| The scale of goaf was increasing with the exploitation of mineral resources. It leaded to several geological issues, especially for some mine with villages on its surface. The surface traffic safety would affect by these goaf stability, even leaded to houses collapsed. It would lead the public great panic and caused possessions lose. So it’s meaningful to carry out goaf stability mechanism research, raised a good goaf prevention project in gypsum type mine.This paper aimed at goaf operation project in Luo Tang gypsum mine in Guixi city, which had taken lots of prior predication works including field investigation and numerical simulation.According to field investigation, the reason of surface collapse was foot goaf instability. Then Theoretical analysis, numerical simulation, similar material simulation experiment these methods were applied for goaf stability mechanisms check. A reasonable goaf operation program was raised in Luo Tang gypsum mine. The main research result as following:(1)The law of stress distribution in stope’s hanging wall was discovered by theoretical analysis. The hanging wall would crashed, which induced by tensile stress in the bottom surface of hanging wall. However, set a certain thickness ore-mass instead of hanging wall rock-mass as protective roof. It could make roof keep a good stability. But the thickness must higher than the height of tensile stress zone. By using Lunder equation to calculate pillar strength could reflect this kind pillar’s strength, which increasing with the size change. Critical safety mining depth also made out by “Three zone” theory. It could avoid surface collapse if mining area near surface.(2)The fracture would came out in the center and corner of similar sample, then fracture developed, becoming wider and through surface at last during the process of similar material simulation experiment. Pillar’s strength would going down as fracture developing, when it could not bear the weight of overburden rock-mass, pillar would crashed. It would lead to roof broken totally.(3)The software FLAC 3d was applied for target region three dimensional numerical stimulation. Mining process and different ratio of height and width were key factor affecting the tectonic stress distribution, displacement of roof transformation and pillar stability. So the stimulation was surrounding these parameters, in order to discover their law because of mining.The result revealed pillar’s stability affecting by the ratio of width and height. It verified the mechanism of goaf stability.(4)This paper was very helpful to control roof stability by control the thickness of reserved rock and the span of ore-room. It could satisfied the requirement of non-important safety on surface when the thickness of pillar was 3m. However, it’s still not good enough for some important building on surface. There’s still no obvious displacement on surface even the mine stopped mining for a long time. This result came from the study of surface displacement monitoring. The goaf areas should be filled on time, the underground water also should be deal.Mortar rubble must be put in the ends of ore-room in order to support roof. It could strengthen goaf keep stability for much longer time. |
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