1970s. The first systematic research on soil nailing, involving both model tests and full-scale field tests, was carried out in Germany in the mid-1970s. Subsequent development work was initiated in France and the United States in the early 1990s. • Tunneling Method in the 1960’s.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. • In Germany, the first use of a soil nail wall was in 1975. • The United States first used soil nailing in 1976 for the support of a 13.7 m deep foundation excavation in dense silty sands. • 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. .
  • 9. 9 CHAPTER 3 FAVOURABLE GROUND CONDITIONS FOR SOIL NAILING Soil nail walls can be used for a wide range of soil types and conditions. Project experience has shown that certain favorable ground conditions make soil nailing cost effective over other techniques. Soil nailing has proven economically attractive and technically feasible when: The soil in which the excavation is constructed should able to stand unsupported in a 1- to 2-m (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). It is advantageous that the ground conditions allow drill holes to be advanced without the use of drill casings and for the drill hole to be unsupported for a few hours until the nail bars are installed and the drill hole is grouted. The results from the Standard Penetration Test provides the SPT value ‘N’ which can be used to preliminary identify the favorable soil conditions for Soil Nailing. Based on the general criteria for favorable conditions noted above, the following ground types are generally considered well suited for soil nailing applications Stiff to Hard Fine -Grained Soils: Fine-grained (or cohesive) soils may include stiff to hard clays, clayey silts, silt clays, sandy clays, sandy silts, and combinations thereof. These types of soils have the SPT value (N) around 9 blows/300mm.Fine- grained soils should have relatively low plasticity i.e. PI<15. Dense to Very Dense Granular Soils : These soils include sand and gravel with SPT N-values larger than 30 and with some fines about 10 to 15 percent and with weak natural cementation that provide cohesion. To avoid excessive breakage of capillary forces thereby reducing apparent cohesion the movement of water toward the
  • 10. 10 excavation face needs to be minimized by redirecting surface water away from the excavation face. Weathered Rock with no Weakness Planes: Weathered rock may provide a suitable supporting material for soil nails as long as weakness planes occurring in unfavorable orientations are not prevalent (e.g., weakness planes dipping into the excavation). Glacial Soils: Glacial outwash and glacial till materials are typically suitable for soil nailing applications as these soils are typically dense, well-graded granular materials with a limited amount of fines. In addition to these above conditions certain other aspects Should be considered for the construction of soil nailed structures: The prolonged exposure to ambient freezing temperatures may cause frost action in saturated, granular soils and silt; as a result, increased pressures will be applied to the temporary and permanent facings. Repeated freeze-and-thaw cycles in the soil may reduce the bond strength at the soil nail grout-ground interface and the adhesion between the shotcrete and the soil. A suitable protection against frost penetration and an appropriate concrete mix must be provided. Granular soils that are very loose (N ≤ 4) and loose (4 < N ≤ 10) may undergo excessive settlement due to vibrations caused by construction equipment and traffic.
  • 11. 11 CHAPTER 4 COMPONENTS OF A SOIL NAIL WALL Fig 4.1: Main Components of a Typical Soil Nail. The components of a soil nailed wall are shown above in the (Fig 4.1) they are as follows: Nail Bars: Steel reinforcing bars used for soil nails are commonly threaded and may be either solid or hollow. Bars generally have a nominal tensile strength of 420 MPa (Grade 60) or 520 MPa (Grade 75). Bars with a tensile strength of 665 MPa (Grade 95) and as high as 1,035 MPa (Grade 150) may be considered for soil nailing, but their use should be restrictive. Bars with lower grades are preferred because they are more ductile, less susceptible to corrosion, and readily available. Grade 150bars should not be used because they are more brittle under shear and more susceptible to stress corrosion than steel at lower grades. Threaded bars applications are available in 19-, 22-, 25-, 29-, 32-, 36-, and 43-mm diameter (No. 6, 7, 8, 9, 10, 11, and 14 in English units) up to approximately 18 m (59 ft) in length.
  • 12. 12 Nail Head: The nail head comprises two main components, the bearing-plate, hex nut, and washers; and the headed-stud. The bearing plate is made of Grade 250 MPa (Grade 36) steel and is typically square 200- to 250-mm (8- to 10-in.) side dimension and 19-mm (¾-in.) thick. The purpose of the bearing plate is to distribute the force at the nail end to the temporary shotcrete facing and the ground behind the facing. Washers and nuts are steel with a grade consistent with that of the nail bar commonly of 420 or 520 MPa (Grade 60 or 75). Grout: Grout for soil nails is commonly a neat cement grout, which fills the annular space between the nail bar and the surrounding ground. Sand-cement grout can also be used in conjunction with open hole-drilling (i.e. for non-caving conditions) for economic reasons. Cement Type I (normal) is recommended for most applications. Cement Type III is grounded finer, hardens faster, and can be used when target grout strength is required to be achieved faster than for typical project conditions. Cement Type II hardens at a slower rate, produces less heat, and is more resistant to the corrosive action of sulphates than Cement Type I. The water/cement ratio for grout used in soil nailing applications typically ranges from 0.4 to 0.5. Fig 4.2: Grout is being placed with the help of pipes Ce ntralize rs: Centralizers are devices made of polyvinyl chloride (PVC) or other synthetic materials that are installed at various locations along the length of each nail bar to ensure that a minimum thickness of grout completely covers the nail bar (Fig 4.3). They are installed at regular intervals, typically not exceeding 2.5 m (8 ft), along the length of the nail and at a distance of about 0.5 m (1.5 ft) from each end of the nail .
  • 13. 13 Fig 4.3: Typical PVC centralizers Co rrosion Prote ctio n Ele me nts: In addition to the cement grout, this provides both physical and chemical protection to the nail bars. Protective sheathings made of corrugated synthetic material [HDPE (High Density Polyethylene) or PVC tube) surrounding the nail bar are usually used to provide additional corrosion protection. Wall Fac ing: Nails are connected at the excavation surface (or slope face) to a facing system, which most commonly consists of a first-stage, temporary facing of shotcrete during construction and, a second-stage, permanent facing of CIP concrete. The purpose of the temporary facing is to support the soil exposed between the nails during excavation, provide initial connection among nails, and provide protection against erosion and sloughing of the soil at the excavation face. The purpose of the permanent facing is to provide connection among nails, a more resistant erosion protection, and an aesthetic finish. Temporary facing typically consists of shotcrete and WWM and additional shorter reinforcement bars (referred to as waler bars) around the nail heads. Permanent facing is commonly constructed of CIP reinforced concrete and WWM-reinforced shotcrete. Drainage Syste m: To prevent water pressure from developing behind the wall facing, vertical geo-composite strip drains are usually installed between the temporary facing and the excavation. The drainage system also includes a footing drain and weep holes to convey collected drainage water away from the wall face.
  • 14. 14 CHAPTER 5 TYPES OF NAILS The types of nails used in the construction of soil nailed walls are as follows: Drilled and grouted soil nail Driven soil nails Self-drilling soil nails Jet-grouted soil nails Launched soil nails These are explained as follows: Drille d a nd gro ute d soil na il: These are approximately 100- and 200-mm (4- to 8- in.) diameter nail holes drilled in the foundation soils. These holes are typically spaced about 1.5 m (5 ft) apart. Steel bars are placed and the holes are grouted. Grouted soil nails are the most commonly used soil nails for FHWA projects and they can be used as temporary and permanent applications, provided that appropriate corrosion protection is in place. Drive n soil na ils: These soil nails are relatively small in diameter [19 to 25 mm (¾ to 1 in.)] and are mechanically driven into the ground. They are usually spaced approximately 1 to 1.2 m (3 to 4 ft) apart. The use of driven soil nails allows for a faster installation as compared to drilled and grouted soil nails. Se lf-drilling soil nails: These soil nails consist of hollow bars that can be drilled and grouted in one operation. In this technique, the grout is injected through the hollow bar simultaneously with the drilling. This soil nail type allows for a faster installation than that for drilled grouted nails and, unlike, driven soil nails, some level of corrosion protection with grout is provided. Je t-gro ute d soil na ils: Jet grouting is performed to erode the ground and allow the hole for the nail to be advanced to the final location. The grout provides corrosion protection to the central bar. In a second step, the bars are typically installed using vibro-percussion drilling methods. La unche d soil na ils: In this method, bare bars are “launched” into the soil at very high speeds using a firing mechanism involving compressed air. Bars are 19 to 25 mm (¾ to 1 in.) in diameter and up to 8 m (25 ft) in length. This technique allows for a fast installation with little impact to project site.
  • 15. 15 CHAPTER 6 MACHINERIES USED IN SOIL NAILING The following tools or machineries are used for soil nailing: Drilling Equipment’s Grout Mixing Equipments Shotcreting / Guniting Equipments Compressor They can be broadly explained further as follows: Drilling Equipme nts: It’s a rotary air-flushed and water-flushed system. It consists of a down the hole hammer with a tri-cone bit(Fig 6.1).It is important to procure drilling equipment with sufficient power and rigid drill rods. Grout M ixing Equipme nts: In order to produce uniform grout mix, high speed shear colloidal mixer should be considered. Powerful grout pump is essential for uninterrupted delivery of grout mix (Fig 6.2).If fine aggregate is used as filler for economy, special grout pump shall be used. Shotc re ting / Guniting Equipme nts: Dry mix method will require a valve at the nozzle outlet to control the amount of water injecting into the high pressurized flow of sand/cement mix (Fig 6.3).For controlling the thickness of the shotcrete, measuring pin shall be installed at fixed vertical and horizontal intervals to guide the nozzle man. Co mpre ssor: The compressor shall have minimum capacity to delivered shotcrete at the minimum rate of 9m3/min. Sometimes, the noise of compressor can be an issue if the work is at close proximity to residential area, hospital and school. Fig 6.1: Typical drilling equipment
  • 16. 16 Fig 6.2: Grout Mixing Instrument Fig 6.3: Shotcreting is done with the help of a pipe with a nozzle
  • 17. 17 CHAPTER 7 MATERIALS USED IN SOIL NAILING This presents information on construction materials used for the construction of a soil nailed wall. They are: Stee l Re info rce me nts: Steel reinforcements are used in the construction of soil nailed walls. For corrosion protection; all steel component shall be galvanized. If machine threading after galvanization is unavoidable, then proper zinc based coating shall be applied onto the thread. For double corrosion protection, the PVC corrugated pipe used shall be of good quality and adequate thickness. Fig 7.1: Reinforcements used in Soil Nailing Grout M ix: For conventional soil nail, the water cement ratio of the grout mix ranges from 0.4 to 0.5.As most cementitious grout will experience some grout shrinkage, non-shrink additive can be used to reduce breeding and grout shrinkage. The resistance at grout-soil interface of nail will significantly reduced when the grout shrink.
  • 18. 18 Fig 7.2: Grout Mix is being formed in the Grout Mixing Machine Shotc re te /Gunite: Shotcrete or gunite can be continuous flow of mortal or concrete mixes projected at high speed perpendicularly onto the exposed ground surface by means of pneumatic air blowing for dry mix or spraying for wet mix. Fig 7.3: Shotcreting is being done on the wire mesh
  • 19. 19 CHAPTER 8 DESIGN REQUIREMENTS The design of a soil nailed wall is organized to first introduce the technical concepts related to the mechanisms underlying soil nail wall response to construction and operation. Following this introduction, specific topics related to analysis and design are introduced, starting with a presentation of the two specific limit states that must be considered by the designer, namely, the strength limit states and service limit states. This is followed by a description of potential failure modes for soil nail walls. Then it introduces and compares calculations resulting from SNAIL and GOLDNAIL, two of the most widely used computer programs in the United States. 8a) LOAD TRANSFER CONCEPT IN SOIL NAIL WALLS Fig 8.1
  • 20. 20 Soil excavation is initiated from the ground surface and the Excavation Phase 1 is completed (Figure 5.1). Because of the soil ability to stand unsupported, the upper portion of the soil behind the excavation is stable (or at least marginally stable) before the first row of nails (Nails 1) is installed. As Nails 1 and the temporary facing are installed, some load derived from the deformation of the upper soil is transferred to these nails through shear stresses along the nails and translate into and axial forces. The top portion of Fig shows schematically the axial force distribution in Nails 1 at the end of excavation Phase 1. At this point, the temporary facing supports the excavation surface and provides connectivity between adjacent nails in row of Nails 1. As excavation proceeds to Excavation Phase 2, the uppermost and the unsupported portions of the soil nail wall deforms laterally. At this point, another potential sliding surface, one originated from base of Excavation Phase 2 is formed. Nails 2 are then installed. Subsequently the temporary facing between the bottom of excavation Phases 1 and 2 is installed and integrated to the facing constructed in Phase 1. Movements of the soil above the Phase 2 depth will cause additional loads to be transferred to Nails 1 and generate loads in Nails 2. To provide global stability, the soil nails must extend beyond the potential failure surface. As the depth of excavation increases, the size of the retained soil mass increases, as shown in Fig. As the size of the retained zone increases, the stresses at the soil/nail interface and the axial forces in the nails increase. The upper portion of Fig shows schematically that the axial force distribution for Nails 1 at the end of the last excavation Phase N does not exhibit the largest values. As the critical failure surface becomes deeper and larger, the contribution of the upper nails to the stabilization of this larger sliding mass diminishes. 8b) LIMIT STATES The analysis and design of soil nail walls must consider two distinct limiting conditions: Strength Limit States and the Service Limit States. Stre ng th limit state s: These limit states refer to failure or collapse modes in which the applied loads induce stresses that are greater than the strength of the whole system
  • 21. 21 or individual components, and the structure becomes unstable. Strength limit states arise when one or more potential failure modes are realized. Se rvice limit state s: These limit states refers to conditions that do not involve collapse, but rather impair the normal and safe operation of the structure. The major service limit state associated with soil nail walls is excessive wall deformation. Othe r se rvice limit state s: These are beyond the scope of this document; include total or differential settlements, cracking of concrete facing, aesthetics, and fatigue caused by repetitive loading. Fig 8.2: Modes of Failure
  • 22. 22 DESIGN CONSIDERATIONS . Vertical and Horizontal Spacing of Soil Nails • Adopt SH = SV = 5 ft. • Check: SH × SV ≤ 36 to 42 ft2 2. Vertical Spacing at the Top and Bottom of the Wall • The spacing between the first row and the top of the wall (SV0) is selected as: SV0 ≤ 3.5ft. • The spacing between the deepest row and the bottom of the wall (SVN) is: SVN ≤ 2 to 3 ft 3. Soil Nail Inclination • between 10 to 20 degrees 4. Soil Nail Length • L = 0.7 H ; generally in between 0.6H to 1.2H 5. Soil Nail Pattern either square or staggered pattern 6.Tendon for soil nail Solid Bar- Dia .86in. To 1.86in. ; Length- 60ft Hollow Bar- Dia. Outer: 1-3in , Dia inner: .3-1in, Length- 10-20ft 7.Maximum tensile forces • In upper two third • In lower one third values reduces to 50% of above. 8. Tensile force at wall facing Tmax = 0.50 Ka γs H SV SH to Tmax = 1.1 Ka γs H SV SH. To= Tmax[0.6+.057(Smax-3)])]
  • 23. 23 9. Pullout Resistance q = nominal bond strength of the nail-grout-soil interface (force/unit area) D = diameter of the drill hole L = pullout development length 10.Nail Tensile Resistance A = cross-sectional area of nail tendon F = nominal yield resistance of nail tendon  . Tmax = min of Rp = πqDL Rt = Af • Tensile Resistance of Nail • Pull out resistance • Facing Resistance
  • 24. 24 CHAPTER9 CONSTRUCTION SEQUENCES The sequence of construction for typical soil nail walls was described in and consisted of: Excavation; Drilling of nail holes; Installation and grouting nails; Construction of temporary shotcrete facing; Construction of subsequent levels; and Construction of a final, permanent facing. Fig 9.1: Steps in constructing a soil nailed wall
  • 25. 25 Fig 9.2: Initial Excavation Lift and Nail Installation Fig 9.3: Typical Drilling of Soil Nails with Rotary Method
  • 26. 26 Construction Sequence The typical sequence of construction of a soil nail wall is described below and shown schematically in Fig Step 1. Excavation. The depth of the initial excavation lift (unsupported cut) may range between 2.5 and 7 ft, but is typically 3 to 5 ft and reaches slightly below the elevation where the first row of nails will be installed. The feasibility of this step is critical because the excavation face must have the ability to remain unsupported, until the nails and initial face are installed, typically one to two days. The type of soil that is excavated may limit the depth of the excavation lift. The excavated platform must be of sufficient width to provide safe access for the soil nail installation equipment. Step 2. Drilling of Nail Holes. Drill holes are advanced using specialized drilling equipment operated from the excavated platform. The drill holes typically remain unsupported. Step 3. A) Nail Installation and Grouting. Tendons are placed in the drilled hole. A tremie grout pipe is inserted in the drill hole along with the tendon; and the hole is filled with grout, placed under gravity or a nominal, low pressure (less than 5 to 10 psi). If hollow bars are used, the drilling and grouting take place in one operation. B) Installation of Strip Drains. Strip drains are installed on the excavation face, continuously from the top of the excavation to slightly below the bottom of the excavation. The strip drains are placed between adjacent nails and are unrolled down to the next excavation lift.
  • 27. 27 Step 4. Construction of Initial Shotcrete Facing. Before the next lift of soil is excavated, an initial facing is applied to the unsupported cut. The initial facing typically consists of a lightly reinforced 4-in. thick shotcrete layer. The reinforcement includes welded-wire mesh (WWM), which is placed in the middle of the facing thickness (Figure 2.1). Horizontal and vertical bars are also placed around the nail heads for bending resistance. As the shotcrete starts to cure, a steel bearing plate is placed over the tendon that is protruding from the drill hole. The bearing plate is lightly pressed into the fresh shotcrete. Hex nuts and washers are then installed to engage the nail head against the bearing plate. The hex nut is wrench-tightened within 24 hours of the placement of the initial shotcrete. Testing of some of the installed nails to proof-load their capacity or to verify the load-specified criterion may be performed before proceeding with the next excavation lift. The shotcrete should attain its minimum specified 3-day compressive strength before proceeding with subsequent excavation lifts. For planning purposes, the curing period of the shotcrete should be considered 72 hours. Step 5. Construction of Subsequent Levels. Steps 1 through 4 are repeated for the remaining excavation lifts. At each excavation lift, the strip drain is unrolled downward to the subsequent lift. A new panel of WWM is then placed overlapping at least one full mesh cell with the WWM panel above. The temporary shotcrete is continued with the previous shotcrete lift. Step 6. Construction of Final Facing. After the bottom of the excavation is reached and nails are installed and tested, the final facing is constructed. Final facing may consist of CIP reinforced concrete, reinforced shotcrete, or prefabricated panels. Weep holes, a foot drain, and drainage ditches are then installed to discharge water that may collect in the continuous strip drain. Variations of the steps described above may be necessary to accommodate specific project conditions. For example, shotcrete may be applied at each lift immediately after excavation and before drilling of the holes and nail installation, particularly where stability of the excavation face is a concern. Another variation may be grouting the drill hole before placement of the tendon in the wet grout.
  • 28. 28 CHAPTER 10 APPLICATIONS AND ADVANTAGES Stabilization of railroad and highway cut slopes Excavation retaining structures in urban areas for high-rise building and underground facilities Tunnel portals in steep and unstable stratified slopes Construction and retrofitting of bridge abutments with complex boundaries involving wall support under piled foundations Stabilizing steep cuttings to maximize development space. The stabilizing of existing over-steep embankments. Soil Nailing through existing concrete or masonry structures such as failing retaining walls and bridge abutments to provide long term stability without demolition and rebuild costs. Temporary support can be provided to excavations without the need for bulky and intrusive scaffold type temporary works solutions. ADVANTAGES Soil nail walls exhibit numerous advantages. Some of these advantages are described below: 11a) CONSTRUCTION: Requires smaller ROW than ground anchors as soil nails are typically shorter Less disruptive to traffic and causes less environmental impact compared to other construction techniques Installation of soil nail walls is relatively rapid and uses typically less construction materials Soil nailing is advantageous at sites with remote access because smaller equipment is generally needed
  • 29. 29 11b) PERFORM ANCE: Soil nail walls are relatively flexible and can accommodate relatively large total and differential settlements Total deflections of soil nail walls are usually within tolerable limits Have performed well during seismic events owing to overall system flexibility. 11c) COST: Soil nail walls are more economical Soil nail walls are typically equivalent in cost or more cost-effective than ground anchor walls Shotcrete facing is typically less costly
  • 30. 30 CONCLUSION • Soil nailing has great advantages, thus there is a need to use this technique on large scale in India in many infrastructure projects wherever applicable to realize the technical and economic advantages associated with the technique. • Soil nailing is being used in many geotechnical applications to improve stability of excavated vertical cuts and existing slopes. • The vertical cut stability/slope stability improved due to the reinforcing effect of nails. The study illustrates that the technique is a viable technique to improve the stability of vertical cuts and stability of existing slopes and its advantages need to be exploited on a large scale in infrastructure projects. REFERENCE
  • 31. 31 REFERENCES • Soil Nail Walls Reference Manual, “AASHTO LRFD Bridge Design Specifications, 7th Edition. “ , U.S. Department of Transportation Federal Highway Administration. • Sivakumar Babu G.L., ”Professor, Department of Civil Engineering, Indian Institute of Science, Bangalore “ , “Case Studies in Soil Nailing”, IGC 2009, Guntur, INDIA. • Arora R.P,Associate Professer, CE, CTAE, Udaipur, India ‘’Soil Nailing for Slope Stabilization’’ , International Journal of Engineering Science and Computing, December 2016 . • Dr. Purnanand P. Savoikar, Professor2Department of Civil Engineering, Goa Engineering College, Farmagudi, Goa, “Study of soil nailing for highway retaining wall in Goa”, Indian Geotechnical Conference IGC2016 15-17 December 2016, IIT Madras, Chennai, India. • Sivakumar Babu G.L, ”Professor, Department of Civil Engineering, Indian Institute of Science, Bangalore Ground improvement, “Ground reinforcement using soil nailing”, NPTEL Courses.