Abstract
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.
Highlights
Deep resource exploitation is an urgent task to solve the bottleneck of resource shortage in China. e deep metal mine shaft construction project is an important foundation and premise to realize the large-scale development of deep mineral resources
The construction of some metal mine shafts in China is stepping into the stage of ultradeep, such as Sanshandao gold mine in Shandong Province. e field test shows that the in-situ stress at 2000 m depth is as high as 70 Max principal (MPa), and the deep rock mass is in a strong compression in-situ state
According to the on-site core discing characteristics, we found the following interesting questions: (1) e surface of some cores was intact when they were just taken out in Sanshandao gold mine, why did the core discing occur after they were placed for a few days to a few weeks? (2) e core discing is very strong when drilling at 1100 m–1200 m depth in Xincheng gold mine (Figure 1), and the pancake thickness is mostly more than 10 mm
Summary
Deep resource exploitation is an urgent task to solve the bottleneck of resource shortage in China. e deep metal mine shaft construction project is an important foundation and premise to realize the large-scale development of deep mineral resources. With the increase of stratum depth, the in-situ stress of rock mass is higher and higher, and the microcrack damage propagation leads to the core fracture into cake, that is, the core discing phenomenon. As a special phenomenon in the deep stratum, the research on the characteristics and mechanical mechanism of core damage and core discing plays an important role in revealing the variation of physical and mechanical properties of deep strata and the original rock stress environment. (2) e core discing is very strong when drilling at 1100 m–1200 m depth in Xincheng gold mine (Figure 1), and the pancake thickness is mostly more than 10 mm. While in Sanshandao gold mine, the core discing is more common when drilling at 1800 m depth, and the pancake thickness is mostly less than 10 mm (Figure 2). Why does the core discing appear in the hanging wall of the ore vein with shallow burial depth rather than the footwall of the ore vein with greater burial depth? is study attempts to answer the above questions through research
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