The deep-buried tunnels in Jinping II Hydropower Station are characterized by great depth, long length, large size in diameter and high geo-stress. During the excavation, by drilling and blasting method, of these tunnels, lots of the time-delayed rockbursts occurred; and blasting disturbance was one of triggering factors of their occurrence. This paper discusses the correlation between time-delayed rockbursts and blasting disturbance profoundly from two aspects of blasting disturbance strength and the delayed time of the time-delayed rockbursts. And the main conclusions were presented as follows:
the number of time-delayed rockbursts does not reduce with the increase of their distance from explosive center;
the risk of the time-delayed rockburst in situations with several working faces is obviously higher than that with single tunnel face;
most of the time-delayed rockbursts occur within seven days to one month after excavation;
the relationship between frequency of the time-delayed rockbursts and their delayed blasting time is a good power function, and the peak period of rockburst activities is within 4 hours after blasting.
The deep-buried tunnels crossing the Jinping Mountain are composed of four diversion tunnels and one drainage tunnel in the Jinping II Hydropower Station in China, with a spacing of 45–60 m, an average tunnel length of 16.7 km and a maximum overburden depth of 2,525 m. Eighty percent of the strata along the tunnels consist of hard, integrated, tight and typically burstprone marble with a uniaxial compressive strength of 55–114MPa, a tensile strength of 3–6MPa, a modulus of elasticity of 25–40 GPa and the modulus of deformation of 8–16 GPa. Based on inverse analysis of the in-situ stress field, the initial geo-stress field is basically dominated by gravity stress field in engineering zone, where the maximum principal stress is up to 70MPa, thus belonging to typical high stress zone. The middle section of these tunnels, where a high risk of extremely intense rockburst existed, was excavated by drilling and blasting method. Multiple working faces, located very close to one another,were arranged, hence causing frequent blasting operations in a small field.