Research on the propagation of shock waves from coal and gas outburst

The reflection and propagation of a shock wave during coal and gas outburst were studied.Stress wave theory was used to estimate wave behavior at the coal interface.An analytical solution for the incident,reflected,and propagated waves has been obtained.Shock wave propagation along a tunnel has been examined using aerodynamic theory.The results show that transmission overpressure is twice the incident overpressure.However,the reflected overpressure is slightly less than the incident overpressure.The impact from blast pressure is proportional to the flow and expansion of energy in the wave and inversely proportional to the area of the ventilation tunnel.A shock wave propagated through a single coal layer is reflected at the free interface at both ends.As the reflection reverses there is an unloading causing the velocity at the free surface to double.This tears the coal into several thinner laminas.A shock wave propagating through an assembled structure of tectonic coal and hard coal rock creates strong propagation and reflection transients at the interface,where the transmitted waves superpose and the stress value doubles.The coal is then fractured and damaged by compression stresses that exceed the yield limit of the soft coal.