| The Sichuan-Tibet Railway is located in the southeast of the Qinghai-Tibet Plateau,starting from Chengdu in the east and reaching Lhasa in the west.It is the second"The Heavenly Road"to Tibet after the Qinghai-Tibet Railway.The Layue Tunnel to be built is one of the important components of the Changdu-Linzhi section of the Sichuan-Tibet Railway.The tunnel is located in the northern part of the East Tectonic Knot of the Himalayas,close to the famous Yarlung Zangbo River suture zone,and the area belongs to the Yarlung Zangbo River's great bend tropical zone Its geological structure and geothermal conditions are extremely complicated.According to the on-site investigation,the hydrothermal activities in the study area are very active.Hot springs are exposed at the entrance of the tunnel and on both sides of the river along the southeast side of the line.In addition,the temperature measurement borehole characteristics in the study area further revealed that this area belongs to the geothermal anomaly area.Therefore,it is extremely necessary to study the cause of underground hot water in the tunnel area and the characteristics of the ground temperature distribution in the tunnel crossing section,so as to provide a certain reference for the prevention and control of thermal damage in tunnel engineering.This article first takes the hot springs exposed in the Layue Tunnel area as the main research object,combined with the regional geothermal geological background,analyzes the hydrogeochemical and isotopic characteristics of each hot spring,and studies the controlled factors and formation and evolution characteristics of each hot spring;Then,taking the rock mass of the tunnel crossing section as the research object,using ANSYS finite element software to establish a two-dimensional numerical model of the tunnel longitudinal geothermal field,simulate the distribution characteristics of the geothermal temperature along the tunnel,and predict the rock temperature of each section of the Layue tunnel.The following conclusions are drawn:1)Layue Hot Spring and Pailong Hot Spring on the north bank of Layuequ are mainly controlled by the Yarlung Zangbo River suture zone,and the Changqing Boiling Spring on the north bank of Yulongzangbu is mainly controlled by the Tongmai-Tongdeng fault,which is exposed near the Yigong Zangbu The Jiazhong Hot Spring and Pat Pai Hot Spring are mainly controlled by the Jiali-Yigong Zangbu fault.2)The characteristics of the hydrogen and oxygen isotopes(?D-?18O)of the hot springs in the study area show that atmospheric precipitation and ice and snow melt are the main sources of recharge water for the hot springs,and the recharge elevation is in the range of 4300?4600m,which is analyzed by the silicon-enthalpy mixed model.It is known that there are shallow underground cold water mixing in the hot springs during the upward movement,so the calculated elevation of the recharge area may be lower than the actual.3)Use the method of SiO2 geothermal temperature scale and multi-mineral balance map to estimate the thermal reservoir temperature of each spring point,and use the geothermal gradient method to estimate its circulation depth.Among them,the thermal storage temperature of Layue Hot Spring is in the range of 116.88?142.94?,its circulation depth is about 4800m;the thermal storage temperature of Pailong Hot Spring is between 131.92?156.35?,and its circulation depth is about 5300m;the heat of Changqing Boiling Spring The storage temperature is between 150.61?162.29?,its circulation depth is about 5500m;the thermal storage temperature of Jiazhong Hot Spring is in the range of 94.58?122.75?,and its circulation depth is about 4100m;the thermal storage temperature of the patting hot spring is between 122.60?148.06?,its circulation depth is about 5000m.4)The evolution model of hot springs in the study area:the heat generated by a series of activities accompanying the collision between the Indian plate and the Eurasian plate and the orogenic process is used as the integrated heat source.Deep migration,drawing heat from deep heat sources to form high-temperature hot water,and then due to the influence of temperature and pressure in the deep environment,it will move upward along weak structural regions?such as fractures and dense fissures?and emerge as a spring near the river valley.The hot springs with different exposed locations have different transport channel properties.Due to the differences in the nature of the surrounding rocks,the degree of water-rock interaction,and the degree of shallow groundwater mixing,the temperature and water of each hot spring spot exposed in the study area The chemical characteristics vary.5)The numerical model of the geothermal field along the longitudinal section of the tunnel shows that the Layue tunnel to be constructed has thermal problems in some sections,and the heat source of the thermal damage is mainly controlled by the Yarlung Zangbo River suture zone.The model predicts that the temperature of the surrounding rock along the tunnel is between 10.44 and 81.93?.Among them,Grade V severe thermal damage accounts for 42%of the total length of the tunnel,Grade IV severe thermal damage accounts for 7%of the total length of the tunnel,and Grade III moderate heat damage The segment accounts for 19%of the total length of the tunnel,the Class II minor thermal damage segment accounts for 16%of the total length of the tunnel,and the Class I non-heat damage segment accounts for 16%of the total length of the tunnel. |
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