Relationship between blasting operation and slope stability: a case study at Borneo Indo Bara open pit coal mine

Bench blasting is commonly used in open-pit coal mines because it effectively increases coal production and aids in overburden removal. However, uncontrolled blasting can generate significant vibrations and accelerations, which may lead to slope failure if the magnitude of permanent displacement exceeds its critical value. A prevalent method for calculating the dynamic factor of safety (FoS) of a slope due to blasting is the pseudo-static approach; however, this method tends to be overly conservative. In this study, we utilized Newmark's sliding block method and the strength reduction factor (SRF) to assess the dynamic FoS of slopes by evaluating the permanent displacement caused by bench blasting. We based our seismic input on a complete vibration waveform obtained through signature hole analysis of a specific bench blast design. The dynamic FoS was defined as the SRF threshold that resulted in a critical slope displacement of 50 mm. The case study was conducted at Borneo Indo Bara, one of Indonesia's largest open-pit coal mines located in South Borneo Province. We analyzed four sidewall slopes that were subjected to repeated blasting events. The results indicated that the slope's LOM design could tolerate blasting vibrations corresponding to a peak particle acceleration (PPA) of up to 0.41 g, which yielded a dynamic FoS of 1.35. This value is significantly higher than the pseudo-static approach, which indicated a pseudo-static FoS of 1.04 for a PPA of 0.12 g. Furthermore, this study assists mining practitioners in predicting the allowable number of blast events to prevent slope failure and recommends avoiding blast events with a scaled distance of less than 8 m/kg^1/2 to prevent sudden slope failures. In conclusion, the study highlights the importance of the integrated approach that combines signature hole analysis, Newmark's sliding block method, and the SRF approach for evaluating the dynamic FoS of mine slopes subjected to bench blasting. The results of this study can offer valuable insights for mining engineers engaged in bench blasting to adopt the proposed integrated approach, which is still overlooked in Indonesia's open pit blasting practices.