Abstract
In view of the randomness of rockfalls shape and irregularity of the bottom floor of working face in steeply dipping coal seams (SDCS), it is difficult to accurately simulate rockfall movement, and it is consequently unable to effectively protect against multirockfalls. Therefore, a method for generating random shape rockfalls based on ellipsoid equation is proposed, and a 3D grid model of real bottom floor of working face is established based on the geographic information system data. In order to verify the accuracy and feasibility of the method and 3D model, the trajectory simulated by Rockyfor3D software is compared, and the proposed method and 3D model prove to be effective in simulating rockfall movement more accurately. Then the proposed method and 3D grid model are applied to solve the problem of multirockfalls protection in numerical simulation, and the main factors affecting the structural stress response of protective netting are analyzed by taking three incident modes of parallel heights, ladder parallel, and the same trajectory. In the simulation, it is found out that the trajectory of irregular rockfalls is greatly affected by the shape of rockfall and working face floor; during the process of multiple rockfalls colliding with the protective netting, the peak stress on the protective netting is inversely proportional to both the time interval between each rockfall and the distance between each rockfall. The findings presented in this research contribute to rockfall prediction and protection against rockfall hazards.
Highlights
In recent years, with the development of steeply dipping coal seams (SDCS) mining and combining mining technology, the number of steep coal mines in China has increased year by year, and the coal production, as well as the economic benefits, has increased [1,2,3,4,5,6,7]
The rockfall hazard, a disaster that occurred in SDCS mining, has become increasingly prominent [8,9,10,11,12,13,14,15,16,17,18,19]
Since the natural-rest-angle of a coal/rock block is smaller than the coal seam inclination angle, it is difficult to stop after the first collision with the bottom plate and will slide downwards along the working face and may collide with people or equipment. e coal seam structural information and the main movement modes of rockfall are shown in Figure 1 [12]
Summary
With the development of SDCS mining and combining mining technology, the number of steep coal mines in China has increased year by year, and the coal production, as well as the economic benefits, has increased [1,2,3,4,5,6,7]. Erefore, studies on the mechanism of rockfalls motion would fundamentally improve the protection against rockfalls that occurred in steep seam mining. While the research on steep seam mining mainly focuses on mining equipment, especially hydraulic supports and shearers [21,22,23,24,25,26,27,28,29,30], and technical management of longwall working faces, only few studies have been carried on the motion mechanism of rockfalls in steep seam mining [9, 10]. Erefore, it is of great significance to explore the mechanism of rockfalls movement for establishing the safety protection system of longwall working face in SDCS mining area. Most of the rockfall and working face floor models used in the above research are idealized models and in lack of research on three-dimensional movement of irregular random rockfall. e innovation of this research is: the previous two-dimensional space rockfall trajectory simulation is upgraded to three-dimensional stepping space rockfall trajectory simulation; the former regular shape rockfall modeling is converted into irregular random shape in model establishment; the idealized simple working face modeling is changed to the working face modeling based on geographic information system. e innovation of the current work contributes to the prediction of rockfall movement and the protection against rockfall disasters. e research is given as follows: the modeling method of irregular rockfall and the modeling method based on geographic information system are put forward; according to the proposed principles, a group of simulation tests of rockfall movement are carried out to find out the most dangerous rockfall model; the protection simulation test is carried out for the most dangerous rockfall model
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