Analysis On The Influence Of The Composite Roof Structure Of Coal Seam Roadway On Its Stability

In China,a third of the coal seam roadway roof is a composite roof.because of its complex and changeable structure,it has bought great difficulties to the stability evaluation and support of the roadway,resulting in frequent accidents of roof caving and seriously affecting the safety of coal production.Therefore,it is important to make clear that the influence of the composite roof structure on its stability,which have a great engineering application value.In this paper,Chenghe mining area as the engineering background,using the method of simplified simulation test and structure simulation experiment combined with theoretical analysis,studied the influence of composite roof lithology,thickness,number and position of different structures on the stability and deformation and failure law of composite roof.On the basis of this,a scientific and reasonable classification method for the stability of composite roof has put forward.It provides a scientific basis for the stability control of the roadway of composite roof.The main conclusions are as follows:(1)The characteristics of composite roof structure of coal roadway are generally shown as a composite structure composed of soft and hard rock layers or soft rock layers.The ratio of each rock thickness to the span of coal roadway meets the thin plate assumption(the thickness of rock is less than the 1/5 of coal roadway span).Its characteristic is that the weak surface(joints,bedding and fissures)of each rock stratum is developed,and the cohesive between two layers is small.(2)Through the analysis of the deformation and destruction law,the rule has be summarized as follows,the composite roof damage presents bottom-up strata caving form,its stability is not only related to roadway engineering,geological conditions,main factors affecting the stability of the composite roof lithology,thickness,location,number of layer structure characteristics.(3)Based on the simplified structural mechanics theory of composite roof composite beams,a simplified mechanical test model of composite beams is established,and the mechanical characteristics of composite beams with different lithology,rock thickness,layer number,rock layer position and interlayer bond force are tested.The test results show that:When the thickness of coal roadway composite roof is certain,the stability of the roof increases with the increase of lithology,the thickness of hard rock,the decrease of the distance between the hard and thick strata and the strengthening of the interlayer bonding force,and decreases with the increase of the number of layers.The stability of the roof is less influenced by the number of layers when the number of layers is greater than four layers.The influencing factors are:Lithology>rock thickness>Layer>rock position>interlayer cohesive force.(4)Based on the similarity theory,the similar simulation test method is adopted.A test model for the surrounding rock structure of four coal roadway composite roof roadway is established,which is geometrically similar and equal in strength.The stress distribution and failure characteristics of surrounding rock under ground stress are revealed.The test results show that the stability of the composite roof is very important to the stability of the roadway surrounding rock.(5)On the basis of the above research,and combined with the current classification method of the stability of the composite roof.A new classification method based on composite roof thickness and composite roof strength coefficient has put forward,which will provide a scientific basis for complex structure roof roadway stability control in future.