Grain-size analysis by laser diffractometry: comparison with the sieve-pipette method

Loess grain size data used to infer transport direction or wind strength are generally derived from vigorously disaggregated samples. However, these data may not adequately represent the effective particle size distribution during loess transport, if the transported dust contained aggregates of finegrained material. Thin sections of minimally altered C and BC horizons in the late Pleistocene Peoria Loess of Nebraska, USA, indicate the presence of aggregates with diameters of 30 -1000 Am. The larger aggregates (>250 Am) are unlikely to have been transported, and are interpreted as the result of soil faunal activity and other pedogenic processes after deposition. Aggregates smaller than 250 Am could have a similar origin, but laser diffraction particle size analysis suggests that many are sedimentary particles. Comparison of minimally and fully dispersed particle size distributions from each sampling site was used to estimate the modal diameter of aggregates. The aggregate modal diameter becomes finer with decreasing loess thickness, representing increasing distance from the source. A similar trend was observed in the modal diameter of fully dispersed particle size distributions, which represents the mode of sand and silt transported as individual grains. We interpret both trends as the result of sorting during transport, supporting the interpretation that many of the aggregates were transported rather than formed in place. Aggregate content appears to increase with distance from the source, explaining a much more rapid downwind increase in clay content than would be expected if clay were transported as particles smaller than 2 Am diameter. this loess were transported as primary particles, were thoroughly exposed to sunlight and are potentially well suited for luminescence dating. D

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“…2). Underestimation of the % < 2 Am was also reported by Beuselinck et al (1998) and Buurman et al (2001).…”

Section: Evaluation Of the Laser Diffraction Particle Size Analysis Msupporting

confidence: 74%

“…These comparisons have previously been made by Beuselinck et al (1998) and Buurman et al (1997, who showed that both the strength and the form of the relationships between methods depends on the type of sediment or soil analyzed.…”

Section: Evaluation Of the Laser Diffraction Particle Size Analysis Mmentioning

confidence: 99%

Sedimentary aggregates in the Peoria Loess of Nebraska, USA

Mason

Jacobs

Greene³

et al. 2003

CATENA

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“…Furthermore, it is not well understood as to why the supposed feedback mechanisms between flow erosivity and bed morphology result in the slope independence of flow velocity. The objective of this paper is to investigate (1) the exact nature of the bed-flow interaction in eroding rills and (2) the extent to which the observed slope independence of flow velocity can be explained by this [Beuselinck et al, 1998]. …”

Section: Introductionmentioning

confidence: 99%

Interaction between bed roughness and flow hydraulics in eroding rills

Giménez¹,

Govers²

2001

Water Resources Research

121

118

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Abstract. Govers [1992] showed that the flow velocity in rills eroding loose, nonlayered materials could be predicted from knowledge of discharge only (without significant slope or soil effect). The objective of this paper is to investigate to what extent the observed slope independence of flow velocity in eroding rills can be explained by the interaction between rill bed roughness and flow hydraulics. In a laboratory study, two situations were compared: (1) rills which can freely erode a uniform soil layer and (2) rills with a fixed bed geometry. During the experiments, rill discharge and flow velocity were recorded. After each experiment, a detailed topographic survey of the rill bed was carried out using a laser scanner. From these data the main hydraulic variables (mean values of flow depth, wetted perimeter, and hydraulic radius) were estimated. The experiments confirmed the slope independence of rill flow velocities on mobile beds. When the bed is fixed, the flow velocity in rills is clearly slope-dependent. The slope independence of flow velocity on mobile beds is due to a feedback between rill bed morphology and flow conditions. The roughness amplitude (which was assessed from the standard deviation of corrected height values) and the frequency of macroroughness elements (which was assessed by counting the number of peaks per unit length in a previously simplified longitudinal profiles) both increase and tend to counteract the effect of the increase in slope gradient on rill flow velocity. The final rill flow velocity appears to be characterized by a constant average Froude number.

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“…The pipette test is conceptually the most simple and accurate test, see [29], although requires the additional use of a drier and a precision scale. At prescribed times, particle concentrations are measured by weighing the dry residual resulting from 35 ml samples taken at a specified and constant depth y pt using a standard pipette.…”

Section: Descriptionmentioning

confidence: 99%

“…Finally, the contact interactions between particles are simulated using the penalization technique from [25]. This paper is centered on the numerical simulation of the ASTM D-422 [26] sedimentation test; in addition and for comparison purposes the less used buoyancy, [27,28], and pipette [29] tests are also studied. The three tests are used in the laboratory to determine the particle size distribution of granular samples with diameters ranging from 2.5 × 10 −6 m to 70 × 10 −6 m; distributions that cannot be easily measured by standard sieving methods as explained in [30].…”

Section: Introductionmentioning

confidence: 99%

Numerical sedimentation particle-size analysis using the Discrete Element Method

Bravo

Pérez-Aparicio

Gómez‐Hernández

2015

Advances in Water Resources

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Sedimentation processes are generally modelled using an equivalent continuum approach based on the coupling of the Navier-Stokes and the advection-dispersion equations; the sediment concentration within an elementary fluid volume is the variable of interest. Continuous advances in computational capabilities have brought up a new type of modelling that simulates the individual motion and contact interactions of grains: the Discrete Element Method (DEM). In this work, DEM interacts with the simulation of flow using the well known one-way-coupling method, a computationally affordable approach for the time-consuming numerical simulation of the ASTM-D422, buoyancy and pipette sedimentation tests. These tests are used in the laboratory to determine the particle-size distribution of fine-grained aggregates. Five samples with different particle-size distributions are modelled by about six million rigid spheres projected on two-dimensions, with diameters ranging from 2.5 × 10 −6 m to 70 × 10 −6 m, forming a water suspension in a sedimentation cylinder. DEM simulates the particle's movement considering laminar flow interactions of hydrostatic thrust, drag and lubrication forces. The simulation provides the temporal/spatial distributions of densities and concentrations of the suspension.The numerical simulation cannot replace the laboratory tests since it needs the final granulometry as initial data; but, as the results show, these simulations can identify the strong and weak points of each method and eventually recommend useful variations and draw conclusions on their validity, aspects very difficult to achieve in the laboratory.

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Grain-size analysis by laser diffractometry: comparison with the sieve-pipette method

Cited by 360 publications

References 13 publications

Sedimentary aggregates in the Peoria Loess of Nebraska, USA

Sedimentary aggregates in the Peoria Loess of Nebraska, USA

Interaction between bed roughness and flow hydraulics in eroding rills

Numerical sedimentation particle-size analysis using the Discrete Element Method

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