Abstract:

The Sichuan-Tibet Railway is a major project being planned and constructed across the eastern part of Tibetan Plateau in China, where is characterized by extremely complex topography and geological structure. The active faults and frequent earthquakes are well distributed along the planned railway line, with ten large-scale regional active fault zones directly crossing or closely distributed along the newly planned Ya’an-Linzhi railway section, such as the Longmenshan fault zone, the Xianshuihe fault zone, and so on, of which the slipping rate could reach up to 10 mm/a, and with high potential risk of strong earthquakes. Under the coupling geological effect of internal and external dynamics, the geohazards are highly developed along the railway line, and densely developed along the Dadu River, Yalong River, Jinsha River, Lancang River, Nujiang River, Yarlung Zangbo River and their first-level tributaries, the active fault zones and the national highway. Especially, the long-runout landslides and geohazard chain, deep-buried creeping landslides, and earthquake-triggered landslides might cause more serious damages, which are the major challenges encountered in the railway construction. The railway is located in high stress environment dominated by horizontal tectonic stress, and there are about five major first-level stress zones along the railway and the adjacent area, i.e.,the south China main stress zone, the Longmenshan-Songpan stress zone, the Sichuan-Yunnan stress zone, the Motuo-Changdu stress zone and the Himalaya stress zone. The maximum principal stress direction of the Ya’an-Kangding railway section is the NWW-NW direction, and deflect into the NNE direction to Linzhi City. The regional stresses show strong differences in plane and vertical space, for example, there is a stress relief zone in the vertical direction of one tunnel revealed by in-situ stress testing results in Zheduo Mountain. Under the high geostress background, there are high risks of rockburst and large deformation in the deep-buried railway tunnels surrounding rocks. The railway construction should take safety distance from active faults, and strengthen necessary measures to monitor, early identify and predict the occurrence of giant geohazards, to measure and predict the geostress,large deformation and rockburst for deep-buried tunnel, which could provide scientific guidances for railway line selection and disaster prevention and mitigation.

Key words: Sichuan-Tibet Railway, geohazard, active fault, geostress, engineering geological problem