An analysis of the genesis and engineering influence of geothermal water in the Kangding tunnel site of the Sichuan-Tibet Railway

The Kangding tunnel of the Sichuan-Tibet Railway crosses the Xianshuihe Fault Zone where geothermal abnormity occurs and is harmful for railway construction. This paper analyzes the genetic mechanism of geothermal waters through the integration of field survey, hydrochemical analysis and D-O isotopic experiments. The results show that HCO₃·Cl—Na and HCO₃—Na types are the main hydrochemical types of hot springs in the Kangding tunnel area, which exists in the Zheduotang, Kangding and Zhonggu geothermal areas. Geothermal waters are immature and the reservoir temperature ranges from 104 ℃ to 172 ℃. Deep initial geothermal waters display the reservoir temperature of 186−250 ℃ and are mixed by 56%−81% of cold water. Hydrogen and oxygen isotopes show that the recharge elevation of the geothermal water ranges from 3768 m to 4926 m. In the study area, geothermal waters are recharged by water source at high elevation. The main fault is the structure of thermal conductivity, and secondary faults and fracture zones are the channel of water migration. Geothermal waters arise and expose as hot springs on the land surface. Simulated geothermal field of 100 m has the temperatures of 35.4−95.1 ℃. Relatively low-temperature channel may be existed among three geothermal areas. High-temperature geohazard induced by geothermal water should be focused in the Kangding area during tunnel construction.