Overlying strata structures and roof control of working face under thin topsoil and thin bedrock in shallow seam

According to the selection of hydraulic support at working face in shallow seam when the thickness of soil layer is less than the lowest arching height of unloading arch,taking Niushan Coal Mine as an example,using the distinct element software 3DEC and nonlinear multiple regression analysis,the stress distribution in topsoil,the basic roof rock stress state and the working face roof subsidence law were studied. The results show that a small bench convergence of basic rock block can lead to the significant unloading effect in soil layer,which results in the support-surrounding rock structure more stable,and the required support intensity reduced,and first weighting unloading coefficient is only affected by bench convergence and internal friction angle of soil;during initial weighting,the force of A and B block is asymmetric,B block applies a downward vertical component of force to A block;during periodic weighting,D block applies a upward vertical component of force to C block,up to 2. 8 MPa;can determine support intensity according to allowed roof subsidence. In addition,the plastic hinge connecting rod model was established. A formula was given for calculating the working resistance in this case.