Numerical and experimental direct shear tests for coarse-grained soils

Khalkhali, Ahad Bagherzadeh; Mirghasemi, Ali Asghar

doi:10.1016/j.partic.2008.11.006

Cited by 114 publications

(36 citation statements)

References 10 publications

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“…Our results that ϕ f controls F R are supported by geotechnical engineering experiments in which bulk sediment failure is partly controlled by the bed grain size distribution and porosity (λ) and grain angularity, shape, and orientation (e.g., Bagherzadeh-Khalkhali & Mirghasemi, 2009;Bareither et al, 2008;Culshaw et al, 1991 . Normalized median F R from all three field sites combined (sample size not large enough at some sites to show relation) were calculated from values binned at 10% p intervals.…”

Section: Controls On Grain Resistance To Motionsupporting

confidence: 75%

Resistance Is Not Futile: Grain Resistance Controls on Observed Critical Shields Stress Variations

2018

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Estimates of the onset of sediment motion are integral for flood protection and river management but are often highly inaccurate. The critical shear stress (τ*c) for grain entrainment is often assumed constant, but measured values can vary by almost an order of magnitude between rivers. Such variations are typically explained by differences in measurement methodology, grain size distributions, or flow hydraulics, whereas grain resistance to motion is largely assumed to be constant. We demonstrate that grain resistance varies strongly with the bed structure, which is encapsulated by the particle height above surrounding sediment (protrusion, p) and intergranular friction (ϕf). We incorporate these parameters into a novel theory that correctly predicts resisting forces estimated in the laboratory, field, and a numerical model. Our theory challenges existing models, which significantly overestimate bed mobility. In our theory, small changes in p and ϕf can induce large changes in τ*c without needing to invoke variations in measurement methods or grain size. A data compilation also reveals that scatter in empirical values of τ*c can be partly explained by differences in p between rivers. Therefore, spatial and temporal variations in bed structure can partly explain the deviation of τ*c from an assumed constant value. Given that bed structure is known to vary with applied shear stresses and upstream sediment supply, we conclude that a constant τ*c is unlikely. Values of τ*c are not interchangeable between streams, or even through time in a given stream, because they are encoded with the channel history.

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Section: Controls On Grain Resistance To Motionsupporting

confidence: 75%

Resistance Is Not Futile: Grain Resistance Controls on Observed Critical Shields Stress Variations

2018

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“…Although PFC 3D is more helpful in modelling real 3D structures, it has the limitation of considerably more computational time and other controlling aspects associated with loading boundary conditions in 3D simulation [15]. On the contrary, 2D simulation can provide insights into the mechanisms of key phenomena with much less computational time while capturing the complex material mechanical properties with consideration of the material shape effect [16][17][18][19]. erefore, the PFC 2D 5.0 version has been adopted to perform the analysis on the MCS material.…”

Section: Construction Of Mesoscopic Model For Mcs Materials Using Pfcmentioning

confidence: 99%

Research on Simulation Analysis Method of Microbial Cemented Sand Based on Discrete Element Method

Tang

Lian

et al. 2019

Advances in Materials Science and Engineering

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A simulation method for microbial cemented sand (MCS) based on the Two-Dimensional Particle Flow Code (PFC 2D) has been developed in this study. It consists of an identification of mesoscopic contact model for structural mesoscopic particles, development of morphological algorithm for irregular crystal particles, and classification and setting of mesoscopic parameters for compositional materials and particle size distribution simulation. Additionally, an acoustic emission algorithm based on moment tensor theory was developed for discrete element simulation analysis on fracture characteristic of cemented sand under the action of the force. e simulation method proposed in this article/paper may reflect the physical and mechanical characteristics of real microbial cemented sand based on physical experiments. Quantification of the fracture process of microbial cemented sand is possible by introducing a moment magnitude (MW) in discrete element simulation analysis. e material may have greater probability of fracture between the MW ranges of −6.8 and −6.6. e relationship between probability of fracture at different MWs and the MW follows the Gaussian curve. e research results are a new trial for fracture analysis on microbial cemented sand.

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“…It was reported that the mechanical behavior of coarse-grained soils is influenced by the cemented properties [16]. e influence of particle size on the shear strength of coarse-grained soils, subjected to different gradation of the specimen, was investigated by numerical and experimental direct shear tests [17]. It is widely believed that the shear resistance of soil is affected by various factors, such as soil type, compactness, and grading properties.…”

Section: Introductionmentioning

confidence: 99%

A Systematic Method to Evaluate the Shear Properties of Soil-Rock Mixture considering the Rock Size Effect

Ren

Guo-fan

Qiu

et al. 2018

Advances in Civil Engineering

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The soil-rock mixture (S-RM) is widely applied in the geotechnical engineering due to its better mechanical properties. The shear strength, an essential aspect of S-RM which governs the stability and the deformation, is rather necessary to be revealed properly. The extraordinary issue of S-RM compared to fine-grained soils is the grain size effect on the strength analysis. This paper proposes a systematic method to obtain the realistic shear strength of S-RM by detecting the rock size effect. Firstly, based on fractal theory, the rock size was determined as 5 mm by the multifractal property of granular size distribution. Then, based on 2 selected specimen sizes combining the engineering dimension, shear gaps (T) effect and specimen size effect on the shear strength of S-RM have been investigated. It is shown that the gap of the direct shear test decides the physical mechanism of particles forming the shear resistance of S-RM based on the variation of apparent cohesion and mobilized internal friction angle. Specimen size effect is weakened by the gap effect considering the boundary effect. Realistic and stable shear strength parameters of S-RM have been researched by a reasonable gap (0.2–0.4D, where D is the largest particle size).

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Numerical and experimental direct shear tests for coarse-grained soils

Cited by 114 publications

References 10 publications

Resistance Is Not Futile: Grain Resistance Controls on Observed Critical Shields Stress Variations

Resistance Is Not Futile: Grain Resistance Controls on Observed Critical Shields Stress Variations

Research on Simulation Analysis Method of Microbial Cemented Sand Based on Discrete Element Method

A Systematic Method to Evaluate the Shear Properties of Soil-Rock Mixture considering the Rock Size Effect

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