Product Development of a Rock Reinforcing Bolt for Underground Hard Rock Mining

The demand for mineral resources has dramatically increased over the past few decades; this increase directly correlates to an increase in underground mining activity. There are different mining methods for different minerals, and each have their risks. In hard rock mining activities such as mining for gold, rockfalls are the most significant deterrent to obtaining mineral resources. This paper focuses on rock reinforcement systems to prevent fatal rockfalls in underground excavations. Presently, there is a global steel shortage and an increase in prices that has impacted the productivity of the mining operations that support most national economies. The paper’s main objective is to present the improvement of a rock bolt design used to support the roof in underground mining activities and keep working personnel and equipment safe from rockfalls. This study presents two rock bolt designs: a preliminary design and an improved model of the rock bolt. The paper discusses the operation of the rock bolt and provides laboratory test results on the bolt in operation. The principle of operation of the yield bolt is based on the science of radial expansion of hollow tubes in tension, to provide integrity to underground excavations. This functional design of the rock bolt requires less steel and has the same performance as the current rock reinforcement elongates. The research methodology involved interviewing rock mining engineers to determine their desired rock reinforcement device that would adequately meet the unpredictable dynamic and static behavior of underground rocks. The methodology also included experimental tests of a rock bolt design that was aimed at meeting the desired and acceptable performance determined from the interviews. The experimental results were obtained from a 60-ton hydraulic press that simulated seismic activity underground. The experimental results showed several modes of failure for the bolt; however, the improved rock bolt yielded at an average of 200 KN, as designed. During testing of the preliminary bolt design, there were failures that resulted from the manufacturing process of the bolt, such as splitting of the tube due to the welded end components. After a dynamic test, the preliminary bolt tube bent, creating huge forces on the tube which may cause fracture. The coefficient of friction during dynamic testing was lower than during static testing, leading to undesirable results for the preliminary bolt. The optimized bolt design addressed the failures and the low yield tonnage of the preliminary bolt design. It successfully yielded at 20 tons, even during the dynamic event. The bolt had similar alignment issues which caused failure during testing, as can be seen from the results. A guide tube was implemented in the design and the manufacturing process changed; these changes resulted in the bolt having a more reliable performance that met the requirements throughout.

Study and Application of Asymmetrical Disk Tools for Hard Rock Mining

In this article, the method of hard rock mining by undercutting or back incision using asymmetrical disk tools as an alternative to the milling method with the use of cutting tools was described. The results of modelling the penetration of a single asymmetric disk tool edge into an artificial and natural rock sample were presented and compared with empirical laboratory tests. The effect of stand tests for mining artificial rock samples using asymmetrical disk tools mounted on the rotating plate was presented. The tests were carried out on two unique test stands. The solution of an innovative mining head with a complex motion trajectory, using the asymmetrical disk tools, was presented. The innovative mining head especially developed at the AGH Kraków Department of Machinery Engineering and Transport for roadheaders, was presented. The results of preliminary field tests with the use of this mining head were also described.

Mathematical model to optimize drilling-and-blasting operations in the process of open-pit hard rock mining

Purpose is to determine a function of the reduced expenditures connected with drilling-and-blasting operations, loading and hauling operations, and rock fragmentation depending upon the cost of machine-shift of the applied facility, its operation modes, hardness of rock being blasted, cost of the used explosive, and rock fragmentation quality based upon the developed optimization mathematical model. Methods. Method of statistical evaluation of natural blockiness structure of the rock as well as quality of its fragmentation by means of explosive energy has been applied. Statistical studies have been carried out concerning the basic indices of rock fragmentation depending upon its largeness and block hardness. Purposely-designed experimental equipment has been applied for sampling analysis of the rock fracturing in the process of its drilling by means of rotary drilling rig. The abovementioned supported representativeness of the sampling. Findings. Statistical distributions of the rock blockiness structure in terms of each bar length involving its place within the drilling assembly as well as in terms of the well depth have been compiled. Visual comparison of experimental data and theoretical data has helped determine that the statistical distributions of natural blockiness structure of the rock have the closest correlation with gamma distribution which differential function has two positive parameters. Statistical dependence has been defined between drilling-and-blasting results and the total expenditures connected with hard rock mining. Originality. A concept of oversize crushing coefficient has been introduced; its statistical dependence upon the mined rock hardness and specific consumption of the applied explosive has been derived. An alternative has been proposed concerning changes in parameters of the differential function of the assumed gamma distribution relative to the predicted granulometric composition of rock mass. Practical implications. Economic and mathematical model has been developed involving a target function of the total expenditures connected with the listed operations as well as a set of constraints avoiding incorrect decisions. The optimization method makes it possible to control drilling-and-blasting parameters at each stage of hard rock mining.