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Taiwan is an island subject to frequent earthquakes and typhoons. Besides taking into consideration the many earthquakes, wind storms, and torrential rains that affect the western corridor of Taiwan, the HSR route is intended to be generally straight, and is also designed to promote balanced regional development while minimizing impact on the environment and natural ecology. In order to ensure safety at operating speeds of 250 to 300 kph, the HSR route avoids earthquake faults and soft ground as much as possible.
The HSR route complies with very high project design standards. The four types of track structures consist of elevated structures, tunnels, embankments, and cuts. The relative proportions of these structures are shown in the following table:
Mountain tunnel/cut and cover tunnel
The HSR project has a full length of 345 kilometers, of which elevated structures accounts for approximately 70% or 251 kilometers. The entire section to the south of Mt. Pakua in Changhua County--approximately 157 kilometers in length--is built as an elevated viaduct. It has set a new Taiwan record for length of continuous viaduct.
HSR viaducts are designed to ensure safety, comfort, and live load capacity while trains pass at high speeds, and the dynamic interaction of track and viaduct are also taken into consideration. As much as possible, viaduct type and span design has adopted uniform prestressed concrete box-beam viaducts with identical cross-sectional size. A standardized simple supported beam viaduct with a span of 30 meters has been chosen. The viaducts have a width of 13 meters, a depth of approximately 2.8-3.15 meters, and a weight of approximately 700 tons. In order to shorten construction time and achieve cost reduction, roughly 95% of the HSR line's elevated structures consists of these standard viaducts. In addition, long-span or continuous multi-span prestressed concrete box-beam bridges, steel bridges, or other non-uniform bridges are employed wherever the line crosses major roads, rivers, or valleys, and in turnouts and crossovers. These sections account for approximately 5% of the HSR line's elevated structures. The following diagram shows the standard viaduct cross-section.
The HSR's drilling tunnels are all constructed using the New Austrian Tunneling Method (NATM). They are single-hole, two track tunnels with double- or triple-heart shaped cross-sectional areas. The cross-section of the tunnel has a height/width area of approximately 0.91; a nearly round cross-section maximizes tunnel stability. HSR tunnels are approximately 13.5 meters in width and 11.7 meters in height; cross-sectional area is roughly 130-140 square meters. In consideration of the dynamic movement of air in a tunnel when passing at high speeds, the net cross-sectional area above the track is 90 square meters. In order to prevent loud, sudden sonic boom when a train exits a tunnel, tunnel mouths have a 45° sloping design. When the tunnel length is greater than three kilometers in length, a pressure relief section is added at entrances. There are openings at two places in the tops of these sections to allow for gradual dispersion of air pressure fluctuations, and there are drifts or shafts to serve as emergency escape routes. In order to avoid affecting the local hydrology, tunnel designs include non-draining tunnels with full waterproof membranes and draining tunnels with half waterproof .
Mountain tunnels and cut and cover tunnel sections are mainly located in the Taipei, Taoyuan, Hsinchu, Miaoli, Taichung, and Changhua areas. Tunnels mainly pass through strata consisting of sandstone, shale, interbedded sandstone and shale, and gravel in the western foothills. There are a total of 63 tunnels, of which four are long tunnels. The Linkou tunnel (6,456m) and Mt. Bagua tunnel (7,360m) pass through gravel layers. The Hueilong tunnel (2,158m) and Hukou tunnel (4,292m) pass through sandstone and shale. The structure of these tunnels includes a lining, track, a walkway, and cable conduits; the standard tunnel cross-section is as shown in the following diagram:
The HSR's roadways consist of roadbeds built on a soil foundation and supporting the track bed. The track beds receive a special treatment in order to withstand and distribute force from the track structure. In order to avoid interrupting traffic on both sides of the HSR line when trains pass, embankments or road cuts account for only roughly 10% of the HSR's length and are used to mitigate impact on the natural environment.
Where the earthworks meets bridges and tunnels, technical backfill is used to compensate for the differential settlement of different structures and rapid changes in stiffness. In view of the fact that faults may cause seismic vibrations and dislocation of the ground surface, appropriate protective facilities have been installed where the route pass active faults. For example, in the embankment section where the route passes the Tunzijiao fault, the edge of the embankment is equipped with a safety mound to keep the train from rolling and leaving the right-of-way.
The HSR route’s embankment and cut sections are mainly located in the Taoyuan, Hsinchu, Miaoli, Taichung, and Changhua areas. These sections mainly pass through strata consisting of sandstone, shale, interbedded sandstone and shale, and gravel in the western foothills. The structure of these sections consists of tracks, track bed, road bed, foundation, and side slopes. The standard tunnel cross-section of embankment and cut sections is as shown in the following diagram: