The development of a blasthole stemming performance evaluation model using a purpose built testing facility

THE DEVELOPMENT OF A BLASTHOLE STEMMING PERFORMANCE EVALUATION MODEL USING A PURPOSE BUILT TESTING FACILITY Supervisor: Prof RJ Thompson Co-Supervisor: Mr B Prout Department: Mining Engineering University: University of Pretoria Degree: M.Eng (Mining Engineering) Abstract The ability of an explosive to break rock is influenced considerably by the extent of confinement in the blasthole and it is believed that confinement is improved by the use of stemming. The aim of this thesis is to present the first and second stages of results in developing a stemming performance testing and evaluation facility for small diameter boreholes. The results showed that different stemming products have differences in terms of their functionality, which can have a major impact on the efficiency of rock breaking. Two test procedures were used, one through the exclusive use of compressed air and the second using a purpose built high pressure test rig with small quantities of explosives. Both tests were used to identify and evaluate the ability of various stemming products to resist the escape of explosive gas through the collar of a blasthole. Extensive research was conducted to determine the types of stemming products most commonly used in South African underground hard rock mines, and the differences in design between the various products are discussed. The first stage of tests using compressed air only did not prove adequate to predict with certainty the pressure behaviour in the borehole of a particular product under high pressure conditions. The purpose built high pressure test rig proved to be a very effective tool to test stemming products under high pressure conditions. The test rig will enable manufacturers of stemming products to optimise stemming design and enable end users to test stemming products under laboratory conditions. Well designed stemming products will improve the rock breaking ability of explosives and decrease energy loss through the collar of the blasthole. With less energy loss through the collar of the blasthole, support and hanging wall damage is reduced, resulting in reduced quantities of explosives needed to provide required fragmentation.The ability of an explosive to break rock is influenced considerably by the extent of confinement in the blasthole and it is believed that confinement is improved by the use of stemming. The aim of this thesis is to present the first and second stages of results in developing a stemming performance testing and evaluation facility for small diameter boreholes. The results showed that different stemming products have differences in terms of their functionality, which can have a major impact on the efficiency of rock breaking. Two test procedures were used, one through the exclusive use of compressed air and the second using a purpose built high pressure test rig with small quantities of explosives. Both tests were used to identify and evaluate the ability of various stemming products to resist the escape of explosive gas through the collar of a blasthole. Extensive research was conducted to determine the types of stemming products most commonly used in South African underground hard rock mines, and the differences in design between the various products are discussed. The first stage of tests using compressed air only did not prove adequate to predict with certainty the pressure behaviour in the borehole of a particular product under high pressure conditions. The purpose built high pressure test rig proved to be a very effective tool to test stemming products under high pressure conditions. The test rig will enable manufacturers of stemming products to optimise stemming design and enable end users to test stemming products under laboratory conditions. Well designed stemming products will improve the rock breaking ability of explosives and decrease energy loss through the collar of the blasthole. With less energy loss through the collar of the blasthole, support and hanging wall damage is reduced, resulting in reduced quantities of explosives needed to provide required fragmentation. Table of contents Abstract 4 Table of contents 5 List of figures 7 List of tables 12 1 BACKGROUND 13 2 PROBLEM DEFINITION 14 2.