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Jun Yang - One of the best experts on this subject based on the ideXlab platform.
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A numerical analysis of the equivalent skeleton Void Ratio for silty sand
Geomechanics and Engineering, 2019Co-Authors: Bei-bing Dai, Jun Yang, Wei ZhangAbstract:Recent research on the behavior of silty sand tends to advocate the use of equivalent skeleton Void Ratio to characterize the density state of this type of soil. This paper presents an investigation to explore the physical meaning of the equivalent skeleton Void Ratio by means of DEM simulations for assemblies of coarse and fine particles under biaxial shear. The simulations reveal that the distribution pattern of fine particles in the soil skeleton plays a crucial role in the overall macroscopic response: The contractive response observed at the macro scale is mainly caused by the movement of fine particles out of the force chains whereas the dilative response is mainly associated with the migRation of fine particles into the force chains. In an assembly of coarse and fine particles, neither all of the fine particles nor all of the coarse ones participate in the force chains to carry the external loads, and therefore a more reasonable definition for equivalent skeleton Void Ratio is put forward in which a new parameter d is introduced to take into account the fraction of coarse particles absent from the force chains.
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State variables for silty sands: Global Void Ratio or skeleton Void Ratio?
Soils and Foundations, 2015Co-Authors: Jun Yang, L.m. Wei, B.b. DaiAbstract:While the global Void Ratio has long been used as a density index to characterize sand behavior, concern has been increasing about its applicability to silty sands (sand–fines mixtures), based on the proposition that the fines may fill in the Void spaces formed by sand grains and make no contribution to the force transfer. The skeleton Void Ratio was proposed in the literature as an alternative index for mixed soils, based on the assumption that all fines act as Voids. It was further modified into an equivalent skeleton Void Ratio by taking into consideRation the fraction of fines that participates in the force transfer. This paper presents a study aimed at evaluating the three state variables as applied to sand–fines mixtures and especially to explore the Rationale behind the concept of the skeleton Void Ratio. Based on a specifically designed experimental program, it is shown that contrasting conclusions can be drawn as to the role of fines in altering the shear behavior of clean sand when different density indices are used as the comparison basis. When comparisons are made at a constant (global) Void Ratio, the fines increase the degree of contractiveness, but when comparisons are made at a constant skeleton Void Ratio, an increase in dilativeness is seen. The equivalent skeleton Void Ratio does not fulfill the intent of providing a universal means for characterizing the stress–strain behavior of silty sands. This is due to the lack of mechanisms to account for the inter-granular contacts which are highly complex. The study suggests that compared with the skeleton Void Ratio and its modified form, the usual (global) Void Ratio remains a simple and useful state variable suitable for the framework of critical state soil mechanics and for geotechnical applications.
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On the Physical Meaning of Equivalent Skeleton Void Ratio for Granular Soil with Fines
2013Co-Authors: Bei-bing Dai, Jun YangAbstract:Recent research on the behavior of silty sand usually involves the use of equivalent skeleton Void Ratio to characterize its packing density state. The equivalent skeleton Void Ratio is a modified Void Ratio by the introduction of a parameter b to account for the participation of fines in the force chains. However, the parameter b is poorly understood. This paper presents an investigation into the physical meaning of the equivalent skeleton Void Ratio by conducting a series of discrete element method (DEM) simulations on biaxial tests of assemblies of coarse and fine particles. The simulation results reveal that the parameter b is a state variable dependent on confining pressure, packing density and particle gradation and it varies during shearing. It should not be treated as a constant as reported in the literature. It is also found that the distribution pattern of fine particles in the skeleton of the assembly plays a crucial role in the overall macroscopic response. Contraction is principally induced by the movement of fine particles out of the force chains and dilation is generally involved with the migRation of fine particles into forces chains. Furthermore, a new expression of the equivalent skeleton Void Ratio is put forward with the introduction of the parameter d to take into account the absence of large particles from force chains, along with comparisons between this new definition for the equivalent skeleton Void Ratio and the existing one.
B.b. Dai - One of the best experts on this subject based on the ideXlab platform.
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State variables for silty sands: Global Void Ratio or skeleton Void Ratio?
Soils and Foundations, 2015Co-Authors: Jun Yang, L.m. Wei, B.b. DaiAbstract:While the global Void Ratio has long been used as a density index to characterize sand behavior, concern has been increasing about its applicability to silty sands (sand–fines mixtures), based on the proposition that the fines may fill in the Void spaces formed by sand grains and make no contribution to the force transfer. The skeleton Void Ratio was proposed in the literature as an alternative index for mixed soils, based on the assumption that all fines act as Voids. It was further modified into an equivalent skeleton Void Ratio by taking into consideRation the fraction of fines that participates in the force transfer. This paper presents a study aimed at evaluating the three state variables as applied to sand–fines mixtures and especially to explore the Rationale behind the concept of the skeleton Void Ratio. Based on a specifically designed experimental program, it is shown that contrasting conclusions can be drawn as to the role of fines in altering the shear behavior of clean sand when different density indices are used as the comparison basis. When comparisons are made at a constant (global) Void Ratio, the fines increase the degree of contractiveness, but when comparisons are made at a constant skeleton Void Ratio, an increase in dilativeness is seen. The equivalent skeleton Void Ratio does not fulfill the intent of providing a universal means for characterizing the stress–strain behavior of silty sands. This is due to the lack of mechanisms to account for the inter-granular contacts which are highly complex. The study suggests that compared with the skeleton Void Ratio and its modified form, the usual (global) Void Ratio remains a simple and useful state variable suitable for the framework of critical state soil mechanics and for geotechnical applications.
Kerry R Rowe - One of the best experts on this subject based on the ideXlab platform.
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water retention of geosynthetics clay liners dependence on Void Ratio and temperature
Geotextiles and Geomembranes, 2019Co-Authors: Ali Ghavamnasiri, Abbas Elzein, David Airey, Kerry R RoweAbstract:Abstract The dependence of the geosynthetic clay liners (GCLs) soil-water characteristic curve (SWCC) on temperature and overburden stress are characterised experimentally. It is shown that changes in Void Ratio and temperature alter the relationship between suction and moisture content and new forms of existing SWCC equations are developed. To cover a wide suction range, the SWCCs are measured using axis-translation and dew point methods. Based on the available experimental data, both proposed SWCCs are shown to perform well in predicting the effects of Void Ratio on SWCC along the drying path when compared to the experimental results. It is found that the air-entry value increases as the net vertical stress increases for the experiments under the same temperature. In addition, elevation of temperature reduces retention capacity of the GCL.
Mohammad Maleki - One of the best experts on this subject based on the ideXlab platform.
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Experimental Study on Mechanical Behavior of Unsaturated Silty Sand in Constant Equivalent Granular Void Ratio
Geotechnical and Geological Engineering, 2021Co-Authors: Erfan Chali, Mohammad MalekiAbstract:In this paper effect of fine mineralogy on mechanical behavior of unsaturated silty sand in different fine contents and divers confining pressure has been studied. All samples were molded with constant equivalent granular Void Ratio well-known parameter already proposed for characterizing silty sand behavior in saturated state. This manner of study allow to investigate also the validity of equivalent granular Void Ratio concept in unsaturated state. For this purpose, a series of triaxial tests were performed on the sand specimens with different percentages of silt in the undrained saturated (CU) and unsaturated (CW) conditions. The results showed that the material types and aggregate distribution of the fines have enormous effects on the silty sand behavior. In addition, the shear strength in the unsaturated specimens changed as a function of the initial applied matric suction. A fewer performance of equivalent intergranular Void Ratio in the case of unsaturated state in comparison of saturated states was observed.
B. Åberg - One of the best experts on this subject based on the ideXlab platform.
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GRAIN-SIZE DISTRIBUTION FOR SMALLEST POSSIBLE Void Ratio. DISCUSSION AND CLOSURE
Journal of Geotechnical and Geoenvironmental Engineering, 1997Co-Authors: B. ÅbergAbstract:A discussion of a technical note with the aforementioned title by B. Aberg, published in this journal (Volume 122, Number 1, January 1996), is presented. Discusser Day disagrees with the author that a gap-graded soil produces the lowest Void Ratio. Day reports that the factors needed for a very low Void Ratio for compacted or naturally deposited soils are: 1) a well-graded grain-size distribution; 2) a high Ratio of the largest and smallest grain sizes; 3) clay particles to fill in the smallest Void spaces; and 4) a process, such as compaction, to compress the soil particles into dense arrangements. Discussion is followed by closure from the author.
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Grain-Size Distribution for Smallest Possible Void Ratio
Journal of Geotechnical Engineering, 1996Co-Authors: B. ÅbergAbstract:In an earlier paper, the writer derived theoretical equations for Void Ratio as a function of grain-size distribution. Here, the equations are used to find the grain-size distributions that give the smallest possible Void Ratio for highly densified, cohesionless soils and similar materials that have different Ratios, x100 /x0, for their largest and smallest grain sizes. Both numerical and analytical methods are used. Depending on the value of x100 /x0, materials that consist of two or three grain-size fractions with grading gaps between them have the smallest Void Ratios. Within the fine and coarse fractions, the grain sizes need to be as uniform as possible. The required grading of the medium fraction depends on the characteristics of the fine and coarse fractions.
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GRAIN-SIZE DISTRIBUTION FOR SMALLEST POSSIBLE Void Ratio. TECHNICAL NOTE
Journal of Geotechnical Engineering, 1996Co-Authors: B. ÅbergAbstract:The author of this technical note previously derived theoretical formulations for Void Ratio as a function of grain-size distribution. Now, these formulations are used to find the grain-size distributions that give the smallest possible Void Ratio for highly densified, cohesionless soils and similar materials that have different Ratios for their largest and smallest grain sizes. Numerical and analytical techniques are applied. Depending on the material values, those that consist of two or three grain-size fractions with grading gaps between them have the smallest Void Ratios. Within the fine and coarse fractions, the grain sizes need to be uniform. The required grading of the medium fraction depends on the characteristics of the fine and coarse fractions.
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Void Ratio of noncohesive soils and similar materials
Journal of Geotechnical Engineering, 1992Co-Authors: B. ÅbergAbstract:A new approach to the topic of numerical description of Void characteristics of noncohesive soils and similar granular materials is presented. Based upon a simple stochastic model of the Void structure and Void sizes, theoretical equations are derived by means of which the Void Ratio of a soil can be calculated from its grain-size distribution. The calculations also give information about type of grain structure, and the grain size that separates fixed grains and possible loose grains is determined. The equations also consider grain shape, degree of densification, and size of compaction container. Results of numerous laboratory compaction tests on uniform to broadly graded sand, gravel, and crushed-rock materials confirm the general forms of the derived equations and are the basis for evaluation of certain parameters. In a companion paper, the theory is extended to hydraulic conductivity (and, in a forthcoming paper, to filter performances).
