Simulated rockburst experiment: Development of a numerical model for seismic wave propagation from the blast, and forward analysis

摘要

A blast was engineered close to a tunnel in a deep-level mine with the purpose of studying the wave interaction with the tunnel. Numerical modelling of seismic wave propagation was used in both the forward planning and the back-analysis of this experiment. This paper presents the forward analysis. A likely model for a propagating blast was investigated and developed. This model predicts the influence of the velocity of detonation of the blast and the rise-time of the blast on the radiation pattern, and hence on the expected positions of maximum velocity at the tunnel surface. An attempt was made to quantify the parameters of the blast model, using waveform data from two other blast experiments. The blast model caused particle velocities which were an order of magnitude lower than these measured velocities. Large values for blast pressure were required to match the amplitudes of the recorded velocities. An alternative 'effective' source with a similar mechanism but increased diameter was proposed to account for the higher velocities. It was established that distant velocities scale with the square of the borehole diameter. A calibration blast at the experimental site was also modeled. Agreement in the waveforms show an encouraging correspondence with some measured waveforms. This gave confidence that the model could be used to examine wave propagation around the tunnel, and allowed a scaled source to be developed for forward analysis of the main experiment.