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Limitations of failure criterion for predicting stope instability.

Limitations of failure criterion for predicting stope instability. Penny Stewart Beng (Mining) PhD. Numerical Modelling. ‘Equivalent continuum’ based numerical models incorporate failure criterion (rock mass tensile failure cutoffs ). Eg. FLAC , FLAC3D , Phases2d and Map3d

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Limitations of failure criterion for predicting stope instability.

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  1. Limitations of failure criterion for predicting stope instability. Penny Stewart Beng(Mining) PhD

  2. Numerical Modelling • ‘Equivalent continuum’ based numerical models incorporate failure criterion (rock mass tensile failure cutoffs). • Eg.FLAC, FLAC3D, Phases2dand Map3d • This presentation provides an explanation as to why rock mass failure criterion are poor predictors of stope failure/instability. • South Crofty case back analysis to assess accuracy of prediction

  3. An Equivalent Continuum (after Hoek and Brown, 1980)

  4. Span 250 m Grey area 3 < -0.69 MPa Predicted Failure zone 60 m Height Width 3 m South Crofty Map3d Predicted Failure zone 3< -0.69MPa (Hoek Brown empirical failure criterion)

  5. Analysis of Numerical Modelling results • Why do the failure criterion based numerical models over predict failure zone? • Possible explanations include; • Just because a rock mass has yielded, it doesn’t necessarily mean it will collapse. • Modelled tensile stresses are not developed in reality - stress redistributed by slip along discontinuities • Have the assumptions of equivalent continuum been met ? anisotropic behaviour ?

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