20 Indian Geotech J (January–March 2013) 43(1):1–29

Fig. 55 Schematic diagram of

the design

Fig. 56 Installation of micro piles

Fig. 57 Installation of capping beam and first row of grouted nails
had stopped. By this time the total deflection of the top of
the Chimney had crossed 135 mm. It was further advised Design of Nailed Wall
to incrementally remove the earth shoring and introduce
the remaining grouted nails and wailer beams along with This is about the construction of driven nailed walls at
the required grouted nails to reach the bottom of the Indian Institute of Science Campus, Bangalore. While
excavation. constructing an underpass across the National Highway in
front of IISc, by box-jacking technique, the approach
ramps were initially designed to be of RCC walls. For this
CASES OF EXCAVATION PROTECTION WITH about 16 well grown trees have to be cut for which IISc had
DRIVEN AND GROUTED NAILS granted permission. Just at that time in another project the
author had developed a method of driving the nails using
A number of projects (more than 200) have been suc- compressor driven percussion Jack-Hammer. Earlier the
cessfully implemented throughout the country and a few of driven nails used to be installed using conventional sludge
them are discussed. hammer, which was not practicable for large size projects

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Fig. 58 Installation of capping beam and first row of grouted nails Fig. 61 Excavation in progress

Fig. 59 Excavation in progress Fig. 62 Earth shoring to control tilting of the chimney

Fig. 60 Excavation in progress

Fig. 63 Grouting of the cracks

[2]. However the full potential of the methodology had not adopted as 0.7H. The interfacial friction coefficient tan/l is
been explored. tan(2//3). With this the nail spacing was obtained as
The nailed wall at IISc was designed based on the princi- 400 9 400 mm from the pullout failure criterion for a FS of
ples Reinforced Earth Walls, assuming the potential failure 1.5. As part of research program an intensive parametric study
plane proposed by [1]. The length of reinforcement was was made on layers of different N, varying the capacity of the

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Fig. 67 Removal of earth shoring and building of RCC wall with

structural shoring in position
Fig. 64 Capping beam on the RCC piles

Fig. 65 Capping beam on the RCC piles

Fig. 68 Removal of earth shoring and building of RCC wall with
structural shoring in position

capacity which directly measures the penetration strength of

the ground. By adopting the correlation between N and / the
spacing was linked to the rate of driving with a given capacity
of the compressor.
It was found that the rate of penetration of 20 TOR bar of
length less than 6 m with a standard compressor of capacity
165 cfm can be directly linked with N as N = 0.8 R0 where R0
is the time in seconds for penetration of 1 m. Similarly cor-
relations have been generated for other sizes of the nail and
compressor capacities. Further the N value has been corre-
lated directly with interfacial shear strength, ss by many
people for piles and anchors. It is related as ss = N to
Fig. 66 Structural shoring 2 N where N is in kPa for small and large displacements
respectively. Adopting this relationship of ss = N, the spac-
compressor which runs the Jack-Hammer and conducting ing has been directly linked with rate of penetration. From the
pull out tests on the driven nails. The N varied from 15 to 40 study it was clear that the spacing can be related to N and
for different layers over a depth of 6 m. The compressor hence to R0 as Sx = Sy = 1.25 N = R0 . The correlation is not
capacity was varied and the adopted capacities were about valid for N [ 50 since in the test site all the N values were less
165, 200 and 330 cfm with delivery pressure rating of than 50 (Figs. 69, 70, 71, 72, 73, 74, and 75).
4.5–6 kgf/cm2. Then a correlation was attempted to link the In Chennai where soft clay and sandy soil layers were
N value with rate of driving the bars with a given compressor alternating, for an excavation of 7.5 m deep next to the

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Fig. 69 Driven nails for the ramp side walls at IISc

Fig. 72 Finished ramp side walls for the underpass at IISc

Fig. 70 Driven nails for the ramp side walls at IISc

Fig. 73 Protection of deep excavation at Air force station by driven

nails

Fig. 71 Concreting of the facing element at IISc

existing building the nails were introduced in both upward

and downward inclination from the clay layers to penetrate
into the sandy layer to provide better fictional resistance Fig. 74 Protection of deep excavation at Air force station by driven
(Figs. 76, 77). nails

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Fig. 75 Finished ramp side walls at Air force station Fig. 78 Excavation for grouted nails at Bangalore

Design of Grouted Nails

Similarly in drilled and grouted nails also the rate of dril-

ling with a driller rig using a standard compressor can be
linked with the interfacial frictional resistance between the
grout and the surrounding geological material. A study
made with a 650 cfm compressor with a delivery pressure
of about 12.5 kgf/cm2 could drill at different rates in dif-
ferent strata. In soils up to N = 50 the rate varied from
1 min to 5 min per meter. The correlation is N = 12 R00
where R00 is the drilling time in minutes per meter. In strata
with N more than 50 and up to rebound condition (which
range identifies soft rock), the speed of drilling varied from
5 min to 15 min. The equivalent N values as applicable to
soft rock can be estimated from N = 15 R00 . The interfacial
frictional resistance between the grout and the soft rock is
given by the equation sf = 15 R00 where sf is in kPa and R00
Fig. 76 Driven nails at a Chennai Project
is time in minutes per meter of drilling with 650 cfm
compressor under a delivery pressure of 12.5 kgf/cm2. In
hard rock drilling speed varied from 15 min to more than
30 min per meter. Using the same logic the interfacial
frictional resistance sf can be estimated from the same
equation in the absence of data from unconfined com-
pression strength of the rock cores.
It is cautioned that while adopting this relationship for
designing, a field trial could be made for a given case since
the efficiency of the compressor, drilling rig and the Jack-
Hammer and the skill of driving and drilling personnel
enormously influence the rate of penetration of the nail.
The sequence of steps of a grouted nail installation
scheme for an excavation depth of 14 m in Bangalore is
presented. Excavate a depth 2 m. Install grouted nails of
11 m long with 25 TMT bars @ 1.6 m c/c at -1 m level.
Fasten MS weld mesh of size 75 9 75 9 4.2 mm with U
hooks to the excavated surface and provide 50 mm thick
Fig. 77 Driven nails below the existing foundation at Chennai shotcrete. After curing of the shotcrete fix the wailer beam

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Fig. 79 Excavation and two rows of grouted nails

Fig. 82 Slope protection at NMDC project -Combination of driven

and grouted nails

Fig. 80 Shotcreted surface after two rows of grouted nails

Fig. 83 Deep excavation with driven and grouted nails as finished

Fig. 81 Deep excavation and grouted nails as finished

to the nails by welding. Fill the gap between the shotcrete

surface and wailer beam with concrete to achieve effective
contact between wailer beam and the shotcrete surface. Fig. 84 Deep excavation with driven and grouted nails as finished

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Fig. 85 Touch piles of 300 mm size with grouted nails

Fig. 87 Slope protection at NMDC project

temporary protection system with driven nails was imple-

Fig. 86 Touch piles of 300 mm size with grouted nails

Repeat the steps with dewatering and with bars of higher

diameter as per design (Figs. 78, 79, 80, and 81).

Fig. 88 Slope protection at NMDC project

Design of Combination of Driven and Drilled Grouted
Nails

The combination of driven nails and drilled grouted nails

can be adopted for steep slopes and footings with no
embedment.
In a project at Whitefield a 19 m deep excavation, where
water table was not met, has been carried out with a
combination of driven and drilled-grouted nails with
shotcrete and wailer beams. At locations close to the
boundary 200 mm dia. MS micro-piles filled with M20
concrete in combination with the driven-grouted nails have
been installed. In another project small diameter RCC
touch piles were installed and as excavation progressed
grouted nails with wailer beams have been installed. No
shotcrete is provided.
A hillock of about 22 m height was to be cut through to
install a conveyor system to run in a RCC duct. The Fig. 89 Slope protection at NMDC project

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Driven nails have been used to improve the stability of

the geo-grid reinforced RE wall which had failed at a few
locations (Figs. 90, 91).
In an underpass construction below National Highway at
Bangalore nails driven on the excavation face prevented
the collapse of the soil from facing due to passage of heavy
vehicles on the surface.

Acknowledgments The author places on record the valuable inputs

received from Professor A. Sridharan and other colleagues in the
Department of Civil Engineering, Indian Institute of Science,
Bangalore.

Fig. 90 Driven nails to strengthen RE walls Appendix

Design of Driven and Grouted Nails

Based on the principles of reinforced earth soil nailing has

emerged as one of the best and economical alternatives for
stabilizing the excavations and protection of cut slopes. Off
late depth up to 25 m of excavation in urban areas and deep
cuts in hilly terrains are being handled by this technique
(Fig. 92). The main design features of such system are.
1. Evaluating the proper earth pressure distribution
expected with-in and behind the stabilized earth mass.
2. Estimation of the probable interfacial shearing resis-
tance using the properly evaluated interfacial friction
value between the soil and reinforcement in driven
Fig. 91 Driven nails to prevent collapse of excavation face
nails and that between the grout and the soil in grouted
nails.
3. Suitable facing system which effectively transfers the
active force into the nails.
4. The potential failure surface beyond which the rein-
forcement in the passive zone resists the pull out of the
reinforcement due to active force on the facing
element.
5. The design requirements of satisfying the basic
mechanics equations of equilibrium in terms of
overturning and sliding are valid. In addition both
frictional failure (pull out) and tensile failure (tension)
criteria need to be satisfied. A check on the bearing
capacity which has been made mandatory during initial
stages of development of the technique is not being
Fig. 92 Design principle of driven and grouted nails
insisted.
6. The interfacial friction between the driven nail with
mented to facilitate construction of RCC duct. The tem- the TOR or TMT bars and the soil could be taken as /
porary system was so effective that the authorities decided of the soil. This is because the volume displacement
to regard the temporary protection as a permanent one and due to driving of the bars will increase the density
abandoned the proposed RCC duct (Figs. 82, 83, 84, 85, locally to provide effective contact in addition to the
86, 87, 88, and 89). surface striations on the bar will hold the soil particles

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resulting in the failure plane to occur between soil and checked and the reinforcement diameter need to be
soil. changed. The governing equation will be
7. Generally since the driven nails are of 20 mm in 1:5 Sx Sy Ka c H ¼ As fs
diameter, twice the projected area which is twice the
diameter multiplied by the effective length (2 d Le) where A is the cross sectional area of the steel bar and f is
need to be considered instead of (p d Le). In case of the allowable tensile strength of the steel bar. 1.5 is the
large diameter nails like grouted nails which are factor of safety.
formed from drilling the hole and grouting the hole
under some pressure after placing the reinforcement in
position the perimeter surface area p d Le may be
considered. References
8. The interfacial shearing resistance at every point along
1. Vidal H (1968) La terre armée. Annales de l’institute technique du
the nail could be computed as c H tan/ bâtiment et des travauvx publics, Série Matériaux 30, Supplement
9. Now the governing equation for the design against No. 223-4, July–August
pull out failure of a driven nail will be Sx 9 2. Sridharan A, Srinivasa Murthy BR (1993) Remedial measures to a
building settlement problem. Proceedings of third international
Sy 9 Ka 9 c 9 H is the active earth force on the
conference on case histories in geotechnical engineering, St. Louis,
elemental area of Sx 9 Sy. Missouri, pp 221–224
3. Nagaraj TS, Sridharan A, Paul Alexander MV (1982) In situ
The resisting force from the effective length of the bar reinforced earth—an approach for deep excavation. Indian Geo-
embedded beyond the potential failure surface will be tech Jl 12(2):101–111
Le c H 2d tan /. With a factor of safety of 1.5 the two
forms of the forces may be equated to get the equation as
Le cH2d tan / 2dLe tan / Author Biography
Sx Sy ¼ ¼
1:5Ka cH 1:5Ka
B. R. Srinivasa Murthy (b.1943)
From the basic mechanics equations of sliding and over graduated civil engineering in
1966 Mysore university and
turning it can be shown that the length of nails should be obtained M Tech in Soil
about 0.7H for a factor of safety of 1.5 for both the Engineering from IIT Powai in
conditions up to a height of 12 m. The potential failure 1968. He was SRF under CSIR
surface for incremental excavation and stabilization Scheme in IIT Delhi during
1968-69 and then served as Lec-
condition can be shown to be a log spiral with initial turer in Civil Engineering at SIT
angle at toe being (45 ? //2) and emerging perpendicular Tumkur during 1969-70. Later
to the horizontal back surface at a distance of about 0.3H. he joined PWD as Junior Engi-
With this it can be assumed to follow the bilinear failure neer and served for two and half
years designing Major Irrigation
surface as shown in the figure. If the bar is driven inclined Project Structures. His passion
by about 10° the effective length will be little more than for teaching brought him back to
0.4H. In the drilled and grouted nails the equation will be the academic line and joined the University Visweswaraya College of
Engineering of Bangalore University as Lecturer in September 1973
pdLe tan / and became Reader in 1981. He obtained his Ph.D. degree from the
Sx Sy ¼
1:5Ka Indian Institute of Science in 1983 under the guidance of Prof. T S
Nagaraj and his Ph.D. thesis was awarded with Prof G. A. Leonard’s
It is possible to compute the interfacial frictional Prize of IGS and Prof. P.S. Narayna Medal of IISc. In 1984 he joined
resistance by considering the corrected average N value Indian Institute of Science, Bangalore and promoted as Associate
Professor in 1991 and as Professor in 1998. He has served as Registrar of
over the effective length of the bar in KPa as the shearing
Indian Institute of Science for over three years. He retired from the
resistance. Then the governing equation against pull out services of the Institute in 2005. In over two decades of service at IISc he
failure will be has guided 14 Ph.D. and 7 M Sc (Engg) theses in addition to scores of
ME dissertations. He has published/presented over 100 Technical
pdNLe tan / papers in international refereed journals, International and National
Sx Sy ¼
1:5Ka cH Conferences. He has also co-authored a book titled ‘‘Prediction of soil
Behavior’’ with Prof. T S Nagaraj and Dr. A Vatsala. He has also
Generally in the case of driven nails tension failure will contributed a Chapter in an international Hand Book. He has handled
not be an issue since drivability requires minimum of 16 or three major sponsored research projects during his stay at IISc. The
20 mm dia. bars which will far higher tensile capacity. areas of research interest of Dr. Murthy were Constitutive Modeling of
Fine grained soils including cemented and unsaturated soils, Cam-Clay
However in the case of grouted nails where the spacing will models, Reinforced Earth and Reinforced Soil Beds and Ground
be in the order of 2 m 9 2 m the tensile force need to Improvement Techniques like Micro-piling and Grouted anchors.

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Dr. Murthy has very widely travelled abroad both East and West. He strong areas of consultancy. Projects of large size pipe line design for
was an International Researcher under NRC Canada for 6 Months at power projects and water supply schemes have been handled as inter-
University of Laval and J S P S Fellow and INSA-JSPS Fellow for two disciplinary area. He has successfully constructed several vehicular and
terms (Nine Months) at Gifu University, Japan. He was a visiting faculty pedestrian under passes below high ways by Box-Jacking technique
for one Semester at AIT Bangkok. He was Visiting Professor for six without disturbing the road or the traffic. Protection of deep excavations
months at Institute of Low Land Technology at Saga Japan. He has (up to 25 m) with soil nailing techniques, in most of the major cities in
delivered Lectures at Rice University and University of Florida at USA, India has been his current field of activity over the last decade. Alter-
Kyoto University, Nagoya Institute of Technology and Institute of Ports native foundations on filled up and week soils are being handled reg-
and Harbor at Japan, Queens University in Canada. Dr. Murthy has been ularly. The number of consultancy projects handled so far in the fields of
conferred with many honors including ‘‘The Fellow of Institution of Geotechnical Engineering, Structural Engineering and Pipeline
Engineers’’, ‘‘Honorary Fellow of ACCE’’, ‘‘Life Fellow if IGS’’. He Engineering by Dr. Murthy is far more than 500. He is on the several
has been awarded the IGS-AFCONS KUECKLEMAN AWARD in committees of the state government either as chairman or as member.
2004, Distinguished Engineer Award of the year 2006 by Institution of He is the Chairman of Technical Advisory Committees of Bruhat
Engineers (India) and Outstanding Civil Engineer’s Award of ACCE in Bangalore Mahanagara Palike, Karnataka Health Services System,
2008. In addition to being an excellent Geotechnical Engineering Karnataka State Police Housing Corporaration and CMTI. He is
Consultant, he has been a very good Structural Consultant. Rehabili- Member of the Taskforce on Quality Assurance in Public works Govt.
tation of old buildings, fire damaged buildings and damaged sewage of Karnataka, Project Management Group of IISc. Karnataka Power
digester domes and old arch bridges under distress conditions are his Corporation and Karnataka Slum Clearance Board.

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