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Comprehensive Investigation of the Role of the Geometrical, Topological, and Mechanical Properties of Discrete Fracture Network, Rock Type, and In-Situ Stress on Over-Excavation Around a Tunnel of El Teniente Mine
Abstract
Over-excavation in underground opening is one of the most significant geo-mechanical hazards in mining and civil projects with potential consequences including cost overruns, time delays, increased rehabilitation, grade dilution, equipment damages, injuries, loss of human lives, and social or environmental consequences. The main objective of this study is to detail study the role of non-controllable parameters, namely rock type, geometrical, topological, kinematical and geo-mechanical properties of the discontinuity network, and in-situ stress on over-excavation around a tunnel of El Teniente Mine. To this end, we investigate the role of each of these parameters on the over-excavation around tunnel using cause–effect approach. We performed extensive sensitivity analysis using Monte Carlo simulation techniques of discrete fracture network and carry out the rigid block failure analysis to capture contribution of the non-controllable parameters on the kinematic state of the rock blocks. It is worth to mention that we assume that the constant value of in-situ stress around tunnel due to low coefficient of variation of the in-situ stress around tunnel (less than 5%). The rock type does not show a significant impact on the over-excavation. The mutual interaction between the induced stress around tunnel and discontinuities shows a significant correlation with observed over-excavation around tunnel. We used the microseismic data to study the potential correlation between over-excavation, fracturing process, and the non-controllable factors. According to the results of this study, the pre-existing discontinuities and their mutual interaction with induced stress around tunnel are the key factors on variational trend of the over-excavation along tunnel at El Teniente mine.
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The primary copper ore at the El Teniente mine is very competent and massive. It is a rock with almost no open discontinuities. Nevertheless, there is a high frequency network of small scale veins coupled with widely spaced faults. A research investigation was implemented to determine what discontinuities are the most relevant in the rock mass disassembly process during cave mining. Rock mass characterization was undertaken at four different scales within the rock mass, in particular the block-forming discontinuities were characterized by studying a significant number of blocks at the caving draw points. Two relevant discontinuity characteristics have been found. The data suggest that discontinuities having approximately less than 1/3 of hard minerals as infill and thicknesses greater than or equal to 2mm are weaker and more likely to define blocks during caving and the subsequent comminution process. The infill characteristics have been used to characterize rock mass quality in different sectors, and the results are in accordance with actual observations at the mine site.
The discontinuities are main factor on discontinuous, anisotropic, and non-elastic behavior of rock mass. The objective of this paper is to present a new discontinuity rating system called “Universal Discontinuity index” (UDi), based on the combination of quantitative and measurable parameters of the discontinuity network, damage mechanics, vectorial based criteria of Warburton for kinematic rock block failure analysis, and Mohr-Columb criteria for shear failure analysis. Applying the UDi permits to capture the heterogeneous and anisotropic nature of the rock mass strength or equivalently the degree of damage. A new, simple, and fast procedure for logging geomechanical drill cores is proposed, which allows UDi to be applicable at every stage of rock engineering projects. We used the UDi for the prediction of the spatial geometry of over-excavation along a tunnel. There is a good agreement between the variational trend computed using UDi and over-excavation along a tunnel observed at El Teniente mine, Chile. Moreover, the good correlation between rock mass quality rating from UDi and Rock Mass index (RMi) demonstrate the reliability of the UDi rating system.
This a new system for characterization of discontinues rock mass. The objective of this new approach is to present a new discontinuity rating system called “Universal Discontinuity index” (UDi), based on the combination of quantitative and measurable parameters of the discontinuity network, damage theory, vectorial based criteria of Warburton for kinematic rock block failure analysis, and Mohr-Columb criteria for shear failure analysis. A new, simple, and fast procedure for inffering the Udi´s parameters for 1D data set, 2D data set and photogrametry data set proposed, which allows UDi to be applicable at every stage of rock engineering projects. Design of the UDi is based on the complete system view using the model integration concept toward digitalization and automatization of the rock mass characterization. At first set of the development, UDi is used to predict rock strength anisotropy and subsequently the spatial geometry of over-excavation along 54 sections of tunnel at New Level of El Teniente mine, Chile. The validation of the results of this approach performed by close collaboration of geomechanics and engineering geology teams of El Teniente, mine. It is worth to mention that there was a good agreement between the variational trend of predictive model computed by UDi and over-excavation along a tunnel observed at El Teniente mine, Chile. This methodology also used to assess the initial damage along tunnel sequences and validate with micro seismic data and rock failures at El Teniente mine.
A critical aspect of rock engineering modelling and rock engineering design is ensuring that all the necessary variables have been included and that the interactions between them are understood-but this is not easy to establish without a guiding methodology. For this reason, the author developed the Rock Engineering Systems (RES) approach in 1992 and, in the 20+ years since then, the RES approach has been used for a wide variety of rock engineering and other problems. As a result, there are now many case studies available which illustrate the application of RES to rock engineering problems. In this paper, the basic RES methodology is outlined and 34 case examples are referenced. The diversity of these 34 case examples illustrates the variety of applications and approaches used by different researchers and practitioners. The link between RES and 'intelligent' methods is emphasised.