Stresses at the base of dry and dense flows of angular rock fragments in 3-D discrete element modeling: Scaling of basal stress fluctuations versus grain size, flow volume and channel width

Abstract. We have carried out 3-D numerical simulations by using a discrete element method (DEM) to study the mobility of dry granular flows of angular rock fragments. These simulations are relevant for geophysical flows such as rock avalanches. The model is validated by previous laboratory experiments. We show that: 1) the finer the grain size, the larger the mobility of the center of mass of granular flows, 2) the smaller the flow volume, the larger the mobility of the center of mass of granular flows and 3) the wider the channel, the larger the mobility of the center of mass of granular flows. The grain size effect is due to the fact that finer grain size flows dissipate intrinsically less energy. This volume effect is the opposite of that experienced by the flow fronts. Six different channel cross sections are tested. We introduce here a new scaling parameter χ that has the product of grain size and the cubic root of flow volume at the numerator and the product of channel width and flow length at the denominator. The linear correlation between the reciprocal of mobility and parameter χ is statistically highly significant. Parameter χ implies that the mobility of the center of mass of granular flows is an increasing function of the ratio of the number of fragments per unit of flow mass to the total number of fragments in the flow. These are two characteristic numbers of particles whose effect on mobility is scale invariant.

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Combined effects of grain size, flow volume and channel width on geophysical flow mobility: three-dimensional discrete element modeling of dry and dense flows of angular rock fragments

Solid Earth ◽

10.5194/se-8-177-2017 ◽

2017 ◽

Vol 8 (1) ◽

pp. 177-188 ◽

Cited By ~ 10

Author(s):

Bruno Cagnoli ◽

Antonio Piersanti

Keyword(s):

Grain Size ◽

Center Of Mass ◽

Three Dimensional ◽

Granular Flows ◽

Discrete Element ◽

Channel Width ◽

Pyroclastic Flows ◽

Flow Volume ◽

Scale Invariant ◽

Rock Fragments

Abstract. We have carried out new three-dimensional numerical simulations by using a discrete element method (DEM) to study the mobility of dry granular flows of angular rock fragments. These simulations are relevant for geophysical flows such as rock avalanches and pyroclastic flows. The model is validated by previous laboratory experiments. We confirm that (1) the finer the grain size, the larger the mobility of the center of mass of granular flows; (2) the smaller the flow volume, the larger the mobility of the center of mass of granular flows and (3) the wider the channel, the larger the mobility of the center of mass of granular flows. The grain size effect is due to the fact that finer grain size flows dissipate intrinsically less energy. This volume effect is the opposite of that experienced by the flow fronts. The original contribution of this paper consists of providing a comparison of the mobility of granular flows in six channels with a different cross section each. This results in a new scaling parameter χ that has the product of grain size and the cubic root of flow volume as the numerator and the product of channel width and flow length as the denominator. The linear correlation between the reciprocal of mobility and parameter χ is statistically highly significant. Parameter χ confirms that the mobility of the center of mass of granular flows is an increasing function of the ratio of the number of fragments per unit of flow mass to the total number of fragments in the flow. These are two characteristic numbers of particles whose effect on mobility is scale invariant.

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Exploring the influence of rock inherent heterogeneity and grain size on hydraulic fracturing using discrete element modeling

International Journal of Solids and Structures ◽

10.1016/j.ijsolstr.2019.06.018 ◽

2019 ◽

Vol 176-177 ◽

pp. 207-220 ◽

Cited By ~ 13

Author(s):

Liuke Huang ◽

Jianjun Liu ◽

Fengshou Zhang ◽

Egor Dontsov ◽

Branko Damjanac

Keyword(s):

Grain Size ◽

Hydraulic Fracturing ◽

Discrete Element ◽

Discrete Element Modeling ◽

Element Modeling

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An Energy-Based Discrete Element Modeling Method Coupled with Time-Series Analysis for Investigating Deformations and Failures of Jointed Rock Slopes

Applied Sciences ◽

10.3390/app11125447 ◽

2021 ◽

Vol 11 (12) ◽

pp. 5447

Author(s):

Xiaona Zhang ◽

Gang Mei ◽

Ning Xi ◽

Ziyang Liu ◽

Ruoshen Lin

Keyword(s):

Time Series ◽

Iterative Process ◽

Discrete Element ◽

Jointed Rock ◽

Modeling Method ◽

Discrete Element Modeling ◽

Rock Slopes ◽

Sliding Surface ◽

Element Modeling ◽

Displacement Based

The discrete element method (DEM) can be effectively used in investigations of the deformations and failures of jointed rock slopes. However, when to appropriately terminate the DEM iterative process is not clear. Recently, a displacement-based discrete element modeling method for jointed rock slopes was proposed to determine when the DEM iterative process is terminated, and it considers displacements that come from rock blocks located near the potential sliding surface that needs to be determined before the DEM modeling. In this paper, an energy-based discrete element modeling method combined with time-series analysis is proposed to investigate the deformations and failures of jointed rock slopes. The proposed method defines an energy-based criterion to determine when to terminate the DEM iterative process in analyzing the deformations and failures of jointed rock slopes. The novelty of the proposed energy-based method is that, it is more applicable than the displacement-based method because it does not need to determine the position of the potential sliding surface before DEM modeling. The proposed energy-based method is a generalized form of the displacement-based discrete element modeling method, and the proposed method considers not only the displacement of each block but also the weight of each block. Moreover, the computational cost of the proposed method is approximately the same as that of the displacement-based discrete element modeling method. To validate that the proposed energy-based method is effective, the proposed method is used to analyze a simple jointed rock slope; the result is compared to that achieved by using the displacement-based method, and the comparative results are basically consistent. The proposed energy-based method can be commonly used to analyze the deformations and failures of general rock slopes where it is difficult to determine the obvious potential sliding surface.

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