Control principle and technology and instability mechanism of surrounding rock in weak regenerated roof

In terms of the large deformation problem of surrounding rock in soft-weak regenerated roof roadway,the in- stability mechanism of surrounding rock of soft-weak regenerated roof is studied by means of on-site investigation,laboratory test and theoretical analysis,and the control principle,support principle and technology for this kind of sur- rounding rock are put forward. The research shows that the soft-weak regenerated roof has self-stabilizing balance arch structure,but it is extremely unstable. Under the action of disturbance,it is loosened and fragmented rapidly,showing the characteristics of local to global instability. Based on the surrounding rock condition of the regenerated roof,an ex- tended mechanics model of “parabola-semi-hyperbola” for the regenerated roof is proposed,that is,the balance arch boundary of the regenerated roof expands upward in the form of “parabola” in the longitudinal direction and extends in the form of “semi-hyperbola” in the transverse direction. According to the calculation of the model,it is found that the load on the scaffolds increases faster when the self-stabilizing balance arch structure of the regenerated roof continu- ously transfers to the deep surrounding rock due to the floor heave of the roadway,which makes the two sides sink as a whole or the corner of the shoulder of the two ribs be destroyed. The non-linear increase of the loose range of the re- generated roof makes the load on the scaffolds increase sharply and the deformation of surrounding rock increase, which ultimately leads to the overall instability of the roadway. Therefore,the basic principle of surrounding rock con- trol of soft-weak regenerated roof of the “protective bottom→solid ribs→control top” is proposed. Combined with the actual situation of regenerated roof roadway in Zhoujing Coal Mine,the floor heave is prevented by drainage,and the scaffold structure is improved to strengthen the support of ribs and roof. The supporting principles of “strengthening the overall restraint,optimizing the scaffold structure and coordinated control between scaffolds” was formed. Then,the combined support technology of “ double-layer metal mesh+pre-supported truss scaffold+shrinkable longitudinal con- nector” has been formed. The engineering test shows that the support technology can effectively control the initial sta- bility of surrounding rock in soft-weak regenerated roof roadway. In the later mining operation,it is recommended to use the “three-in-one” support system to strengthen the support and control the stability of surrounding rock.