University of Manchester
Russell, Aaron Stephen.
Frictional Hysteresis in Granular Avalanches.
Degree: 2019, University of Manchester
Geophysical mass flows often occur on inclines
covered by a static layer of erodible granular material, which once
disturbed initiates a flow downslope that grows in size as it
erodes additional material, posing a hazard to the local
population. If the slope is sufficiently steep, material upslope of
the disturbance can also be eroded via an upslope-propagating
erosion wave, or retrogressive failure, which increases the volume
of the flow, posing an increased hazard. This thesis aims to gain
an insight into this complex phenomenon using a combination of
continuum models, small-scale laboratory experiments and numerical
simulations. Shallow dry granular flows over a rough plane inclined
at an angle ζ to the horizontal exhibit a wide range of hysteretic
behaviour, the simplest of which is that when a steady uniform
granular flow is brought to rest it leaves a deposit of thickness
hstop(ζ), but this layer will not start to flow spontaneously
unless it is inclined to a greater angle ζstart. This frictional
hysteresis is directly responsible for flows with co-existing
regions of solid-like and fluid-like behaviour such as
retrogressive failures, self channelised flows with static levees
and erosion-deposition waves. This thesis proposes a new
non-monotonic friction law for granular materials, consisting of
static, intermediate and dynamic friction regimes, that when
combined with a depth-averaged avalanche model can capture all the
hysteretic phenomena observed as well as predicting the correct
deposit depths left behind by steady uniform flows. Retrogressive
failures can be observed in small-scale dry granular flow
experiments by creating a static layer of thickness hstop(ζ), which
due to frictional hysteresis can remain static when inclined to a
steeper angle. If the increase in angle is small, a perturbation to
the layer results in only a downhill propagating avalanche, but if
the increase in angle is large enough an additional upward
retrogressive failure is observed. These retrogressive failure
experiments give indirect measurements of the functional form of
the inherently unstable intermediate friction regime. This thesis
shows that a simple depth-averaged avalanche model combined with
the hysteretic non-monotonic friction law proposed here is
sufficient to capture the observed planar retrogressive failures.
An investigation into the stability of the downstream flow produced
by retrogressive failures provides further constraints on the
functional form of the friction law.
Advisors/Committee Members: JOHNSON, CHRISTOPHER CG, Gray, Nico, Johnson, Christopher.
Subjects/Keywords: Geophysical and geological flows; Granular flow; Shallow water flows; Waves/free-surface flows
to Zotero / EndNote / Reference
APA (6th Edition):
Russell, A. S. (2019). Frictional Hysteresis in Granular Avalanches. (Doctoral Dissertation). University of Manchester. Retrieved from http://www.manchester.ac.uk/escholar/uk-ac-man-scw:322853
Chicago Manual of Style (16th Edition):
Russell, Aaron Stephen. “Frictional Hysteresis in Granular Avalanches.” 2019. Doctoral Dissertation, University of Manchester. Accessed January 25, 2020.
MLA Handbook (7th Edition):
Russell, Aaron Stephen. “Frictional Hysteresis in Granular Avalanches.” 2019. Web. 25 Jan 2020.
Russell AS. Frictional Hysteresis in Granular Avalanches. [Internet] [Doctoral dissertation]. University of Manchester; 2019. [cited 2020 Jan 25].
Available from: http://www.manchester.ac.uk/escholar/uk-ac-man-scw:322853.
Council of Science Editors:
Russell AS. Frictional Hysteresis in Granular Avalanches. [Doctoral Dissertation]. University of Manchester; 2019. Available from: http://www.manchester.ac.uk/escholar/uk-ac-man-scw:322853