Substantiation of the optimal mining sequence of an ore deposit under conditions of high stress and low rock mass strength

Abstract

Introduction. When choosing the mining sequences of an ore deposit, technological and organizational factors are mostly taken into account. However, when using systems with caving which involve considerable mined-out spaces, the geomechanical factor, which determines stability of mine workings, plays a determining role. The research objective is to reveal the dependence between the stability of the development and face-entry headings within the mined-out space influence zone and the excavation sequence of the isolated ore block under conditions of high stress and low ore and rock mass strength. Methods of research. Numerical modeling of the enclosing ore and rock mass secondary stressstrain state formation was carried out by the finite element method in the Rocscience RS3 program together with the original FEM software package. Modeling was performed for two variants of block excavation – from the center to the flanks and from one flank to the other along the strike. For the analysis, we proposed a coefficient representing the product of compressive stress concentration zones length by their existence duration. Results. Based on the analysis of the maximum stress concentration areas distribution in the marginal rock mass, as well as the time of their influence, the optimal sequence of actual mining was substantiated according to the factor of influence on bottom workings stress-strain state – from flank to flank along the strike. Conclusions. The obtained result confirms the model representations about the mechanism of rock mass stressed redistribution in the process of lens-shaped deposit excavation. The representations suggest that during mined-out space development along the strike, compressive stresses concentrate at its ends. However, the intensity of end sections expansion in the flank to flank variant is two times as high as in the center to flank variant. The duration of the stress concentration zones impact on the bottom workings is therefore less, which is indicated by the proposed coefficient.