Jacked-in Pipe Reinforcement of a Deep Excavation in Soft Soil
CHEANG W.L., TAN S.A., YONG K.Y.
Department of Civil Engineering, National University of Singapore ,Singapore
GUE S. S.
Gue & Partners Sdn. Bhd., Malaysia
AW H.T., YU H.T., LIEW Y.L.
Specialist Grouting Engineers Sdn. Bhd., Malaysia
ABSTRACT: Soil nailing is an in-situ ground improvement method which has gained increasing
acceptance in this region, but is not generally recommended for clayey and organic soils. This restriction
is empirically based, and little information exists on the performance of soil nails when the method is
applied in these soil conditions. To address this gap, a deep excavation for the construction of a 3/12
storey deep basement carried out using a novel technique, which combines Contiguous Bored Piles and
Jack-in pipe reinforcements, was instrumented to monitor its performance. This paper will highlight
briefly the instrumentation program, which was set up mainly as a safety control and to monitor the
interaction of this retaining system with the surrounding soft soil. In addition, numerical analyses were
conducted to study the soil-structure interaction of this new construction technique. Data from the field
monitoring and FEM analyses will be presented with regard to the effectiveness this system particularly
the jacked-in pipes in supporting the deep excavation. It follows from this comparison that the field
instrumentation and numerical analyses have proved to be valuable tools in assessing the deformations to
be expected at critical stages of the excavation. The project shows that jacked-in pipe in soft clayey soils
is possible, at least for short term and can be effectively used as temporary support in deep excavation.
1.0 INTRODUCTION
Deep basement construction is becoming
increasingly expensive, nullifying the justification
for overconservative designs. One of the ways in
which construction cost can be reduced is by
employing fast and cost-effective deep basement
construction techniques. This paper will highlight
the use of Jacked-in Pipe Reinforcement in support
of Contiguous Bored Pile walls.
The field instrumentation has proven to be a
valuable tool in assessing the validity of the initial
design assumptions The Observational method
(Peck, 1969) was practised whereby field results
obtained from the adequately instrumented soil
nailed retaining system were used in the back
analysis of design parameters. The back calculated
parameters were implemented in the Finite
Element Analyses to predict deformations in the
subsequent construction phases.
Soil nailing is an in-situ soil reinforcement
technique, which in the last three decades has been
successfully used in France, United Kingdom,
United States and Southeast Asia. The origins of
soil nailing partly stems from the Reinforced Earth
techniques, rock bolting and multi-anchorages
systems (Recommendations Clouterre 1993). Soil
nailing has been primarily used for temporary
retaining structures for basement excavation and
permanent cut-slope stabilisation. Jacked-in pipe
retaining system, which is similar to soil nailed
system is not common. This technique has gained
momentum in Malaysia mainly for the ease and
speed of installation and it is also very cost
effective.
However, with the advent of numerous research
programs (Schlosser, 1986; Elias and Juran, 1990),
increase in the state-of-understanding and
experience, both abroad (Schlosser, 1982;Bruce
and Jewell, 1986, Bruce and Jewell 1987, Juran et
al., 1990;) and local (Tan, et al., 1998; Luo et al.,
1998; Tan et al., 1999) will promote the use of this
technique, both as a temporary and permanent
structure.
2.0 DESCRIPTION OF PROJECT
The condominium project which is located at UEP
Subang Jaya of Malaysia consists of three
1
S P T 'N ' V S D E P T H ( m ) P L O T
'N '
0
10
20
30
40
50
60
0
S P T 'N ' G R E A T E R
THAN 50
10
DEPTH ( m )
condominium towers of 33 storey and a single 20
storey office tower. Due to the huge demand for
parking space, an approximately three storey deep
vehicular parking basement will be required. The
deep excavation, through a filled layer of very
loose silty sand and soft peaty clay varies from
11m to 13m. The presence of very soft soil
condition and the fast track requirement of the
project, Contiguous Bored Pile (CBP) walls
supported by Jack-in Pipes in six to seven rows
were utilised to stabilise and control the lateral
displacement and surface settlement. The
supported face is approximately 6900 m2.
20
30
40
BH
BH
BH
BH
/
/
/
/
DA
DA
DA
DA
7
11
5
14
BH
BH
BH
BH
/
/
/
/
DA
DA
DA
DA
8
2
9
1
BH / DA 10
BH / DA 3
BH / DA 12
BH / DA 6
BH / DA 4
BH / DA 13
Fig. 2: SPT ‘N’ Values: Scatter Plot
3.0 GEOLOGICAL INFORMATION
Photo 1: The Retaining System; Contiguous Bored Piled
Walls (CBP) and Jack-in Soil Nails
BH / DA8
'N'
Depth
SHEAR STRENGHT 'KPa)
0
0 10 20 30 40 50 60
10 20 30 40 50
0
0
Firm Reddish
Final Water
7
5
Table
5.8mbgl
5
8
5
Loose to Medium
11
Dense Grey Fine
to Coarse SAND
10
clayey SILT
5
4
5
Dense Grey Fine
to Coarse SAND
6
7
0
10
10
and decay roots
21.5
0
30.5
15
0
1
0
with Fine Sand
40.5
15
10
Very Soft Dark
Grey Silty CLAY
36
6.8
0
and decay roots
0
10
4.8
0
with Fine Sand
Loose to Medium
2
11.8
Very Soft Dark
Grey Silty CLAY
15
9
Brown Yellowish
clayey SILT
10
0
Firm Reddish
5
Brown Yellowish
Final Water
Table
5.8mbgl
'N'
10 20 30 40 50 60
0
BH / DA7 Depth
15
0
15
0
20
31
0
The general subsurface soil profile of the site,
shown in Fig.1 consists in the order of succession a
firm clayey SILT, a loose to medium dense SAND
followed by firm to hard clayey SILT. The soils
are inter-layered by thick deposits of very soft dark
peaty CLAY.
The plot of SPT’N’ values, illustrated in Fig.2,
shows significant scattering which is commonly
found in tropical residual soils in the area.
However the trend of the scatter plot shows that the
SPT ‘N’ values increases with depth. For the
underlain soft clayey material, the registered SPT
‘N’ values were zero and Vane Shear strength
varies from 5 kPa to 20 kPa. For analysis purposes
the subsoil was simplified into representative
layers, namely Granular material and Cohesive
material.
0
31
0
Very Soft Grey
20
25
Silty Clayey Fine
SAND
Medium Dense
Grey Fine to
Coarse
SAND
Very Stiff to
Hard Whitish
Grey Brown
Clayey SILT
30
20
3
20
20
Silty Clayey Fine
4.0 THE JACKED-IN PIPES AND
CONTIGUOUS BORED PILE SYSTEM
6
Very Soft Grey
20
9
SAND
18
15
20
27
25
25
25
29
Medium Dense
Grey Fine to
Coarse
SAND
13
14
25
16
50
38
50
30
50
30
30
End of B/H
35
35
35
35
40
40
40
40
Very Stiff to
Hard Whitish
Grey Brown
Clayey SILT
Very Dense
Whitish Grey
Brown Fine
to Coarse SAND
End of Borehole
Typical Subsoil Profile
Fig. 1:Typical Subsoil Profile
47
30
44
37
39
35
40
50
40
Jacked-in Pipes Reinforcement
Mild steel pipes which functions as soil nails are
installed by hydraulic jacking. This method has
proven to be an efficient and effective technique
for excavation support, where conventional soil
nails and ground anchors have little success in such
difficult soft soil conditions. Such conditions are
sandy collapsible soil, high water table and in very
soft clayey soils where there is a lack of short-term
pullout resistance.
2
In view of the close proximity of commercial
buildings to the deep excavation, a very stiff
retaining system is required to ensure minimal
ground movements the retained side of the
excavation. Contiguous Bored Piles which acts as
an earth retaining wall during the excavation works
were installed along the perimeter of the
excavation and supported by Jack-in pipes.
In the initial design of the retaining system,
conventional ground anchors were proposed, but
the jacked-in pipes were accepted as an alternative
to ground anchors due to speed and costeffectiveness of the system. Relatively, larger
movements are required to mobilised the tensile
and passive resistance of the jacked-in pipes when
compared to ground anchors. However it was
anticipated that the ground settlement at the
retained side and maximum lateral displacement of
the wall using this system would still be within the
required tolerance after engineering assessment.
of this paper, construction has only reached the 4th
level of excavation):
Stage 0
Stage 1
Stage 2
Stage 3
Stage 4
Stage 5
Stage 6
Stage 7
Stage 8
Installation of Contiguous Bored Pile
Wall
Excavation 1: Excavation to 2.7m below
ground level
Jacked-in pipe: Level 1 at 1.7m below ground
level.
Excavation 2. Excavation to 4.5m below
ground level.
Jacked-in pipe: Level 2 at 3.5m below ground
level.
Excavation 3: Excavation to 6m below ground
level.
Jacked-in pipe: Level 3 at 5m below ground
level
Excavation 4: Excavation to 7.5m below
ground level
Jacked-in pipe: Level 4 at 6.5m below ground
level
6.0 GEOTECHNICAL INSTRUMENTATION
INSTALLATION OF SOIL NAILS
TEMPORARY BOLT
CONTIGUOUS BORED PILE WALL
JACKING PLATFORM
SOIL NAIL (1 5 0 m m
DIAMETER STEEL TUBE)
HYDRAULIC JACK
REACTION PLATE
RIG NO.1
RIG NO.2
Fig. 3: Schematic of Jack-in Soil Nails
5.0 SEQUENCE OF CONSTRUCTION
The layout of Contiguous Bored Pile retaining wall
as detailed in Fig. 3 forms the basement wall of the
substructure. The retaining wall system consists of
closely spaced 1000mm diameter bored piles near
the commercial buildings and 800mm diameter for
area away from the commercial buildings. To
facilitate the Top-Down excavation of the deep
basement, roller pipes of 150mm diameter were
jacked in sub-horizontally after each excavation
stage. The phases of the basement construction are
described as follows (currently during the writing
In view of this relatively new excavation support
technique, in-situ soft soil conditions and the close
proximity of the commercial buildings to the deep
excavation, a performance monitoring program
was provided. Firstly, as a safety control. Second,
to refine the numerical analysis using field
measurements obtained at the early stages of
construction and third, to provide an insight into
the possible working mechanisms of the system.
The geotechnical instrumentation program
consists of 18 vertical inclinometer tubes located
strategically along the perimeter of the Contiguous
Bored Pile wall and 30 optical survey makers
(surface settlement points) near the vicinity of the
commercial buildings. This instrumentation would
provide sufficient readings to monitor the
performance of the excavation system.
The locations of these instruments are detailed
in Fig. 4 for the inclinometers and Fig. 5 for the
optical survey points. Vertical inclinometer
readings were taken once weekly and the surface
settlement readings were taken once every two
weeks. However when critical stages were
involved, the frequency of the readings was
increased both as a safety control and to provide
sufficient field data for numerical modelling.
Fig. 6 illustrates the trend of horizontal
displacement of the wall as measured through
inclinometers installed at the site.
3
1
2
5
4
3
6
7
8
PROPOSED UNDERGROUND CARPARK
18
9
CONTIGUOUS BORED PILE WALLS
17
10
15
16
14
11
13
VERTICAL INCLINOMETERS
12
Fig. 4: Layout of Vertical Inclinometers
30
30
30
30
- INCLINOMETER 2 -
- INCLINOMETER 10 -
-INCLINOMETER 9-
- INCLINOMETER 8 -
25
25
25
20
20
20
20
15
15
15
10
10
10
5
5
Depth (m)
25
15
10
5
5
0
-0.02
0
0.02
0.04
0.06
0
0.08
-0.02
Horizontal Displacement (m)
0
0.02
0.04
0.06
0.08
0
0
0
Horizontal Displacement (m)
30
0.04
0.06
0.08
Horizontal Displacement (m)
0
0.1
0.02
0.04
0.06
0.08
Horizontal Displacement (m)
30
30
-INCLINOMETER 11-
0.02
30
-INCLINOMETER 15-
-INCLINOMETER 12-
INCLINOMETER -16
25
25
25
25
20
20
20
20
15
15
15
15
10
10
10
10
5
5
5
AFTER STAGE
6(NAIL LEVEL
3,5m BGL)
AFTER STAGE
5(EXCAVATION
NO.3,6mBGL)
AFTER STAGE
7(EXCAVATION
NO 4 7 5 BGL)
5
0
0
0.02
0.04
0.06
0.08
Horizontal Displacement (m)
0
0.1
0
0
0.02 0.04 0.06 0.08
Horizontal Displacement (m)
0.1
0.1
0
0
0.02 0.04 0.06 0.08
Horizontal Displacement (m)
0.1
-0.08
-0.06 -0.04 -0.02
0
Horizontal Displacement (m)
Fig. 6: Measured Horizontal Displacements of Contiguous Bored Pile Walls supported by Jacked-in Soil Nails
4
COMMERCIAL BUILDINGS
7.0 NUMERICAL MODELLING
5
4
5
4
5
4
5
4
5
4
Design methods recommended at the present time is
still based on classical limit equilibrium methods,
which only evaluate the stability of the structure.
However when constructing deep excavations in
highly urbanise areas, the Serviceability Limit State
of a retaining system will be the governing factor.
The Contiguous Bored Pile wall supported by
internally stabilising jacked-in pipes is essentially a
3-D numerical problem. This can be seen from the
Fig. 5: Layout of Settlement Markers
results of the instrumentation as indicated in Fig. 6
where deformations are restrained at the corners due
to edge effect (inclinometer 8) and the maximum
occurring approximately at the centre of the wall
(Inclinometer 9 & 10).
Due to the complex soil-pipe, soil-wall and pipewall interaction, a global soil arch will be formed
(Schlosser et al., 1997;Benhamida et al, 1997). In
addition to this, local arching will develop between
the pipes, and therefore creating concentration of
SURFACE SETTLEMENT OF RETAINED GROUND
stresses. With good engineering judgement and
A. 3-DIMENSIONAL PLOT & B.CONTOUR PLOT
practise a 3-D problem can still be effectively
Fig. 7: Variation of vertical settlement from field
modelled as a 2-D plane strain problem. The
performance
numerical analyses were performed using “Plaxis”
PLANE STRAIN ANALYSIS CONDITION
(Brinkgreve and Vermeer, 1998) a Finite Element
Method computer program under plain strain
condition (Fig. 8). The Contiguous Bored Pile wall
and hollow steel pipes were modelled using a linear
elastic model and its material properties converted
to the equivalent 2D parameters through area ratio
factors (Al-Hussaini & Johnson, 1978). The model
pipes were elastic and pinned to the Contiguous
Bored Pile wall. An elastic -perfectly plastic model
was used to model the behaviour of the soil-pipe
Fig. 8: Plane Strain Analysis (Plaxis V 7.11)
Stiffness G vs Working Strain
interface. The model, which uses the Coulomb
criteria, distinguishes between the elastic behaviour,
where small displacements can occur within the
interface, and plastic interface behaviour (slip).
It is well established that the subsoil stiffness is
not a constant value and is dependent on strain
levels. Mair (1993) reported the changes of soil
stiffness with different working strain levels for
various geostructural systems as detailed in Fig. 9.
The typical working range of retaining walls is in
the order of 0.01-0.1%.It highlighted the inadequacy
Fig. 9: Typical Shear Modulus and working shear strains of conventional laboratory tests in evaluating the infor different geostructures (after Mair, 1993)
situ soil stiffness and the soil
RETAINED SIDE
3
2
3
2
3
2
3
2
3
2
1
1
1
1
1
EXCAVATED SIDE
ROW E
ROW D
ROW B
ROW C
ROW A
CONTIGUOUS BORED PILE SUPPORTED
BY JACK-IN SOIL NAILS
LEGEND
SETTLEMENT POINTS
OPTICAL SURVEY POINTS FOR SETTLEMENT MONITORING
TYPICAL STRAIN RANGES
Stiffness G
RETAINING WALLS
FOUNDATIONS
TUNNELS
0.0001
0.001
0.01
0.1
1
10
Shear Strain %
5
HORIZONTAL DISPLACEMENT : NUMERICAL MODELLING
AND MEASURED
Excavation Lvl 3
105
100
Lo?se Sandy SILT
Excavation Lvl 1
Excavation Lvl 2
95
Excavation Lvl 3
Loose Silty
SAND
DEPTH (m)
Dark Soft
Peaty
CLAY
90
Final Excavation Level
85
Medium Dense
Grey Fine Coarse SAND
80
Very Stiff-Hard Brownish SILT
75
70
-0.1
-0.08
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
0.08
0.1
HORIZONTAL DISPLACEMENT ( m)
Inclinometer 8/6/99
Excavate 3
Nailing Lvl 2
Fig. 10 a
HORIZONTAL DISPLACEMENT : NUMERICAL MODELLING
AND MEASURED
Nailing Lvl 3 & Excavation Lvl 4
105
100
Loose Sandy
Excavate Lvl 1
SILT
Excavate Lvl 2
95
Exacavte Lvl 3
Excavate Lvl 4
Loose Silty SAND
90
DEPTH (m)
Dark Soft Peaty
CLAY
Final Excavation Level
85
Medium Dense
Grey Fine Coarse SAND
80
Very Stiff-Hard Brownish SILT
75
70
-0.1
-0.08
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
0.08
0.1
HORIZONTAL DISPLACEMENT ( m)
Inclinometer 21/6/99
Excavate-4
Nail-3
Fig. 10b
Fig. 10: Measured Field Performance and Finite
Element Analysis for; a) Nail Level 2 & Excavation
Level 3, b) Nail Level 3 & Excavation Level 4
stiffness obtained from these tests is several
magnitudes lower than the in-situ soil stiffness.
The undrained soil modulus for the Soft Peaty
Clays were assumed to be Eu = 700 Su (Gue,
1997(b); Gue, 1998) for all stages of excavation.
The soil modulus for the fill soils (Sands) were
assumed to be E’ = 3500N based on Stroud and
Butler (1975), where the N Standard Penetration
Test Value. For the Clayey Silt, Eu = 700 Su and Su
= 5.5N was adopted. In addition to this, the soil is
undergoing unloading and therefore the in-situ soil
stiffness will be a few magnitudes higher compared
to loading condition.
Fig. 10a and 10b presents comparisons between
the FEM analysis and field performance for 6m and
7.5m deep excavation respectively. The results show
that the Young’s modulus for the various soil layers
were very close to the assumed values and were
used in the subsequent deformation predictions and
parametric studies.
The predicted deflections of the wall at the 3rd
and 4th stage of excavation show approximately a
very similar deflection profile to the measured field
profile. The wall is behaving in a fashion very
similar to a cantilevered wall and the pipes seemed
to be restraining the deflection at the upper section
of the wall. Generally, most of the measured field
performance displays such a restraint cantilever
profile as shown in Fig. 6. However, the prediction
for all stages particularly the 4th stage was slightly
over-predicted. There are few possibilities that may
have influenced the predicted deformation profile,
notably small strain behaviour, where at very small
strains the soil exhibits a much higher soil modulus
(Jardine et al 1985; Burland, 1989) and therefore the
soil tends to deform less.
An analysis was performed without the nail
inclusions, where the retaining wall was modelled as
a cantilever wall. Fig. 11 compares the deflection
profile between the cantilevered wall and
‘improved’ wall at 7.5m deep of excavation. It
shows a distinct restraint offered by the jacked-in
pipe inclusions. The influences of pipe bending on
the reinforcement mechanism and has been a subject
of great debating (Bridle & Barr, 1990; Jewell &
Pedley; 1990; Schlosser, 1991; Jewell & Pedley,
1991). Fig. 12 compares the deflection profile of
retaining wall where the jacked-in pipes were
modelled using;
6
(geotextile element in Plaxis) with only the axial
stiffness. Fig. 12 shows that bending stiffness has an
influence in the reinforcement mechanism, where
jacked-in pipes modelled using the beam elements
show a smaller displacement compared to the
geotextile elements in all of the numerical stages. A
large-scale experimentation in soft clays conducted
by Oral et al (1998) has indicated that due to lack of
nail-pullout, nail bending played a major role in the
reinforcement mechanism. A similar behaviour was
observed in this project where the initial nail pullout
was extremely low and increases through time. This
reinforced the idea that additional analyses of
different failure mechanisms should be addressed in
different soil types particularly in soft soils.
The numerical surface settlement was found to
be less compared to the measured field surface
settlement. This may be due to the fact that the
jacked-in pipes were modelled as beam elements
which are essentially plate elements ‘smeared’
across a unit width in the plain strain analysis. This
will restrain the soil from ‘flowing’ around the nails.
However this assumptions is valid if the horizontal
spacing of the pipes is closely spaced. The other
possible reason could be the increase in effective
overburden pressure when water table has dropped
after excavation.
HORIZONTAL DISPLACEM ENT OF CONTIGUOUS BORED
PILE WALL WITH AND WITHOUT SOIL NAIL INCLUSIONS
105
100
DEPTH (m)
95
90
85
80
75
70
0
0.05
0.1
0.15
0.2
0.25
0.3
HORIZONTAL DISPLACEMENT ( m )
Inclinometer 21/6/99
Excavate-4
CANTILEVER-WITHOUT SOIL NAILS
Fig. 11:Parametric: Contiguous Bored Pile wall
with and without Soil Nail Inclusions
The In fluence o f B end ing S tiffness in the R einforcem en t
M echanism )
SURFACE SETTLEMENT
DISTANCE FROM WALL (RETAINED SIDE)
0
Settlement (m)
105
100
-0.01
-0.02
-0.03
Finite Element Analysis
Measured
-0.04
-0.05
-45
Depth of wall (m)
95
-35
-25
-15
Distance from Wall (Retained Side) m
-5
Fig. 13: Surface Settlement: Measured Field
Performance and Prediction from Finite Element
Analysis
90
8.0 CONCLUSION
85
Instrumentation has an important role in
geotechnical engineering, specifically when the
state-of-practice of a particular geosystem is ahead
of the state-of-art.
The
performance
monitoring
program
A xial R esistance A lone ( E xcavation Level 4)
implemented
in
this
project
was
not
solely
used
as a
A xial and B ending S tiffness (E xcavation Level 4)
A xial R esistance A lone ( E xcavation Level 3)
safety
control,
but
as
well
as
to
gain
an
insight
into
A xial and B ending R esistance (E xcavation Level 3)
the possible working mechanisms. Back calculated
design parameters were used in the prediction of
Fig. 12: Parametric Analysis, Influence of Bending
deformations in the subsequent construction phases
Stiffness on the Reinforcement Mechanism
and this has greatly reduced the risks, which comes
a) beam elements with an axial stiffness and a from the implementation of the new retaining
flexural rigidity, and b) flexible elastic elements system. This project shows that jacked-in pipes in
7
80
75
0
0.02
0.04
0.06
H o rizo n tal D isp lac em en t (m )
0.08
0.1
soft clayey soils is possible at least for short term 13. Jewell, R.A, Pedley, M.J, (1990), Soil Nailing
Design: The Role of Bending Stiffness, Ground
and can be effectively used as a temporary support
Engineering, March, pp.30-36.
in deep excavation.
14. Jewell, R.A, Pedley, M.J, (1991), Discussion to
F.Schlosser, Ground Engineering, Nov, pp.3439.
9.0 REFERENCE
1. Benhamida, B., Schlosser, F., Unterreiner, P., 15. Luo,S.Q,Tan,S.A,Yong,K.Y,(1998),
Stabilisation of Basement Excavation with Soil
(1997), Finite Element Modelling of Soil Nailed
Nails and Ground Anchors, 2nd International
Wall: Earth Pressures and Arching Effects,
Numerical Models in Geomechanics, Balkema,
Conference on Ground Improvement techniques:
pp.245-250.
8-9 October ,Singapore pp.327 –336
2. Brinkgreve, R.B.J., Vermeer, P.A., (1998), 16. Mair,R.J,(1993) Developments in Geotechnical
PLAXIS-Finite Element Code for Soil and Rock
Engineering Research: Application to Tunnels
Analyses-Version 7.A.A.Balkema.
and Deep Excavations, Unwin Memorial Lecture
3. Bruce, D.A, Jewell, R.A, (1986) Soil Nailing
1992,Proc.of.the.Inst.of Civil Engineers-Civil
Application and Practice-Part 1,Ground
Engineering.pp.27-41.
Engineering, Vol.19, No.8, pp.10-15.
17. Oral,T,Sheahan,T.C.,(1998)The Use of Soil
4. Bruce, D.A, Jewell, R.A, (1987) Soil Nailing
Nails in Soft Clays, Design and Construction of
Application and Practice-Part 2, Ground
Earth Retaining Systems,Proc. Of Sessions of
Engineering, Vol. 20, pp.21-33.
geo-Congress 1998,pp. 26 –40.
5. Bridle, RJ, (1989) Soil Nailing-Analysis and 18. Peck,R.B,(1969),Advantages and Limitations of
Design, Ground Engineering, Sep 1989,pp.52the Observational Method in Applied Soil
56.
Mechanics,Geotechnique,Vol.19,No.2pp.1716. Bridle, R.J., Barr, BIG, (1990) Soil Nailing,
187
Ground Engineering, July/August, pp.30-33.
19. Schlosser, F., (1982), Behaviour and Design of
7. Burland, J.B., (1989) Small is Beautiful-The
Soil Nailing, Proc. Intl. Symp, Asian Institute of
Stiffness of Soil at Small Strains, Ninth Laurits
Technology,
Bangkok,
29Nov-3
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