226 / 2018-05-04 22:29:35

Precursory changes in wave velocity for coal and rock samples under cyclic loading

ultrasound precursors,coda waves,cyclic loading,wave velocity,damage evolution

矿山动力灾害 > 岩爆冲击

Wave velocity is a critical parameter in evaluating rock stability and integrity. Temporal changes in wave velocity during mine dynamic hazards including rockburst and gas outburst might potentially illuminate physical processes associated with stress concentration, crack propagation and fault slip behaviors. Laboratory and theoretical studies predict changes in wave velocity before rock failure; however, these dynamic hazards occur in a range of modes and little is known about precursors for those modes. Here, we show that precursory changes of wave velocity occur in laboratory tests for coal and sandstone samples under cyclic loading. We carefully measure ultrasonic wave velocity using coda wave interferometry method to show the special variation of wave speed with a resolution of 10-5 by 13 PZT transmitters. We find fluctuations of wave velocity during the cyclic loading correspond with the stress change and may be explained by crack nucleation and propagation, which can be monitored by acoustic emission technique. Our data show that accumulated micro-cracks cause significant reduction of ultrasonic wave velocity and elastic moduli during the transitional phase preceding failure, which suggests that continuous wave velocity monitoring may be a means to detect mine dynamic hazards precursors.