Stress characteristics of casing pipes filled with slurry and its application in grouting reinforcement for coal seam floor strata

In order to study the influence mechanism of casing pipes filled with slurry on the deformation of rock strata in coal seam floor,the spatial stress model of grouting reinforced casing pipes in floor rock under distributed abutment pressure is established,and the influence mechanism of casing pipes filled with slurry on surrounding rock is theoretically deduced,and the numerical verification is carried out.According to the stress solution in half space under concentrated force,the stress state of any point under the corner of the abutment pressure zone is obtained by integration and corner method.The spatial stress state of any point of the casing pipes in the floor rock below the goaf is obtained by superposition method.Based on the bending rigidity and fracture form of casing pipes,combined with the deformation characteristics of floor strata and casing pipes layout under mining conditions,the stress model centered on casing pipes filled with slurry is established.The deformation characteristics of strata and casing pipes stress characteristics under elastic plastic limit equilibrium conditions are analyzed,and the influence mechanism of casing pipes on the deformation of strata in the failure zone is clarified.The theoretical formula of bending moment and the allowable deformation formula are obtained based on the bending stiffness and allowable stress of casing pipes.Finally,the numerical model is established according to the example of grouting engineering in the floor.The results show that the vertical displacement form of the casing pipes along the axis can be divided into two sections with the failure area as the boundary,and the casing pipes displacement in the failure section is larger.The distribution law of the axial displacement of the casing pipe is consistent with the theoretical analysis,and the process of the casing pipe bending deformation is clarified.When the casing pipes is applied,the displacement and deformation of the monitoring point is less than that when the casing pipes is not applied,and the larger the casing pipes length,the smaller the deformation.The numerical results are consistent with the theoretical analysis,and the group of slurry filling casing pipes can improve the deformation resistance of floor rock.