Investigation of key techniques on floor roadway support under the impacts of superimposed mining: theoretical analysis and field study

摘要

Various sizes of coal pillars will be formed after the mining of close-distance coal seams. The concentrated stress formed on the coal pillars can cause serious deformation and failure to the roadway below (floor roadway). Wantian coal mine in Guizhou was taken as an example to study the stress propagation and distribution of roadway by Kirsch equations. Based on the stope condition, a numerical model was established to analyze the changes of stress, displacement, and plastic zones around roadways, and the cause for roadway deformation during the mining of the upper coal seams. The new support scheme was designed and applied at the study site. The results show that the vertical stress, the maximum shear stress, and the plastic zones of the rock surrounding the roadway increase with the mining of the upper working faces. Roadway deformation and failure mainly occurs at floor, sides, and corners. The key of roadway support was to control floor heave, and then to recover the integrity and strength of the surrounding rock of two sides. The developed omnidirectional rotatable drilling equipment can guarantee the success rate of floor drilling. The broken surrounding rock of floor was enhanced through grouting. The high prestress cable was used to support the roof and two sides, and the birdcage cable was for the floor. By the new support system, the roadway deformation was controlled, which could meet the support requirements.