Blasting vibration criterion for a rock-anchored beam in an underground powerhouse

The design approach for a rock-anchored beam (RAB) in an underground powerhouse is briefly introduced, and the dynamic response characteristics of an RAB under blasting vibration are presented. It is found that the key to ensure the safety of RAB under blasting vibration is to prevent the split of the bonding interface between the RAB and a vertical rock wall, and to control the horizontal peak particle velocity (PPV). On the basis of the practices at Longtan hydropower station and other projects, and taking into account the comprehensive factors such as the structure characteristics of RAB, the age of concrete and the strength of bonding interface, the safe PPV for an RAB in a large underground powerhouse are thoroughly studied. It is concluded that a PPV of 7 cm/s for an RAB with an age older than 28 d would be of some safety. The safe PPV for young concrete proposed by GB6722-2003 could be adopted as those for an RAB with an age no older than 28 d, i.e., a safe PPV of 3–7 cm/s for an RAB at an age range from 3 d to 7 d, and 2–3 cm/s for an RAB at age range from 0 d to 3 d.