Browsing by Author "Suorineni, Fidelis T."

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    Failure Mechanisms of Pillars under Shear Loading
    (2010-10) Mgumbwa, Juma J.; Suorineni, Fidelis T.; Kaiser, P. K.
    Pillars are any structures left between two or more underground openings. The stability of pillars is normally considered to depend on shape (defined by width to height ratio), rock mass strength, extraction ratio, in situ stresses and the gross structural features (i.e. joints, contacts, faults etc). Recent experience has shown that pillar stability is also controlled by the relative orientation of the orebody with respect to the in situ principal stress. In inclined orebodies, pillars are loaded in compression and shear, thus creating unsymmetrical stress distribution. Failure mechanisms of these pillars are little known. This paper investigates the failure mechanisms of pillars under shear loading. Two dimensional elastic numerical modeling was used to examine the behavior of pillars in different orebody inclinations relative to the major farfield stress orientation. First, the paper reviews pillar design approaches including the empirical pillar design chart and uses numerical modeling to investigate the effect of the major farfield stress orientation on pillar stability. It is concluded that the empirical pillar design chart be used with caution, and that for orebodies under shear loading mine planning and design should take this into consideration since such geometrical orebody/stress relations put mine structures at higher risk of instability.
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    Mining Of Orebodies under Shear Loading Part 1 - Case Histories
    (Maney Publishing, 2011) Suorineni, Fidelis T.; Kaiser, P. K.; Mgumbwa, Juma J.; Thibodeau, Denis
    The conditions for rockbursts occurrence are traditionally identified as: high stress, highextraction ratio, strong brittle rocks, folding, faulting and unfavourable excavation geometry.Some rockbursts cannot be explained by any one or a combination of these factors. Salamon(1983) stated that a disconcerting feature of rockbursts is that they defy conventional explanation.Based on detailed review of case histories, this paper identifies oblique loading of orebodies bythe major far field principal stress as a cause of rockbursts. Orebodies subjected to this loadingcondition are termed orebodies in shear. Orebodies in shear are subjected to compressive andshear loads. This paper shows it is risky to generalise that tabular orebodies have their axisperpendicular to the major far field principal stress. This study identifies characteristics oforebodies in shear and the consequences of not taking this loading mechanism into account inthe planning, design and mining of such orebodies.
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    Mining Of Orebodies under Shear Loading Part 2 -Failure Modes and Mechanisms
    (Taylor and Francis, 2014) Suorineni, Fidelis T.; Mgumbwa, Juma J.; Kaiser, P. K.; Thibodeau, Denis
    Part 1 of the paper defined shear loaded orebodies and showed through case histories that bothpillars and excavations are at elevated risks of failure when mining these orebodies. Part 2 of thepaper presents new knowledge on the behaviour of pillars and excavations when mining suchorebodies. Numerical modelling is used to understand the behaviours of these structures in theorebodies. It is established that pillars in shear suffer confinement loss compared to theirequivalents under pure compression. The confinement loss increases with increasing shearloading in pillars with width : height (W : H)§1. For pillars with W : H §1, the Lunder andPakalnis (1997) empirical pillar design chart should be used with caution. For excavations ineccentrically loaded orebodies, passive and active high stress envelopes are created in theexcavation process. The combined effect of the active high stress and tension zones often resultsin excavation surface sloughing.
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    Stability of Pillars and Tabular Excavations under Shear Loading Conditions
    (2011-05) Suorineni, Fidelis T.; Mgumbwa, Juma J.; Mfanga, Reginald D.; Kaiser, P. K.
    Rockbursts are a major hazard in deep hard rock underground mining and tunneling. To date a significant number of rockbursts still defy conventional explanations. A review of rockburst case histories in the literature has shown that pillars and tabular excavations under shear loading are prone to rockbursting in situations where they are least expected under conventional knowledge of rockburst causes. Despite the evidence of the effects of shear loading on underground infrastructure, and the frequency of their occurrence, little is known about how this loading mechanism causes such large magnitude events and extensive damage. In this paper analytical and numerical modeling are used to understand the behaviour of pillars and tabular excavations under shear loading. The numerical modelling results show that pillars under shear loading are less confined than their equivalents in loaded in pure compression in the same geologic environment, and are therefore more brittle and weak. For tabular excavations under shear loading, the behaviour depends on whether such excavations are continuous, co-planar or offset with rock bridges. Analytical results based on slit theory show releasable potential energy in tabular excavations increases nonlinearly with excavation half-span. The study results are important for the safe and economic extraction of orebodies under shear loading.