Difficulties in Sichuan-Tibet Railway Construction
- Chinese keyword
- railway works; Engineering geology; Bridge engineering; Tunnel Works
- English keyword
Sichuan-Tibet railway starts from Chengdu and reaches Lhasa via Ya'an, Kangding, Qamdo, Nyingchi and Shannan. The main line is about 1740km long. Under the arrangement and guidance of China Railway Corporation and relevant ministries and commissions, and with the strong support of departments at all levels in Tibet Autonomous Region and Sichuan Province and local governments along the line, the construction of the eastern section of sichuan-tibet railway from Chengdu to Ya'an, which is 41.2 km long, started at the end of 2014. The western section of Lhasa to Nyingchi is 403.1 km long and construction started in June 2015. The length from Ya'an to Kangding in the middle section is 294.7 km, and the revision of the project feasibility study has been completed. The most complicated and dangerous section from Kangding to Nyingchi is 998.6 km long and is currently in the pre-feasibility study stage.
Sichuan-Tibet Railway is a long trunk line built in the region with the most active neotectonic movement in the world. It faces four environmental challenges: "significant terrain elevation difference", "strong plate activity", "frequent mountain disasters" and "sensitive ecological environment". Railway engineering geological problems are prominent, there are many restrictive factors in route selection, and the amount of bridge and tunnel projects is large. It is the most difficult and risky railway project in the world.
The Sichuan-Tibet Railway travels along the Qinghai-Tibet Plateau where the Indian Plate and the Eurasian Plate collide and uplift, Through Hengduan Mountain, Nianqing Tanggula Mountain, Himalayas and other three mountain ranges, across the Yalong River, Jinsha River, Lancang River, Nujiang River, Yarlung Zangbo River and other five major water systems, the altitude climbed from 500 to 5000m, the route is eight and eight volts, the terrain is high in the northwest and low in the southeast, the canyons are in line, and the snowy mountains are piled up. Along the line, it passes through four primary tectonic units and eleven secondary tectonic units. Plates are strongly compressed and neotectonic movements are active. It passes through seven Holocene active faults. Earthquakes are frequent and strong. Stratigraphic ages are distributed from Sinian to Cenozoic. Railway construction faces tunnel rockburst, large deformation, high temperature boiling water above 90 ℃ and high temperature steam under high ground stress value of more than 60Mpa, which is unprecedented in the history of engineering construction in the world. The huge scale of unfavorable geology is even more prominent along the Sichuan-Tibet Railway. Hundreds of millions of cubic meters of huge landslides and ultra-high dangerous rocks with elevation difference of thousands of meters are widely distributed and have huge impact energy, further causing difficulties in geological route selection and engineering construction. The severe climate with great temperature difference has led to further deterioration and fragmentation of rock mass. Geological disasters such as glacier flow, rock flow and glacial lake outburst are not only large in scale, but also the valley disaster chain such as blocking rivers formed in the canyon area has further increased its destruction scope and destructive power. Complex geological environment disasters under the comprehensive action of internal and external dynamics have a great impact on railway construction and operation safety, and a series of new rock mechanics and engineering problems need to be solved.
In order to cross the 1,000-meter V-shaped deep canyon, avoid geological disasters, reduce engineering risks and reduce the length of the extension line, Sichuan-Tibet Railway plans to adopt 600m arch bridge and over 1,000-meter suspension bridge. At present, the maximum span arch bridges built or under construction at home and abroad are not more than 500m, and the maximum span suspension bridges under construction are 660m m. The reasonable structural form, rigidity control, influence of structural deformation on driving, seismic performance, construction scheme and other technologies of super-large span arch bridges and railway suspension bridges are all difficult problems in the world. Sichuan-Tibet Railway needs to arrange several bridges near more than 10 strong active fault zones such as Longmen Mountain and Xianshui River. The large amplitude of near-site vibration, the remarkable characteristics of long-period pulses and the obvious vertical earthquake components cause great damage to the bridge structure, and there are few related researches. The design risk of the bridge in the near-site earthquake area is extremely high. Under the harsh environmental conditions of high altitude, high cold, large temperature difference and strong ultraviolet rays along Sichuan-Tibet Railway, concrete bridges will appear chapped concrete, frost heaving cracking, harmful ion erosion and steel bar corrosion. Steel structure bridges are prone to low temperature fatigue damage and steel coating aging, which pose a serious threat to the operation, maintenance and durability of bridges.
There are a large number and scale of deep-buried long tunnels in Sichuan-Tibet Railway, which is rare in the world. Sichuan-Tibet Railway is located in the strongly compressed Himalayan orogenic belt, and the horizontal in-situ stress field value of tunnel engineering is generally relatively high. The construction of extra-long tunnels crossing Erlang Mountain, Zheduo Mountain, Gaoersi Mountain, Sharuli Mountain, Haizi Mountain, Mangkang Mountain, Yela Mountain, Boshulaling Mountain, Sejila Mountain, etc. with a buried depth of 1,000 ~ 2600m will face severe challenges of high in-situ stress. Kangding, Litang-Batang, Jinsha River, Zuogong-Dongcun, Bomi-Tongmai and other regions are the regions with the strongest geothermal activities on the mainland of China. Highland temperature and high temperature hot water have great influence on tunnels. The Sichuan-Tibet Railway Tunnel Project is basically located in a special geographical location such as high mountains, inaccessible, harsh climate and high altitude. Environmental geology is special, High environmental protection requirements, deep and long construction auxiliary tunnels and difficult layout, long construction ventilation distance, coupled with the coupling of complex environments such as ultra-high buried depth, extremely high ground stress, ultra-high ground (water) temperature, active faults, strong unloading of deep rock mass, high water inrush risk, etc., make the tunnel construction, operation, maintenance and disaster prevention and rescue system face great challenges.
After the completion of Sichuan-Tibet Railway, in order to ensure the safety of railway operation and maintenance, it is necessary to combine "Internet plus" with modern monitoring and identification technologies to study the monitoring and early warning and full information coverage technologies for the construction safety of major railway infrastructure, so as to provide full life cycle services for the construction of Sichuan-Tibet Railway.
Sichuan-Tibet railway is of great significance in China's road network planning. Sichuan-Tibet Railway is an important passage into and out of Tibet. Upon completion, it will bear more than 48% of the passenger traffic and 41% of the freight traffic in and out of Tibet, and completely change the backward transportation conditions in Ganzi Tibetan Autonomous Prefecture in western Sichuan, Qamdo, Nyingchi and Shannan regions of Tibet. Sichuan-Tibet Railway is also an important national defense trunk line.
Sichuan-Tibet railway is also the main line for the construction of "the Belt and Road Initiative" facing South Asia, "connecting inside and outside" and realizing the interconnection between China and the South Asian subcontinent. The research results of Sichuan-Tibet Railway's construction technology can provide scientific basis and engineering experience for China-Pakistan Railway, China-Nepal Railway and other outbound railways on the southern edge of the Qinghai-Tibet Plateau, and inspire ideas and point out directions for railway construction in similar complicated and dangerous mountain areas.