Effect of Bench Blasting on Vibration in Underground Roadways during Open Pit-Underground Combined Mining

In order to control the lining damage of underground roadways induced by the vibration effect of bench blasting in an open-pit quarry, the dynamic response of the existing adjacent roadway at the transition mining stage from open pit to underground in Lara Copper Mine were studied by means of field vibration monitoring, theoretical calculation and numerical simulation. Through regression analysis of the monitoring data, the vibration attenuation law was obtained, and the dominant frequency and instantaneous energy of the vibration were analyzed. Six models with different relative spatial positions between the open-pit bench and underground roadway were established using the LS-DYNA software. Subsequently, double-hole delayed blasting models were developed to investigate the dynamic response of adjacent existing roadways under blasting loads. The results show that for the existing roadway located below the explosion source of the open pit bench, its maximum vibration velocity mainly appears in the arch and the side wall on the explosion-facing side. The direction and position of the peak vibration velocity change with the different relative spatial position of the roadway and the explosion source. When the vertical distance between the roadway vault and the bottom of the blast hole is fixed at 10 m, and the horizontal distance between the roadway sidewall and the blast hole is less than 15 m, the vibration velocity in the vertical direction of the tunnel structure is greater after explosion. Beyond this 15 m horizontal distance, the vibration velocity in the horizontal and radial directions of the tunnel structure is larger. By fitting the relationship between peak effective stress and peak particle velocity and utilizing the ultimate dynamic tensile strength of the roadway, a vibration velocity threshold of 19 cm/s was derived. After adjusting blasting parameters according to the safety threshold, the safety of adjacent existing roadway can be ensured.