Research On Roof Structure And Support Load Of Fully Mechanized Coal Face With Large Mining Height In Shallow Coal Seam

Shallow thick coal seam with rich reserves in northern shaanxi,fully mechanized mining technology with large mining height be widely used.In recent years,the support type is increasing and costs of support rapid increase with the mining height increase,there is no scientific basis for the determination of reasonable support resistance,this will seriously restrict the safety and economic exploitation of coal mine.To research on roof structure and reveal to mechanism of weighting and determine a reasonable support resistance of large mining height coal face in shallow coal seam,this is important significance for theoretical and reality.This paper is based on analysis of the measured data of 5?7m mining height coal face in typical shallow coal seam and nearly shallow coal seam,the support resistance increase along with the increase of mining height,especially when the mining height are reach to 6.8m,the support resistance has risen sharply;the dynamic load coefficient are mainly distributed in 1.4.There is obvious cyclical changes with weighting support load in nearly shallow coal seam,in generally the large periodic weighting step is 2 times of the small periodic weighting step.Through physical simulation and numerical simulation to research the breaking features of roof with large mining height coal face in typical shallow coal seam and nearly shallow coal seam,with the increase of mining height,the thickness of equivalent immediate roof will increase and articulated point of roof structure will move up,the thick equivalent immediate roof breaking has certain hysteresis,that show“cantilever”breaking,the overhanging and breaking of equivalent immediate roof are appear alternately,at ordinary times,the static load of support is bigger.The main form of overlying strata is single key strata and roof structure for "high oblique step voussior beam" in typical shallow coal seam,the common form of overlying strata is double key strata in nearly shallow coal seam,the form of key strata in down group is " lower oblique step voussior beam" structure,the form of key strata in up group is "upper voussior beam" structure,the root cause of large and small periodic weighting is movement of double key strata structure.The degree of filling with equivalent immediate roof for gob will be divided into full filling type and general filling type,the roof structure of nearly shallow coal seam is divided into "double voussior beam" structure and“oblique step voussior beam-voussior beam”structure,the later type is the main form of stope in nearly shallow coal seam.According to analysis of roof structure,the static load of equivalent immediate roof account for higher percentage in support load with large mining height coal face in typical shallow coal seam,about 60%?65%,that result in the support resistance is bigger in not weighting during,the coal face should maintain a reasonable setting load of support,this is based on control with load of equivalent immediate roof,the mechanism of synchronous movement of double key strata leads to large periodic weighting and single movement of lower key strata leads to small periodic weighting in nearly shallow coal seam coal face is explored,the calculate of reasonable support resistance is basic on large periodic weighting in nearly shallow coal seam.Finally,the calculating formula of reasonable setting load of support and support resistance is given,and the reliability of the calculation formula is verified by engineering example,which provide the basis of roof control and support selection in similar coal face,to ensure the safe and economic mining in shallow coal seam.