Abstract: The Layue tunnel of the SichuanTibet railway is influenced by geothermal heat. Thus, geothermal and geological structure surveys, borehole explorations, and temperature measurements are conducted to obtain the optimal tunnel route and to avoid hightemperature hazards. Then, the distributions of the geotherm and geothermal gradient are determined. By analyzing the influence of groundwater upon the geotherm, the principles of line selection are determined. The geothermal test data and geothermal curves show that: (1) High geotherms are a common hazard in the test area and the maximum measured geotherm and geothermal gradient are 93.5 ℃ and 40 ℃/100 m, respectively; (2) Obvious stratification characteristics exist in the vertical direction of the geothermal gradient, and the difference in this plane is closely related to the structure, topographic cutting, and elevation. Based on 〖JP+1〗this analysis, it is recommended that the line should be built far away from the Yarlung Zangbo River suture zone, and that the altitude of the line should be elevated to reduce hightemperature hazards. According to the established geothermcalculation formula based on constanttemperature surface, constanttemperature layer thickness and geothermal gradient, it is predicted that there might be a section with a severe geotherm above 60 ℃ in Layue tunnel.

Key words: SichuanTibet railway, east syntaxis; Layue tunnel, Milin fault, geothermal gradient, geotherm prediction, hightemperature hazard