Blast Induced Damage to Surrounding Rock Mass in an Underground Excavation

Authors have conducted experiments to measure blast induced rock mass damage at L&T-(Singoli-Bhatwari Hydro-Power Project SBHP) Rudraprayag. Repetitive NX size rock core up to 5.0 m depth were taken from side wall and face with triple tube core barrel drill. CR (core recovery) and RQD (rock quality designation) of the rock cores is computed to evaluate effect of blasting on the surrounding rock mass. RQD and CR values for the initial one meter from the line of excavation in each case reflect maximum damage due to blast. RQD for initial one meter reduced to as high as 40% of the average RQD. The rock samples were also tested using ultrasonic techniques. Ultrasonic tests on NX size core reveal that the 2.0 m of the zone surrounding the opening are adversely affected by the tunnel excavation blasting process. The ultrasonic velocities reduce to approx. 80% of the average values in the initial 0.5 m from the excavation line.