Experimental study on the influence of roadway structure on impact characteristics of outburst fluid

The dynamic impact effect of outburst fluid is one of the main disaster⁃causing factors of coal and gas out⁃ burst disasters. To further understand the disaster⁃causing mechanism of coal⁃gas two⁃phase flow in this process，some physical simulation tests of outbursts under different roadway layouts were carried out to analyze the spatial and tempo⁃ ral evolution characteristics of impact force， impact force characteristic parameters， and the distribution of disaster⁃causing damage level in the outburst process. The results show that in the straight roadway，the evolution trend of impact force in the airflow and thin two⁃phase flow stages becomes more and more complicated with the increase of distance from the coal seam. The impact force increases with the increase of the solid⁃gas ratio，and the peak impact force is in the dense two⁃phase flow stage. There is an undulation phenomenon in the decay of impact force，which in⁃ dicates that the release of outburst energy is completed in stages. The tail structure has a great influence on the impact force in the straight section，which is L⁃shaped >T⁃shaped >L (arc) shaped. Over time，the middle of the straight roadway gradually develops into a serious disaster area，and the disaster⁃causing range of the roadway gradually ex⁃ pands，mainly in the direction of the coal seam. In the turning roadway，the impact force evolution is much more influ⁃ enced by the gas phase than the solid phase. There are disaster concentration areas in the turning roadway. The impact force shows a tooth⁃like distribution in the roadway，especially in the turning roadway，which shows a strong⁃weak phase distribution. The dynamic disaster intensity and disaster area of the L⁃shape are greater than those of the L (arc) and T⁃shape. The hardest⁃hit areas are mainly located in the middle and front of the straight roadway， while there are safety areas at the end of the straight roadway and in some areas of the turning roadway. The right⁃an⁃ gle turning structure and the flat⁃angle bifurcated structure both have the mechanism of concentrated energy release which leads to enhanced impact force. Arc structure can effectively reduce the disaster intensity caused by impact pow⁃ er，reduce the number of disaster concentration areas of turning roadway，and avoid or weaken the centralized release of energy. The time of positive pressure is distributed in a periodic V⁃shape. The specific impulse volume shows multi⁃ peak fluctuation distribution along the roadway. Compared with the peak impact force， the difference is mainly reflected in the front end of the straight roadway after adding the positive pressure action time factor. The time evolu⁃ tion of impact force at the end of the straight roadway and the turning roadway is influenced by the tail structure.