Characteristics and Mechanical Mechanism of In Situ Unloading Damage and Core Discing in Deep Rock Mass of Metal Mine

Based on the phenomena of core damage and core discing in deep strata of metal mines in Laizhou area, the physical and mechanical mechanism behind these phenomena and characteristics is discussed. The analysis shows that the damage effect of deep high stress rock is obvious after in-situ unloading, the core discing occurs when the damage reaches a certain degree, and the time effect of damage increases with the increase of buried depth. The characteristics of core discing are closely related to the stress environment and the mesostructure and mineral composition of the rock. Monzogranite with a large particle size and high content of potassium feldspar is easier to occur core discing than granodiorite in this area. The mechanism of core discing in Sanshandao gold mine is as follows: tensile failure occurs in the middle of the core, and composite failure of shear and tension occurs at the edge. The crack extends from the middle of the core to the outer edge, and finally, the tensile crack and shear crack intersect and connect to form a cake crack. Considering the stress condition and strength conditions of core discing, the energy release rate of rock mass in the core discing area is large, which has the conditions for strong rock burst. In addition, the ratio of maximum stress to tensile strength at the starting position of core discing is about 6.5 in this area, which is consistent with the previous analysis, so as to provide a strong basis for calculating in-situ stress based on the core discing phenomenon.