Abstract：Due to the developed columnar joints in basalt III1 around the diversion tunnel at Baihetan Hydropower Station along the Jinsha River，the relaxation and failure of basalt with columnar joints during the excavation had the severe influence on the personnel and construction progress. Microseismic monitoring technology was utilized during the excavation of columnar jointed basalt. Along the tunnel，the microseismic activity in columnar jointed basalt was found to obey the Logistic(3P) distribution. Three typical microseismic activity zones in columnar jointed basalt along the tunnel near the working face were obtained，i.e.，a strong unloading area，a comprehensively influenced area and a time relaxation effect area. Rock bolting should be completed in the strong unloading area. In the period of working face around the researched area，the fractures developed rapidly into the inner rockmass. When the working face was far away，the microseismic activity in the sidewall was weak. Meanwhile，the area of micro-fracture concentration stabilized in the ranges of 6 meters in sidewall finally. A low excavation rate weakened the influence of unloading of excavation on columnar jointed basalt.
2015, Vol. 34 
