Transition Fines Content Research Articles

The Effect of Fines Content on Compressional Behavior When Using Sand–Kaolinite Mixtures as Embankment Materials

In South Korea, Honam High-Speed Railway has a relatively large residual settlement issue and high fines content has been pointed out as one of the causes. Design guidelines regulate not to use soils containing fines content higher than 25%. However, there is no background information on the effect of fines content on settlement. Therefore, this paper aims to investigate compressional behavior according to fines content using sand and kaolinite. Oedometer test results showed that the compression index is lowest with fines content of 15% to 20% at which the mixture produced maximum density. The optimum fines content for inducing low settlement would be 15% to 20% for the sand–kaolinite mixture. Transition fines content (TFC), which shows sand-like to claylike behavior, was observed to have between 21% and 26% of fines content. Critical fines content (fcrit) where a minimum void ratio occurs was estimated as 21.67%. These behavioral changes appear when fines content is greater than the optimum fines content. SEM also shows that the kaolinite particles were overlapped, creating flat surfaces with a fines content higher than 30%, and showing clay-like behavior. Based on the analysis results, engineers can simply identify the behavior of embankment materials to ensure optimum fines content and consequently minimize long-term settlement potential.

Effect of ocean environmental particles on compressibility, electrical resistivity, and stiffness characteristics of mixtures

The influence of diatoms, which have distinct physico-chemical characteristics, is a key factor in the investigation of deep-sea sediments. The objective of this study was to investigate the compressibility, electrical resistivity, and stiffness of sand–silt–diatom mixtures performing oedometer tests. The specimens were prepared by mixing fines containing silts and diatoms into sand, and the fines contents were 0%, 10%, 20%, and 30% in weight (FC00, FC10, FC20, and FC30). The oedometer test was carried out from 5 to 640 kPa, and the electrical resistivity, shear wave velocity, and compressional wave velocity were obtained during loading and unloading. The test results show that the electrical resistivity and compressional wave velocity have transitional behavior at FC10 owing to the dominant effect of fines. The shear wave velocity decreases with an increase in fines contents despite a lower void ratio due to the fines. Moreover, the equivalent bulk modulus of the mineral from back-calculation also exhibits a transition at FC10. However, both compression indices from the measured data and the asymptotically-sound compaction model equation exhibit the transition at FC20. In addition, FC20 is located on the boundary between the sand-dominant and transitional mixtures in the triangular chart of ternary mixtures. The results suggest that the transitional fines content of mechanical behavior changes at the points of large and small strains.

Effect of Composition on the Compressibility and Shear Strength of Dredged Cohesive Sediment

Progressively, more dredged sediments are being reused for engineering projects. For example, the Marker Wadden is a new wetland constructed in lake Markermeer, the Netherlands, with dredged cohesive sediments originating from the bed of the lake. Such dredged sediments are often dominated by cohesive sediment particles with varying amounts of sand and organic matter. In addition, during and after the construction process, the material consolidates and is often compressed from a very loose state into a significantly denser condition. To assess the mechanical behavior of this material, the compressibility of the Markermeer dredged sediment samples with various sand and organic matter contents was analyzed with incremental loading oedometer tests, whereas the undrained shear strength was studied using the fall cone test. The behavior was theoretically analyzed assuming a fractal structure of the sediment and applying power law constitutive equations for effective stress, hydraulic conductivity, and undrained shear strength. These constitutive equations, usually used at low initial sediment densities, worked well at the relatively high initial densities studied and proved to be a useful tool to identify the transition fines content TFC. The constitutive equations were put in context with indicators traditionally used in soil mechanics. Samples, each with an identical composition of the fines fraction (particles< 63 μm), but with a sand content varying from 9 to 40%, showed the same compressibility and undrained shear strength behavior when considering the sand a filler material. For a natural sand content of 70%, the behavior was dominated by sand. The organic matter oxidation was observed to drastically decrease the compressibility and the shear strength, and even to decrease the amount of sand needed to exhibit sand-dominated behavior, showing the importance of the reactivity or state of organic matter on the TFC.

Liquefaction Resistance of Different Size/Shape Sand-Clay Mixtures Using a Pair of Bender Element–Mounted Molds

Abstract The aim of this study is to assess the influences of both the size and shape of sand grains mixed with a clay on shear modulus (Gmax)– and shear wave velocity (vs)–based liquefaction resistance (cyclic resistance ratio, CRR) using an intensive series of bender element (BE) tests. A low plasticity clay (CL) was added to two specific particle gradations (0.15–0.30 mm, and 1.0–2.0 mm) of clean sands with particular shapes (angular and rounded) at the percentages of 5, 10, 15, 20, 30, and 40, by dry weight. The BE tests were performed on the remolded specimens of different size/shape sands containing various amounts of CL in a recently designed mold used specifically for cohesionless soils, and then the values of vs, Gmax, and CRR were investigated. In most of the cases, the testing results indicated that, up to 20 % fines, which is named as transition fines content (FCt), Gmax and CRR values decreased, and then they increased for the specimens tested. Eventually, Gmax and CRR values of the specimens were significantly changed by the physical features (size, shape) of the sand grains with all the clay inclusions and frequencies applied.

Influence of particle size distribution of iron ore fines on liquefaction during marine transportation

In recent decades, many bulk carrier incidents, including loss of life and vessels, have occurred owing to the liquefaction of solid bulk cargoes. Currently, the transportable moisture limit (TML) is the only parameter used to determine the liquefaction potential of a mineral for maritime transport. This study aimed to investigate the influence of the particle size distribution of iron ore fines (IOF) on the liquefaction potential of bulk cargoes for maritime transport. The correlation of liquefaction potential with IOF particle size distribution is of great interest to ore transport companies, as they have a variety of IOF sizes that can be mixed to improve liquefaction potential. The effect of IOF particle size distribution on TML was investigated using the flow table test and the Proctor–Fagerberg test, and the behavior of the shear strength parameters was studied by performing a direct shear test for different IOF gradations. The samples were prepared in four different gradations, containing particle sizes from 9.5 mm to 25 μm with fines contents (< 150 μm) of 5.2%, 15.6%, 19.3%, and 22.6%. We concluded that the liquefaction phenomenon is significantly influenced by the IOF particle size distribution, the liquefaction potential decreases with an increase in the IOF content, and the shear strength parameters are altered by the fines content of IOF, having one transitional fines content for the internal friction angle. There is a complex relationship between the IOF particle size distribution and the Coulomb cohesion factor that is influenced by the moisture content, the fines content, and the void ratio. In this study, a methodology is proposed for classifying the liquefaction potential of IOF samples, with the objective of helping transport companies to define the mixes of IOF sizes. Agreement between the experimental and theoretical data is observed and discussed.

Effects of Fine Content on Undrained Shear Response of Sand–Clay Mixture

The aim of this paper is to investigate the influence of fines content on the undrained shear behavior of sand–clay mixtures with fines contents at 0%, 5%, 10%, 12.5%, 15%, 17.5%, 20%, 22.5 and 25%. The shear strength of the mixture has been evaluated in terms of skeleton void ratio and transitional fines content. Materials used are poorly graded sand from the eastern coast of Famagusta, and swelling clay from Nicosia, North Cyprus. Direct shear (DS) tests were used to evaluate the shear strength parameters of sand–clay mixtures at constant strain rate of 1 mm/min under normal stresses of 27.78, 55.56 and 83.33 kPa. The DS test results indicated a unique relation between the transitional fines content and the angle of internal friction, in which the internal friction angle increased with increasing fines until reached maximum value of 45.68° at the transitional fines content (10%). Therefore, additional fines content increased the shear strength up to the transitional fines content after which decrement occurred for all normal stresses.

Fall-cone testing of unsaturated sand–clay mixtures

This paper presents the results of an intensive series of laboratory fall-cone tests undertaken on mixtures of sand with different grain size/shapes and a low-plasticity clay. The mixtures were prepared with various water contents from a fully dry to a fully saturated condition. The clay was added to two different gradations (0·15–0·30 mm and 1·0–2·0 mm) of clean sand with specific shapes (rounded and angular) at the ratios of 5, 10, 15, 20, 30 and 40% by dry weight. The results obtained suggest that penetration depth primarily depends on water content, size/shape of the sand grains and the amount of clay in the mixtures. The relation between penetration depth and water content displays three distinct behaviours in that the penetration depth (a) is relatively large for dry mixtures, (b) decreases with increasing water content, and (c) increases to values approximately 20% larger than those for dry mixtures. Observations revealed that the transition fines content, the boundary between sand-governed and fines-governed behaviour, was mainly affected by intergranular void ratio.

Critical state interpretation of effects of fines in silty sands

The effect of the fines content in silty sands on the location of the critical state line (CSL) has been investigated by performing standard drained and undrained triaxial tests on reconstituted samples containing Sydney sand, feldspar fines and mixtures of the two at 20, 40 and 60% fines content. In the e-log p′ plane, CSLs of silt–sand mixtures shifted parallel to one another. The transitional fines content of silt–sand mixtures was 40%. Transitional soil behaviour was also observed in silt–sand samples that contained 40 and 60% fines as densely and loosely prepared samples with these fines contents failed on two different and parallel CSLs.

Determination of the transitional fines content of sand-non plastic fines mixtures

The transitional fines content is the boundary between fines-dominated and sand-dominated behaviour. Experimental and calculation methods for the determination of the transitional fines content of sand-non plastic fines mixtures are summarized based on former studies. Different methods have been applied to data from several published sources in order to make a comparison. The results indicate that the calculation methods, which use the property indices of the sand and fines, may not always predict the value of the transitional fines content observed in laboratory tests. These differences and their possible causes are discussed. The relative size of the fines and sand particles has been considered as a parameter which influences the value of the transitional fines content. The analysis indicates that when the ratio of large to small grain diameter is large enough, the value of the transitional fines content remains within a relatively small range.

Compressional behaviour of various size/shape sand–clay mixtures with different pore fluids

Sand–clay mixtures can be considered as a composite matrix of coarser and finer particles. Nature of the interaction between coarser (sand) and finer (clay) particles can be demonstrated using intergranular void ratio (es), and transition fines content (FCt). The common aspect of the intergranular void ratio equations is based on the determination of an empirical relationship between es and effective stresses (σ′), fines content (FC), and void ratio (e). However, there is a lack of theoretical basis for determining consistent es and FCt values. This paper presents an investigation carried out to relate the various sizes (0.3mm–0.6mm; 1.0mm–2.0mm) and shapes (R=0.43, S=0.67; R=0.16, S=0.55) of sands with clay in different viscosity pore fluids (0.94mm2/s; 10.65mm2/s) to compressional behaviour by determining es and FCt values. Oedometer tests performed during this investigation indicate that the higher viscosity pore fluid in a specimen could cause a lower compressibility, and the sand with lower roundness (R) and sphericity (S) values exhibit higher FCt and Cc–s values.

The Effects of Fines on the Behaviour of a Sand Mixture

Intergranular void ratio, es, can be used as an alternative indicator to assess the mechanical properties of composite matrix of coarse and fine grains. In this paper, an intensive laboratory study of saturated coarse rotund sand and fine angular sand mixtures with various mix ratios is investigated by a series of oedometer and direct shear tests. Oedometer tests performed on the mixtures show that fines percentages and stress conditions affect the compression behaviours. Tests indicated that, up to a fraction of fines, which is named as transition fines content (FCt), compression behaviour of the mixture is mainly governed by the sand grains. As the percentage of fines exceeds FCt finer grains govern the compression. Performed direct shear tests revealed that there is a relationship between the FCt and shear strength, which is harmonic with the oedometer test results.

Applications of the oedometer, triaxial and resonant column tests to the study of micaceous sands

Intergranular void ratio, e s, can be used as an alternative indicator to assess the mechanical and dynamic properties of composite matrix of coarse and fine grains. In this paper, an intensive laboratory study of saturated coarse rotund sand (i.e., Leighton Buzzard Sand) and fine (i.e., mica) mixtures with various mix ratios is performed by a series of oedometer, triaxial and resonant column tests. Oedometer tests performed on coarse rotund sand–fine mixtures show that initial conditions, fines percentages, and stress conditions affect the compression behaviours. Tests indicated that, up to a fraction of mica, which is named as transition fines content (FC t), compression behaviour of the mixture is mainly governed by the sand grains. As the percentage of mica exceeds FC t, mica governs the compression. In the triaxial tests, deviatoric stress ( q), pore pressure ( u), and undrained Young's modulus (Eu) have been obtained in a triaxial testing apparatus. Results revealed that there is a close relationship between the FC t and q, u, and Eu values. In the resonant column tests, a study of dynamic properties of saturated mixtures was investigated by measuring its shear modulus ( G) and damping ratio ( D), which is harmonic with the oedometer test results.

Effects of Clay Content on Liquefaction Characteristics of Gap-Graded Clayey Sands

A series of undrained, cyclic simple shear tests were performed on reconstituted specimens with various clay contents to study the effects of clay content on liquefaction characteristics of clayey sands based on a framework of an idealized binary packing model and intergrain state parameters. From observed liquefaction characteristics, clayey sands with different clay contents can be grouped as sand-like or clay-like soils depending on the clay content and the transitional fines content of the sand-clay mixture. A simple equation is derived and verified to correlate the transitional fines content with the void ratios of the clean sand and the pure clay consisting of the mixture. In addition, a new relationship for clay content correction is proposed based on the linear relationship between the cyclic resistance ratio and the clay content at the same intergranular void ratio. The cyclic resistance ratio of sand-like clayey sands can be divided into two components: (1) the resistance of the sand skeleton at the specific intergranular void ratio, and (2) the increment of cyclic resistance from clayey fines. The rate of increment for cyclic resistance varies with the properties of contained clay particles. Data from three independent studies have shown the proposed procedure is promising.

Compressional behavior of clayey sand and transition fines content

Clayey sand can be considered as a composite matrix of coarse and fine grains. The interaction between coarser and finer grain matrices affects the overall stress–strain behavior of these soils. Intergranular void ratio, e s (which is the void ratio of the coarser grain matrix) can be utilized as an alternative parameter to express the compressive response of such soils. Oedometer tests conducted on reconstituted kaolinite–sand mixtures indicate that initial conditions, percentage of fines, and stress conditions influence the compression characteristics evidently. Tests showed that, up to a fraction of fines, which is named as transition fines content (FC t), compression behavior of the mixtures is mainly controlled by the sand grains. When concentration of fines exceeds FC t, kaolinite controls the compression. It was found that FC t varies between 19% and 34% depending on the above mentioned factors. This range of fines content is also consistent with various values reported in literature regarding the strength alteration. Performed direct shear tests revealed that there is also a close relationship between transition fines content and shear strength, which is harmonic with the oedometer test results.

Steady-state lines of sand–silt mixtures

The steady-state lines (SSLs) for sand–silt mixtures with various fines contents (0%, 5%, 10%, 15%, 20%, 30%, 50%, 70%, and 94%) were studied. It was indicated that the location of the SSL in the e–p′ space is different for each mixture, but the SSLs are parallel. In the e – ln p′ plot, the SSLs are similar for the mixtures with a fines content of less than the transitional fines content (TFC) when tested under drained and undrained conditions and the intergranular and interfine void ratios are used. The data diverge when the fines contents are equal to or greater than the TFC, even though the interfine void ratios are used. The results of the tests conducted under drained and undrained conditions produced a unique SSL in the p′–q space for each material. Different SSLs in the p′–q space were observed for the studied materials, and the friction angle at steady state varied in the range of 37.3°–42.2°. The study showed that the SSLs can be represented by one line in tests under drained conditions if the fines contents are less (0%–30%) than the TFC and the corrected intergranular void ratios are used. The lines can also be represented by one line for sand–silt mixtures with high fines contents (50%–94%) if the corrected interfine void ratios are used instead of void ratios. Key words: steady-state line, sand–silt mixtures, transitional fines content, drained and undrained triaxial tests.

Determination of the Transitional Fines Content of Mixtures of Sand and Non-plastic Fines

Abstract Sand-silt mixtures show different behavior with different fines content. The transitional fines content (TFC) is a key parameter which can indicate if the soil behaves as a sand-dominated or as a fines-dominated material. The determination of the TFC for a sand-silt mixture and the possible ways of obtaining the TFC from index data and the triaxial test results are discussed in this study.

Instability of sand–silt mixtures

The instability of the sand–silt mixtures with different amount of fines contents were studied in this paper. It showed that the slope of the instability lines increases with the increasing relative densities, and it approaches the slope of the failure line (steady state line) at a high relative density. The relationship between the peak stress ratio and the intergranular void ratio can be described by a common curve for all the mixtures with fines contents less than the transitional fines content. There may also exist a unique curve for the relationship between the peak stress ratio and interfine void ratio for the mixtures with fines contents higher than the transitional fines content. If the yield strength ratio is used instead of the peak stress ratio, the relationships can be characterized in the same way.