Overburden Failure Mechanism And Surface Movement Law Due To Sub-critical Extraction In Yanzhou Mining Area

With the development of deep mining, sub-critical excavation problems are becoming increasingly prominent, and it is very necessary to study overburden failure mechanism and surface subsidence law of sub-critical excavation completely. Based on actual geology and mining conditions of Yanzhou Mining Area, field measured data analysis, many research methods were employed, such as, similar material simulation test, discrete element numerical simulation and physical detection, so that overburden failure mechanism and surface subsidence law of sub-critical excavation were analyzed and studied completely.Measured data of surface movement observation station due to sub-critical extraction in Yanzhou mining area were analyzed and summed up, some conclusions are as follows: (1) as the numbers of working faces increased, surface mining degree aggravated, mainly from sub-critical excavation to full mining. (2) surface subsidence ratio changes piecewise with mining degree changes, and appears the laws of'gently increase→suddenly increase→slowly increase→stability'. Given thin alluvium, mining degree is determined in term of mining width rate to mining deep, while thick alluvium, in term of mining width rate to the bedrock height. (3) Surface subsidence ratio formula under large mining deep and thick alluvium is (4) The probability integral method was employed to predict sub-critical excavation only if strata movement parameters were modified. As mining degree increases, inflection point deviation direction change from coal pillar side to gob side, while, deviation of inflection point become smaller from maximum outside deviation value, ultimately become maximum inside deviation value.Similar material and numerical simulation tests were employed to study strata movement mechanism of sub-critical excavation, and determine the judging method of mining degree under thick alluvium. The results show that, (1) overlying strata form smaller pressure arc, the caved zone smaller, strata movement not sufficient, and surface movement values very small. (2) Mining degree can't use the index of mining width rate to mining deep, and should wholly consider the alluvium height, bedrock height and proportional relationship under the condition of thick alluvium.Coal pillar stability was analyzed by numerical simulation method. The results show that the width and strength of isolated coal pillars among working faces have a decisive influence on coal pillar stability, and a certain impact on surface subsidence value. When small sizes, coal pillars easily lose stable, and take up rock burst.Above laws are applied to Yanzhou mining area. Mining reserves under Sihe River (Baodian coal mine) and high voltage line (Nantun coal mine) has great economic and social benefits. Applications prove the research results of paper are correct and reasonable.