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The rapid release of strain energy is an important phenomenon leading to seismic events or rock failures during the excavation of deep rock. Through theoretical analysis of strain energy adjustment during blasting and mechanical excavation, and the interpretation of measured seismicity in the Jin-Ping II Hydropower Station in China, this paper describes the characteristics of energy partition and induced seismicity corresponding to different energy release rates. The theoretical analysis indicates that part of the strain energy will be drastically released accompanied by violent crushing and fragmentation of rock under blast load, and this process will result in seismic events in addition to blasting vibration. The intensity of the seismicity induced by transient strain energy release highly depends on the unloading rate of in-situ stress. For mechanical excavation, the strain energy, which is mainly dissipated in the deformation of surrounding rock, releases smoothly, and almost no seismic events are produced in this gradual process. Field test reveals that the seismic energy transformed from the rock strain energy under high stress condition is roughly equal to that coming from explosive energy, and the two kinds of vibrations superimpose together to form the total blasting excavation-induced seismicity. In addition, the most intense seismicity is induced by the cut blasting delay; this delay contributes 50% of the total seismic energy released in a blast event. For mechanical excavation, the seismic energy of induced vibration (mainly the low intensity acoustic emission events or mechanical loading impacts), which accounts only for 1.5‰ of that caused by in-situ stress transient releasing, can be ignored in assessing the dynamic response of surrounding rock.

The strain energy adjustment processes and rock failure modes corresponding to different excavation methods, such as Tunnel Boring Machine (TBM) or blasting, are quite different during construction of deep tunnel. Based on the diversion tunnel excavation of Jin-Ping II hydropower station (JPII) in southwestern China, the distribution characteristics of damage zones and adjustment process of rock strain energy under different excavation methods are analyzed and discussed, and the occurrences of rock bursts in the diversion tunnels are also monitored and analyzed. Research reveals that, the adjustment process of rock strain energy and the distribution of damage zones are obviously different under different excavation methods, and the depth and distribution of damage zone are positively correlated with the accumulation depth of rock strain energy. For blasting excavation, due to the combined effects of blast loading and in situ stress transient unloading, the surrounding rock is damaged seriously. The accumulation depth of rock strain energy is significantly larger than that by TBM excavation, while the accumulation peak of rock strain energy is smaller. For TBM excavation, the strain energy releases smoothly and slowly, and much more strain energy is accumulated in the vicinity of excavation face. Under similar geological conditions in the JPII, the rock bursts of intensive and mediate grades can be more frequently observed after blasting for the impact of severe excavation disturbance, and the strain energy transient adjustment may be the main disturbance contributor. While during TBM excavation, due to the smooth adjustment process of rock strain energy, the disturbance to surrounding rock is limited, and the accumulation peak of rock strain energy is higher and closer to the excavation face, which may result in more spalling events or minor rock bursts.