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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