Volume 3, Issue 2 June 2018

Case-history
Steel Tubular Pile Cofferdam Foundations in Bangladesh
Mr. Tsunenobu Nozaki
General Manager
International Construction Design and Planning Department
Giken Ltd.
1. Introduction
The Japanese ODA loan project, named the Kanchpur, Meghna and Gumti 2nd Bridges Construction and Existing Bridges
Rehabilitation Project, was undertaken in Bangladesh. This is the biggest ODA project ever, in Bangladesh, which aims at
shortening travel times and increasing the freight capacity of Dhaka-Chittagong National Highway No.1 (NH-1).
The project involves the rehabilitation and retrofitting of existing bridges and the construction of 2nd bridges alongside
the existing bridges. In order to construct high quality infrastructures, Japanese technologies, such as Tubular Pile
Cofferdam Foundations and narrow box steel girder type monolithic with Steel Concrete Composite Slab, were adopted
on the project. In this report, the Tubular Pile Cofferdam Foundation and the selected construction method, “The Pressin Method”, are highlighted.

Fig 1 Project Location Map
2. Background of the Project
In Bangladesh, the economic growth was steady in the 2000’s, maintaining a GDP growth rate of around 6% per annum.
The amount of freight has increased at a rate of 6-7% in recent years at the same pace as the GDP growth.
Profile of Bangladesh
Population: 159M (the 8th largest in the world), Land area: 147,000 square kilometers, GDP: 227.9B US dollars.
Reasons for Project Demand1)
Substantial shortage of capacity for present and future traffic demand
The traffic capacity on the main roads connecting the major cities and metropolitan areas in Dhaka cannot keep up withthe year-after-year increase of traffic volume, and eliminating bottlenecks on distribution routes is the major priority.
The NH-1, namely the Dhaka-Chittagong Highway, is the lifeline for the economy of Bangladesh. The capacity, Annual
Average Daily Traffic (AADT), of the NH-1 is 25,000 vehicles. The NH-1 will be a part of the Asian Highway that connects
10Volume 3, Issue 2 June 2018with neighboring countries. Along this highway, the existing Kanchpur, Meghna and Gumti Bridges are major structures
which cross the Lakhya, Meghna and Gumti Rivers. The Government of Bangladesh has planned to widen the NH-1 into
4-lanes in order to increase traffic capacity and remove traffic bottlenecks in the earthwork section. However, theseexisting bridges remain critical bottlenecks hindering the widening of the NH-1.
In 2012, the Average Daily Traffic (ADT) of the NH-1 was 75,000PCU at the existing Kanchpur Bridge and 65,000CPU at
the existing Meghna/Gumti Bridges. The amount of ADT has already exceeded its traffic volume capacity by more than
10% at the Kanchpur Bridge and 60% at the Meghna/Gumti Bridges. In addition, due to the increase traffic trend, theforecast traffic volume in 2025 will exceed capacity by 100% at the Kanchpur Bridge and 200% at the Meghna/Gumti
Bridges. It is obvious that the existing bridges will fail to cope with the increase traffic volume of the NH-1. This will cause
serious traffic congestion. Therefore, the construction of new 2nd Kanchpur, 2nd Meghna and 2nd Gumti Bridges became
an essential issue.
2) Introduction of new seismic design
standards
In addition, the “Bangladesh National
Building Code (BNBC)” was implemented in
1993, and Bangladesh earthquake
standards were raised in 2006, which mean
existing bridges no longer meet theearthquake standards. The existing bridges
were designed in accordance with theseismic coefficient of 0.05. The revision of
the BNBC (2006) substantially increased
the coefficient to 0.15. Therefore, therestoration and reinforcement of thebridges have undoubtedly become apressing issue.
Thus, in June 2011, the Government of
Bangladesh requested JICA to undertake astudy for the repair and reinforcement of
the existing Kanchpur, Meghna and Gumti
Bridges on the NH-1, and the constructionof the 2nd Kanchpur, 2nd Meghna and 2ndGumti Bridges. The Kanchpur, Meghna andGumti Bridges are important bridges,
located on the NH-1 connecting Dhaka andChittagong which is the key corridor that
supports the economy.

Fig 2 The NH-1 and Existing Bridges
3. Project Objectives
In accordance with the context of the preceding section, it was concluded that the three existing bridges needed to beretrofitted and three new 2nd bridges needed to be constructed to meet the increase traffic demand of the NH-1. As such,the overall objective of this project consists of the rehabilitation of the three existing bridges and the construction ofthree new 2nd bridges.
1) Construction of new 2nd Kanchpur, 2nd Meghna and 2nd Gumti Bridges to facilitate the increase traffic demand11Volume 3, Issue 2 June 2018

Table 1 shows vehicle traffic forecasts and required additional lanes for the bridges. The traffic volume of the Kanchpur
Bridge was 76,732 cars per day in 2012 and will be 123,301 in 2021 and 192,687 in 2030. This sharp increase requires anadditional 4 lanes to the current 4 lanes. The traffic volume of the Meghna and Gumti Bridges was 65,008 cars per day in2012 and will be 105,374 in 2021 and 165,168 in 2030. These 2 bridges also require an additional 4 lanes to the current
2 lanes. Therefore, the new 2nd Kanchpur, 2nd Meghna and 2nd Gumti Bridges are all designed as 4-lane bridges.
BridgeKanchpur
Meghna/Gumti

Vehicle Traffic (cars / day)
2012
2021
76,732
123,301
65,008105,3742030
192,687
165,168

Number of Lanes
CurrentAdd
4+42+4

Table 1. Traffic Demand and Traffic Forecast
Taking into consideration the above project objectives, a survey work was carried out in order to appraise the Japanese
ODA loan that will cover the total project cost, the project implementation framework and the environmental and socialaspects of the construction.
2) Retrofitting of the existing bridges
The three existing bridges are damaged due to the use of much overloaded trucks and the continual scouring on thebridge piers over time. At the same time, they were designed in accordance with the outdated seismic design standard
and need to be upgraded using the new seismic design standard of BNBC (2006). The extent of rehabilitation of theexisting bridges depends on the inspection and assessment of their above condition and retrofitting them to secure theirreliability as bridge structures.
4. Outline of the Project1) Project Name: The Kanchpur, Meghna and Gumti 2nd Bridges Construction and Existing Bridges Rehabilitation
Project2) Execution Agency: RHD (Bangladesh Roads and Highways Department) under Ministry of Communication
3) Main Contractor: Obayashi-Shimizu-JFE Engineering -IHI Infrastructure Joint Venture4) Construction Budget: International Yen Loan of JPY29 Billion
5) Project Duration: 7 years and 8 months from December 20156) Duration of Piling Works: February to October 2017
5. Type of Foundation
In order to satisfy the design requirements, a“Steel Tubular Pile Cofferdam Foundation” wasadopted on the project. A steel tubular pile
cofferdam foundation comprises steel tubularpiles with interlocks, which form an enclosed
area. The wall acts as a cofferdam during theconstruction of the substructure and eachinterlock is initially emptied and filled with grout
to provide necessary water tightness for thecofferdam. After dewatering and excavation to
the required depth, the tubular piles are joined tothe base RC slab as a permanent substructure.
The tubular piles are then cut off at the top of theRC slab to allow water flow around thefoundation.
Fig 3 Overview of Steel Tubular Pile Cofferdam Foundation
The steel tubular pile cofferdam foundation originated in Japan and can achieve substantial cost savings for bridgefoundations that need to be constructed underwater or under soft ground conditions. The main advantage of thisfoundation system it that it acts as both a temporary cofferdam and a permanent foundation, leading to a reduction inconstruction costs and time simultaneously. Also, this system is very effective as it provides anti-seismic reinforcement
and scour protection for bridge piers.
Fig 4 shows the comparison of a steel tubular pile cofferdam foundation and a traditional RC pile foundation. New bridge
12Volume 3, Issue 2 June 2018

piers are constructed adjacent to existing piers, enclosed with a shared cofferdam and joined together.
Steel Tubular Pile Cofferdam Foundation

Fig 4 Comparison of Steel Tubular Pile Cofferdam Foundation and RC Pile Foundation
RC pile foundations require a temporary sheet pile cofferdam to provide a dry working space, for a piling machine to carryout RC pile installation in a water environment. Also, the footprint of the RC pile foundation is much larger than that of
the steel tubular pile cofferdam foundation. This results in nearly twice as much construction cost and time using the RC
pile foundation, compared to the steel tubular pile cofferdam foundation, on this particular project.
6. Overview of the Foundation
1) Kanchpur Bridge. (Fig 5)
Bridge Length: 400m with 6 piers.
Steel Tubular Piles: 352 no. 1,000mm diameter tubular piles L=28m - 41.5m

Completion Image

Existing Bridge
Fig 5 Kanchpur Bridge
13Volume 3, Issue 2 June 20182) Meghna Bridge. (Fig 6)
Bridge Length: 930m with 11 piers.
Steel Tubular Piles: 765 no. 1,000mm diameter tubular piles L= 45.5m - 56mExisting Bridge

Completion Image
Fig 6 Meghna Bridge

3) Gumti Bridge (Fig 7)
Bridge Length: 1,410m with 16 piers.
Steel Tubular Piles: 510 no. 1,000mm diameter tubular piles L=41.5m - 55m (6 piers only)

Existing Bridge

Completion Image
Fig 7 Gumti Bridge

7. Ground Conditions and Pile Installation Method
The typical ground condition on this project is layered soil, comprised of clay, silt and sand as shown in Fig 8. As themaximum SPT N value exceeds 30 or 50, the Press-in with water jetting mode was utilized.
1) Ground Conditions
Kanchpur Bridge(Nmax>50)

Gumti Bridge(Nmax>50)

N value

Sand

Piles L=56m

Piles L=55m

Piles L=41.5m

Silty finesandMeghna Bridge(Nmax<50)

ClayDepth
Silty finesandFig 8 Typical Borehole Logs
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2) Pile Installation Mode
When the ground is medium dense/stiff or denser/stiffer, pile installation by the standard Press-in Method can be difficult
due to the increase of installation resistance. The water jetting mode is suitable for dense or stiff ground conditions withSTP N value of up to about 50 or undrained compressive strength Cu of up to about 150kPa. The water jetting can minimize
the tendency of pressure bulbs and pile plugs, which are created at the pile toe during press in operations. At the sametime, the water jetting can temporarily reduce skin friction during pile installation. The operation of Press-in with Water
Jetting comprises the Silent Piler, the Piler Jet Reel atop the Silent Piler, the Power Unit of the Silent Piler and the Water
Jet Unit, as shown in Fig 9.

Fig 9 Machine Layout of Press-inwith Water Jetting3) Overhead Clearance Method
On such projects, the steel tubular cofferdam foundations are installed within a low headroom under the existing bridges.
Therefore, during pile installation work, after the bottom pile is installed, the next pile is spliced atop. This process isrepeated until the full length of pile is installed. On these projects, the traditional circle welding method was utilized tospliced piles. Before the steel tubular piles were delivered, they were cut into designated lengths in accordance with theavailable overhead clearance under the bridges. The bottom of each upper spliced pile was beveled to allow full
penetration butt welding with multiple passes. At the splice joint inside each pile, a backing strip is tightly fitted prior towelding. This provides support for a fully penetrated root pass. The circle welding is carried out in the vertical positionand care should be taken to prevent the overflow of welded material. A temporary copper strip is attached to the top of
the lower pile, to help to prevent this overflow. Some of the details of the execution of the projects are given in Fig 10 toFig 13.
Details of Backing Strip

Details of Copper Strip

Fig 10 Preparation Details for Circle Welding
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Fig 11 Machine Layout (Plan)

Fig 12 Machine Layout (Front View)

16Volume 3, Issue 2 June 2018

Fig 13 Machine Layout (Side View)
8. Conclusion
In urban construction scenarios, working conditions are much more complicated when upgrading/retrofitting
infrastructures as the construction often needs to be carried out adjacent to existing everyday activities. Also, space
limitation as a result of existing infrastructures is especially hindering on foundation construction, as it usually restricts
implementation of the works.
Steel tubular pile cofferdam foundations are effectively used not only for new bridge foundations, but also these typesof bridge foundation retrofitting works. This simple and effective solution enables bridge foundations to be constructedwithin a minimal period of construction time. With the Press-in Method, steel tubular pile cofferdam foundations can beconstructed under extremely restricted working conditions, such as overhead restrictions, restricted working platformsor hard ground conditions without impacting on the surrounding environment.
In the service phase, functional adaptations of infrastructures may be required due to a higher demand of functional
requirements, shorter structural lifetimes than planned or the necessity of further usage of the same structure at the endof its planned life. To meet the functional adaptations, traditional structures with the “Scrap & Build” design concept
ultimately need high renovation construction and demolition costs. However, with the above combination, structures canmore effectively and efficiently satisfy the stipulated functional adaptation. Therefore, the total investment costs i.e.
construction, operational, maintenance, renovation construction and demolition costs can meet the optimum
cost/quality balance.
REFERENCES[1] Japan International Cooperation Agency: Website https://www.jica.go.jp/english/index.html[2] Preparatory Survey for Dhaka-Chittagong National Highway No.1 Bridge Construction and Rehabilitation Project Final
Report 5517