A Seminar Report On Soil Nailing By More Abhijit Ashok Under the guidance of Prof. R. R. Sorate Submitted in partial fulfilment of the requirement for T. E. (Civil Engineering) 2014-2015 Savitribai Phule Pune University Department of Civil Engineering Sinhgad Technical Education Society’s Sinhgad Academy of Engineering, Kondhwa, Pune-411048
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A
Seminar Report
On
Soil NailingBy
More Abhijit AshokUnder the guidance of
Prof. R. R. SorateSubmitted in partial fulfilment of the requirement for
T. E. (Civil Engineering)
2014-2015
Savitribai Phule Pune University
Department of Civil Engineering
Sinhgad Technical Education Society’s
Sinhgad Academy of Engineering, Kondhwa, Pune-411048
Soil Nailing 2014-15
Sinhgad Technical Education Society’s
Sinhgad Academy of Engineering, Kondhwa, Pune
Certificate
This is to certify that More Abhijit Ashok, Examination No T120430086 of TE (Civil Engg.)
has submitted his Seminar Report on “Soil Nailing ” under the guidance of Prof. R. R. Sorate
towards the partial fulfillment of the requirement for T.E.(Civil Engineering), Savitribai Phule
Pune University for the Academic year 2014-15.
Prof. R. R. Sorate External Examiner
(Seminar Guide)
Prof. R. B. Bajare (HOD) Prof. A. Dhananjay
Department of Civil Engineering (Seminar Co-ordinator)
Dr. Vijay N. Wadhai
Principal
SINHGAD ACADEMY OF ENGINEERING, PUNE-48 Page 2
Soil Nailing 2014-15 SAOE, Pune.
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ACKNOWLEDGEMENTI would like to take this opportunity to express my honour, respect, deep gratitude
and genuine regards to my seminar guide PROF. R. R. SORATE for giving me all guidance required for my seminar entitled “SOIL NAILING” apart from being a constant source of inspiration and motivation. It was indeed my privilege to have work under him. I am also extremely grateful to staff member of CIVIL ENGINEERING DEPARTMENT for their constant encouragement and kind help during my seminar for providing all facility & help for smooth progress of seminar work.
Last but not least, the backbone of my success & confidence lies solely on blessings of my parents & my friends.
Thanking You,Date: / / 2015
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Soil Nailing 2014-15
ABSTRACT
Since its development in Europe in the early 1970s, soil nailing has become a widely
accepted method of providing temporary and permanent earth support, underpinning
and slope stabilization on many projects in the United States. In the early years, soil
nailing was typically performed only on projects where specialty geotechnical contractors
offered it as an alternate to other, conventional systems. More recently, soil nailing has
been specified as the system of choice due to its overall acceptance and effectiveness.
However, although the theoretical engineering aspects of soil nailing may be well
understood, there is a far lesser degree of understanding, even within the geotechnical
community, as to the site conditions – where, when and why – under which soil nailing
should, and should not, be used. The purpose of our seminar, therefore, is to study the
technique to decide if soil nailing is the right system for engineering projects or not.
Typical soil nail details, procedures, design, monitoring and testing considerations and
case studies are presented as a tool to aid in making those decisions.
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 formulation determinate, the slope stability analysis takes into account
the passive force of reinforcement.
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CHAPTER-1
INTRODUCTION
The slope stabilization method of soil nailing is used to reinforce the existing
ground by installing threaded steel bars into the slope or cut wall as construction
proceeds from the top down. Soil nails are installed to create a stable mass of soil. This
process creates a single block of earth that is stable and able to hold back the soil behind
it. Soil nailing is an economical means of constructing shoring systems and retaining
walls. Many times soil nailing can be the least disruptive way to construct retaining
systems.
Soil nailing not only works in tension but also with bending and shearing forces.
Generally, the soil nails increase the bonding of the soil through their ability to carry
tensile loads. A constructed face is usually required and is typically made of shot Crete,
which is reinforced with wire mesh and steel plates. Permanent walls are usually
constructed with cast in place facing.
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Soil Nailing Construction
CHAPTER NO.2
SOIL NAILS
2.1 NAILS
Soil nails are installed in a pattern designed to ensure both internal and external
stability of the wall. A relatively large number of nails are placed so they can resist the
tensile, compressive, and shear stresses within the wall and transfer them into the ground.
Engineers use a method of equilibrium analysis to make certain that the number and
placement of nails guard against sliding and guarantee stability.
The nails used in construction are generally steel bars that resist tensile and shear
stresses and bending moment. Therefore, ductile steel is preferred over brittle. Most
projects are designed to use nails with a uniform length and cross-sectional area. Nail
length is usually about 60-80% of the height of the wall, depending on soil conditions
(e.g., rocklike material may get shorter nails). Prior to construction, nails are tested to
determine nail-soil adhesion and their resistance to pullout failure.
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2.1.1 Typical Section Of Soil Nail
2.2 TYPES OF NAILS
● Driven nail
● Grouted nail
● Corrosion-protected nails
● Launched nails
● Jet grouted nail
2.2.1 DRIVEN NAILS: Driven nails are small-diameter (15 to 46mm) rods or bars, or metallic sections,
with a relatively limited length (to about 20m) made of mild steel with a yield strength
of 350MPa (50ksi). They are closely spaced (2 to 4 bars per square meter) and create a
rather homogeneous composite reinforced soil mass. The nails are driven into the ground
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Soil Nailing 2014-15 at the designed inclination using a vibropercussion pneumatic or hydraulic hammer with
no preliminary drilling. Special nails with an axial channel can be used to allow for grout
sealing of the nail to the surrounding soil after its complete penetration. This installation
technique is rapid and economical (4 to 6 per hour). However, it is limited by the length
of the bars (maximum length about 20m) and by the heterogeneity of the ground (e.g.,
presence of boulders).
2.2.2 GROUTED NAILS:
Grouted nails are generally steel bars (15 to 46mm in diameter) with a yield
strength of 60 ksi. They are placed in boreholes (10 to 15cm in diameter) with a vertical
and horizontal spacing varying typically from 1 to 3m depending on the type of the in-
situ soil. The nails are usually cement-grouted by gravity or under low pressure. Ribbed
bars can be used to improve the nail-grout adherence, and special perforated tubes have
been developed to allow injection of the grout through the inclusion.
2.2.3 CORROSION-PROTECTED NAILS:
Corrosion-protected nails generally use double protection schemes similar to
those commonly use in ground anchor practice. For permanent applications of soil
nailing, based on current experience, it is recommended that a minimum grout cover of
1.5 inches be achieved along the total length of the nail. Secondary protection should be
provided by electro statically applied resin-bonded epoxy on the bars with a minimum
thickness of about 14 mm. In aggressive environments, full encapsulation is
recommended. It may be achieved, as for anchors, by encapsulating the nail in corrugated
plastic or steel tube grouted into the ground.
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2.2.4 LAUNCHED NAILS:
The nail launching technology consists of firing directly into the ground, using a
compressed air launcher, nails of 25mm and 38mm in diameter, made from bright bar
with nail lengths of 6 meters or more. The nails are installed at speeds of 200 mph with
an energy transfer of up to 100kJ. This installation technique enables an optimization of
nail installation with a minimum of site disruption. During penetration the ground around
the nail is displaced and compressed. The annulus of compression developed reduces the
surface friction and minimizes damage to protective coatings such as galvanized and
epoxy. The technology is presently used primarily for slope stabilization although
successful applications have also been recorded for retrofitting of retaining systems.
However, a rigorous evaluation of the pull-out resistance of launched nails is required
prior to their use in retaining structures.
2.2.5 JET-GROUTED NAILS:
Jet-grouted nails are composite inclusion made of a grouted soil with a central steel
rod, which can be as thick as 30 to 40 cm. a technique that combines the vibropercusion
driving and high pressure (greater than 20 MPa) jet grouting has been developed by
Louis (1986). The nails are installed using a high frequency (up to 70Hz) vibropercussion
hammer, and cement grouting is performed during installation. The grout is injected
through a small-diameter (few millimeters) longitudinal channel in the reinforcing rod
under a pressure that is sufficiently high to cause hydraulic fracturing of the surrounding
ground. However, nailing with a significant lower grouting pressure (About 4MPa) has
been used successfully, particularly in granular soils. The inner nail is protected against
corrosion using a steel tube.
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Soil Nailing 2014-15 2.3 SOIL NAIL INTERACTION:
In soil nailing, similarly to ground anchors, the load transfer mechanism and the
ultimate pull-out resistance of the nails depend primarily upon soil type and strength
characteristics, installation technique, drilling method, size and shape of the drilled hole,
as well as grouting method and pressure used.
To date, estimates of the pull-out resistance of nails are mainly based upon
empirical formulae (or ultimate interface shear stress values) derived from field
experience. These formulae are useful for feasibility evaluation and preliminary design.
Table (Elias and Juran, 1991) provides a summary of estimated ultimate interface shear
stress values for soil nails as a function of soil type and installation technique.