| Qamdo area,as the bridgehead for the crossing of soil between Tibet and Sichuan,is the first natural danger for the Sichuan-Tibet railway.Zilashan traffic corridor starts from Jinshajiang River in the east and ends at Duomuqu in the west.It is located in the tropical zone of Sanjiang Region,and the geological structure and geothermal conditions are extremely complex.According to the field investigation,the geothermal water in the study area was rarely exposed,only in Summer Village at the exit of the tunnel.However,drilling data show that there are geothermal anomalies in the tunnel.Therefore,it is necessary to study the characteristics of ground temperature distribution in the tunnel crossing section in the study area.In this paper,the site of the planned tunnel in Zilashan traffic corridor in Qamdo area is taken as the study area,and the geothermal geological conditions of the study area are determined based on the topography,geomorphology,regional geological structure and hydrogeological conditions of the study area.Satellite remote sensing was used to delineate the distribution range of surface geothermal anomalies,and combined with regional hydrochemical characteristics,the geothermal temperature transmission mode in the study area was explored.Combined with the regional literature and borehole data,the spatial distribution characteristics of the regional geothermal field were identified,and the controlling factors affecting the geothermal field were given.The temperature of the geothermal field at different elevations in the study area was predicted based on the tunnel lines.The conceptual model of regional geothermal field was built by comprehensively utilizing various information of hydrogeological conditions and engineering geological conditions,and the evolution characteristics of regional geothermal field were simulated with numerical simulation methods to reveal the distribution of high temperature and heat damage along the length of the tunnel.The following conclusions are drawn:(1)The remote sensing interpretation of Zila Mountain traffic corridor shows that the geothermal anomaly points are mainly distributed in the west and southeast outside the tunnel site,and the temperature of summer hot springs at the geothermal anomaly points can reach43℃ through field investigation.(2)Based on the analysis of regional hydrochemical characteristics and the origin of summer hot springs,combined with drilling data,it is concluded that there is basically no deep hot water in the tunnel site,and the high ground temperature of the proposed tunnel is mainly caused by the deep buried temperature increase.(3)According to the drilling temperature measurement results,the average geothermal gradient of granodiorite in the tunnel site is 28.3℃/km,and that of gneiss is 8.03℃/km;The average geothermal gradient of monzogranite is 14.82℃/km.(4)The measured drilling temperature curve in the study area shows that the temperature in the study area is positively correlated with the depth as a whole,and the underground coldwater convection in some Wells decreases first and then increases.The vertical distribution of geothermal gradient in the study area shows that the geothermal gradient increases slowly with the change of depth,and the degree of local rock fragmentation fluctuates greatly.(5)The temperature distribution in the study area is mainly controlled by stratigraphic lithology and thermal conductivity active faults.Different thermal conductivity of stratigraphic lithology leads to different heat transfer rates,and thermal conductivity faults provide good thermal conduction channels for deep heat sources.The study area is less affected by shallow cold-water circulation,which is a secondary factor.(6)Using the fitting equation of drilling curve to predict the deep ground temperature in the tunnel site,the temperature at the abnormal point of ground temperature at 3055 m elevation can reach 54℃,and the temperature at the abnormal point of ground temperature at3388 m elevation can reach 42℃.(7)According to the numerical simulation results of the temperature field in the tunnel site area,the high temperature heat damage section of the tunnel is mainly in the mileage D4K724～D4K733 section.The highest temperature of the tunnel body can reach 52℃,and this section is also the area with the largest buried depth in the whole section of the tunnel.In the classification of heat damage,it belongs to slight heat damage ～ severe heat damage.The rest of the mileage section is lower than or slightly higher than the 28℃ geothermal line. |
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