Field test and numerical simulation of preconditioning by hydraulic fracturing in hard rock iron mine

Preconditioning by hydraulic fracturing (HF) is a vital technique for assisted caving in block caving mines with poor caveability. Selection of suitable powerful fracturing equipment and the layout of fracturing boreholes need to be fully considered before industry application. For this study, simulation of the HF process was first conducted to determine rock breakdown pressure. The simulation was based on field tests of HF preconditioning in an iron mine, and included: rock breakdown pressure, fracture orientation and extending range. The results show that the data for rock breakdown pressure obtained during this HF simulation could be a guideline for allowable water pressure when selecting water injection pumps for real field applications. Additionally, rock breakdown pressure increased linearly with fracturing depth and had a maximum value of 31.64 Mpa in these tests. Based on microseism positioning analysis of hydraulic fractures, the maximum extending distance was measured at about 34 m when the pumping flow rate was 150 L/min. The extension face of the hydraulic fractures was determined to be horizontal, and this was indirectly verified by the increasing water pressure of a nearby monitoring borehole. The results obtained in this study could be a support for the successful application of preconditioning by hydraulic fracturing in hard rock metal mines.