Geology and Geological Aspects of Taiwan High Speed Rail Project
The Taiwan High Speed Rail Project refers to a new 345 km (220 miles) line designed for train speeds up to 350 kph, a US billion costing fully electrified domestic passenger railway. Completed in early 2007, the Taiwan High Speed Rail Project is one of the largest infrastructure projects undertaken in Asia ever. It stretch largely on elevated structures and connecting Taipei, the capital city in the North and Kaohsiung, the second largest city in the South through a 90 minute journey time as it basically aimed to improve travel times. According to Saleem (2006), the railway passes through or close to Taiwan’s main cities, manufacturing areas, and business and administration centers, crossing a mix of agricultural land, freeways, rivers, military bases, residential areas and open countryside.
The geological conditions in the project area are extremely variable, as Change, Lemke and Noda (n.d.) put it. This is because the ground conditions along the line range from weak sandstones and conglomerates to sands, silt and clay and exacerbated by the presence of groundwater up to 80 m. The high seismic activity encountered on the island poses significant challenge to the construction. Taiwan shares similar earthquake characteristics with Japan, with an average return period for seismic events in excess of Richter scale 6 to 15 years. The Linkou Tunnel in particular could encounter crushed rock comprising gravel and cobbles that are embedded on weakly cemented silty and sand matrix. On account of the groundwater table which is located up to 80 m above the tunnel as well as the relatively high permeability of the materials. As expected problems could occur in conjunction with groundwater and the presence of sand layers which could adversely affect the stability of excavation. Therefore, controlling the groundwater is important.
Taiwan High Speed Rail Project was built and implemented through a Build Operate Transport Model which introduces Japan’s latest Shinkansen technologies. This five-year construction project conducts a construction railway operational readiness planning which separates major contract areas during the design and construction phase such as civil works; stations; depots and depot equipment; track works; core system, and automatic fare collection system and related contracts. One of the challenges to the High Speed Rail Project civil works includes tunnels and viaduct and bridges. The system has more than 50 tunnels, 39 of which are mined tunnels. The three longest tunnels are: Paghuashan Tunnel, 7.4-km (4.6-miles) long; Linkou Tunnel, 6.4-km (4.0-miles) long and Hukou Tunnel, 4.3-km (2.7-miles) long. Further, there are no vertical low points except in those tunnels in urban areas and number of high points are minimized.
Shallow and deep foundations are the commonly used foundation systems in Taiwan to cater for the various types of subsoil conditions. Bored piles installed by reverse-circulation method due to its popularity, efficiency and availability in Taiwan are widely used in the High Speed Rail Project. More than 30, 000 piles were installed. Due to significant variations in ground conditions, different construction methods also were adopted for the installation of piles along the route. In these ground conditions, the bored holes would have to be protected by casings, and hammer grab (within gravel layer) or drilling bucket (within rock) would need to be used for excavation. For the southern 155 km-segment of the route, over 20,000 bored piles with diameters of 1.5 to 2 m and lengths of 35 to 72m have been installed to support the viaducts. Rotary bucket type of drilling also was used in one of the contract sections for pile installation for pile length not exceeding 60 m in sedimentary deposits (Chin and Chen, 2007).
All tunnels have a cast in-situ reinforced concrete lining over the length. This was designed to prevent deterioration of the rock and to support the rock mass. For the drained tunnel, the lining either forms a controlled path to duct any groundwater to an invert drain while for undrained tunnels, lining is designed to prevent water from entering the tunnel. Inherently, the tunnels encountered geological conditions that vary between soil, gravel and sedimentary rock, or the combination of these conditions. These are excavated mechanically and are either mined or cut-and-cover type. The mined tunnels were advanced using sequential excavation and support construction method, considered to be the most suitable excavation considering the size and geometry of the tunnels.
For the viaducts, design and construction integrates bored cast-in-place piled foundations, or footings supporting single or multiple reinforced concrete columns, with piles pile caps and columns that are constructed in-situ. Deck beams/guideways were either pre-cast or cast-in place. Multi-techniques was incorporate consisting of full-span pre-cast launching method, free cantilever method/balance cantilever method, movable scaffolding system/advance shoring method, and full support method. Moreover, twelve steel truss bridges are distributed across the railway that is comprised of 17 pans for a total length of 2533 m (8,310 feet), with the majority are having spans ranging from 55 m to 150 m (180 feet to 497 feet) to satisfy specific site conditions, such as crossings for significant highways, railways, rivers and ravines (Saleem, 2006).
Because of Taiwan’s unique geographic features, the route crosses three active earthquake faults, one of which is the Tuntzuchiao Fault. Hence, there is a potential for soil liquefaction in specific areas and tunneling conditions are also difficult in a mountainous sub-tropical environment with dense forestation (Saleem, 2006). To address the safety level earthquake, the bridge comprised of a 55 m span steel truss with 30 and 35 m concrete approach spans was designed for a 95o year return period ground motion. The features of the bridge include the utilization of large pier caps and abutment settings, allowing the bridge to be moved and reseated after fault rapture and the use of large monopile foundations instead of multi piled caps (Seismic Design and Assessment Procedures for Bridges).
References
Case Study – Rail Services: Taiwan High Speed Rail Project.
Chang, M F, Lemke, M and Noda, J n.d., Taiwan High Speed Rail Project C210 – Sealing work under difficult conditions in seismically affected ground.
Chin, C T and Chen, J R 2007, Foundation Engineering Practice in Taiwan – High Speed Rail Experiences, The state of the practice geotechnical engineering in Taiwan and Hong Kong, pp. 28-51.
Design for Active Fault Crossing, Seismic Design and Assessment Procedures for Bridges, retrieved on 27 March 2009, from http://seismic.cv.titech.ac.jp/committee/FIB/PDF/5-Chapter8.pdf.
Saleem, A 2006, ‘Taiwan’s High Speed Rail: Technical Challenges,’ Engineering System Solutions, vol. 21, no. 63, p. 2.
Sources of Images:
http://seismic.cv.titech.ac.jp/committee/FIB/PDF/5-Chapter8.pdf
http://www.daiho.co.jp/english/fpd/taiwan/taiwan.htm
www.hochtief-construction.de/…/35.jhtml?all=1
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