Study of change in the physical-mechanical properties of hard rocks and their fracturing with depth using the example of the Khibiny massif

As the mining operations expand, the issue of the change patterns in the physical and mechanical properties of rocks and parameters of their fracturing with burial depth is becoming increasingly relevant. Information available in the published literature does not provide a clear understanding of how these characteristics vary, thereby explaining the need for field and laboratory investigations during the deposit development. This paper presents the results of a comprehensive analysis of structural fracturing and physical and mechanical properties of the core material taken from a subvertical borehole at one of the deposits within the Khibiny massif. In the interval from 340.0 to 841.0 m below the ground surface, the rock mass quality index, linear fracture frequency, density of four rock types and their uniaxial compressive and tensile strength were determined; fault structures and core discing zones were also identified. It is shown how the physical-mechanical properties of the investigated rocks and their fracturing vary with increasing burial depth.