RESEARCH ON TBM TYPE-SELECTION AND KEY CONSTRUCTION TECHNOLOGY FOR JINPING II HYDROPOWER STATION

Jinping II Hydropower Station is characterisized by the four diversion tunnels which are very long and deep-buried.Two of the tunnels are excavated with open-type hard rock tunnel boring machine(TBM) which has an excavation diameter of 12.4 m,the 2nd largest of the same type in the world.The hydrogeological conditions at the tunnel site are very complicated.Three key problems might be met during tunneling,including the forecast and treatment of the groundwater,the ventilation,and the prevention of rockburst.Based on the study of a large amount of data and project case studies of the TBM development,the development of TBM over the past 50 years,its use in tunneling and the encountered problems,are summarized.Based on the research and analysis of the regional geological conditions,main engineering geological problems,and TBM construction experiences at home and abroad,the TBM type selection and tunneling method in case of rock unstability,high geostress and rockburst,water gushing,karst cavity,harmful gas,fractural zones,etc.,are studied.Construction strategies are suggested for TBM tunneling in Jinping II Hydropower Station in case of different unfavourable geological conditions;which hopefully would also benefit similar future projects.