Study on the safety thickness of roof in mining of inclined orebody under filling based on the theory of thick plate and loose body

Abstract

[Objective] The determination of roof thickness between different sections in underground filling mining of metal mines is very important for stope stability, especially the research on the calculation method of roof safety thickness under the condition of large thickness span ratio and inclined ore bodies is not sufficient. [Methods] Based on the Reissner theory of thick plate(thickness to span ratio >0.125~0.2) and considering the transverse shear deformation of thick plate, the expression of roof deflection under the condition of four sides fixed support is derived. Based on the traditional Janssen's theory of granular pressure, the expression of granular pressure under the inclined Angle is derived for the situation of the roof covered with loose backfill after mining of inclined orebody. Finally, according to the first strength theory, a mechanical model is established to calculate the critical safety thickness of the roof under the inclined backfill. [Results] The result show that the influence of friction Angle on the safety thickness of the roof is more significant than that of the internal friction Angle. The safety thickness is also influenced by the roof size. When the aspect ratio is less than 1.5, the safety thickness increases linearly and rapidly. Between 1.5 and 3.0, the increase rate of safety thickness gradually slows down, and it is a transition stage from rapid growth to stability. When the aspect ratio is greater than 3.0, the safety thickness will become stable. When the dip Angle of the ore body gradually changes from horizontal to vertical, the friction force of the rock side wall on the backfill body decreases, more loads are gradually transferred to the roof, and the reserved safety thickness will increase accordingly. [Conclusion] Through engineering examples, the calculation of roof safety thickness by Reissner theory of thick plate and the extended Janssen's theory of granular pressure can provide a reasonable critical safety thickness of roof after mining and filling of inclined orebody, and the obtained value of roof safety thickness is both economical and safe, the method of determining the safety thickness of underground mining roof in metal mines is further enriched, and the theoretical basis for the safety management of mining roof in similar mines is provided.

Keywords

Reissner thick plate theory / inclined orebody / scattered body pressure / backfill / thickness of the roof / deformation / mechanical properties / influence factor