 |
| Titel |
A new Parameter to Determine Degree of Fragmentation of Rockslides |
| VerfasserIn |
Øystein Thordén Haug, Matthias Rosenau, Karen Leever, Onno Oncken  |
| Konferenz |
EGU General Assembly 2015
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250105923
|
| Publikation (Nr.) |
 EGU/EGU2015-5511.pdf |
|
|
|
|
|
| Zusammenfassung |
| When a rock slope fails, the consequent transport of materials depends on the bulk state of the
rock mass. For example, if the rock mass collapses and disintegrates into a granular material,
appropriate transport models need to consider the physics of granular material to
determine the rock mass transport and final travel length. In contrast, should the failure
occur on a well-defined failure zone and the block have sufficient cohesion, the rock
mass can be considered as an elastic block. However, were the block to experience
high stresses during its travel, for example from impacting the ground after free
falling, it may still fragment and turn into a granular material. Determination of
which systems immediately collapses, which remain intact and which is likely to
fragments during transport is of key importance to choose appropriate transport
models.
To do this requires a quantitative description of which systems will undergo
fragmentation and which will not. To simplify matters somewhat, we only consider
the question whether or not the material experiences enough stresses during its
travel for fragmentation to occur. Fragmentation of a rock mass is determined by
numerous variables such as its intact rock strength, pre-existing fracture density,
size and geometry, as well as the topography of the slope. However, as it is not yet
understood how these variables interact, such a description is still lacking. Here we
suggest such a description for a special case of a cuboid sample traveling over a slope
break.
We perform a series of tests using a newly developed analogue rock material of which the
bulk material cohesion can be controlled. In the tests, a cuboid shaped sample of the analogue
material is released down a slope of 45° at a height of 0.7 m and impacts on a horizontal
plate. The tests show that the degree of fragmentation depends on aspect ratio, kinetic energy
and material strength of the samples.
To collapse of the data from all three variables, we characterize a sample proneness to
fragmentation by a parameter (Seff) consisting of the estimated peak tensile stress in a
samples normalized by its bulk cohesion. The peak tensile stresses in the sample is estimated
from elastic thin plate theory (Kirchhoff’s theory) modified with a factor (h/l)2 due to the
samples non-negligible thickness, where h is the thickness and l is the length of the sample in
the direction of travel.
Combining the experimental test results and the new parameter Seff, we determine
thresholds of the parameter value which discriminate whether fragmentation occur, as well as
between intermediate and high degree of fragmentation. Since Seff is determine solely from
initial conditions, this new parameter can be used to predict the degree of fragmentation. To
test the applicability of our new parameter, we calculate the value of Seff for the Seymareh
rock avalanche and find that its value predicts it to be within the range of highly fragmented
materials, as expected. |
|
|
|
|
|
|