Pillar burst is one of the most frequent dynamicdisasters in deep mining

which poses a serious threat to safe and efficientmining. In this study

the failure mechanisms and precursors of pillar burst areinvestigated by active ultrasonic survey and passive acoustic emission (AE) monitoringin uniaxial compression tests on Zigong red sandstone. Combining active andpassive AE monitoring data

a P-wave velocity tomography inversion is performedto analyse the temporal and spatial variations of P-wave velocity structureduring the sample failure. Results show that the velocity structure of thesandstone sample is highly heterogeneous during loading

and a low-velocityzone emerges

within which most of the acoustic emission events are present.The dispersion of P-wave velocity reflects the global variations of P-wavevelocity. It changes drastically during the peak stage

and increases with theongoing loading. The AE events differ significantly between the pre-peak andpost-peak stages. In the pre-peak stage

AE events are randomly distributed inthe sample

while in the post-peak stage

clustered AE events are identified.In addition

it is found that using the homogeneous velocity structure for AEevents location results in a higher positioning error. The decreasing value before the eventual failure ofthe sample indicates that large-scale crack activities are intensified

leadingto the increase of sample heterogeneity

which also proves the necessity ofapplying the heterogeneous velocity structure for AE events location. Theresearch results can be further used for on-site pillar stability monitoring

and the periodic P-wave velocity tomography provides precursors for pillarbursts.