78 / 2021-09-20 19:46:00

Development of a protective structure on Continuous Miners against coal burst hazards

coal and rock failure; AE-EMR responses; damage evolution; silent period; rock burst

As mining progresses into deep mineral deposits, geo-hazards such as coal/rock burst and outbursts are becoming a major threat to mining safety and sustainability. The occurrence of these hazards involves the ejection of coal or rock fragments with high impact energy and sometimes the release of large volume of gases such as methane and carbon dioxide, which can cause great damage to mine equipment and workings, and in the worse case, lead to injuries and deaths of mine workers. The development of underground mine roadways is typically achieved by using Continuous Miners (CM) in conjunction with other transport and roof support system. During an incident of coal burst or outburst, the CM can be engulfed by ejected coal blocks and rocks. In this study, a specialised modular protective structure has been designed, developed, and tested under drop hammer impact loads utilising a fabricated prototype structure for installation on the CM to improve the safety of mine workers against such dynamic incidents.



The developed protective system consists of two main components; 1) a modular cellular core sandwich panels, and 2) a steel frame to hold the sandwich panels. The cellular core sandwich panel system is designed to absorb most of the impact energy via localised plastic deformation of the core and the face sheets while the steel frame limits the global deformations of the frame. The steel frame includes anti-rotating, energy-absorbing connections which are used to connect the developed protective system to the CM working platform. The cellular core sandwich panel consists of a square honeycomb core sandwiched between two face sheets. The core is fabricated from 0.7 mm thick Grade 250 steel sheets using a strip-slotted metal sheet assembly method while face sheets are from 5 mm thick Grade 350 steel plates welded to the core. The steel framing system has overall dimensions of 1500 mm height and 700 mm width, is fabricated using standard size square hollow sections from Grade 450 mild steel and 10 mm steel plates from Grade 350 mild steel. The full CM protective structure (CMPS) utilises three modular square honeycomb core sandwich (SHCS) panels.



Drop hammer impact tests were performed for the individual SHCS panels and full CMPS under heights varied from 1 m to 3 m. The SHCS panels showed superior impact resistance with high energy absorption through the plastic deformation of the core without any pullout damage from the edges of the panel. The prototype CMPS structure was tested under repeated impacts of 600 kg mass and successfully resisted the impact from 3 m height with a 158 mm permanent deflection at the top edge of the CMPS. Finite element numerical models were developed using LS-DYNA software and the numerical results agreed well with the experimental results (see Figure 1). The response of the CMPS under multiple impacts of coal blocks with different masses was also numerically evaluated. The numerical results showed that the peak displacement of the CMPS towards the work position where the CM operators stand, was well below the acceptable limit for the maximum displacement for the safety of workers.