Application of the HF, DRA and DCDA technologies for in situ stress determination in Iron Quadrangle rock masses

ABSTRACT

This study presents an unprecedented campaign of measurements (magnitudes and orientations) of the in situ stresses in itabirite rocks of the Brazilian Iron Quadrangle region using the hydraulic fracturing (HF), deformation rate analysis (DRA) and diametrical core deformation analysis (DCDA) methods. The previous studies of this rock mass consider estimated values of k, and the practice of using in situ stress tests to support geotechnical analyses of the rock mass of this region has not been adopted. The study site is located at a depth of up to 400 m around a pit. The rock mass under study shows the presence of different geological structures, which made performing the tests difficult. The DRA results show a marked difference compared to the HF and DCDA results; the horizontal stresses were greater than the vertical stresses, which is a finding that may occur due to local geodynamic influences. The results contribute to the understanding of the strains and stresses induced by mining activities in the Brazilian Iron Quadrangle. For a better determination of the regional in situ stresses in the rock mass of the Brazilian Iron Quadrangle, new HF tests, as well as hydraulic testing of pre-existing fractures are recommended.

KEYWORDS:

• In situ stress
• hydraulic fracturing
• deformation rate analysis
• diametrical core deformation analysis
• mining slope
• Brazilian iron quadrangle

Acknowledgments

The authors thank Vale Technological Institute, The University of Western Australia and the companies Vale SA, Japan Oil, Gas and Metals National Corporation, Fukada Geological Institute, and Rede e Geosol for providing the data. Special thanks to the individuals who contributed to the planning, guidance, and interpretation of the results of this study, including geologist Teófilo Costa, Dr. Allan Maia, and Associate Professor Pedro Alameda Hernandez.

Disclosure statement

No potential conflict of interest was reported by the author(s).