Study on the mechanism of zonal disintegration around an excavation

• Slowly unloading P-waves can induce material discrete failures.
• Numerical simulation results show that zonal disintegration could happen.
• As P-wave amplitude is in a certain range, it could cause zonal disintegration.
• Quickly unloading P-waves cannot induce zonal disintegration.

Zonal disintegration is a curious phenomenon and has received considerable attention recently. Using traditional static mechanics cannot well explain the phenomenon of the alternately distributed cracked zones. In this paper, the process of a slowly unloading P-wave reflecting from a free surface has been investigated and the result shows that as a slowly unloading P-wave encounters a free surface, it could cause the phenomenon of zonal disintegration. In order to confirm this result, two numerical models of defected rock around an excavation under the action of a slowly unloading P-wave are established. The slowly unloading P-wave is induced by a steel plate impacting the target rock with a proper speed, and their interaction lasts for a long time. The simulation results show that if the strength of slowly unloading P-waves is in a certain range, the phenomenon of zonal disintegration could be observed, and if the incident wave is not a slowly unloading P-wave, such as a rectangle wave, the phenomenon of zonal disintegration will not occur.