Abstract: Tunnel boring machine(TBM) should face the risk of very strong rockburst directly in intact and brittle rock mass section with ultrahigh stress concentration for full-face excavation in deep tunnel; then safety of equipment and personnel will be under great threat. The excavation test through “part-pilot heading + TBM” is carried out in the diversion tunnel #3 of the Jinping II hydropower station and the rockburst risk of TBM part-pilot excavation is researched via real-time microsesimic monitoring. The results show that: (1) The daily number of microseismic events, the daily accumulative radiated seismic energy, number of big events and frequency and strength of rockburst in the field during part-pilot excavation are far lower than in the period of full-face advance. (2) The time domain evolution of logarithm of energy index and accumulative apparent volume indicates that the risk of strong rockburst in part-pilot section is smaller; and the excavation in field also proved this. (3) In comparison to full-face advance, the degree of concentration, number, magnitude and radiated energy of microseismic events in space in section of part-pilot are far lower. Therefore, the rockburst risk of TBM for part-pilot driving is more less than for full-face advance. In very strong rockburst section, when construction condition is indispensable, the part-pilot can be excavated in advance and then TBM pass, the risk of rockburst can be controlled availably.

Key words: deep tunnel, tunnel boring machine, part-pilot, very strong rockburst, microseismic monitoring, Jinping II hydropower station