• Admin
    UC Research Repository
    View Item 
       
    • UC Home
    • Library
    • UC Research Repository
    • College of Engineering
    • Engineering: Theses and Dissertations
    • View Item
       
    • UC Home
    • Library
    • UC Research Repository
    • College of Engineering
    • Engineering: Theses and Dissertations
    • View Item
    JavaScript is disabled for your browser. Some features of this site may not work without it.

    Browse

    All of the RepositoryCommunities & CollectionsBy Issue DateAuthorsTitlesSubjectsThis CollectionBy Issue DateAuthorsTitlesSubjects

    Statistics

    View Usage Statistics

    Numerical Modelling of the Micromechanical Behaviour of Catastrophic Long Run-Out Rock Avalanches

    Thumbnail
    View/Open
    De Graaf, Kim_Final PhD Thesis.pdf (39.01Mb)
    Author
    de Graaf, Kim L.
    Date
    2016
    Permanent Link
    http://hdl.handle.net/10092/13589
    Thesis Discipline
    Civil Engineering
    Degree Grantor
    University of Canterbury
    Degree Level
    Doctoral
    Degree Name
    Doctor of Philosophy

    Long runout rock avalanches occur in steep mountainous areas, typically due to the effects of heavy rain, freeze-thaw cycles or seismic shaking among others. The runout is renowned for travelling a large horizontal distance in comparison to the vertical fall height and the extent is largely determined by the volume of source rock. The material dynamically disintegrates during runout depositing angular fragments surrounded by rock flour and preserving the original stratigraphy.

    The propagation mechanism of long runout rock avalanches has been debated for over a century. The majority of the mechanical theories suggested to explain the long runout behaviour may focus on a particular aspect noted from one or several events, however, do not properly explain the angularity of the grains within the deposit or the possible internal behaviour of the avalanche.

    This thesis aims to investigate the fragmentation theory of rock avalanche propagation from a soil mechanics perspective. The rapid application of load and high speed shearing is postulated to cause the dynamic fragmentation of debris, where the rapid movement of fragments and fines reduces effective stress and therefore friction, increasing mobility. Material then moves rapidly until all available kinetic energy has been dissipated or no further dynamic fragmentation can occur. The potential influence of multiple dynamic fragmentation events occurring at once provides useful information for the prediction and extent of rock avalanches, along with micro scale behaviour of rock under rapid loading and high speed shearing for mining purposes.

    Discrete Element Modelling (DEM) via the use of PFC3D has been utilised to undertake oedometer and shear box testing of idealised samples. These tests are used to represent dominant mechanisms that occur in the two key periods of a long runout rock avalanche — the fall (modelled by high strain rate oedometer testing) and the runout (modelled by high speed shear box testing). Synthetic and fully calibrated bonded particle models are used to investigate the response of rock boulders under these conditions. The calibrated materials of sandstone, weak chalk and extremely weak chalk were chosen to represent typical large and small scale long runout events.

    Numerical oedometer testing reveals that the application of high strain rates normal to the ground surface produces fast and significant breakage along with a noticeable response in kinetic energy and a reduction in mobilised friction. The additional kinetic energy remains available in the system for a longer period of time than that produced by semi-static strain rates. The high strain rate oedometric tests suggest that dynamic fragmentation occurs under fast loading rates. It is plausible that dynamic fragmentation in a sturzstrom due to rapid loading at the transition point from fall to runout can enhance mobility.

    High speed shear box testing indicates a significant rise in normal and shear stresses resulting in intense crushing and dilation rather than dynamic fragmentation. Kinetic energy produced from breakages is quickly dissipated through dilation and does not remain in the system long enough to influence mobility. The majority of the shearing is likely to occur in a small zone at the base of the debris. The minimal mixing of layers during the shear testing and substantial dilation supports the observed preservation of stratigraphy and increase in debris volume seen at the majority of sturzstrom sites.

    Collections
    • Engineering: Theses and Dissertations [2267]
    Rights
    https://canterbury.libguides.com/rights/theses

    UC Research Repository
    University Library
    University of Canterbury
    Private Bag 4800
    Christchurch 8140

    Phone
    364 2987 ext 8718

    Email
    ucresearchrepository@canterbury.ac.nz

    Follow us
    FacebookTwitterYoutube

    © University of Canterbury Library
    Send Feedback | Contact Us