________________ A big step to improve the traffic situation in Malaysia's capital with its about 7 million inhabitants is the new Klang Valley Mass Rapid Transit (KVMRT) system. For the construction of the demanding underground sections through the heart of the metropolis, 6 newly developed Variable Density TBMs from Herrenknecht are also on track.

Kuala Lumpur’s international airport is as 21^st century as it comes; vaulted terminal spaces match any modern flight hub. The rail link to the high rise city center of Malaysia’s capital is a fast 50 minutes, through palm oil plantations interspersed with new town developments, numerous multi-story apartment blocks clustered together for the fast growing population.

________________ But once in the city’s crowded center transport is a little more difficult. Past decades have seen the provision of a small two-car monorail system and two light rail transit (LRT) lines but the city still relies on roads which, while numerous, can be clogged and jammed at rush hour. The crowds thronging the shopping malls in the “Golden Triangle” or sitting under monsoon rainproof awnings over the rows of street restaurants serving every kind of delicious food, from Malay and Chinese to Thai and Indian, will mostly get back home by car. 

Marcus Karakashian, project director with the newly-created Mass Rapid Transit (MRT) Corporation says a good network of mainly tolled expressways spans across the 70 kilometers of “Greater Kuala Lumpur”. This has developed as the city has grown, but goes hand in hand with high car ownership encouraged by the country’s development of its own Proton car industry, meaning that the population has to endure long waits in traffic at rush-hours.

________________ Karakashian is now overseeing the building of a new public transport system to alleviate the problems. He sketches out the city’s shape on a whiteboard at the fifth story offices of the MRT Corporation, set up by the government as the project client. “The population has expanded significantly” he explains “particularly since independence in 1957.” Kuala Lumpur proper covers 243 square kilometers and had an estimated 1.6 million inhabitants in 2012, while the overall urban area has about 7 million. In some years’ time the city could face much greater problems with traffic, Karakashian says, and it is already almost impossible to get a parking space in the center, something we found out on our way to the MRT Corp offices.

“It is not good for modern life if you cannot get people around” he comments. In particular, it does not square with ambitions for the city to become one of the world’s top urban centers and business destinations, and get on to the top twenty list of “liveable cities” by 2020. Heavy seasonal monsoon rains exacerbate the situation. “When weather conditions are bad, things can get even more difficult” says Karakashian. So when the big contractor MMC-Gamuda investigated an MRT scheme and then proposed it to government in 2010, the idea was taken up.

________________ “The whole concept is for three lines, two running north-west to south-east through the city and a third circle line which will link these and the existing LRTs” says Satpal Bhogal, outlining the scheme at a spacious office in the contractor’s project headquarters, in one of many new office and retail complexes - this one just south of the city center. Bhogal is currently project director for the central tunnel section of the project for joint venture contractor MMC-Gamuda. For the moment, he says, the government has agreed on the first line, running from Sungai-Buloh to Kajang in the south. The go-ahead was given in July 2011 and decisions on the second and third lines are pending.

The first line has an overall length of 51 kilometers from the north-east to the south-west. Much is on viaducts along the Klang Valley, the main area of the urban spread of the growing city, but there is a critical underground section through the central area running past the main railway station, the business district with its famous Petronas twin towers, and through the crowded Golden Triangle. Fitting the Bukit Bintang underground station into the narrow streets of shops, food and bars here, is one of the major challenges of the project.

________________ MMC-Gamuda, well established in Malaysia, has two distinct roles on the project. Firstly it was taken on by the government as a special “project delivery  partner” (PDP) to work with the MRT Corporation to oversee the construction management of the entire line. Most of this is the elevated viaduct track with around 24 elevated stations and is being let out by the PDP in a series of packages which are currently in construction by a variety of contractors.

“But really MMC-Gamuda was interested in the central tunnelled section” says Karakashian “which is 9.5 kilometer long with seven underground stations”. This tunnelled section has been let to MMC-Gamuda as a single large design-and-build contract, one of Malaysia’s biggest and large in global terms for a single contract. “It followed an open international bidding process which the government allowed them to participate in” says Karakashian. “They won with a MYR 8.28 bn (€1.85 bn) bid on combined technical competence and lowest cost grounds.” Mott MacDonald and Aecom are the main consultants in the JV. For this large central work package, of course, MMC-Gamuda's PDP role does not apply and  MRT Corp as the project owner is overseeing the job directly.

________________ The tunnelled section runs through the heart of the busy city. Its twin tunnels and underground stations are the major challenge facing the entire MRT project. However, it is a section where MMC-Gamuda felt it could do well based on past experience. 

The geology of the city splits into three types, a hard granite rock area, softer mixed ground known as Kenny Hill formation and a limestone area. The line runs in the last two. “The Kenny Hill is relatively good mixed soft tunnelling ground but the limestone on the east side is highly karstic” explains Bhogal “with multiple fissures, caverns, filled sinkholes and sudden voids.” Sudden drops in the rockhead are common.

There are few more difficult tests for a TBM and this is where Herrenknecht’s new “variable density” TBM concept is proving its worth. The first 1,100 meters drives have just been completed and six of the newly designed machines are on site now for the project.

________________ One highly experienced tunnel engineer working on the metro is Hungarian-born Gusztáv Klados whose expansive figure and loquacious expertise is well-known in the world tunnelling community. He has worked on projects from the Channel Tunnel to the Budapest metro and many in south-east Asia and is now back in Kuala Lumpur as the project manager, the main man for the tunnel work. 

Outside one of the coffee shops in the shaded atrium of the office complex where MMC-Gamuda is resident, he chats about the challenges. “The karstic limestone is” he says “just about the most difficult ground to get through for a tunneller”. Having worked on Kuala Lumpur’s first major project in this ground, the famous SMART tunnel project completed in 2007, he should know. The highly unusual scheme, for a unique combined monsoon floodwater relief tunnel which doubles as a road bypass in dry conditions, was successfully completed by MMC-Gamuda using two huge 13.8 meter diameter Herrenknecht Mixshield TBMs. But it was not without its troubles, including a few sinkholes and some damage to buildings.

The problem is that not only is the rock riddled with cavities, which can be empty voids, or filled with soft running ground and water, but many of them are joined together. “They can run for more than a kilometre producing the cave systems loved by potholers” he declares. In Kuala Lumpur, the old lead mine workings have also left many areas backfilled with old mine waste which is unconsolidated. This means that tunnel excavation alone cannot suddenly be letting in pressurised water, or soft infill material, but rather that settlement resulting from such inrush can run to the surface far from the tunnel line.

________________ Using the Mixshield TBMs for SMART illustrated the challenges, because, although the slurry provides good face support, when voids suddenly occurred the bentonite mixture could flow into them uncontrolled. But tackling these challenges also gave the contractor new ideas about how to deal with such ground. What they did was first carry out extensive ground investigation along the route line, to locate voids and fissures as much as possible and grout them tight. “Some have swallowed 60 cubic meters of grout” says Klados. “But you can easily miss them.”

So the team also came up with the idea to use a denser type of slurry which would balance both groundwater and earth pressure in the TBM face. Back in his office Klados draws a quick diagram to show the pressure gradient for thick and thin slurry; extrapolating the line for normal bentonite sees it cut the surface whereas the less steep graph line for a denser material does not. “That means it does not come to surface” he says “Unlike normal bentonite mix, it would also not flow easily into a void.”

________________ MMC-Gamuda asked Herrenknecht to explore such a concept. The task for the company was twofold: firstly to find a way to make a thicker and more dense slurry without inordinate expense and secondly to devise ways to handle it on a TBM. The outcome after much design work and research in conjunction with universities such as Bochum was to use slurry thickened with limestone dust.

To handle this thick, dense slurry meant design changes. For example, the dense slurry requires a concrete pump rather than a normal one. It will not flow easily out of the cutting face chamber to carry the spoil back to the surface. That meant incorporating features from both an EPB machine and a slurry shield TBM. A normal slurry circuit provides the basic face support using a compressed air bubble the same way as in a Mixshield. 

An additional pipeline is needed to bring the much more dense slurry added to thicken the face support. Variable amounts can be added according to ground conditions. But the thicker “paste” this creates at the face will not exit the cutterhead in the usual way by pipe outlet. Therefore a screw conveyor is used in the same way it is used in an EPB machine. This does not discharge onto a conveyor belt for muck removal, but drops the thick material into a special “slurryfier” unit. This first has a crusher box to reduce larger chunks of face rock, and then a mixing unit where thin, or normal, slurry is mixed into the paste. 

With this diluted spoil, the machine can again behave as a slurry TBM. The slurry and its spoil are pumped to the surface through pipes where the spoil is extracted as usual in a separation plant.

________________ An additional advantage of this system is that by changing from slurry to belt conveyance the TBM can quickly be converted to a full EPB directly in the tunnel. The back-up system is provided with a belt conveyor along the length for just this purpose and a small extension conveyor at the front, which is retracted until the conversion is made.

For the Kuala Lumpur project, MMC-Gamuda currently has five of these machines in operation and one more in reserve. It is also using two conventional EPBs from Herrenknecht and two other EPB machines, the last four for drives in the Kenny Hill formation. Each is 6.62 meters in diameter to form the single running tunnels of the new line.

________________ Most of the Variable Density TBMs have now set out, four of them in the Cochrane station box in the southern section of the tunnel route. As with several other stations in the limestone area, an excavation more than 30 meters deep was formed, supported by secant piling in the upper area. This was driven through the overburden, then drilling and blasting was done into the limestone below. The station is the main base for the contractor which has a large, well-appointed work camp nearby and offices, as well as a big separation plant for servicing the four machines. A rank of large silos hold the special limestone-enriched bentonite slurry. 

“Two TBMs headed north, the first starting in May 2013, and two headed south in September 2013” explains Klados. “They have worked well” he says. Two of the TBMs will reach the boundary between the limestone and the Kenny Hill formation on their drives. “They will be converted to EPB mode with dry mucking for the remaining drive” says local Herrenknecht manager Lorenz Nummsen. The work will take only a few days, as the Variable Density Machines are designed for quick conversion.

________________ The first of the machines is already heading north. Meanwhile a second TBM driving from the Cochrane station completed its drive in early January without any serious mishaps, breaking through at a well-publicized event on January 9. Both have made good rates says Klados, averaging around 7 to 8 rings a day and reaching 11 on good days. Rings are 1.4 meter long so this is about 12 meters a day.

“We use a seven segment universal ring with a half segment key” he says “and for the first time in Malaysia, steel fibre reinforcement.” Herrenknecht Formwork precision moulds have been used for the segments which are manufactured by suppliers outside Kuala Lumpur. 

They are delivered to the machines by crane at the Cochrane station excavation and then along the tunnels using rubber tired segment carriers from Techni-Métal Systèmes of France. That too is part of the Herrenknecht delivery, since the firm was acquired by Herrenknecht two years ago.

________________ The contract team is pleased with the performance of the machines, which have proved able so far to control the potential problems that karstic cavities can bring. They are keeping their fingers crossed that the success so far will continue and that the equipment and the experience in using it will stand them in good stead for the next sections of the metro, assuming that the Malaysian government chooses to go ahead.

For Herrenknecht’s local representative Lorenz Nummsen, the progress so far vindicates the new design of machine, particularly for use in karstic ground which occurs in many countries. “Listen, I am a practical engineer not a salesman. But this is the future technology” he says “and not just for limestone. It is suitable for many types of mixed ground.” 

There is a chance that the machines will get further use in KL however, if the next two lines go ahead. MMC-Gamuda will bid if it comes to pass, and believes it has a good chance with its skills and the still almost new TBMs, being stored long term when they finish their work.

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