Abstract:

The average cover depth of the tunnels of Jinping II Hydropower Station ranges from 1 500 m to 2 000 m. These tunnels have high ground stress and complex engineering geological conditions. Rock burst, groundwater with superhigh pressure and large flow rate, and large deformation occurring during the construction of these tunnels are worldwide difficult problems. The difficulties in the construction of the deepcovered tunnels of Jinping II Hydropower Station are discussed in the paper. The main contents of the study are as follows: 1) The principle of “taking waterstopping as the main measure, with water releasing as the assistant measure” is followed. Water coping technologies, such as guided water drainage, local water stopping, high pressure grouting, and water releasing through distributary tunnel, are used. 2) The prevention and control of rock bursts are discussed in terms of “taking prevention as the main measure” and “taking the control as the main measure”. The technology of distress blasting and rock burst prevention in TBM tunneling are discussed with emphasis. 3) The causes and countermeasures for serious deformation of soft rock mass are analyzed. The determination of the diameter the enlarged top heading of the tunnel and the strengthening support made before tunnel bottom excavation are discussed with emphasis. 

Key words: Jinping II Hydropower station, deepcovered tunnel, groundwater with superhigh pressure, rock burst, serious deformation