Research on the stability of mine workings and the risk of rock caving at the Zhaysan deposit, Kazakhstan

Purpose. This research aims to predict the stability of mine workings and assess the risk of rockbursts in conditions of insufficient knowledge of the mechanical rock properties at the Zhaysan deposit (Kazakhstan), while taking into account the depth of the rock mass occurrence and quality, as well as the orientation of the mine workings relative to the tectonic stress field. Methods. The research employs a set of methods: laboratory testing of granitoid and diabase samples, assessment of rock mass disturbance using the Rock Quality Designation (RQD) index, analysis of metasomatically altered rocks, as well as the construction of a simplified 3D geomechanical model using the kriging method. The rock mass strength was predicted using the Hoek-Brown criterion, while the risk of rockbursts was assessed using the Fragility Index (UCS/UTS) and the Canadian method for assessing rockburst potential. The stability of mine workings in different directions was determined by the indicator of weighted frequency of rockfalls and analysis of their ratio with respect to orientation relative to σ1. Findings. It has been found that with increasing depth, the average RQD values increase from 60 to 90%, reflecting a decrease in fracturing and an improvement in rock mass quality. However, in fresh granitoids, there remains a high risk of elastic energy accumulation and its release during destruction. The critical depth at which rockburst risk begins has been determined to be approximately 400 m. The rocks altered metasomatically are characterized by reduced strength and fragility, which reduces their susceptibility to bursts, but increases the probability of caving. It has been revealed that the stability of the mine workings depends on their orientation: minimal damage is fixed when coinciding with the direction σ1 (azimuth ~300°), and the critical is the angle of intersection 45°, after which the volumes of rockfalls increase sharply. Originality. For the first time for the Zhaysan deposit, laboratory tests, geomechanical parameters (RQD, GSI), analytical strength criteria and analysis of the orientation of mine workings relative to the tectonic stress field were integrated to determine the depth boundary of rockburst hazard occurrence. The necessity of distinguishing between fresh and metasomatically altered granitoids is demonstrated when assessing risks and taking into account the direction of mine workings in project solutions. Practical implications. The results make it possible to identify high danger zones and depths, starting from which an enhanced monitoring of the stress state of the rock mass and the application of special safety measures are required. The proposed approach can be tailored for similar solid mineral deposits with limited source data, as well as can be used when selecting a safe direction for mine workings in the tectonic stress field.