Shifting Highwall Blast Vibration Frequencies Higher Maintaining PPV Lower from Near-Field Blasts

ABSTRACT: Shifting blast dominant frequency at highwalls has been a desired target for an improved blast design. However, documented cases of successful frequency shifting have been little in literature. This paper presents a successful case of shifting frequency of blasts. The blast monitoring collected useful data for the site rock characterization – vibration (stress) attenuation versus scaled distance; site resonant frequency, and ground p-wave velocity from signature hole blasts. Using the multiple seed waveforms that are encoded within the site frequency response, the Multiple Seed Waveform (MSW) model accurately predicted the dominant frequency at highwalls from near-field blasts. Blast design scenarios were then modeled for blast vibration PPV's and dominant frequency. With parameters from the signature hole blast vibration and fragmentation measurement, the Multiple Blasthole Fragmentation (MBF) and MSW models are established for the site. The models can be used to explore benefits from various blast design scenarios. The delay timing in terms of lower PPV and higher dominant frequencies for the pits were recommended – an increase in frequency of 10 Hz at a hard rock pit using the recommended timing and an increase in frequency of 5 Hz at another relatively soft rock pit with the recommended timing. 1. BACKGROUND In a typical mine operation, productivity and efficiency begin with drilling and blasting efforts, however, additional challenges related to blasting can be impactful to a mining operation. Blast designs must be adapted to the site geological features and rock properties to achieve improved operations. To support the mining operator's effort, a suite of blasting technologies is required at the mine to drive blast optimization and wall control. A large gold mine has two production pits – one with relatively competent rock and the other one with fractured rock. Current timing templates used by the short-term planning were created over 5 years ago – and given changes in geology and rock structures, the timing templates may not be providing suitable vibration or wall control outcomes.