2D-/3D-stress analysis of deep-seated gold mines in South Africa

Today many mines are built in higher depths to prospect for the needed resources and obtaining them. Not only mines but also many construction and tunneling projects like the Gotthard base tunnel or the Brenner base tunnel advances into these deep laying rock zones where typical high stress phenomena like rock bursts can occur. Higher stress can also lead to problems like high costs caused by high wear or less performance of the rock cutting tools. Due to the complexity of the measurement methods the stress rates were seldom directly quantified. In most cases the stress is only determined by numerical models. This paper and the associated research project deals with the influence of high stress rates on wear and performance of rotary hammer drills in deep-seated mines in South Africa up to a depth of 3900 m. The encountered rocks are high abrasive quartzites with high uniaxial compressive strength. These rocks were mined to reach the decimeter thick gold bearing layers - the so called reefs. The most common geomechanic properties including the rock strength like uniaxial compressive strength or brazilian tensile strength and the abrasivity (e. g. Cerchar abrasivity index, LCPC abrasivity coefficient, petrographic composition with thin section analysis) were determined. In addition to the laboratory testing, the drilling performance and the wear data are collected directly in the mines and will be generated in additional drilling tests. For the evaluation and the interpretation all gathered data will be combined in a MySQL database and will be analyzed statistically using Matlab (The MathWorks). Three 2D cross sections of a regular stope geometry were modeled and calculated with Phase ² (Rocscience) to define the occurring stress and its distribution. For a detailed analysis further complex 3-D models (Flac 3D, Itasca) are calculated. The previous collected field data will be compared to the calculated stress data from the numerical models to benchmark the influence of stress on wear and performance of the used tools. The aim of this research work is to take the advantage of these effects, to increase the efficiency and to optimize the mining progress.