ISSN: 2277-3754 ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 6, December 2012
258
Study Of Instrumented Segmental / Meter Panels
For Basements: Comparison of Theoretical and
Actual Behavior D.K. Kanhere
Joint Executive Director, STUP Consultants Private Limited, Navi Mumbai, India
Dr R A Hegde,
Professor, Sardar Patel college of Engineering, Andheri-Mumbai,
Dr. V.T. Ganpule
V. T. Ganpule & Associates, Mumbai, India
Abstract: Growing need of basements for vehicles storage and
services in city of Mumbai is problematic. Proximity buildings,
services, narrow lanes, traffic and crowds preclude open excava-
tions or diaphragm walls. Building subways under crowded
roads with utilities and closure is not possible, led to using
segmental / meter panel construction. These are panels of small
width designed as cantilever sheet piles adequately anchored in
sub-stratum to develop necessary passive resistance and balanc-
ing couple. When constructed in succession, full length of the
wall can be constructed. This is a fast, flexible and cheap engi-
neering solution to the problems encountered in crowded locali-
ties. A number of such structures have been constructed. Some
panels were instrumented for verification of in-situ behavior.
Points of interest concerning stress patterns and distribution
were monitored. A comparative study of the observed readings
of the instrumented meter panels and the results of theoretical
analysis and design principles are presented.
I. METHODS OF ANALYSIS OF RETAINING
STRUCTURE/SYSTEMS
A. Analytical Methods
Usually, following methods for analysis of cantilever pile
walls, all of which involve simplifications of net pressure
distributions to allow calculations of critical retaining height
are in use:
a. Factored Moment Method (FMM)
b. King’s Method (1995)
c. Day’s Method (1999)
d. Water Lum’s Rules of Thumb (2000)
B. Empirical Design Methods
a. Strut Load: An important aspect in excavation sup-
port design is to estimate the strut load. Most of the me-
thods are empirical and based on limit equilibrium of wedge
(Terzaghi, 1941) and the apparent earth pressure diagrams
(Terzaghi. 1943; Peck. 1969)
b. Base Stability: Another important aspect is the ef-
fect of base heave. (Bjerrum and Eide 1956) proposed the
use of stability numbers against base heave.
C. Field Measurements:
Ground movement is a major concern in the design of
excavation support systems. In built-up areas where the
ground contains a soft layer, thorough investigation is re-
quired. The following observations are made for analysis:
a. Lateral wall deflections
b. Ground surface settlements
c. Stress state of soil near excavation
D. Finite Element Analysis
It is generally accepted that the Finite Element Analysis
(FEM) is the major technique used in the numerical analysis
of geo-technical problems. FEM in excavation related prob-
lems was first carried out between 1969 and 1971. Some
fundamental techniques in excavation process simulation
were developed in 1978.
E. Design Considerations
For general design purpose it is recommended to use the
trial and error method for analyzing the system and its sta-
bility. Meter panels like circular touching piles or diaph-
ragm walls are structural elements, which are constructed
underground. These are basically used as retention systems
and permanent foundation walls. These can be installed in
close proximity to existing structures, with minimal loss of
support to existing foundation. In addition construction de-
watering is not required. Structural meter panel can be em-
ployed for forming underground retaining or load bearing
walls for practically any purpose. Panels of small width are
designed as cantilever sheet piles adequately anchored in
sub-stratum to develop necessary passive resistance and ba-
lancing couple. When constructed in succession, full length
of the wall can be constructed. The stability of excava-
tion/meter panel, control of wall deflections, ground move-
ments/ ground water problems have been analyzed with in-
strumentation as well as with FEM models as a case study.
The most important consideration in proper design and in-
stallation is that the retained material is attempting to move
forward and down-slope due to gravity. This creates soil
pressure behind the wall. The same is to be balanced by
passive earth pressure on other side. Further couple formed
by active and passive earth pressure has to be balanced by
trial & error method. The section of meter panel happens to
be depth of cantilever and is function of excavation depth
and soil properties of retained earth. The enabling structure
derived its support from the passive reaction offered by
ISSN: 2277-3754 ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 6, December 2012
259
formation below excavation level and the resisting counter-
balancing couple developed on going further deep.
The forces on enabling wall are;
1. The active earth pressure from back of wall which
tries to push wall away or towards excavated side.
2. The passive pressure generated below dredge line
in direction opposite active pressure which resists
the movement of the wall
3. The passive pressure in the direction of active
pressure which will counterbalance the moment
formed by active pressure.
4. These passive forces are calculated by using equi-
librium conditions namely summation of moment
and summation of horizontal forces are zero at all
points.
5. The passive pressure can be idealized to rectangu-
lar block in case of stiff clay or rock and as first
trial considers suitable pile length below excava-
tion level depending upon the formation
6. Using equilibrium conditions the pressure intensi-
ties are calculated and they are not equal or
slightly less than permissible. The length of em-
bedment below excavation is changed. The pres-
sure is repeated till above condition is satisfied.
7. The maximum bending moment is calculated
where shear force becomes zero.
Fig 2. Step-1 – Active Earth Pressure - Soil
Fig 3. Step-2 – Equilibrium of Horizontal
Forces
Fig 4. Step-3 – Equilibrium of Horizontal Forces &
Moments – Soft Soils
II. PRESENTED STUDY
The past concerns about the stability of excavation have
now shifted emphasis on control of wall deflections and
ground movements under working conditions especially in
densely built-up areas. The numerical methods with appro-
priate consideration of relevant factors have the potential to
give relatively accurate solution for both stability and
ground movements for an excavation. However, a perfect
model to predict the collapse of support system and evalua-
tion of ground movements at some distance behind the re-
taining wall under working conditions is still not available.
III. INSTRUMENTATION SETUP
In order to physically verify the developed pressure both
active and reactive, worked out from theoretical considera-
tion, the retaining elements are instrumented as described
below; In arranging instrumentation of meter panel, several
aspects must be considered. The use of instrumentation is
complex process. Right from selection of appropriate tool
for gathering the data as an even a small mistake leads to
failure of investigation program In and around the city of
Mumbai, a number of basements/ subways have been and
are being instrumented and constructed. Normally, bending
L m
P3
P2
P1
Excavation level
0 m
Fig 1. Earth Pressure Diagram (Theoretical)
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International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 6, December 2012
260
strains in wall are measured along its depth giving bending
moment response. The evaluated geo-technical properties of
soil and observed bending strains along with theoretical
bending moment, shear force, deflection and earth pressure
are presented and comparison made between theoretical and
experimental values. The measurements have been taken us-
ing electrical resistance strain gauge. These adhesive type
strain gauges were mounted on the panels, had the follow-
ing specifications:
Type: BE 120 – 6AA (11)
Gauge resistance: 119.9 0.1
Gauge factor: 2.08 1.0%
Make: Tokyo Sokki Kenkyujo Company Limited
A. Strain Gauge Arrangement:
Connections are made using red, black, yellow and green
wires as indicated in Fig.1.
B. Strain Measuring Instrument
A strain measuring device in the SYSCON product range
was used. It accepts input from 10 numbers of strain gauge
bridges simultaneously and signals are selected one by one
through an electronic channel selector to a signal condition-
er which consists of a high gain, stable, low noise, low drift,
instrumentation type amplifier, GF setting control and
bridge configuration select facility. The conditioned outputs
provide 5V DC signal for an input of 20,000 micro strains.
This output is connected to a micro-controller based 41/2
digit panel meter that can display strains up to 20,000 micro
strains with one micro strain resolution. This voltage output
is also made available to the user on the rear panel for pur-
pose of monitoring or recording. (Strain indicator SI – 38
MS)
IV. FIELD SETUP
As indicated in Fig.2, the meter panel is instrumented be-
fore concreting and all lead wires are taken out at the top of
the pile.
V. CASE PRESENTED
1. Soil profile at Andheri site (Fig.3)
2. Observed strains at each strain gauge station
i) Location of site: New Link Road, Andheri
ii) Size of Meter panel: 1000mm x 600mm
iii) Total depth of Meter panel: 9.00m from original
ground level
iv) Total depth of excavation: 6.00m
v) Total number of strain gauge installed: 5 on tension
side and 5 on compression side
Table No 1 Observed Strains
S t r a i n
g a u g e f r o m G L . ( m ) Tension side Compression side
Init
ial
Str
ain
Rea
din
g
Fin
al S
trai
n
read
ing
To
tal
trai
n
(m
/m)
Init
ial
stra
in
read
ing
Fin
al s
trai
n
read
ing
To
tal
trai
n
(m
/m)
0 0 0 0 0 0 0
1 36 43 7 38 54 16
3 -71 20 91 -126 -214 88
5 215 732 517 -394 11 405
6 254 1153 899 -1225 -240 985
8 345 70 275 -210 42 252
9 0 0 0 0 0 0
Calculated bending moment from observed strain: See table 2
Lo
cati
on
of
stra
in g
aug
e
fro
m G
L
Are
a o
f st
eel
(mm
2)
Lev
er a
rm
(mm
)
Str
ess
in
(N/m
m2)
Ben
din
g m
o-
men
t in
KN
-m
0 7238.23 0 0 0
1 7238.23 378.26 1.40 3.83
3 7238.23 409.48 25.20 74.69
5 7238.23 407.14 118.00 347.74
6 7238.23 408.51 179.80 531.64
8 7238.23 416.61 62.40 188.17
9 7238.23 0 0 0
Calculation of Deflection, shear force and earth pressure:
Deflection is second integral of bending moment; shear
force the first derivative of bending moment and earth pres-
sure the second derivative of bending moment. Therefore,
equation of observed bending moment was worked out by
using curve-fitting techniques. Origin Lab 7.0 Software was
used. Lorentz curve best fitted the observed bending mo-
ment. By solving the differential equations, observed def-
lections, shear force and earth pressure on meter panel were
calculated (See Fig.4).
VI. COMPARISON OF THEORETICAL (AS
MENTIONED IN 1.6 DESIGN CONSIDERATION)
AND OBSERVED BEHAVIOR
Tabulated results are given in Tables-3a & 3b, and for
graphical representation refer Fig.11, 12, 13 & 14. Table-3a
Lo
cati
on
of
stra
in
gau
ge
fro
m t
op
of
the
Pil
e in
m
Th
eore
tica
l E
arth
Pre
ssu
re k
N/m
Ob
serv
ed E
arth
Pre
ssu
re k
N/m
Th
eore
tica
l S
hea
r
forc
ekN
Ob
serv
ed S
hea
r
for
kN
0 6.7 4.85 0 10.5
1 13.9 9.25 10.70 17.273
3 64.0 45.24 87.09 61.199
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Volume 2, Issue 6, December 2012
261
5 33.85 63.7 186.21 251.06
6 -422.6 -532.74 227.38 -0.1598
8 442.1 105.64 -442.14 -133.33
9 0 2.3 0 -16.172
Table-3b
Lo
cati
on
of
stra
in
gau
ge
fro
m t
op
of
the
Pil
e in
m
Th
eore
tica
l b
end
ing
mo
men
t k
N-m
Ob
serv
ed b
end
ing
mo
men
t k
N-m
Th
eore
tica
l D
efle
ctio
n
mm
Ob
serv
ed D
efle
ctio
n
mm
Ten
sile
Str
ess
in S
teel
0 0 0 12.44 3.530 0
1 4.52 3.83 5.33 1.520 1.40
3 84.55 74.69 0.79 0.140 25.20
5 380.22 347.74 0.35 0.010 118.00
6 585.38 531.64 0 0 179.80
8 221.07 188.17 0 0 62.40
9 0 0 0 0 0
VII. COMPARISON OF THEORETICAL (FEM
MODEL) AND OBSERVED BEHAVIOR
Soil profile with properties is given below;
Table-4
Depth
(m.) C
EP
(kN/m2)
WP
(kN/m2)
Total
(kN/m2)
0 0 30 8 6.66667 0 6.66667
0.5 20 30 2 9.66667 0 9.66667
2 20 26 2 -24.3333 15 -9.3333
4 40 26 2 -12.2772 35 22.7228
6 100 30 4 -42.9061 55 12.0939
7.25 100 30 4 -162.5 55 -107.5
9 100 30 14 312.5 55 367.5
The water table is located at 2m below GL.
Results are graphical represented in Fig.15, 16, 17 & 18.
VIII. CONCLUSION
On the basis of field measurements, the observed flexural
behavior of cast-in-situ reinforced concrete cantilever seg-
mental/ meter panels leads to the following conclusions:
Theoretical and observed profiles of earth pressure, bending
moments, shear force and deflection in the structure due to
excavation are matching well. Nature of variation in theo-
retical and observed values of force functions along the
depth of the panel wall matches well with slight differences
in magnitudes. Differences in theoretical and observed val-
ues are due to variations in soil properties, inconsistent la-
boratory results of soil samples, changes in groundwater ta-
ble, etc. Magnitudes of observed values through
instrumentation are less than the theoretical values. The dif-
ference occurred because the theoretical magnitude of later-
al earth pressures and consequently theoretical bending
moment considered c value much less than actual. Earth
pressure diagram clearly shows that the actual passive earth
pressure developed is greater than the assumed theoretical
passive earth pressure in rock strata. This reflects a high
factor of safety taken for design of panels and an underesti-
mated c value of rock.
IX. SCOPE FOR FUTURE ENHANCEMENT
There is a need to extend the work further so as to collect
more information for inferring the design parameters from
the field and laboratory test results of cohesion and angle of
internal friction. The selection of design parameters from
soil properties at present is very much empirical and based
on subjective interpretation of the designer as per his expe-
rience. Some sort of relation needs to be established be-
tween the design parameters and properties of soil as re-
vealed by investigation to serve as a guide for designers.
The realistic evaluation of earth pressure, either active or
passive, is possible only by collecting the behavior data of
the instrumented piles / meter panels / diaphragm walls as
retaining elements, particularly since the laboratory results
conducted on soil samples is still a grey area. The authors
are making efforts in that direction.
Fig 5. Strain Readout Unit
Fig 6. Instrumented Plate
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Volume 2, Issue 6, December 2012
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Fig 7. Strain Gauge Arrangement
Fig 8. Strain Gauge Locations
Fig 9. Soil Profile
Fig 10. Best Fitted Curve
Fig 11. BM Comparison
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Volume 2, Issue 6, December 2012
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Fig 12. SF Comparison
.
Fig 13. Deflection Comparison
Fig 14. Observed Earth Pressure
`
Fig 15. SF Comparison (FEM with Instrumentation)
Fig 16. BM Comparison (FEM with Instrumentation)
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Fig 17. Deflection Comparison (FEM with Instrumentation)
Fig 18. Theoretical (FEM) BM, SF and deflection.
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the bending moment in a concrete-diaphragm wall, The
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[2] Yoo Chungsik, Behavior of braced and anchored walls in
soils overlying rock Journal of geotechnical and geoenviron-
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[3] Charles. W.W., Douglas. B.R., Sean W.L., Lei.G.H. Field
studies of well instrumented barrette in Hong Kong, journal
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ing, January 2000, 60-72.
[4] Symons I.F. and Carder D.R. Field measurements on embed-
ded retaining wall, geotechnique 42, No.1, 117-126.
[5] Kanhere D. K., Dr. Hegde R A, and Dr. Ganpule V T; Seg-
mental / Meter Piles for Basements and Subways; Proceed-
ings of Indian Geotechnical Conference December 13-15,
2012, Delhi.
[6] Kanhere D. K., and Dr. Ganpule V T; Behavior of ‘Segmen-
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and presented in FIB International Conference, Amsterdam,
2008.