Determination of the block volume and the geological strength index (GSI) using photogrammetry approach in Golgohor iron mine of Sirjan

The most common method for surveying of discontinuities is the scanline method which has the shortcomings of low safety, low number of measurements and low accuracy of measurement. Furthermore, determination of the block volumes generated by discontinuities and measurement of the geological strength index (GSI) are other issues in characterization of the rock mass mechanical properties. The Golgohar iron mine has encountered with the above noted issues and due to highly fractured walls of mine No. 1 with high risk of failure, the need for a sophisticated and accurate method for measurement of discontinuities is inevitable. This paper aims to develop a new approach for measurement of the mean block volume, rock quality designation RQD, and the geological strength index GSI of rock masses. To this end, the geometric properties of discontinuities in the 14th bench of the Northwest of mine No. 1 were measured using the photogrammetric method. To determine the geometric properties of the discontinuities on the slope face, control points were marked on the rock face and photos were prepared from the rock surface. Then, using 3DM CalibCam, 3D point clouds were generated and 3D photos were generated. The measurements were used to create a discrete fracture network (DFN) model. To generate the DFN model, FracMan software were used, which ultimately led to the determination of the mean block size, GSI, the mean spacing of each joint set and the RQD of the rock mass. Results of this study showed that the mean block volume is 0.13 m3 and the GSI were measured 65. In order to investigate the ability of proposed method in measurement of RQD and GSI, results of twenty eight core logs from geotechnical boreholes were used. This investigation showed that the results of proposed model are in good agreement with the measured ones.