Borehole Camera and Extensometers to Study Hanging Wall Stability – Case Study Using Voussoir Beam - Cuiabá Mine

Cuiabá mine, owned by Anglogold Ashanti Córrego do Sítio Mineraç ão, is located in Sabara-MG, with excavations more than 1100m below surface, is one of the most important underground gold mines in Brazil. In recent years, there have been significant problems of instability of the hanging wall (HW) in some stopes (production excavation). In order to understand and anticipate the problems of instability of the hanging wall, a monitoring system was implemented consisting of televised boreholes, in the walls of the excavation. This was in addition to the large number of Multiple Point Borehole Extensometers (MPBX) and SMART cables (Stretch Measurement to Assess Reinforcement Tension) installed in the mine. This paper presents an example of the identification from monitoring, in the Fonte Grande Sul orebody – level 10.2 stope (about 680m below surface), with evidence of instability in the hanging wall. The observation of borehole cracks, shears, failures, and displacements, indicated the beginning of instability in the hanging wall, which allowed measures to be taken to stabilize this area. A detailed follow-up confirmed the stabilization after actions have been implemented. In order to exploit the data collected during the process of study and to attempt to validate a simple method for evaluating the stability of the hanging wall in schist, a stability study was performed using the voussoir arch theory. Despite the identification of the thickness of the beams formed within the hanging wall, the geological complexity, evidenced by interbedded rocks with different elastic characteristics and strength, folds and boudinage, which was beyond the simplification of the calculations, did not allow a proper assessment of the stability of the studied area using the voussoir arch theory.