SCHWANAU (Germany): Schwanau is located in Ortenaukreis, Baden-Wurttemberg, in the south of Germany, with a population of only 6,800.
However, the 38.34 square km wide Schwanau is ‘not really small’, as it is the home of a high-technology machine manufacturer that specialises in underground tunnel work.
Created in 1977, and renamed Herrenknecht AG in 1998, the Allmannsweier-based firm is known as the leader in the manufacturing and marketing of tunnelling machinery.
To date, Herrenknecht AG has supplied the Tunnel Boring Machine (TBM) in sizes of 0.10-19.0 metres and completed more than 1,900 km of tunnels.
In 2005, Herrenknecht AG set a world record by building a TBM measuring 19 metres (62 feet) in diameter. The firm is also involved in the construction of the Smart Tunnel in Sungai Besi, Kuala Lumpur.
The first TBM for the My Rapid Transit’s (MRT) Sungai Buloh-Kajang alignment is ready to be shipped to Malaysia from Schwanau to start tunnelling work for the MRT project, expected to take off in May 2013.
The shipment of the TBM followed the recent success of the Factory Acceptance Test (FAT) conducted by engineers from MRT Corp and the contractor for the underground tunnel work, MMC-Gamuda KVMRT (T) Sdn Bhd and Herrenknecht AG here.
MRT Corporation’s Strategic Communication and Public Relations Director, Amir Mahmood Razak, said the first MRT alignment, which has 31 stations including seven located underground, will require tunnelling through karstified limestone and the Bukit Kenny geological structures.
Karst is an area of irregular limestone in which erosion has produced fissures, sinkholes, underground streams, and caverns.
Geological studies show that part of the underground area east of Kuala Lumpur is made up of karstified limestone, while the Bukit Kenny zone has granite, sand and mudstones.
This requires a suitable TBM, and MRT tunnels are to be constructed using two types of TBMs – six Variable Density (VD) modern TBMs and two Earth Pressure Balance (EPB) TBMs to ensure the safety of workers during construction of the tunnels.
VD TBM will be used to drill through the karstified limestone area, while EPB TBM will be used in the Kenny Hill geological area, explained Amir.
The first of the 10 TBMs, 6,620mm in diameter, 135 m-long and weighing 1,100 tonnes with cutterhead power of 1,280KW, will be used for the construction of the Sungai Buloh-Kajang MRT tracks.
MRT Corp and MMC-Gamuda ordered the TBM in March 2012. It took nine months for completion before receiving the FAT scrutiny and approval.
This machine will be dismantled and shipped to Malaysia after the FAT clearance and is expected to arrive in the country in March 2013, said Amir.
This TBM and another (still in construction) will be used to bore a tunnel through Cochrane, Kampung Pandan and ending in Pasar Rakyat in Kuala Lumpur.
Ten TBMs, worth RM450 million, will be used for tunnel-boring works at the 9.5 km stretch from Semantan to Maluri, passing seven underground stations (KL Sentral, Pasar Seni, Merdeka, Bukit Bintang Sentral, Pasar Rakyat, Cochrane, and Maluri).
Eight of the TBMs will be manufactured by Herrenknecht AG, while the other two will come from China Railway Tunnel Engineering Ltd factories.
Also, about two-thirds of the company’s 3,300 workers are at the Herrenknecht AG headquarters, and another 300 at three different locations in China.
A tunnel boring machine (TBM) is a sophisticated machine used to bore through any type of soil or rock, explained the project manager for MMC Gamuda Joint Venture Sdn Bhd (MGJV), Gusztav Klados, to Malaysian journalists who recently visited the plant in Schwanau.
“It is shaped like a cylinder, which is lying on its side and has a rotary cutter head at its front. This cutter head cuts and “eats away” the soil or rock as it rotates and as the TBM pushes itself forward.
“A TBM also has a system which assembles the concrete lining for the tunnel immediately after the TBM has done its excavation work,” he said.
This consists of a mechanical arm that lifts and puts pre-cast concrete pieces together to form a ring in the excavated portion of the tunnel. This maintains the integrity of the tunnel by preventing the tunnel from caving in.
The TBM also has a set of hydraulic jacks that are fixed against the last concrete ring, slowly extended to push the TBM forward.
Another important component of the TBM is the system that disposes of the soil or rock material which the TBM has excavated. Depending on the type of machine used, excavated material can be brought out from the back of the machine via a conveyor belt or loaded into wagons which are then transported out, or can be mixed into a liquid clay called bentonite and pumped out, he said.
Gusztav explained that by using the EPB shields, the soil is excavated by tools on the rotating cutting wheel at the tunnel face and passes through the openings in the cutting wheel into the excavation chamber.
There, it mixes with the other soils.
The force from the thrust cylinders is transmitted via the pressure bulkhead to the soil to support the tunnel face and control the entry of material into the excavation chamber.
The excavated material is then removed by the screw conveyor from the excavation chamber, which is under pressure in the tunnel. With the help of an erector, the tunnel lining segments are built directly behind the shield. All activities are monitored from the control cabin.
EPB Shields, made by Herrenknecht AG, are in their element in soft ground. Cohesive and incohesive soils with high clay or silt content and low water permeability provide the ideal conditions for EPB tunnelling.
Gusztav explained, the soil excavated by the cutting wheel is used to support the tunnel face. Foam injected in front of the cutting wheel turns the excavated soil into a paste, guaranteeing the exact control of the support pressure, as well as the efficient removal of the excavated soil.
One other method for constructing a tunnel for the MRT without using a TBM is by digging from the surface, said Amir.
This method is usually called “cut and cover” because it literally involves cutting and digging the soil or rock from the surface, and then covering it over to make a tunnel once the desired depth is reached.
This is obviously not a feasible method when building an MRT tunnel, or any other type of tunnel, through a busy city like Kuala Lumpur, as the “cut and cover” method will cause constant disruptions on the surface.
Further, cut and cover through a city will mean closing all roads and demolishing all buildings that the tunnel will run under.
“The FAT is an important milestone in the MRT project as it marks the completion of the TBM’s manufacturing process. MRT Corp and MMC-Gamuda has inspected the TBM to ensure that it complies with its required specifications and that it functions properly. The TBM is now ready for action in Malaysia”, said Amir.
During the FAT, the engineers jointly went through a check-list of 450 items which stretched over 43 pages. The checks range from a simple visual of the external surface of the TBM to ensuring that every valve in the TBM is in good working order.
According to Amir, an added significance to this event was that this first TBM, code-named S-774 for the MRT project, is also the world’s first Variable Density TBM. The design of the Variable Density TBM was the result of a joint effort between MMC-Gamuda and Herrenknecht and was specially invented for tunnelling through the challenging Kuala Lumpur limestone which lies under the eastern part of Kuala Lumpur.
“The designing of the Variable Density TBM is the result of combined Malaysian and German ingenuity. This is something which Malaysians can be truly proud of,” said Amir.
Amir added that a TBM owner has several options upon completion of the work. One is for the TBMs to be decommissioned and dismantled. Parts that can be reused will then be salvaged.
The second option is to tunnel the TBMs into the ground and cap them.
The third choice is to dismantle the TBMs and then re-assemble them for displaying to the public.
The fourth option is to dismantle the TBMs, relocate them to a factory for refurbishment with replacement parts, and deliver them to another project requiring similar TBMs, all tested and approved for new tunnelling work, he said. — Bernama