soil nailing seminar report by ankush choudhury

VISVESVARAYA TECHNOLOGICAL UNIVERSITY, BELAGAVI

A SEMINAR REPORT ON

“SOIL NAILING”

A seminar report submitted in partial fulfillment of requirements of 8th semester of bachelor of engineering course during the year 2014-2015

Submitted by:ANKUSH CHOUDHURY

Under the Guidance ofProf. MANIK DESHMUKH

DEPARTMENT OF CIVIL ENGINEERING

GURU NANAK DEV ENGINEERING COLLEGEBIDAR-585403, (KARNATAKA)

SOIL NAILING

GURU NANAK DEV ENGINEERING COLLEGE BIDAR, 585401(KARNATAKA)

DEPARTMENT OF CIVIL ENGINEERING

CERTIFICATE

This to certify that the seminar on “SOIL NAILING” is a bonafide work

carried out by ANKUSH CHOUDHURY in partial fulfilment of the

requirements for the award of Degree of Bachelor of Engineering in Civil

Engineering from the Visvesvaraya Technological University, Belagavi

during the academic year 2014-2015. It is certified that the seminar report

satisfies the academic requirement in respect of seminar work described for the

Bachelor of Engineering degree.

Prof. Manik Deshmukh Prof: Manik Deshmukh Prof: Obappa Agrahar Seminar Guide Seminar Co-ordinator Head of Civil dept

DEPT. OF CIVIL ENGG. G.N.D.E.C BIDAR

SOIL NAILING

ACKNOWLEDGEMENT

I would like to express my deep sense of gratitude to our principal Dr. Ashok Biradar,

Guru Nanak Dev Engineering College, Bidar for his motivation and for creating a

inspiring atmosphere in the college by providing state of art facilities for preparation and

delivery of seminar.

My sincere thanks to Prof. Obappa Agrahar Head of Department Civil Engineering for

his whole hearted support in complementation of the seminar.

I am highly indebted to my seminar co-ordinator and my seminar guide Prof. Manik

Deshmukh for guiding and giving timely advices and suggestion in the successful

completion of the seminar.

Last but not least, I would like to thanks The Teaching & Non-Teaching Staff of Civil

Engineering Department, I would like thank one and all who have helped me during the

course of this seminar.

ANKUSH CHOUDHURY


SOIL NAILING

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 behaviour is typical

of that of composite materials and involves essentially two interaction mechanisms:

The soil- reinforcement friction and the normal earth pressure on the reinforcement. The

mobilization of the lateral friction requires frictional properties for the soil, while the

mobilization of the normal earth pressure requires a relative rigidity of the inclusions.

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.


SOIL NAILING

CONTENTS

Page no.

1. INTRODUCTION 3

2. ORIGIN AND DEVELOPMENT 4

3. FAVOURABLE GROUND CONDITIONS FOR SOIL NAILING 5-6

4. COMPONENTS OF A SOIL NAIL WALL 7-9

5. TYPES OF NAILS USED 10

6. MACHINERIES USED IN SOIL NAILING 11-12

7. MATERIALS USED IN SOIL NAILING 13-14

8. DESIGN REQUIREMENTS 15-17

9. CONSTRUCTION SEQUENCES 18-19

10. APPLICATIONS 20

11. ADVANTAGES 21

12. CONCLUSION 22

13. REFERENCES 23


SOIL NAILING

CHAPTER 1

INTRODUCTION- WHAT IS SOIL NAILING ?

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 behaviour of three components—the native 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.


SOIL NAILING

CHAPTER 2

ORIGIN AND DEVELOPEMENT

Tunnelling 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

The origin of soil nailing can be traced to a support system for underground

excavations in rock referred to as the New Austrian cut-slope in sand was stabilized

using soil nails.

In Germany, the first use of a soil nail wall was in 1975 (Stocker et al. 1979).

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.


SOIL NAILING

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 favourable 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 favourable soil conditions for Soil

Nailing. Based on the general criteria for favourable 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


SOIL NAILING

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

unfavourable 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.


SOIL NAILING

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.


SOIL NAILING

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

Centralizers : 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.


SOIL NAILING

Fig 4.3: Typical PVC centralizers

Corrosion Protection Elements : 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 Facing : 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 System : 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.


SOIL NAILING

CHAPTER 5

TYPES OF NAILS USED

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:

Drilled and grouted soil nail : 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.

Driven soil nails : 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.

Self-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.

Jet-grouted soil nails : 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.

Launched soil nails : 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.


SOIL NAILING

CHAPTER 6

MACHINERIES USED IN SOIL NAILING

The following tools or machineries are used for soil nailing:

Drilling Equipments

Grout Mixing Equipments

Shotcreting / Guniting Equipments

Compressor

They can be broadly explained further as follows:

Drilling Equipments : 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 Mixing Equipments : 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.

Shotcreting / Guniting Equipments : 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.

Compressor : 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


SOIL NAILING

Fig 6.2: Grout Mixing Instrument

Fig 6.3: Shotcreting is done with the help of a pipe with a nozzle


SOIL NAILING

CHAPTER 7

MATERIALS USED IN SOIL NAILING

This presents information on construction materials used for the construction of a soil nailed

wall. They are:

Steel Reinforcements : 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 Mix : 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.


SOIL NAILING

Fig 7.2: Grout Mix is being formed in the Grout Mixing Machine

Shotcrete/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


SOIL NAILING

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


SOIL NAILING

Fig 8.1

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.


SOIL NAILING

Strength limit states : 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

or individual components, and the structure becomes unstable. Strength limit states

arise when one or more potential failure modes are realized.

Service limit states : 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.

Other service limit states : 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


SOIL NAILING

CHAPTER 9

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


SOIL NAILING

Fig 9.2: Initial Excavation Lift and Nail Installation

Fig 9.3: Typical Drilling of Soil Nails with Rotary Method


SOIL NAILING

CHAPTER 10

APPLICATIONS

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.


SOIL NAILING

CHAPTER 11

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

11b) PERFORMANCE:

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


SOIL NAILING

CHAPTER 12

CONCLUSION

Conventional design procedure using FHWA (2003) provides a safe but conservative

design.

Provision of facing results in the significant improvement of the stability and

performance of soil nail walls.

Intermittent facing with a small offset in each construction stage is found to be more

effective in reducing the lateral deformation of soil nail walls than regular continuous

vertical facing.

The overall stability (i.e. external as well as internal) and performance of the soil nail

walls is dependent on the other spectral properties (e.g., strong motion duration and

peak displacement) of the time history data of an earthquake.

Pseudo-static analyses are found to provide conservative estimate of displacements

and factor of safety values.


SOIL NAILING

REFERENCES

http://www.deepexcavation.com/en/soil-nail-wall http://www.moretrench.com/b_literature_article.php http://en.wikipedia.org/wiki/Soil_nailing Manual for Design and Construction Monitoring of Soil Nail walls,

US Department of Transportation, Federal Highway

Administration.

Guide to Soil Nail Design and Construction, Geotechnical Engg

Office, Civil Engineering and Development Department, The

Government of the Hong Kong.

http://www.google.com


http://www.google.com/

http://en.wikipedia.org/wiki/Soil_nailing

http://www.moretrench.com/b_literature_article.php

http://www.deepexcavation.com/en/soil-nail-wall

soil nailing seminar report by ankush choudhury

Engineering

seminar report

seminar coordinator

delivery of seminar

engineering course

civil engg

respect of seminar work

bachelor of engineering

abstract soil nailing