Research on coal gangue transport and shield beam bearing pressure law based on FLAC3D-PFC3D coupled simulation and physical similar simulation

Top coal movement and real-time access to the caving state of top coal is the core scientific problem of intelligent longwall top coal caving, focusing on the pressure change law of the shield beam of hydraulic support during the process of top coal crushing and moving, the use of theoretical analysis, numerical simulation and physical simulation methods, research the rule of top coal movement and its impact on the change of the pressure of the shield beam. The stress state of shield beam under static state and coal caving state of hydraulic support is analyzed, and the results show that the force of the shield beam at rest is directly proportional to the support force of the column, and the moving state is positively correlated with the bearing capacity of the top beam. Based on the FDM-DEM coupling method, a FLAC^3D-PFC^3D coupling physical model was established, and the optimal initial coal discharge position was determined to be three steps away from the top coal caving, and the morphology surface of the top coal caving body gradually evolved from an ellipse with the long axis of 3.54 m and the short axis of 1.95 m to an ellipse with the long axis of 7.51 m and the short axis of 4.25 m, and the ellipse’s long axis was deflected by 18° in the direction of the pointer; and the position of the lowest point of line of demarcation between coal and gangue was linear and gradually deflected downward. Linear relationship and gradually downward offset, the offset point is located directly above the support shield beam. This phenomenon leads to the overall decrease of shield beam pressure, and the pressure of shield beam decreases rapidly and then increases slowly during the process of initial top coal caving and periodic coal caving. Finally, through the self-developed large-size physical similarity simulation platform for top coal caving, it was verified that in the cycle coal caving, the shield beam pressure showed the characteristic of rapid decrease and then slow increase, and the pressure before and after coal caving was generally reduced by 10%–30%. In the two research methods, the ratio of rapid change time and slow change time of shield beam pressure from the start of coal caving to the time when the gangue rate reaches 20% is approximately 5:2, so when the pressure of the shield beam is monitored to decrease during coal caving, it can be stopped when the time from the start of coal caving to the time of the lowest point of the pressure drop is 0.4 times, and at this time, the gangue rate is about 20%.