|CHEERS Wei-Chaung Lee and RESA team toast a hole-through that took 12 years eight more than scheduled. (Photo courtesy of RESA)|
Taiwanese engineers showed relief as much as pleasure at completing the pilot drive on what they say is South East Asias longest highway tunnel. After battling nearly eight years longer than planned, the pilot tunnel boring machine holed through last month on the 12.9-kilometer-long Pinglin tunnel on the emerging expressway between Taipei and Ilan, on the islands northeast coast.
"Its a thrill," says Wei-Chaung Lee, deputy project manager with tunnel contractor RSEA Engineering Corp., Taipei. He admits also to being "fed up" at the years of "struggle" against treacherous rock that has plagued the project with torrential leaks. With the nearly 5-meter-dia pilot now in, he hopes no more shocks lie ahead. The two main tunnels should hole-through by next fall, some six years late, he says.
The Pinglin is the longest of several tunnels on the 55-km expressway. Most of the road is elevated in mountain terrain. State-owned RSEA negotiated a contract for the pilot and another for two main drives, set 60 m apart, with the governments Taiwan Area Expressway Engineering Bureau (TANEEB). The pilot began in 1991, partly to probe ahead for the main drives. Completion was expected in 1995, but the job has "lasted 12 years," laments Wan-Ning Liu, an RSEA vice president.
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The problem: numerous, hidden, water-bearing fissures in the variable sedimentary rock. Site investigations revealed the main faults, but not smaller breaks, says Lee. Hitting many leaks, the Robbins TBM was out of action more often than not. In 1993, two German-built 11.7-m-dia main drive TBMs set off through the difficult rock. Trouble was a near certainty.
"The major disaster happened in the west-bound tunnel," says Lee. In December 1997, water burst through the lining at 740 liters per second, burying the shield in some 100 m of muck. Lee says efforts to resume were abandoned after nearly two years. The contractor turned to drill and blast. A small bypass tunnel driven to the TBM for its rescue let tunnelers secure the face and begin scrapping.
To safeguard the east-bound drive, a similar bypass was driven so the top heading could be drilled and blasted. This lets slow-moving TBM operators spot trouble ahead, explains Lee. Meanwhile, other crews are drilling and blasting both main tunnels from the opposite ends. With over 90% of the westward drive and about 75% of the eastbound complete, final breakthroughs are due next year, says Liu.
RSEA, meanwhile, has received change orders worth about 15% of the roughly $680 million in contracts, adds Liu. But unless more is provided, the firm faces a loss on the job, he says. With RSEAs privatization due next summer, observers suspect the government will be kind to Taiwans largest contractor.
In hindsight, using TBMs now seems questionable. Sung-Maw Lin, a project resident engineer with Taiwan High Speed Rail Corp., recalls advising drill and blast 20 years ago as part of an international consultants team. But the consen-sus favored TBMs, according to TANEEBs director, Cheng Wen-Lon. In a recent report, he wrote: "During construction, well-known experts and experienced consulting firms had been invited to study and evaluate...the adopted construction. Selecting TBM construction is considered the appropriate choice."