At 12.9 kilometers long, it is the longest road tunnel in Southeast Asia and the fifth-longest in the world. The Ministry of Transportation and Communications announced June 7 that it would be open to traffic June 16. The tunnel's completion also marks the opening of the Fifth National Expressway, also known as the Taipei-Yilan Expressway. It links metropolitan Taipei with Yilan County in a 40-minute drive, a journey that previously took drivers well over two hours in a route along the northern and northeastern coast of the island.
To many Taiwanese, Yilan is known as a vacation destination, and locals are fiercely proud of their home region. The county government has promoted it as a "garden in Taipei's backyard" because of the unspoiled scenery. For decades, successive administrations in the county government have attempted to link Yilan with Taipei more efficiently in order to promote a more balanced development between Taiwan's east and the west coasts. The new expressway carries with it these high hopes.
According to Tseng Dar-jen, chief engineer of the MOTC Taiwan Area National Expressway Engineering Bureau, the 55-kilometer expressway cuts through mountain areas and river valleys. To facilitate drainage, minimize excavation work and preserve the natural landscape, the expressway is composed mainly of tunnels and viaducts. There are 11 tunnels with a combined length of 20.1 kilometers. All tunnels are two-lane, twin-tube and two-way tunnels, including the Hsuehshan Tunnel.
Tseng explained that the geology of the mountain range posed the greatest challenge to construction, especially the section near the southeastern end, where it is composed of hard, fractured sandstone. In addition, the area is home to various complex fault lines, being the point where the Eurasia Plate presses up against the Philippine Sea Plate. The mountain range also preserves a source of high-pressure water, causing groundwater inflows that submerged the tunnel several times during construction.
According to Tseng, there were 71 occurrences of collapse during the 15 years of excavation. The most serious incident took place Dec. 18, 1997. The cave-in buried an entire tunnel-boring machine under a hill of earth and stone. "Fortunately, all crewmembers managed to escape the area just 10 minutes before the total collapse of the excavation face," Tseng said. He added that the machine was totaled, and the work gang had to resort to conventional drilling and blasting.