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Metro mania

Tunnelling - Taiwan metro

Typhoons and recession have had little effect on Taiwan's ambitious metro projects, says Adrian Greeman.

Despite devastating floods which knocked out sections of the brand new Taipei line last September, the Taiwanese seem to like their metro.

It had been open less than two years when the electronics in the main control centre failed after 850mm of rain per day swelled the city's rivers during a three day typhoon. It took several months to get running again.

Now passenger levels are high once more, and the country is looking to build more lines.

Crowded capital Taipei is currently adding another 24km of line, and in the south Taiwan's second city Kaohsiung has begun work on the first two lines of a 40km four line network. Several other cities are investigating light rail systems.

Taiwan has been one of the strongest economies in Asia and despite the 1997 currency meltdown and recession, or perhaps to help counter it, government is putting several billion dollars of its trading surpluses into the work. But in a sign of the times, it is also looking to the private sector for more involvement and the US$6bn Kaohsiung scheme is to be a partial BOT project, albeit with a large element of government funding.

'In Taipei too there is also to be 50% private investment on a new line being planned for the main airport, ' says Alex Wei Wang, section chief for planning at the Department of Rapid Transit Systems (DORT). Chiang Kai Shek International Airport is 35km outside the city and currently connected by highways which are frequently congested.

The airport line is part of the long term second phase of the city's metro, which will eventually stretch to 200km by 2021. It is possible some of the other planned lines will also look for private investment too, Wei Wang believes, because there is 'not enough in the budget'. First phase lines, running 90.5km, have been funded jointly by city and national government. The system currently carries 900 000 people daily, and numbers are expected to grow to 1.4M.

Some of the second phase lines have already been approved and design work has begun at DORT for alignment and basic designs. Construction focus at present, however, is on the central blue line - so recently flooded - which is being extended into the city's western Panchiao district.

Work on this extension had been held up for about a year by local opposition, in particular fears of earthquake problems in the wake of the huge '9/21' event which devastated the country in September 1999. Tunnelling is now under way (see box).

'The whole 7.2km section is underground including six stations and a 20ha ground level depot area, ' says Wang. There are two main contracts, one with Continental Engineering Corporation and the other with RSEA Engineering Corporation, Taiwan's biggest contractor.

Just over 350km to the south, 14 contracts are beginning or in the process of being let for the first two lines on the NT$200M ($6bn) Kaohsiung metro, all of which will run at the same time.

'And that will be our main problem, ' says Sati Bhogal, project manager for British consultant Mott MacDonald which is quality control engineer for the scheme. 'We shall soon have 22 TBMs operating.'

His team and the 150 or so strong group from its city government client, the Department of Kaohsiung Mass Rapid Transit (DOKMRT), must check, validate and monitor design and construction, to be carried out by BOT concessionaire Kaohsiung Rapid Transit Corporation.

This multi-firm joint venture is led by China Steel Corporation and includes RSEA Engineering Corporation, Taiwan Trade Bank and others, cement companies and other contractors.

'The concessionaire is in turn letting the contracts as design build projects, ' explains GwanShyong Wang, chief engineer for DOKMRT. 'We have set out the overall design and construction plan that they have to follow. We have to see they are keeping the project on track, on budget and time and that they follow construction specs, safety and risk management.'

It will mean a busy time, he says, and one of his problems will be attracting sufficient engineers to the project at a time when the high speed rail scheme is in full swing (NCEI May).

The system must be 'modern and comfortable', he says, using Taipei, Hong Kong and Singapore as its references. It will feature full platform screen doors for example, mainly because of air conditioning requirements of Kaohsiung's semi-tropical climate. Hong Kong MRT is operational consultant to the project along with Taipei DORT.

Sinotech was the basic designer and Siemens is also involved as systems adviser.

The municipal authority to which DOKMRT belongs should have a substantial say. Though described as a BOT, the bulk of the money comes from city and central government - some NT$170M covering the whole civil engineering infrastructure.

Without that level of funding it would not have been possible to get the project off the ground, thinks Wang. Taiwan is also concerned to boost Kaohsiung, at present the world's third largest container port but facing stiff competition from mainland China.

Passenger numbers of 700,000 daily are expected by 2020, though figures will be less when the first two lines open in six years time. The concessionaire initially sought a subsidy if numbers fell short of projections, 'but it is their risk', says Wang.

Construction is not expected to present any problems. Kaohsiung is spacious with wide streets - often 60m or more. There is plenty of room for cut and cover work on stations, and tunnelling, some 20m below ground, will follow the line of the streets, seldom affecting buildings. Ground is alluvial; mixed sand and silt with some clay in places. The 5.7m internal diameter tunnels will be lined with precast concrete segments.

'The only difficult part could be a section of limestone at the end of one line, ' says Wang. He thinks this will be tackled with NATM, though a final decision has yet to be made. The bulk of the contracts are currently being let, though some half dozen have been under way since early this year. The only visible sign of major construction are the diaphragm walls for the first of the eight underground stations on the Red Line and the 14 on the Orange line. A further 15 stations will be at grade.

Extension progress

A little bit of gravel mixed in with the sands and clays of the Taipei alluvium has slowed progress on the third drive for the CD 550 contract on the Blue Line Tucheng extension.

'We cannot push too fast because the torque rises too high, ' says site supervisor Jeff Lan for the Continental Engineering Corporation. The team is working with a pair of perfectly good Mitsubishi EPB machines to drive the 5.4m internal diameter twin tunnels, he says, but these were designed for the typical soft clay and sand of the area, with a fairly open six-armed star configuration.

The patches of harder stones did not show up in the ground investigation.

Instead of a hoped for six to 10 rings daily on the 266m drive, the team is so far achieving only four, though he hopes progress will speed up.

Tunnelling is actually fairly straightforward Lan claims, with the main problems being a high water table and the presence of buildings close to or above the tunnel line. 'We have 24 big dewatering wells to reduce pressures but are still beneath the water level, ' he says.

Ground conditioning with chemicals is used to make the sand more cohesive and, with no gravel, progress is good. On an initial 400m drive the two machines each achieved 10 rings a day, he says, despite the discovery of timber remnants in the ground. These were dated at 400 years old and are thought to be river debris from a sedimented watercourse.

For the shorter drive, which connects to the next contract, a single machine is being used heading south from the cut and cover Nanxi station and then U-turning at a reception shaft to drive the parallel tunnel.

It will then set out on the second bore of the central section; the longest at 1077m. Great care is needed as the twin tunnels pass under a 12 storey Agricultural University building, at one point just 3m below a three level basement.

Lan says extensive instrumentation, with marker points on many of the buildings, has been installed and so far there have been no problems.

Below ground the tunnellers are using a pressure monitoring system to check the annulus grouting pressure behind the machine: a secondary gel grout injection system carried out through holes eight rings back allows for compensation if ground movement is detected.

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