Abstract: The classification of engineering rockmass is a most basic content in rock mechanics and rock engineering application research area. However, current applied rockmass classification system doesn’t cover the rockmass classification method for surrounding rockmass under special geological conditions, such as high ground temperature and high temperature gradient. On background of a hydropower station construction in south Xinjiang, a segment of diversion tunnel with high ground temperature is chosen for surrounding rockmass classification research. On the basis of field geological mapping, in-situ acoustic test and laboratory rock mechanics test results, the RMR, GSI, BQ and HC systems are applied respectively to the rockmass classification and rockmass quality evaluation for the research segment. According to actual surrounding rockmass grade as well as qualitative and quantitative grading results, the influence factors and threshold indexes of high ground temperature are proposed. The evaluation method of surrounding rock quality method of tunnel under complex geological conditions is obtained. Results show that the rockmass quality evaluation grade results with the proposed method are reduced by 1/4~1/2 grade, much closer to the actual grading results.

Key words: classification of engineering rockmass, RMR, GSI, BQ, HC, high geothermal gradient, influence factors