Incipient motion conditions for single rock fragments in simulated rill flow

AbstractGranular flows of angular rock fragments such as rock avalanches and dense pyroclastic flows are simulated numerically by means of the discrete element method. Since large-scale flows generate stresses that are larger than those generated by small-scale flows, the purpose of these simulations is to understand the effect that the stress level has on flow mobility. The results show that granular flows that slide en mass have a flow mobility that is not influenced by the stress level. On the contrary, the stress level governs flow mobility when granular flow dynamics is affected by clast agitation and collisions. This second case occurs on a relatively rougher subsurface where an increase of the stress level causes an increase of flow mobility. The results show also that as the stress level increases, the effect that an increase of flow volume has on flow mobility switches sign from causing a decrease of mobility at low stress level to causing an increase of mobility at high stress level. This latter volume effect corresponds to the famous Heim’s mobility increase with the increase of the volume of large rock avalanches detected so far only in the field and for this reason considered inexplicable without resorting to extraordinary mechanisms. Granular flow dynamics is described in terms of dimensionless scaling parameters in three different granular flow regimes. This paper illustrates for each regime the functional relationship of flow mobility with stress level, flow volume, grain size, channel width, and basal friction.

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Effect of Mean Velocity-to-Critical Velocity Ratios on Bed Topography and Incipient Motion in a Meandering Channel: Experimental Investigation

Water ◽

10.3390/w13070883 ◽

2021 ◽

Vol 13 (7) ◽

pp. 883

Author(s):

Nargess Moghaddassi ◽

Seyed Habib Musavi-Jahromi ◽

Mohammad Vaghefi ◽

Amir Khosrojerdi

Keyword(s):

Experimental Investigation ◽

Critical Velocity ◽

Velocity Ratio ◽

Scour Depth ◽

Incipient Motion ◽

Mean Velocity ◽

Straight Path ◽

Meandering Channel ◽

Bed Topography ◽

The Mean

As 180-degree meanders are observed in abundance in nature, a meandering channel with two consecutive 180-degree bends was designed and constructed to investigate bed topography variations. These two 180-degree mild bends are located between two upstream and downstream straight paths. In this study, different mean velocity-to-critical velocity ratios have been tested at the upstream straight path to determine the meander’s incipient motion. To this end, bed topography variations along the meander and the downstream straight path were addressed for different mean velocity-to-critical velocity ratios. In addition, the upstream bend’s effect on the downstream bend was investigated. Results indicated that the maximum scour depth at the downstream bend increased as a result of changing the mean velocity-to-critical velocity ratio from 0.8 to 0.84, 0.86, 0.89, 0.92, 0.95, and 0.98 by, respectively, 1.5, 2.5, 5, 10, 12, and 26 times. Moreover, increasing the ratio increased the maximum sedimentary height by 3, 10, 23, 48, 49, and 56 times. The upstream bend’s incipient motion was observed for the mean velocity-to-critical velocity ratio of 0.89, while the downstream bend’s incipient motion occurred for the ratio of 0.78.

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Spatial distribution patterns of rock fragments and their underlying mechanism of migration on steep hillslopes in a karst region of Yunnan Province, China

Environmental Science and Pollution Research ◽

10.1007/s11356-019-05658-1 ◽

2019 ◽

Vol 26 (24) ◽

pp. 24840-24849 ◽

Cited By ~ 2

Author(s):

Juan Liu ◽

You-xin Shen ◽

Xi-ai Zhu ◽

Gao-juan Zhao ◽

Zhi-meng Zhao ◽

...

Keyword(s):

Spatial Distribution ◽

Yunnan Province ◽

Distribution Patterns ◽

Underlying Mechanism ◽

Karst Region ◽

Spatial Distribution Patterns ◽

Rock Fragments

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Flume experimental evaluation of the effect of rill flow path tortuosity on rill roughness based on the Manning–Strickler equation

CATENA ◽

10.1016/j.catena.2014.01.011 ◽

2014 ◽

Vol 118 ◽

pp. 226-233 ◽

Cited By ~ 13

Author(s):

Stefan Martin Strohmeier ◽

Sayjro Kossi Nouwakpo ◽

Chi-Hua Huang ◽

Andreas Klik

Keyword(s):

Experimental Evaluation ◽

Flow Path ◽

Path Tortuosity ◽

Rill Flow

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Late Wisconsinan glacial stratigraphy and history of southeastern Manitoba

Canadian Journal of Earth Sciences ◽

10.1139/e80-002 ◽

1980 ◽

Vol 17 (1) ◽

pp. 19-35 ◽

Cited By ~ 22

Author(s):

James T. Teller ◽

Mark M. Fenton

Keyword(s):

Carbonate Rocks ◽

Lacustrine Sediment ◽

Precambrian Rock ◽

Lake Agassiz ◽

Rock Fragments ◽

Lithostratigraphic Units ◽

Stratigraphic Position ◽

History Of ◽

International Boundary ◽

Late Wisconsinan

The history of Late Wisconsinan glaciation in southwestern Manitoba has been established by identifying and correlating ice-laid lithostratigraphic units in the subsurface. Five Late Wisconsinan tills are defined on the basis of their texture, mineralogic composition, and stratigraphic position. These new formations are, from youngest to oldest, Marchand, Whitemouth Lake, Roseau, Senkiw, and Whiteshell Formations.Late Wisconsinan ice first invaded southeastern Manitoba 22 000 to 24 000 years ago. This Laurentide glacier advanced from the northeast across the Precambrian Shield and deposited the sandy Whiteshell and Senkiw tills, which contain abundant Precambrian rock fragments and minerals and few Paleozoic carbonate grains. Shortly after this, Keewatin ice advanced from the northwest over Paleozoic carbonate rocks, depositing the loamy carbonate-rich Roseau Formation throughout most of the area. This ice remained over southeastern Manitoba until after 13 500 years ago, when it rapidly retreated northward with Lake Agassiz on its heels. Two brief glacial readvances occurred. The first overrode Lake Agassiz lacustrine sediment as far south as central North Dakota shortly after about 13 000 years ago. The clayey Whitemouth Lake till was deposited in southern Manitoba at this time. After a rapid retreat, the ice briefly pushed southward over southeastern Manitoba about 12 000 years ago to just south of the International Boundary. The sandy carbonate-rich Marchand Formation was deposited at this time as the ice overrode its own sandy outwash. By 11 000 years ago, ice had disappeared from southeastern Manitoba.

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