Optimization analysis of layered materials of composite filling body beside gob-side entry retaining

Along the hollow stay lane roadside filling body is divided into letting pressure layer and compression layer, letting pressure layer material should have the characteristics of large deformation, slow down the violent activities of the basic roof rock beam. The compressive layer material should be characterised by high strength and rigidity, and effective control of the overlying rock beams should be achieved after flexible letting pressure. Therefore, this paper analyzes the mechanical properties of different ratios of yield layer and compressive layer materials, and analyzes the microstructure of the control group and optimization group of yield layer and compressive layer by scanning electron microscope ( SEM ). Finally, the optimal ratio of yield layer and compressive layer is tested. The results of the study showed that the optimum ratio of the material for letting the compaction layer was 1.5:1 for the water-cement ratio, 0.06% for the blowing agent dosage and 0.2% for the fibre dosage. The compressive strength of the optimised group reached 8.84Mpa at 28d. Strain at different ages was 1.8 to 2.6 times higher in the optimised group than in the control group. The compressive layer material ratio of 40% fine gangue rate, slurry mass concentration of 78%, cement dosage of 20% is optimal, the average compressive strength of 13.21MPa, tensile strength of 0.97MPa, modulus of elasticity of 0.75GPa, the angle of internal friction of 26 °, cohesion of 2.85MPa. The filler at this ratio showed a gradual increase in strength with the increase in cement dosage in the later stages. When the yield layer accounts for 10 % -20 % of the composite specimen, it has good yield capacity and certain key bearing capacity. The research results provide a reference for the material ratio of roadside filling body in gob-side entry retaining.