Abstract: The unfavourable geological conditions of tunnels of Ya′anNyingchi section of SichuanTibet railway, such as very high stress and soft rock deformation, rockburst, high ground temperature, active fault, high pressure and water rich tectonic zone, etc. are systematically expounded in this paper. Based on the research and analysis of similar tunnel construction experience in China and abroad, the corresponding treatment principle and engineering countermeasures are put forward: tunnels in soft rock subject to deformation should be treated by principle of optimizing tunnel crosssection shape, active reinforcement, deformation control according to deformation grade, and strengthening support; tunnel subject to rockburst should be treated by principle of early warning first, active control, more machines and fewer people, and ensuring safety; high temperature tunnel should be treated by principle of strengthening geological prediction, classified prevention and control of heat damage, comprehensive cooling, reasonable matching materials, and strengthening labour safety; the overall goal for the active fault section is: the tunnel will not be damaged by small earthquakes, it can be repaired after moderate earthquakes, and it will not collapse after large earthquakes, and the treatment principle are: reserve space, optimize cross section, design by sections and promote operation monitoring; the highpressure waterrich tectonic zone should be treated by principle of longdistance prediction in advance, water discharge and pressure reduction in advance, water stopping and drainage limitation in advance, surrounding rock reinforcement in advance, support structure strengthening and monitoring strengthening.

Key words: Sichuan Tibet railway tunnel; unfavorable geological condition, active control, prevention and control according to geological grades, high ground stress, large deformation of soft rock, rockburst, high ground temperature, active fault, high pressure and water rich tectonic zone