Abstract: In view of the collapse and rockfall disaster occurred in the K279 section of the EmeiPanzhihua section of the ChengduKunming railway, the Rockfall software is employed to analyze the rockfall trajectory and impact kinetic energy and assess the damage degree of rockfall to the railway. Furthermore, based on the calculation results of impact kinetic energy, the setting range of the slope curtain protection net and the setting of the passive net and other protective measures are determined, and the extension range of the opencut tunnel is determined based on the impact range of falling rocks. For the extension of the opencut tunnel, an innovative proposal that use the castinplace inner and outer walls of the opencut tunnel and the prefabricated assembly of the opencut tunnel arch ring when adding an opencut tunnel during railway operation is proposed based on the onsite terrain. Finally, the design and construction of the castinplace inner and outer walls of the opencut tunnel and the prefabricated assembly plan of the opencut tunnel arch ring are introduced. According to the final rectification effect, the use of prefabricated and assembled opencut tunnel structures can safely and quickly add opencut tunnel structures to existing lines.

Key words: Chengdu-Kunming railway, collapse and rockfall, prefabricated and assembled open-cut tunnel