Stability Analysis Of Rib Pillar In Highwall Mining Under Dynamic And Static Loads

Base on the investigation and statistics of the amount of end slope residual coal in China,the total amount of coal remaining in the open-pit coal mines reaches billions of tons.Highwall miner can be used to exploit the large amount of end slope residual coal in open-pit mines,however,the instability mechanism of rib pillar reserved in the mining process is still not clear,which has greatly restricted the application of highwall mining system.In this paper,the instability mechanism of rib pillar under the dynamic loads of the truck and the static loads of the slope is studied thoroughly,and the design method of the rib pillar width is put forward,which will be of great significance to the exploitation of opencast coal resources in China.The main research results obtained in this paper are as follows.(1)Based on the mechanical model of rib pillar during highwall mining,combined with cusp catastrophe theory and simultaneously taking into account the requirements of safety factors,a criterion for the stability of rib pillars is established.The mechanical criteria of the instability of rib pillar are mainly determined by three factors: the plastic zone width of rib pillar,the ultimate stress of rib pillar and the compression of rib pillar corresponding to the loads.(2)Based on the limit equilibrium theory,the ultimate stress of rib pillar is analyzed and calculated,the calculation formula of the plastic zone width of rib pillar was obtained.Meanwhile,based on the theory of Winkler's elastic foundation beam,the elastic foundation model composed of pillar and roof was established and the calculation formula of the compression of rib pillar under loads was also derived.(3)With the increase of rib pillar width,the plastic zone width of rib pillar decreases approximately linearly;the total compression amount of rib pillar decreases approximately as an inverse function type.The compression of rib pillar under slope overburden and truck static loads play a decisive role in the total compression amount of rib pillar.(4)Based on the actual mining conditions of open-pit coal mines as the engineering background,the coal seam with a depth of 122 meters and a thickness of 3 meters is exploited by highwall miner.According to the instability model of rib pillar of the highwall mining system,it is calculated that when the width of mining chamber is 3 meters,the reasonable width of rib pillar should be at least 1.3 meters and the safety factor of rib pillar is 1.3.(5)Based on the numerical calculation model of highwall mining,the rationality of the theoretically calculated rib pillar width is numerically analyzed under the actual mining conditions of the open-pit mine.From the analysis results,it can be known that the rib pillar in the middle of the pillar group did not produce perforated plastic zone,and also the overall end slope did not peoduce obvious plastic zone when the width of rib pillar is same to the theoretical model.So the rib pillar and the end slope are both in a stable state in this mining condition.The research results can provide important reference for stability analysis of rib pillar in highwall mining under dynamic and static loads.