Akhmedya, Madyar2024-12-242024-12-242024-04Akhmedya, M. (2024). DETERMINATION OF THE STRESS INDUCED DAMAGE INITIATION THRESHOLDS FOR SOME SELECTED ROCK TYPES. Nazarbayev University School of Mining and Geoscienceshttps://nur.nu.edu.kz/handle/123456789/8378Underground mining operations result in a shift of the initial stress field, leading to the formation of large stress concentrations and relaxation resulting in rock failures. The current failure criteria are insufficient in completely describing the damage caused by stress in excavations, making it difficult to evaluate excavation performance and avoid accidents. The parameter s in the Hoek-Brown failure criterion indicates the cohesive strength of the rock. Typically, its value is entirely determined by the quality of the rock mass at a large scale in the field. In the modified failure criterion known as the brittle Hoek-Brown damage initiation criterion, the parameter s is equal to 0.11. Recent findings indicate that the Hoek-Brown parameter, s, varies across different types of hard, strong, brittle, moderate to massive rock masses, and is influenced by the specific rock composition. This thesis highlights the need to revise the existing relationships by determining the brittle Hoek-Brown parameter s for certain chosen rock types in Kazakhstan. The primary goal of the thesis is to determine the stress damage thresholds for eventual estimation of the Hoek-Brown brittle material parameter s for different rock types utilizing uniaxial compression tests (UCS) instrumented with acoustic emission (AE) sensors. The damage initiation stress threshold is the stress level at which cracks begin to occur in a rock under compressive load. For silica-rich rock types, this threshold is shown to be more than 0.8, however according to Martin (1999) it is indicated to be 0.33 for all rock types. The data obtained further demonstrate that the brittle Hoek-Brown parameter s is not the same for all rock types and depends on the genesis of the rock type and mineralogical composition. The analysis also included the impact of grain size and mineralogical composition on the unconfined compressive strength (UCS) and the thresholds for damage initiation. The results indicated that the thresholds for damaging stress and uniaxial compressive strength drop as the grain size increases. Furthermore, more experiments need to be done in order to verify and enhance the database used to determine s values for different kinds of rocks.enAttribution-NonCommercial-ShareAlike 3.0 United StatesMaster`s thesis