Trabajo presentado en el VII Simposio Peruano de Geoingeniería.

Por: Fredy Valeriano y Juan Mayhua, Universidad Nacional del Altiplano; David Córdova, DCR Ingenieros; Fredy Elorrieta, Itasca Perú, y Clyde Bustamante, CORI Puno.

Abstract

Technological advances in rock mechanics and the increase in computational capacity allow us to represent, characterize and understand the behavior of the rock mass from the interaction between its basic components (intact rock and discontinuities) through 3D models. 

Thus, digital photogrammetry is applied to produce a virtual model of the rock mass surface in three dimensions that subsequently allows the user to determine the orientation of exposed discontinuities, its application in underground and open pit mines has been of interest because this method offers quick and easy data acquisition, detailed mapping of the exposed walls can be completed in the office in a timely manner, something that is limited in the field, which is also beneficial in minimizing the risk to personnel associated with being exposed to potentially unstable underground slopes and excavations and working in operating mines that have equipment and machinery around them. 

Photogrammetry is a complementary technology to discrete fracture network (DFN) modeling as it can provide many of the input parameters required for its modeling. Thus, the use of DFN models serves to define equivalent rock mass parameters based on a realistic representation of the rock mass structure and has the potential to improve the predictions achieved by various geomechanical simulations. These models are integrated to the stability analysis of mining excavations with the application of the discrete element method (DEM) with which we can obtain results of the stability conditions of the rock blocks, involving the strength and deformation properties of the intact rock and discontinuities. 

The objective of this technical paper is to present the results of the rock block stability analyses carried out in two mining excavations developed at the Untuca mine, using photogrammetry, discrete fracture network (DFN) model and the application of the discrete element method (DEM). These analyses consider the geological and geomechanical characterization of the rock mass, taking of photographs, construction of 3D photogrammetric models, digital mapping of discontinuities, trace analysis of discontinuities, construction of the discrete fracture network (DFN) model and block stability analyses with the application of the limit equilibrium method and the discrete element method (DEM) that insert the DFN model. 

The results obtained from the characterization of the site establish that the local geology is comprised of porphyroblastic shales, defining four main families of discontinuities comprising stratification, schistosity and two vertical discontinuities, the rock mass is of regular strength with a GSI value between 50 and 60. The structural information obtained using photogrammetry contrasts with the orientations measured using conventional methods, however, this allowed the recording of a greater number of discontinuities in inaccessible locations. 

Photogrammetry allowed obtaining data on orientation, size and fracture intensity, data that were used for the construction of the DFN model, which allowed to adequately represent the geometric characteristics of the rock mass. 

Finally, the stability analysis results were congruent with the observations and stability conditions present on site, obtaining stability evaluations that show with great approximation the instability processes in the underground and surface excavations at local scale through DEM numerical models. It is concluded that the interaction of photogrammetry works, generation of discrete fracture network (DFN) models and the application of the discrete element method (DEM) for the stability analysis of mining excavations at local scale are useful and show with great approximation the instability processes in the excavations.