Static And Dynamic Stability Of Coal Pillars In Strip Mining

With urban development and the level of coal mining enhanced in China, the proportion of coal mining under buildings, railways and water-bodies that is called the three-underground mining increases rapidly. Strip mining is widely used in three-underground mining for its low cost and simple technology, Stability of coal pillars in strip mining is related to the safety of mined-out areas, ground buildings and structures, thus it is important significance to study the stability of coal pillars. This paper research focusing on the coal pillars strength, static and dynamic stability in strip mining, and the main contents and conclusions are summarized as follows:(1) The uniaxial and triaxial compression tests of coal are carried out, and the results are analyzed. After summarizing domestic and foreign strength theory on coal pillars, a mechanical model is established and a new strength formula is proposed for the coal pillar based on the assumption of A. H. Wilson strength theory about stress distribution.(2) The expression for calculating the width of coal pillars is deduced according to the Effective Area theory and the above strength formula, and the yield region width and peak stress of coal pillars designed by the method are calculated. The results show that the conclusion is close to the one on the Wilson theory.(3) Numerical simulation is applied to contrast the stability of coal pillars with different width. The results indicate that the stability of wide coal pillars is better than narrow ones. If the coal pillars are too wide, however, it will cause stress concentration increasing and lead to uneven ground surface subsidence.(4) The dynamic problem of coal mining area caused by earthquake, rock burst, blasting, roof collapse in adjacent mining area etc. is concerned. Firstly, the elasticity plane wave theory is introduced to discuss the mechanism of coal pillar instability caused by seismic waves, then the response characteristics of the coal pillars in strip mining under anâ…¶degree earthquake are analyzed on the base of FLAC3D software, and the results show that its stability of the coal pillars designed by static conditions will tend to deteriorate.(5) The effects of different intensity and direction of seismic waves on the stability of coal pillars are investigated. The conclusions reveal that the greater seismic intensity is, the stronger its influence of destructive disturbance is. The horizontal seismic waves increase the plastic zone width on both sides of coal pillars, the vertical seismic waves mainly make plastic zones extent to the roof and floor, and the effect of horizontal seismic waves is greater than that of the vertical ones.