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Proceedings of Indian Geotechnical Conference December 15-17, 2011, Kochi (Paper No. Q-143)
GROUND IMPROVEMENT OF DEEP SOFT CLAY LAYERS USING VIBRO
REPLACEMENT FOR CONSTRUCTION OF A PORT AND CONNECTING HIGHWAY AT
KOCHI, INDIA
Deepak Raj, General Manager, Keller Ground Engineering India Pvt Ltd., deepak@kellerindia.com
Sridhar Valluri, Senior Geotechnical Engineer, Keller Ground Engineering India Pvt Ltd., sridhar@kellerindia.com
ABSTRACT: Kochi is underlain by deep soft marine clay deposit. These clay layers are highly compressive and of very
low shear strength. In order to develop infrastructure like Ports, Transshipments terminals, highways in such type of soil, it
is necessary to provide suitable foundation technique. Ground improvement using vibro replacement is the one of the suited
technique to increase the shear strength of soils and to reduce the compressibility. This paper presents case history of
application of vibro replacement columns to support Jetty facilities at ICTT (International Container Transshipment
Terminal) at Vallarapadam port and to support the connecting 4 lane highway to ICTT. The various aspects of sub soil
conditions, design, construction methodology, quality control and test results are discussed in this paper.
INTRODUCTION
As the Indian economy integrates with the global economy,
maritime infrastructure will play an ever growing role. This
rapid growth in trade can be sustained only if the port
infrastructure keeps pace with the increasing volumes of
cargo. Road and rail connectivity forms an integral part of
the of the port infrastructure to have an end to end solution.
With this in view perspective plans have been prepared by
Government of India for developing major ports along with
a consolidated National Development Plan.
The subsoil’s along the coastal belt are generally very
weak. These soils pose challenges to the designers with
their variable thickness, low shear strength and high
compressibility for designing a robust foundation design
keeping life span of the facility in mind. This paper gives
details of application of the ground improvement using
vibro replacement technique to create suitable platform to
support the port infrastructure.
PROJECT DETAILS
Dubai Ports (DP World) is developing an International
Trans-shipment terminal (ICTT) at Vallarpadam, Kochi,
India. This all-weather port is strategically located on the
east west trade route on the south west coast of India. The
project involves construction of 600m of deep water quay (
-16.5m CD Dredge depth) with associated container storage
yards, rail container terminal and container freight station
facilities. National Highways Authority of India (NHAI) is
developing a dedicated new four lane road connecting
ICTT at Vallarpadam and NH-47 at Kalamassery. The total
route length of the proposed road is approximately 17.2km.
Figure 1 shows the location of the proposed terminal and
connecting highway. The work includes construction of
several culverts, bridges, flyover, underpasses and a toll
plaza.
Fig. 1 Layout showing ICTT and alignment of connecting
highway.
SUB SOIL PROFILE
The sub soil at the proposed terminal and the connecting
highway indicates the presence of an upper compressible
layer which is a mixture of sandy, silty and clayey deposits.
These are underlain by medium to dense silty sand layer.
Firm to stiff silty clay layer was observed below silty sand
layer. The thickness of the upper compressible strata is
varying in thickness. The thickness of this layer was
observed as 22m at the terminal and along the connecting
highway it is varying from 7m to 25m. Typical borelogs
with the subsoil strata are presented below in Figure.2.
The SPT, N values in the upper compressible strata are
ranging from 2 to 8 and Cu is in the range of 10 to 40 kPa.
The presence of weak subsoil resulted in the requirement of
ground improvement prior to development of infrastructure
facilities at the port.
GROUND IMPROVEMENT SCHEME
Vibro replacement is proposed as the ground improvement
scheme to support the structures proposed at the facility.
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Deepak Raj & Sridhar Valluri
Fig. 2 Typical borelogs at the proposed site
Ground improvement using Vibro Replacement (Vibro
Stone Columns) technique has a long proven track record.
The technique is widely used to support, industrial and
commercial developments on poor ground. It has been used
extensively beneath road/rail embankments, bridges,
projects requiring protection against potential liquefaction
caused by earthquakes, slope stability and coastal
reclamation works (Raju V.R. et. al., 2004a and Raju V.R.
et al.2004b).
In this method, the soil is stabilized by displacing
horizontally with the help of depth vibrator, refilling the
resulting space with granular material and compacting the
same with the vibro-float. The resulting matrix of
compacted soil and stone columns will have improved load
bearing and settlement characteristics.
Vibro Replacement is employed for the following purposes
at ICTT and along the connecting highway:
To improve soil strength along the dredged slope area
below the quay
To improve the soil strength and bearing capacity
immediately landward of the sheet pile wall
To improve the soil strength throughout the active zone
of the sheet pile wall and the active and passive zone of
anchor wall.
To support the embankments, reinforced cantilever
wall (RC Wall) and under passages with adequate
bearing capacity and without excess settlement.
To achieve the performance criteria and design
requirements following vibro replacement design scheme is
used:
At ICTT, Vallarpadam
Diameter of columns : 1100mm
Spacing of columns : 2.1 to 2.5m Triangular grid
pattern
Average Depth of columns : 22.5m
Area replacement ratio : 17 to 25%
Along NH Connectivity Road
Diameter of columns : 1000mm
Spacing of columns : 1.65 to 2.0m Triangular grid
pattern
Depth of column : 7m to 25m
Area replacement ratio : 22% to 33 %
Figure 3 and 4 shows a typical sketch showing the
application of vibro replacement technique at ICTT and
connecting highway, respectively.
Fig.3 Cross-section showing vibro replacement columns
along quay and associated yard at ICTT
Fig.4 Typical Cross-section showing vibro replacement
columns beneath the RC Wall
EXECUTION OF VIBRO REPLACEMENT WORKS
Subsoil in the top layer was found to be very soft. Hence,
working platform made up of granular materials is laid for
the movement of heavy machinery required for the ground
improvement works. Vibro replacement works were carried
by top feed wet method. A typical picture showing the
Vibro Replacement works at ICTT and along the
connecting highway is shown in figure 5 and figure 6,
respectively.
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Ground Improvement of Deep Soft Clay Layers using Vibro Replacement for Construction of a Port and Connecting Highway at Kochi, India
Fig. 5 Picture showing the vibro replacement works at
ICTT for the quay wall
Fig. 6 Picture showing the installation vibro replacement
columns along the connecting highway for RC Wall
foundation
A total of about 600,000 linear meters of vibro stone
columns were installed in phased manner starting from
August 2008 to June 2010.
QUALITY CONTROL
Quality management of the vibro replacement works was
carried during the construction process and after the
construction by means of load tests.
Monitoring of the installation process was carried out using
an “M4” computer, which measures the depth of
penetration, time and amperage. The M4 Display unit was
mounted inside the crane with a visual display to aid the
operator in constructing the column. The data was printed
out real time in the crane cabin for the review of the
engineer and for daily report for the site. A typical printout
of the vibro stone column of 25m deep is presented in
figure.7.
Fig. 7 Typical quality control output (M4 Graph) during
installation of Vibro Replacement column
LOAD TEST
As part of the quality control process single column and
three column group load tests were conducted over the
improved ground intervals to assess effectiveness of ground
improvement. The results of some of the tests are
summarized in the table.1.
Table.1. Details of load test
SNo Location/
Chainage
Type of
Test
Design
Load
(tons)
Settlement at
Design load
(mm)
1 ICTT Single
column 36.4 9
2 ICTT 3 column
group 123 22
3 4 +980 m Single
column 32.5 8
4 9 +010 m 3 column
group 54.5 8
30.00 0.00 Depth [m]
Penetration
Flushing
Column Building
&
Compaction
Ground Improvement of Deep Soft Clay Layers using Vibro Replacement for Construction of a Port and Connecting Highway at Kochi, India
1021
Deepak Raj & Sridhar Valluri
Typical arrangement of the vibro stone columns layout for a
three column group and single column load test is presented
below in the figure .8. Load settlement graph for the single
column and three column group load test is presented in
figure 9 and 10, respectively.
Fig. 8 Typical arrangement of vibro stone columns for three
column group and single column load test
0
2
4
6
8
10
12
0 5 10 15 20 25 30 35 40
Se
ttle
men
t (m
m)
Load (Tons)
Load vs Settlement Plot
Single Column Load Test on Vibro Stone Column ( at Ch.4+980)
Fig. 9 Load-settlement plot for single column load test on
vibro stone columns at Ch.4+ 980
0.0
4.0
8.0
12.0
16.0
20.0
24.0
28.0
32.0
0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0
Sett
lem
en
t (m
m)
Load in MT
Load vs Settlement Plot Three Column Group Load Test on Vibro Stone
Column ( at ICTT)
Fig. 10 Load-settlement plot for a three column group load
test on vibro stone columns at ICTT
The results from plate load test indicate that settlements are
well within the permissible limits and Vibro Replacement
columns are adequately and satisfactorily designed and
constructed to serve the purpose.
CONCLUSIONS
Subsoil in Kochi consists of deep soft upper compressible
layer having very low shear strength. Construction of
foundations in these soils has been always challenging to
foundation designers keeping the in view the time and cost
of the project. Vibro Replacement has been successfully
used to increase shear strength along dredge soil below
quay wall and in turn stabilizes the slope below quay wall.
It is also used successfully as reinforced cantilever wall
foundation. Vibro Replacement has proven to be a good
solution for both ICTT and its connecting highway both
technically and commercially. It also reduces the
construction time of the project significantly.
ACKNOWLEDGEMENTS
The authors wish to thank the owner of the development
DP World and NHAI for their kind support. In addition, the
support and contribution of Mr Suketu Shah, COO, Man
Infra and Mr M B Suresh of SOMA Infra Structure Ltd
during the construction works is gratefully acknowledged.
REFERENCES
1. Ground Improvement using Vibro Replacement in
ASIA 1994 to 2004 A 10 Year Review Dr. V.R. Raju.
Y. Hari Krishna, R. Wegner Keller (M) Sdn. Bhd.,
Malaysia.
2. Raju, V.R., Yee, Y.W., Tam, E. and Sreenivas, P.
(2004), “Vibro Replacement for the Construction of a
15 m High Highway Embankment over a Mining
Pond”, Malaysian Geotechnical Conference, Kuala
Lumpur.
3. Raju, V.R., Wegner, R. ands Vetriselvan, A. (2003),
Application of Vibro Techniques for Infrastructure
Projects in India, Proceedings of the Indian
Geotechnical Conference, Roorkee, India.
4. Priebe, H.J. (1995). The design of Vibro Replacement,
Ground Engineering, Vol. 28, No.10. pp.31-37.
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