FRACTAL MODEL FOR SURFACE EROSION OF COHESIVE SEDIMENTS

Fractals ◽  
2014 ◽  
Vol 22 (03) ◽  
pp. 1440006 ◽  
Author(s):  
YONGFU XU ◽  
HAO JIANG ◽  
FEIFEI CHU ◽  
CHUANXIN LIU
Keyword(s):  
Erosion Rate ◽  
Aggregate Size ◽  
Fractal Model ◽  
Surface Erosion ◽  
Physical Interaction ◽  
Cohesive Sediments ◽  
Erosion Threshold ◽  
Median Diameter ◽  
Excess Density ◽  
The Relationship

On the basis of the physical interaction of turbulent bursts with cohesive sediments, a fractal model is proposed for the erosion threshold and the erosion rate of the surface erosion. The existed models for the surface erosion of cohesive sediments in general are lacking in considering the aggregate size distribution in cohesive sediments. In this paper, the aggregate structure within cohesive sediments is described by the fractal model. The relationship is developed for the erosion threshold and the erosion rate as functions of the median diameter and excess density from the fractal model. A stochastic formulation for the surface erosion of cohesive sediments is incorporated in the proposed relations. The proposed relations from the fractal model for aggregates are validated against a bulk number of experimental data. The proposed relations have a series of advantages over other methods of direct measuring erodibility.

scholarly journals Comparison of Methods for Determining Erosion Threshold of Cohesive Sediments Using a Microcosm System

2021 ◽  
Vol 8 ◽  
Author(s):  
Hun Jun Ha ◽  
Ho Kyung Ha
Keyword(s):  
Suspended Sediment ◽  
Sediment Concentration ◽  
Surface Erosion ◽  
Intertidal Flat ◽  
Cohesive Sediments ◽  
Mean Values ◽  
Erosion Threshold ◽  
Mud Flat ◽  
Em Method ◽  
Tidal Emersion

Erosion of cohesive sediments is a ubiquitous phenomenon in estuarine and intertidal environments. Several methods have been proposed to determine the surface erosion threshold (τc0), which are still debatable because of the numerous and uncertain definitions. Based on erosion microcosm experiments, we have compared three different methods using (1) eroded mass (EM), (2) erosion rate (ER), and (3) suspended sediment concentration (SSC), and suggested a suitable method for revealing the variation of erodibility in intertidal sediments. Erosion experiments using a microcosm system were carried out in the Muuido tidal flat, west coast of South Korea. The mean values of τc0 for three methods were: 0.20 ± 0.08 Pa (EM); 0.18 ± 0.07 Pa (ER); and (3) 0.17 ± 0.09 Pa (SSC). The SSC method yielded the lowest τc0, due to the outflow of suspended sediment from the erosion chamber of the microcosm. This was because SSC gradually decreased with time after depleting the erodible sediment at a given bed shear stress (τb). Therefore, the regression between SSC and applied τb might skew an x-intercept, resulting in the underestimation (or “not-determined”) of τc0. The EM method yielded robust and accurate (within the range of τb step at which erosion begins) results. The EM method represents how the erodible depth thickens as τb increases and therefore seems better suited than the SSC and ER methods for representing depth-limited erosion of cohesive sediments. Furthermore, this study identified the spatiotemporal variations of τc0 by EM method in an intertidal flat. The τc0 in mud flat was about two times higher than that in mixed flat. Compared to the end of tidal emersion, the sediment was 10–40% more erodible at the beginning stage.

scholarly journals FRACTAL APPROACH TO EROSION THRESHOLD OF BENTONITES

Fractals ◽  
2018 ◽  
Vol 26 (02) ◽  
pp. 1840012 ◽  
Author(s):  
Y. F. XU ◽  
X. Y. LI
Keyword(s):  
Fractal Model ◽  
Model Verification ◽  
Surface Erosion ◽  
Clay Particles ◽  
Fractal Approach ◽  
Erosion Threshold ◽  
Proposed Model ◽  
Buffer Material ◽  
High Sorption ◽  
High Level

Bentonite has been considered as a candidate buffer material for the disposal of high-level radioactive waste (HLW) because of its low permeability, high sorption capacity, self-sealing characteristics and durability in a natural environment. Bentonite erosion caused by groundwater flow may take place at the interface of the compacted bentonite and fractured granite. Surface erosion of bentonite flocs is represented typically as an erosion threshold. Predicting the erosion threshold of bentonite flocs requires taking into account cohesion, which results from interactions between clay particles. Beyond the usual dependence on grain size, a significant correlation between erosion threshold and porosity measurements is confirmed for bentonite flocs. A fractal model for erosion threshold of bentonite flocs is proposed. Cohesion forces, the long-range van der Waals interaction between two clay particles are taken as the resource of the erosion threshold. The model verification is conducted by the comparison with experiments published in the literature. The results show that the proposed model for erosion threshold is in good agreement with the experimental data.

The relationship between aggregation and other soil properties in cracking clay soils

Soil Research ◽  
1984 ◽  
Vol 22 (1) ◽  
pp. 59 ◽  
Author(s):  
KJ Coughlan ◽  
RJ Loch
Keyword(s):  
Hydraulic Conductivity ◽  
Salt Content ◽  
Chemical Properties ◽  
Aggregate Size ◽  
Strong Relationship ◽  
Clay Soils ◽  
Coarse Surface ◽  
Seedbed Preparation ◽  
The Relationship ◽  
Dispersion Ratio

This paper explores the processes responsible for clay dispersion, and the formation of large dry aggregates, in cracking clay soils. It also isolates the soil factors causing variations in dry aggregate size using regression analysis. Twelve cracking clay soil samples were selected on visual differences in dry aggregate size distribution following seedbed preparation, and a range of soil structural and chemical properties were measured. The per cent dry aggregates > 5 mm was found to increase with resistance to mechanical abrasion, stability to wet sieving after capillary wetting, and dispersion ratio, indicating that large dry aggregates are formed as a result of binding by dispersed clay. Both raindrop impact and puddling by cultivation may be involved in dispersion. There was a strong relationship between dry aggregate size in the 0-10 cm layer and salt content in the subsurface (60-90 cm) layer. Coarse surface aggregation is explained in terms of limited profile hydraulic conductivity. For the soils studied, the properties of the surface layer appear to be responsible, at least in part, for the limitation in profile hydraulic conductivity. Dry aggregate size in the 0-10 cm layer was not simply correlated with any of the chemical properties of that layer. However, equations containing two (ESP and CEC per gram of clay) or three (ESP, per cent clay and CEC) independent variables were derived to explain variations in dry aggregate size, both for the 12 soils studied and for a wider range of Queensland cracking clay soils.

scholarly journals Weaving the Common Threads of Simulation and Formation studies in Archaeology

2017 ◽  
Author(s):  
Benjamin Davies
Keyword(s):  
Computer Simulation ◽  
Human Activity ◽  
Computational Models ◽  
Experimental Studies ◽  
Surface Erosion ◽  
Archaeological Record ◽  
The Common ◽  
The Relationship ◽  
Material Record

Computer simulation is a tool increasingly used by archaeologists to build theories about past human activity; however, simulation has had a limited role theorising about the relationship between past behaviours and the formation of observed patterning in the material record. This paper visits the argument for using simulation as a means of addressing the gap that exists between archaeological interpretations of past behaviours and their physical residues. It is argued that simulation is used for much the same reason that archaeologists use ethnographic or experimental studies, and that computational models can help to address some of the practical limitations of these approaches to record formation. A case study from arid Australia, examining the effects of episodic surface erosion on the visibility of the record, shows how simple, generative simulations, grounded in formational logic, can be used to compare different explanatory mechanisms and suggest tests of the archaeological record itself.

Effect of Coarse Aggregate Morphology on the Resilient Modulus of Hot-Mix Asphalt

2005 ◽  
Vol 1929 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Tongyan Pan ◽  
Erol Tutumluer ◽  
Samuel H. Carpenter
Keyword(s):  
Surface Texture ◽  
Coarse Aggregate ◽  
Resilient Modulus ◽  
Asphalt Binder ◽  
Aggregate Size ◽  
Asphalt Mixtures ◽  
Maximum Aggregate Size ◽  
Asphalt Mixes ◽  
Aggregate Morphology ◽  
The Relationship

The resilient modulus measured in the indirect tensile mode according to ASTM D 4123 reflects effectively the elastic properties of asphalt mixtures under repeated load. The coarse aggregate morphology quantified by angularity and surface texture properties affects resilient modulus of asphalt mixes; however, the relationship is not yet well understood because of the lack of quantitative measurement of coarse aggregate morphology. This paper presents findings of a laboratory study aimed at investigating the effects of the material properties of the major component on the resilient modulus of asphalt mixes, with the coarse aggregate morphology considered as the principal factor. With modulus tests performed at a temperature of 25°C, using coarse aggregates with more irregular morphologies substantially improved the resilient modulus of asphalt mixtures. An imaging-based angularity index was found to be more closely related to the resilient modulus than an imaging-based surface texture index, as indicated by a higher value of the correlation coefficient. The stiffness of the asphalt binder also had a strong influence on modulus. When the resilient modulus data were grouped on the basis of binder stiffnesses, the agreement between the coarse aggregate morphology and the resilient modulus was significantly improved in each group. Although the changes in aggregate gradation did not significantly affect the relationship between the coarse aggregate morphology and the resilient modulus, decreasing the nominal maximum aggregate size from 19 mm to 9.5 mm indicated an increasing positive influence of aggregate morphology on the resilient modulus of asphalt mixes.

The stabilization of morphological field size during slime mold morphogenesis

Development ◽  
1978 ◽  
Vol 44 (1) ◽  
pp. 45-51
Author(s):  
Michael Peacock ◽  
David R. Soll
Keyword(s):  
Dictyostelium Discoideum ◽  
Aggregate Size ◽  
Slime Mold ◽  
Field Size ◽  
Cellular Slime Mold ◽  
Slime Mold Dictyostelium Discoideum ◽  
Cellular Slime ◽  
The Relationship ◽  
Tip Formation

The relationship between aggregate size and morphological field size has been investigated in the cellular slime mold Dictyostelium discoideum. Evidence is presented that aggregate size and field size exhibit different temperature sensitivities and that an aggregate can be induced to separate into several morphological fields by a decrease in temperature. In addition, evidence is presented that field size is stabilized at a point in time just prior to tip formation.

Study about Characteristics of Cement Paste on Fractal Theory

2013 ◽  
Vol 423-426 ◽  
pp. 1051-1054
Author(s):  
Tian Yang Zhai
Keyword(s):  
Compressive Strength ◽  
Fractal Dimension ◽  
Cement Paste ◽  
Permeability Coefficient ◽  
Fractal Theory ◽  
Fractal Model ◽  
Concrete Compressive Strength ◽  
Internal Pore Structure ◽  
The Relationship ◽  
Internal Pore

A fractal model to simulate cement paste internal pore structure, and on this basis deduce that fractal dimension is D and the corresponding pore is r, the relationship between porosity is P. MIP was measured test. Then calculated the different ages of the fractal dimension of cement and concrete compressive strength, tensile strength and permeability coefficient. The results showed that: compressive strength, permeability and fractal dimension has a good correlation. Whey in cement in the process of hydration of cement products continue to fill the pores, making the compressive strength increased 70%, permeability is declining.

scholarly journals Applicability of the photogrammetry technique to determine the volume and the bulk density of small soil aggregates

Soil Research ◽  
2016 ◽  
Vol 54 (3) ◽  
pp. 354 ◽  
Author(s):  
D. Moret-Fernández ◽  
B. Latorre ◽  
C. Peña ◽  
C. González-Cebollada ◽  
M. V. López
Keyword(s):  
Strong Correlation ◽  
General Trend ◽  
Conservation Tillage ◽  
Soil Aggregates ◽  
Three Dimensional ◽  
Digital Camera ◽  
Aggregate Size ◽  
Soil Disturbance ◽  
The Relationship ◽  
Dimensional Surface

Aggregate density (ρ) is defined as the relationship between the mass and the volume occupied by an aggregate. Previous studies have characterised ρ on large to medium-sized soil aggregates (>4 mm diameter); however, little information is available for smaller aggregates (<4 mm). The objective of this study was to test the viability of the photogrammetry (PHM) technique to determine the volume and subsequent ρ of small soil aggregates (1–8 mm diameter). The method uses a standard digital camera that photographs a rotating aggregate and reconstructs its three-dimensional surface and the corresponding volume. To validate the method, the volume estimated with PHM on rough stones of different sizes (1–16 mm diameter) was compared with the corresponding volume measured by the Archimedes’ principle. The method was tested on soil aggregates 1–8 mm in diameter, collected from two sites under conventional and conservation tillage treatments. The strong correlation (R2 > 0.99, P < 0.0001) between the volumes estimated on rough stones with the PHM and Archimedes methods demonstrates that this technique can be satisfactorily used to estimate the volume and, consequently, the ρ of small soil aggregates. The results showed an increase in ρ with decreasing aggregate size. A general trend of increasing ρ with the degree of soil disturbance by tillage was also observed.

scholarly journals Combined linear regression and Monte Carlo approach to modelling exposure age depth profiles

2021 ◽  
Author(s):  
Yiran Wang ◽  
Michael E. Oskin
Keyword(s):  
Monte Carlo ◽  
Erosion Rate ◽  
Profile Analysis ◽  
Radioactive Decay ◽  
Northwest China ◽  
External Information ◽  
Surface Erosion ◽  
Linear Inversion ◽  
Practical Applications ◽  
Depth Profiles

Abstract. We introduce a set of methods for analyzing cosmogenic-nuclide depth profiles that formally integrates surface erosion and muogenic production, while retaining the advantages of the linear inversion. For surfaces with erosion, we present solutions for both erosion rate and total eroded thickness, each with their own advantages. For practical applications, erosion must be constrained from external information, such as soil-profile analysis. By combining linear inversion with Monte Carlo simulation of error propagation, our method jointly assesses uncertainty arising from measurement error and erosion constraints. Using example depth profile data sets from the Beida River, northwest China and Lees Ferry, Arizona, we show that our methods robustly produce comparable ages for surfaces with different erosion rates and inheritance. Through hypothetical examples, we further show that both the erosion rate and eroded-thickness approaches produce reasonable age estimates so long as the total erosion less than twice the nucleon attenuation length. Overall, lack of precise constraints for erosion rate tends to be the largest contributor of age uncertainty, compared to the error from omitting muogenic production or radioactive decay.

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