In April 2016 Manchester eScholar was replaced by the University of Manchester’s new Research Information Management System, Pure. In the autumn the University’s research outputs will be available to search and browse via a new Research Portal. Until then the University’s full publication record can be accessed via a temporary portal and the old eScholar content is available to search and browse via this archive.

Frictional Hysteresis in Granular Avalanches

Russell, Aaron Stephen

[Thesis]. Manchester, UK: The University of Manchester; 2019.

Access to files

Abstract

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.

Bibliographic metadata

Type of resource:
Content type:
Form of thesis:
Type of submission:
Degree type:
Doctor of Philosophy
Degree programme:
PhD Mathematical Sciences
Publication date:
Location:
Manchester, UK
Total pages:
154
Abstract:
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.
Thesis main supervisor(s):
Thesis co-supervisor(s):
Language:
en

Institutional metadata

University researcher(s):

Record metadata

Manchester eScholar ID:
uk-ac-man-scw:322853
Created by:
Russell, Aaron
Created:
16th December, 2019, 16:52:08
Last modified by:
Russell, Aaron
Last modified:
6th January, 2020, 08:30:18

Can we help?

The library chat service will be available from 11am-3pm Monday to Friday (excluding Bank Holidays). You can also email your enquiry to us.