Experimental study on migration characteristics of coal and gas outburst two-phase flow in L-shaped roadway under true triaxial conditions

Coal and gas outburst two-phase flow has a strong impact dynamic effect, which could cause seriousinjuryto underground personnel and damage to equipment. In order to fully understand the migration law and disaster-causing mechanism of coal and gas outburst two-phase flow, a physical simulation test of coal and gas outburst under true triaxial conditions was carried out by using a large physical simulation test system of multi-field coupling coal mine dynamic disaster. The migration characteristics and impact characteristics of coal and gas outburst two-phase flow in aL-shaped roadway were analyzed. The results show thatin the L-shaped roadway, there are three flow states of jet, dilute phase flow and dense phase flow in the main roadway. Affected by the right angle turning structure, only a small amount of pulverized coal enters the branch roadway, mainly distributed at the front end of the right angle turning structure, indicating that the turning structure greatly inhibits the flow of pulverized coal. The pulverized coal is mainly composed of particles with a particle size of less than 0.15 mm. Its migration in the roadway can be divided into three stages:initial acceleration, secondary acceleration and attenuation. The maximum velocity of pulverized coal flow in the initial stage can reach 25.0 m/s.In the process of outburst, the impact force of coal and gas two-phase flow in the roadway presents an evolutionary trend of rapid increase and slow attenuation.After the impact force reaches the peak, it does not decrease smoothly, but it is a shock attenuation process with multiple peaks, indicating that the outburst has intermittent characteristics. In the main roadway, the maximum impact force presents a fluctuating distribution along the roadway. With the increase of the propagation distance, the duration of the growth zone gradually increases, and the attenuation of the impact force gradually decreases. The impact damage characteristics of coal and gas two-phase flow are mainly reflected in its front and middle parts.There is a risk of serious injury to human body at 2, 6 and 8 m away from the outburst place.With the development of the outburst, the disaster-causing area ofimpactforce gradually develops from the front of the roadway to the middle. In the branch roadway, the impact force of two-phase flow increases sharply, showing a strong-weak alternating distribution, which indicates that right angle turning structure enhances the dynamic disaster-causing degree caused by two-phase flow.