Ensuring the safe and timely arrival of 21 state of the art, EPBMs into the Gulf country of Qatar requires multinational cooperation and a pinch of good fortune. The majority of the journey sees the TBMs embark upon a month long ocean voyage as they are moved from Schwanau in Germany over to Belgium before beginning their Atlantic passage, which then takes them along the Mediterranean, the Gulf of Suez and into the Middle East before reaching their final destination of Doha. "The delivery of the new TBMs into Qatar had to go through a long logistic procedure.
The TBM manufacturer, Germany’s Herrenknecht, arranged the maritime transportation from the factories where the machines were manufactured in both Germany and China," explains Engineer Daniel Leckel, who is chief technical officer and chief programme officer at Qatar Rail. Upon arrival at Doha Port the operator Milaha Company enabled the discharge of the lorries carrying the TBM components on the enormous vessel.
"Milaha’s team was very cooperative with us and the Doha Port prepared some unique solutions to meet technical requirements for bringing the TBMs in," says Leckel.
"Qatar Rail’s logistics team monitored the discharge of the machines from the vessels and accompanied the TBMs all the way to the dedicated construction sites where they are set to operate in Doha."
More coordination was also required between the logistics team and Qatar Customs Authority, to assist the contractors with the clearance procedures from the port. And of course conferences had to be held with the Traffic Police Department, for the assignment of the most appropriate roads from the port to the contractors’ sites, and the scheduling of the police escort to guarantee a secure transfer of all machines.
Of course with the TBMs weighing up to 900 tonnes the EPB machines are split into 22 segments before being transported – and according to Herrenknecht the heaviest of these is around 64t. A ship sets sail from Antwerp every two weeks.
"The vessels are driving on a fixed schedule so we know that every two weeks the ship is going to Doha so we can optimise this. Each shipment usually takes between 28 and 31 days," says Gerhard Wehrmeyer, division manager for traffic tunnelling at Herrenkecht, who also points out that there have been no storms or bad weather to delay shipping.
By June 2014 five of the 7.05m diameter EPBMs had arrived in Doha with a total of 21 set to be delivered in total. Between them this fleet of state of the art machines will bore the first phase of Doha’s planned metro system consisting of 115km of tunnels over three lines; Red, Gold and Green.
The first machine arrived in April 2014 and is being used by the consortia building the Red Line North. This involves 23km of tunnel excavation to be done with four machines and consists of contractors Italy’s Salini Impregilo, SK Engineering & Construction Co. from South Korea and Qatar’s Galfar Al Misnad Engineering & Contracting W.L.L. JV.
Named ‘Lebretha’ the first EPBM on site will travel approximately 8km over 22 months and is expected to complete its bore half way through 2016. Its average speed is forecast at 14 to 20m/day depending on the ground conditions, excavating around 5.4Mm3 during its journey.
Lebretha’s arrival was followed by four more machines: Al Mayeda, Al Khor, Lehwaila and Al Wakra which are also to be used on the Red Line, which has been split into two major contract packages: Red Line North and Red Line South. Al Mayeda and Al Khor will join the Italian led consortia on the northern packages and Lehwaila and Al Wakra will be used by the Red Line South team led by the French-Qatari company QDVC and comprising of South Korea’s G. S. Engineering and Construction and Qatar’s Al Darwish Engineering.
A total of five TBMs will be used on the southern section, which has 33km of tunnelling to undertake.
Naming Tradition
Naming the machines gave the team an opportunity to ensure that the TBMs reflect the Qatari culture explains Leckel. "Since our TBMs will be operating across Qatar and since we are keen on integrating the Qatari culture in our operation system, we decided to name our TBMs after historical towns and cities, each carrying its own story and background," he says.
Al Khor TBM, for example, operating at the Red Line North, is named after Al Khor coastal city in northern Qatar. Al Khor is known for its large concentration of modern and historical mosques and is home to the Al Khor Museum, as well as the city’s renowned Corniche and Port.
Al Zubara, for its part, operating at the Red Line South, was named after a town located north of the country. Dating back to the ancient 18th century, Al Zubara Fort in the town tells the story of its great history and remains a destination for visitors wanting to explore Qatar’s historical landmarks. "Naming a TBM after this remarkable town is a way preserving it and expressing appreciation to its value and heritage," says Leckel.
The Doha TBM, also operating along the Red Line South, was named after the capital of Qatar, an urban and vibrant city, considered as the hub of Qatar State.
The name of Al Rayyan TBM, operating at the Green Line, refers to Al Rayyan district, embracing many landmark and historic sites. Besides having a distinguished heritage for being home of many ancient castles, Al Rayyan is also a hub for education, comprising a number of universities, colleges and institutes of the Qatar Foundation for Education, as well as Science and Community Development.
As for the Lusail TBM, operating at the Gold Line, it is named after the ultra-modern city that is becoming the most unique city in Qatar.
"The same concept applies to our 16 other TBMs, which are called Lebretha, Al Mayeda, Al Bidda, Lehwaila, Al Wakra, Mushaireb, Al Sheehaniya, Al Gharrafa, Al Messila, Leatooriya, Lijmayliya, Sharq, Al Sadd, Al Waab, Muaither and Al Sailiya," says Leckel.
Technical Considerations
For the Doha project Herrenknecht has designed a new cutterhead to ensure maximum efficiency through the ground. "The solution takes into account Doha’s soft ground with Simsina limestone, Rus Formation and shale, the hydrology as well as other requirements of jobsite and customer," says Wehrmeyer. "The design of the cutterhead with its openings, position and quantity of the different excavation tools was one important aspect for the Doha TBMs. The project specific and state-of-the-art design includes a sophisticated cutterhead center with a high opening ratio."
For back filling of the annular gap all machines work with bi-components consisting of the mortar and the accelerator sodium silicate.
Ground Adaptability
That Qatar opted for an EPB shield model is not surprising for the limestone bedrock under Doha has a shale layer within it that may require closed mode operation. In poor ground the EPB Shields can use the excavated soil directly as support medium. The rotating cutting wheel equipped with tools is pressed onto the tunnel face and excavates the material.
The soil enters the excavation chamber through openings, where it mixes with the soil paste already there.
Mixing arms on the cutting wheel and bulkhead mix the paste until it has the required texture.
The bulkhead transfers the pressure of the thrust cylinders to the pliable soil paste. When the pressure of the soil paste in the excavation chamber equals the pressure of the surrounding soil and groundwater, the necessary balance has been achieved.
A screw conveyor transports the excavated material from the base of the excavation chamber onto a belt conveyor for removal away from the tunnel face.
The interaction between the screw conveyor’s throughput and the TBM’s advance rate ensure that the support pressure of the soil paste can be controlled precisely.
Looking ahead
Over the next few months the remaining TBMs will arrive in Doha and be distributed to the network of contractors that are creating Qatar’s first major mass transit system in line with the aspirations of the country’s strategic plan known as the Qatar National Vision 2030.
This kind of tunnelling may be new to the emirate but by pairing local contractors with the world’s best tunnelling companies, Qatar is ensuring that not only will it get a state of the art system, it will get a sustainable one.
By the time the 2022 FIFA World Cup kicks off in Qatar locals and visitors alike will be using what is perhaps the largest metro ever to be built in a single phase and the 21 TBMs will perhaps have set sail again bringing the same benefits to other cities.
