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Back analysis of the strainburst associated rock fragment ejection in an underground crosscut
Highlights Underground crosscut faced abrupt rock fragment ejection ascribed to strainburst. Fragment ejection due to extra stress from seismic wave onto initial stress. Wave raised the tangential stress thus triggered the rock fragment ejection. Rockmass exhibited post peak brittleness response resulted in energy dissipation. Suitable critical plastic strain multiplier value was 0.3 in the Mafic rock unit.
Abstract Deep, highly stressed hard rock underground mines tend to experience elevated elastic strain energy which can dissipate around excavations causing rock fragment ejections and damage attributed to strainbursts. Prediction of this mechanism is challenging as its occurrence leads to operation delays, a high possibility of excavation collapse and fatalities. This paper outlines the back analysis of a strainburst associated rock fragment ejection displayed in an underground crosscut. This investigation is based on the preliminary rockmass structure review, an Institute of Mine Seismology (IMS) microseismic spectral analysis, mXrap stope blast event monitoring, the rock fragment ejection velocity and elastic strain energy computation. Coupled with an explicit finite volume numerical simulation to identify the initial and modified tangential stress around the crosscut. This FLAC3D numerical simulation employs an advanced strain-softening IMASS constitutive model governed by the peak and residual bounding Hoek-Brown (HB) strength envelopes. In this simulation, a plastic multiplier takes into account the rockmass's post-peak brittle behaviour, characterised by the dynamic response to strainbursts. For this post-peak brittleness behaviour, the critical plastic shear strain multiplier is varied between 0.0 and 1.0. It is deduced from this study that the strainburst associated rock fragment ejection was not fault-slip linked only triggered by a dynamic disturbance from the seismic event. It was ascribed to a tangential stress component overlaid with a stress pulse which emanated from the 1.6 ML seismic event 30 m above the crosscut. The shear wave from the event created a dynamic stress pulse that modified the initial static tangential stress that exacerbated the rock fragment ejection process. In addition, the deviatoric stress increment (45 MPa to 58 MPa) measured from the seismic source was directly proportion to the strainburst potential and its increment raised the brittle shear ratio (BSR) from 0.22 to 0.42.
Back analysis of the strainburst associated rock fragment ejection in an underground crosscut
Highlights Underground crosscut faced abrupt rock fragment ejection ascribed to strainburst. Fragment ejection due to extra stress from seismic wave onto initial stress. Wave raised the tangential stress thus triggered the rock fragment ejection. Rockmass exhibited post peak brittleness response resulted in energy dissipation. Suitable critical plastic strain multiplier value was 0.3 in the Mafic rock unit.
Abstract Deep, highly stressed hard rock underground mines tend to experience elevated elastic strain energy which can dissipate around excavations causing rock fragment ejections and damage attributed to strainbursts. Prediction of this mechanism is challenging as its occurrence leads to operation delays, a high possibility of excavation collapse and fatalities. This paper outlines the back analysis of a strainburst associated rock fragment ejection displayed in an underground crosscut. This investigation is based on the preliminary rockmass structure review, an Institute of Mine Seismology (IMS) microseismic spectral analysis, mXrap stope blast event monitoring, the rock fragment ejection velocity and elastic strain energy computation. Coupled with an explicit finite volume numerical simulation to identify the initial and modified tangential stress around the crosscut. This FLAC3D numerical simulation employs an advanced strain-softening IMASS constitutive model governed by the peak and residual bounding Hoek-Brown (HB) strength envelopes. In this simulation, a plastic multiplier takes into account the rockmass's post-peak brittle behaviour, characterised by the dynamic response to strainbursts. For this post-peak brittleness behaviour, the critical plastic shear strain multiplier is varied between 0.0 and 1.0. It is deduced from this study that the strainburst associated rock fragment ejection was not fault-slip linked only triggered by a dynamic disturbance from the seismic event. It was ascribed to a tangential stress component overlaid with a stress pulse which emanated from the 1.6 ML seismic event 30 m above the crosscut. The shear wave from the event created a dynamic stress pulse that modified the initial static tangential stress that exacerbated the rock fragment ejection process. In addition, the deviatoric stress increment (45 MPa to 58 MPa) measured from the seismic source was directly proportion to the strainburst potential and its increment raised the brittle shear ratio (BSR) from 0.22 to 0.42.
Back analysis of the strainburst associated rock fragment ejection in an underground crosscut
Kabwe, Eugie (author) / Banda, Webby (author) / Bowa, Victor Mwango (author) / Kabwe, Eurie (author)
2023-06-16
Article (Journal)
Electronic Resource
English
Numerical Analysis of Unloading-Induced Rock Failure: Insight into Strainburst Mechanism
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