ICGCM Papers:
Numerical Modeling Developments and Applications
 
 
Investigation of Rock Mass Stability around Tunnels in an Underground Mine in USA by 3-D numerical modeling
35th International Conference on Ground Control in Mining
Investigation of Rock Mass Stability around Tunnels in an Underground Mine in USA by 3-D numerical modeling
by
Yan XingPinnaduwa H.S.W Kulatilake, The University of Arizona, Tucson, United StatesL.A. Sandbak, Barrick Gold Inc., Golconda, United States
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[Conference] 35th International Conference on Ground Control in Mining
[Price] Free  [Comments] 0
[Topical Area] Numerical Modeling Developments and Applications
[Author] Yan XingPinnaduwa H.S.W Kulatilake, The University of Arizona, Tucson, United StatesL.A. Sandbak, Barrick Gold Inc., Golconda, United States
[Abstract] 
Key Conclusions:
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A numerical modeling method was used to investigate the rock mass stability around a complex tunnel system in an underground mine having a complex geology. It was possible to capture the salient features of the complicated stratigraphic condition as well as geological structures. The effects of several factors, such as the lateral stress ratio, the block constitutive model, and rock bolt system, on the stability around the tunnels were evaluated in a detailed way. The results for different cases were compared with the field monitoring data, and from that the most applicable case is suggested. A reliable prediction is made for further maintenance as well as future development of the tunnels in this underground mine.
Key Findings:
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In-situ stresses were calculated by applying appropriate boundary conditions to the numerical model. With the increase of the lateral stress ratio (K0), the maximum vertical displacements on the roof and floor of the tunnels decrease while the maximum horizontal displacements on the walls of the tunnels increase. The case with K0 value of 1.0 is the most stable case with the least failure zones around tunnels. By considering the nonlinear softening behavior of the material, more deformation and larger failure area occur in the surrounding rock masses of the underground tunnels. Under the case with the support system, the numerical model is more stable with decreased displacement and failure elements around the tunnels. It was found necessary to increase the bolt yield capacity or bolt density to improve the stability of the rock bolts on the walls of the tunnels.
Objective of the Paper:
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The main objective of the paper is to evaluate stability around tunnels in three dimensions using a methodology which has the capability of modeling the aforementioned complex features of the mine. A three-dimensional numerical model is set up using the 3DEC (Three Dimensional Distinct Element code) software package. It is based on the distinct element method (DEM), which can accommodate large displacements, rotations and complex constitutive behavior for both intact material and discontinuities. Based on the available information on the stratigraphy, geological structures and mechanical properties of rock masses and discontinuities from the underground mine, stress analyses of the 3-D numerical model were performed to investigate the rock mass stability around underground tunnels. Results of the stress, displacement, failure zone, accumulated plastic shear strain and post-failure cohesion distributions were obtained for different cases. Comparisons are made between the field deformation measurements and numerical simulations.
Problem Statement:
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The studied underground mine currently produces between 20,000 and 30,000 tons of ore monthly; based on that more than 20 years of mining life is remaining. Besides two shafts for ventilation, for men and materials transportation, and ore hoisting, development drifts have been designed to extract and transport the ore. The cut-and-fill mining method is adopted due to the relative low rock quality in ore zones and the dipping geometry of ore body around 25 – 45 degrees. The stratigraphy at this mine consists of cabornaceous mudstones and limestone, tuffaceous mudstones and limestone, polylithic megaclastic debri flows, fine-grained debri flows and basalts, all part of the Cambrian-Ordovician Comus formation. These units are overlain by more basalts, mudstone and cherts that may be part of Ordovician Valmy formation or may be a continuation of the Comus formation. The regional geology of the mine area is structurally and stratigraphically complex with intrusive dikes and sills. Most faults in this mine area are roughly striking NS or NW with high dip angles. Faults with small offsets are observed commonly underground and it is difficult to trace most of the faults for more than a few hundred feet. Due to the complexities in geology, some weak rock mass mechanical properties and a complex tunnel geometry system, evaluation of stability around tunnels is very challenging and requires a methodology which can appropriately model the aforementioned complexities and material properties.