| This thesis takes the Sejila Mountain tunnel site as the research area,and takes the high temperature thermal damage of the tunnel in the area as the research object.On the basis of indepth understanding of the geological background in the study area,combined with the field survey of the Sejila Mountain area of Sichuan-Tibet Railway,the geological structure background,the distribution law of hot springs and the inversion temperature of Landsat8 thermal infrared land surface are systematically analyzed in this area.It is found that the study area is close to the Yarlung Zangbo suture zone,with strong tectonic activity in the area,but no hot springs are exposed,and no abnormal temperature is seen on the land surface.According to the temperature measurement data of boreholes in the study area,polynomial curve fitting and temperature prediction were carried out using the principle of least square method in statistics.The average geothermal gradient in the tunnel site area was found to be 0.55 ～ 4.10℃/100 m.The analysis of the curve characteristics of the temperature measuring hole shows that the lithology,geological structure and hydrogeological conditions in the study area have a control effect on groundwater,which can change the local temperature of the tunnel site,thus affecting the curve characteristics of the temperature measuring hole and the average geothermal gradient revealed by the borehole.On the basis of analyzing the measured and predicted values of borehole temperature measurement,the Kriging interpolation method is used to study the spatial distribution law of ground temperature in the tunnel site,and the ground temperature at the bottom of the tunnel rail is predicted in sections,and the heat damage grade is divided.The results show that the temperature of the tunnel track bottom in DK1225+500 ～ DK1227+500,DK1232+000 ～ DK1243+100 and DK1247+500 ～DK1250+500 mileage sections is greater than 28℃ and less than 37℃,which belongs to the grade of slight heat damage,and the other mileage sections are no heat damage.Combined with the comprehensive analysis of the geothermal gradient,structural geological conditions,characteristics of hot spring water system,surface temperature,classification of tunnel heat damage and topographic conditions of the tunnel site,it is concluded that the high ground temperature in Sejila Mountain tunnel site is mainly caused by the depth of burial,and there is no high temperature heat damage caused by structural geothermal anomalies.Finally,the finite element two-dimensional steady-state thermal analysis numerical simulation method is used to simulate the ground temperature at the bottom of the tunnel rail.It is found that the high temperature heat damage section predicted by the tunnel ground temperature is consistent with the high temperature heat damage section length and temperature range simulated by the tunnel.It shows that the method of establishing the ground temperature field in the research space is feasible,and the results of the tunnel ground temperature segmentation prediction are accurate.Based on the results of the prediction of the thermal damage classification of the ground temperature at the bottom of the tunnel rail,reasonable prevention measures are given. |
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