Intergranular Void Ratio Research Articles

Engineering behavior and correlated parameters from obtained results of sand–silt mixtures

The results of an experimental study on sands with low-plastic silt content are presented. Flexible wall permeameter tests, drained and undrained triaxial compression tests, one-dimensional consolidation tests, and undrained cyclic triaxial tests were performed on specimens with a low plastic silt content of 0%, 15%, 30%, 40%, 50% and 60% by weight. The soil specimens were tested under three different categories: (1) at a constant void ratio index; (2) at the same peak deviator stress in a triaxial test; and (3) at a constant relative density. The results were observed to be somewhat different from previous studies with non-plastic silt content and plastic fine content. Cyclic triaxial tests showed that an increase in silt content causes a decrease in the cyclic resistance ratio with a silt content up to 40–50% and thereafter causes an increase in the cyclic resistance ratio with further increases in silt content. The results of triaxial tests indicated that the value of the peak deviator stress changed with different types of specimens, and the greater internal friction an angle has, the stronger is the liquefaction resistance. Flexible wall permeameter tests concluded that the saturated hydraulic conductivity slowly decreases with an increase in silt content in the range from 0% to 30% and considerably decreases with a silt content greater than 30%. A one-dimensional consolidation test postulated that increasing silt content decreases the coefficient of consolidation. In addition, the global void ratio did not appear to be a pertinent parameter in explaining the behavior of sand–silt mixtures, while fine content and intergranular void ratio were suitable parameters for explaining the behavior of sand–silt mixtures. Finally, correlated parameters from obtained results were also presented in this study.

CRITICAL UNDRAINED SHEAR STRENGTH OF LOOSE-MEDIUM SAND-SILT MIXTURES UNDER MONOTONIC LOADINGS

Empirical relationships are developed for estimating the undrained critical shear strength based on experimental triaxial tests under monotonic loadings. The effect of fines content on the undrained shear strength is analyzed for different combinations of density states. The parametric study indicates that in terms of the soil void ratio and fines content proper- ties, the undrained critical shear strength may increase, or decrease as the amount of fines content increases, consequently showing vulnerability to liquefaction influenced by the fines content percentage. A series of monotonic undrained triaxial tests have been undertaken on a reconstituted saturated sand-silt mixtures specimen. Beyond 30% of fines content, it is shown that a fraction of silt participates in the soil skeleton chain force. In this context, the concept of the equivalent intergranular void ratio may be an appropriate parameter to express the critical shear strength of the soil under investigation. This parameter is able to control the undrained shear strength of non plastic silt and sand mixtures for different density states.

Critical undrained shear strength of sand-silt mixtures under monotonic loading

<p>This study uses experimental triaxial tests with monotonic loading to develop empirical relationships to estimate undrained critical shear strength. The effect of the fines content on undrained shear strength is analyzed for different density states. The parametric analysis indicates that, based on the soil void ratio and fine content properties, the undrained critical shear strength first increases and then decreases as the proportion of fines increases, which demonstrates the influence of fine content on a soil’s vulnerability to liquefaction. A series of monotonic undrained triaxial tests were performed on reconstituted saturated sand-silt mixtures. Beyond 30% fines content, a fraction of the silt participates in the soil’s skeleton chain force. In this context, the concept of the equivalent intergranular void ratio may be an appropriate parameter to express the critical shear strength of the studied soil. This parameter is able to control the undrained shear strength of non-plastic silt and sand mixtures with different densities.</p><p> </p><p><strong>Resumen</strong></p><p>Este estudio utiliza evaluaciones experimentales triaxiales con cargas repetitivas para desarrollar relaciones empíricas y estimar la tensión crítica de corte bajo condiciones no drenadas. El efecto de contenido de finos en la tensión de corte sin drenar se analizó en diferentes estados de densidad. El análisis paramétrico indica que, basado en la porosidad del suelo y las propiedades del material de finos, la tensión de corte sin drenar primero se incrementa y luego decrece mientras la proporción de finos aumenta, lo que demuestra la influencia de contenido de finos en la vulnerabilidad del suelo a la licuación. Una serie de las evaluaciones se realizó en mezclas rehidratadas y saturadas de arena y cieno. Más allá del 30 % de los contenidos finos, una fracción del cieno hace parte principal de la cadena de fuerza del suelo. En este contexto, el concepto de porosidad equivalente intergranular puede ser un parámetro apropiado para expresar la tensión crítica de corte del suelo estudiado. Este parámetro nos permite controlar la tensión de corte sin drenar de cieno no plástico y mezclas de arena de densidades diferentes.</p>

Experimental Study on the Pore Water Pressure Generation Characteristics of Saturated Silty Sands

The excess pore water pressure produced during earthquake shaking causes liquefaction and influences significantly the shear strength, deformation and settlement characteristics of granular soil deposits. Therefore, the stability of the structures constructed from these deposits or founded on them is adversely affected. The mechanisms of pore pressure generation and, in turn, liquefaction resistance of granular soils are still not fully clear and require further research. For the purpose of clarifying and evaluating pore pressure buildup characteristics of sandy soils, a series of undrained monotonic triaxial tests were carried out on different reconstituted samples of sand–silt mixture at various intergranular void ratios. The soil samples were tested under a constant confining pressure (\({\sigma_{3}'=100 {\rm kPa}}\)) and at three relative densities (Dr = 20, 53 and 91 %). The results obtained from this study reveal that the fraction of low plastic fines plays an important role in the generation of excess pore water pressure in samples of the Chlef sand–silt mixtures. It was found that excess pore water pressure can be correlated with the undrained shear strength at the peak for the range of fines’ content under consideration. The gross and intergranular void ratios appear as pertinent parameters to represent the pore water pressure response of the sand–silt mixtures for a given fines’ content.

A simple critical state approach to predicting the cyclic and monotonic response of sands with different fines contents using the equivalent intergranular void ratio

This paper focuses on developing a simple approach to describing the monotonic and cyclic behavior of sands with fines by employing the concept of equivalent intergranular void ratio, e , in the critical state soil mechanics framework. To establish and evaluate this approach, which facilitates the process of predicting the soils behavior and minimizes the experimental work required, a large number of datasets published in the literature for 10 different types of soils are processed and analyzed. The proposed approach makes it possible to predict the behavior and resistance of sands in a unique way for all the fines contents, stress levels and densities, without the need for performing tests at different fines contents. The issue of determining the b value, used as a physical constant in the definition of e , and the factors affecting it is studied. In this context, a recently established b-predicting equation is evaluated and its empirical parameters are calibrated with various datasets. Examining the influence of grading parameters on the b value resulted in a strong relationship between b and the particle size ratio. The results also show that the b value can be reliably estimated using the experimental data available at only two fines contents of 0 and 23 %.

Recommendations for extension and re-calibration of an existing sand constitutive model taking into account varying non-plastic fines content

Experimental findings have revealed that up to a certain transitional threshold, adding non-plastic silt to coarse soils like sands leads to the increase in susceptibility of liquefaction. In silty sands, silt grains fill voids between the coarse constituent, but do not actively participate in stress transmitting microstructure. To consider the partial participation of fines in load bearing structure, an equivalent intergranular void ratio is suggested. The proposed empirical relationship, takes into account the combined influence of fines content, soil gradation, and the average shape of coarse and fine constituents. An equivalent intergranular state parameter is employed in the model formulation to define soil state uniquely. Moreover, recent experimental studies indicate that the consequences of initial anisotropy on the mechanical behavior of silty sands are mitigated with the increase in fines content. To consider this phenomenon, vector magnitude, a measurable index of anisotropy, is related to fines content. Then, proper constitutive equations are introduced to modify plastic hardening modulus and critical state line in loading paths involving rotation of principal stress axes. The simulative capability of the model is evaluated by direct comparison of its predictions with experimental data of triaxial and hollow cylindrical cells reported by four research teams.

Laboratory Study on the Hydraulic Conductivity and Pore Pressure of Sand-Silt Mixtures

The hydraulic conductivity plays a major role on the excess pore pressure generation during monotonic and cyclic loading of granular soils with fines. This paper aims to determine how much the hydraulic conductivity and pore pressure response of the sand-silt mixtures are affected by the percentage of fines and void ratio of the soil. The results of flexible wall permeameter and undrained monotonic triaxial tests performed on samples reconstituted from Chlef River sand with 0, 10, 20, 30, 40, and 50% nonplastic silt at an effective confining stress of 100 kPa and two relative densities (Dr = 20, and 91%) are presented and discussed. It was found that the pore pressure increases linearly with the increase of the fines content and logarithmically with the increase of the intergranular void ratio. The results obtained from this study reveal that the saturated hydraulic conductivity (k) of the sand mixed with 50% low plastic fines can be, on average, four orders of magnitude smaller than that of the clean sand. The results show also that the hydraulic conductivity decreases hyperbolically with the increase of the fines content and the intergranular void ratio.

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.

Effect of fines content and void ratio on the saturated hydraulic conductivity and undrained shear strength of sand–silt mixtures

The hydraulic conductivity represents an important indicator parameter in the generation and redistribution of excess pore pressure of sand–silt mixture soil deposits during earthquakes. This paper aims to determine the relationship between the undrained shear strength (liquefaction resistance) and the saturated hydraulic conductivity of the sand–silt mixtures and how much they are affected by the percentage of low plastic fines (finer than 0.074 mm) and void ratio of the soil. The results of flexible wall permeameter and undrained monotonic triaxial tests carried out on samples reconstituted from Chlef river sand with 0, 10, 20, 30, 40, and 50 % non-plastic silt at an effective confining pressure of 100 kPa and two initial relative densities (D r = 20, 91 %) are presented and discussed. It was found that the undrained shear strength (liquefaction resistance) can be correlated to the fines content, intergranular void ratio and saturated hydraulic conductivity. The results obtained from this study reveal that the saturated hydraulic conductivity (k sat) of the sand mixed with 50 % low plastic fines can be, in average, four orders of magnitude smaller than that of the clean sand. The results show also that the global void ratio could not be used as a pertinent parameter to explain the undrained shear strength and saturated hydraulic conductivity response of the sand–silt mixtures.

Experimental Study of Undrained Shear Strength of Silty Sand: Effect of Fines and Gradation

Two strong earthquakes occurred in the region of Chlef (north western part of Algeria) during the last century. From the geological context, there were several great masses of sandy soil ejections on to the ground surface level and severe damages to civil and hydraulic structures. These damages were due to the soil liquefaction phenomenon. The objective of this laboratory investigation is to study the effect of low plastic fines and gradation characteristics on the undrained shear strength (liquefaction resistance) response of sand-silt mixture samples. For this purpose, a series of undrained monotonic triaxial tests were carried out on reconstituted saturated silty sand samples with different fines content ranging from 0 to 50 % at two initial relative densities (Dr = 20 and 91 %). The initial confining pressure was kept at 100 kPa. The evaluation of the data indicates that the undrained shear strength at the peak (qpeak) can be correlated to the undrained residual strength (Sus), the excess pore pressure (Δu), the fines content (Fc) and the intergranular void ratio (es). The test results indicate also that the undrained shear strength at the peak decreases with the increment of the coefficient of uniformity and fines content as well as with the decrement of the mean grain size in the range of 0–50 % fines content for both relative densities (Dr = 20 and 91 %).

Undrained shear strength of sand-silt mixture: Effect of intergranular void ratio and other parameters

The determination of the appropriate undrained residual shear strength of silty sands soils that are prone to liquefaction to be used in the assessment of the post-liquefaction stability of different types of earth structures is becoming a major challenge.The objective of this laboratory investigation is to study the effect of intergranular void ratio on undrained residual shear strength of loose, medium dense and dense (Dr = 12, 50, and 90% before consolidation) sand-silt mixtures under monotonic loading and liquefaction potential under cyclic loading. For this purpose, a series of undrained monotonic triaxial tests were carried out on reconstituted saturated silty sand samples with fine contents ranging from 0 to 50%. The confining pressure was kept constant to 100 kPa in all tests. The results of undrained monotonic tests indicate that the global void ratio does not represent the actual behaviour of the soil and the undrained residual shear strength decreases linearly with the increase of the intergranular void ratio and similar trend is happening with the fine content of the sand-silt mixtures up to 50% as well. Undrained cyclic test results show that the increase of the intergranular void ratio and the fine content accelerate the liquefaction phenomenon for the stress ratio under study and the liquefaction resistance decreases with the increase of the intergranular void ratio and the loading amplitude.

Predicting the engineering and transport properties of soils using fractal equivalent circuit model: Laboratory experiments

Frequency-dependent electrical measurements of soils contain useful information about their texture and structure that can be linked to their engineering and transport properties. We performed frequency-dependent electrical measurements on 29 natural soils with wide variability in physical and textural properties in a laboratory environment at a constant stress level and in the frequency range of 0.01 Hz–10 kHz. The engineering and hydraulic properties of these soils, that is, the hydraulic conductivity [Formula: see text], void ratio [Formula: see text], fines content [Formula: see text], intergranular void ratio [Formula: see text] and the dry density [Formula: see text] are concurrently measured. The electrical behaviors of the soils are modeled with an equivalent circuit model, which are described by six circuit parameters. Relationships between the circuit parameters and the soil properties (geotechnical engineering and hydraulic) are investigated. Crossplots of frequency exponent [Formula: see text] and resistivity [Formula: see text] and that of [Formula: see text] and grain percent resistivity [Formula: see text] clusters soils with high and low values of hydraulic conductivity, whereas crossplots of relaxation time [Formula: see text] and [Formula: see text] clusters soils with high and low intergranular void ratio. Regression models are developed using the parameters [Formula: see text] and [Formula: see text] to predict the hydraulic conductivity with [Formula: see text]; [Formula: see text] and [Formula: see text] to predict the intergranular void ratio with [Formula: see text] and [Formula: see text] and [Formula: see text] to predict the dry density with [Formula: see text].

Influence of silt size and content on liquefaction behavior of sands

This study investigates the fines content influence on liquefaction potential of a single base sand mixed with three different essentially nonplastic silts through strain-controlled monotonic undrained triaxial compression tests. Confining stress (30 kPa) and deposition method (dry funnel deposition) were kept the same, while fines content was varied, to solely focus on how different silts and their contents influence the undrained response of the sand under comparable conditions. It was found that if the mean grain diameter ratio (D50-sand/d50-silt) of the sand grains to silt grains is sufficiently small, the liquefaction potential of the sand increases steadily with increasing fines content for the studied range (0%–20%). As D50-sand/d50-silt increases, the liquefaction potential of the silty sand might actually be less than the liquefaction potential of the clean sand. Test results also revealed that commonly used comparison bases (i.e., void ratio, intergranular void ratio, relative density) are not sufficient for assessing the influence of fines on liquefaction potential of silty sands. Finally, relative size of the silt grains should also be considered in geotechnical engineering practice in addition to content and plasticity of fines to characterize the influence of silt on liquefaction potential of sands.

Comment on: “Influence of inter-granular void ratio on monotonic and cyclic undrained shear response of sandy soils” by M. Belkhatir, A. Arab, H. Missoum, T. Schanz [C. R. Mecanique 338 (2010) 290–303

The authors should be commended for their interesting experimental work on sandy soils presented in Belkhatir et al. (2010) [1]. They used the inter-granular void ratio, e s , to interpret the experimental results and developed some useful correlations with e s . However, the Note fails to address the further development of e s over a decade to a more generalized form of equivalent granular void ratio, e ⁎ . This comment aims at adding missing literature on e ⁎ and presents a re-interpretation of the experimental data based on e ⁎ . The advantages of using e ⁎ over e s are significant and explained in subsequent sections.

The undrained shear strength characteristics of silty sand: an experimental study of the effect of fines

This laboratory investigation has been conducted to elucidate how the fines fraction affects the undrained residual shear strength and liquefaction potential of sand-silt mixtures (Algeria). A series of monotonic and cyclic undrained triaxial tests were carried out on undrained, reconstituted, saturated samples of sand with varying fines content ranging from 0 to 50%. These were undertaken in order to evaluate the effect of the fines fraction on the undrained residual shear strength and liquefaction potential of loose, medium dense, and dense sand-silt mixtures (Dr = 17%, 53%, 62% and 91%), under an initial confining pressure of 100 kPa. The results of the monotonic tests indicate that the stress-strain response and shear strength behaviour is controlled by the percentage of the fines fraction and the samples become contractive for the studied relative density (Dr = 17% and 91%). The undrained residual shear strength decreases as the gross void ratio decreases, and the fines content increases up to 30%. Above this level of fines, it decreases with increasing gross void ratio. Moreover, the undrained residual strength decreases linearly as the fines content and the intergranular void ratio increase. Cyclic test results show that for the studied amplitude, the increase in fines content leads to an acceleration of liquefaction. The liquefaction resistance decreases with the increase in gross void ratio and the loading amplitude.

Reply to the comment by M. Rahman on “Influence of inter-granular void ratio on monotonic and cyclic undrained shear response of sandy soils” by M. Belkhatir et al. [C. R. Mecanique 338 (2010) 290–303

Reply to the comment by M. Rahman on “Influence of inter-granular void ratio on monotonic and cyclic undrained shear response of sandy soils” by M. Belkhatir et al. [C. R. Mecanique 338 (2010) 290–303

Effect of Mixing Fine Sand on the Drained Shear Strength of Completely Decomposed Granite Soil

Experimental test results presented in this paper were from a series of triaxial compression tests studied under drained conditions for Completely Decomposed Granite (CDG) soil mixed with fine sand content of (0, 10, 20, 30, and 40%). The CDG soil showed high compressibility during isotropic consolidation, probably due to the use of the moist tamping method and the effect of weathering degree on the soil structure. The tests results produced a unique Critical State Line (CSL) in the e-lnp plane, and these lines were parallel for each mixture and moved downward with increasing fine sand content. The fine sand content, at which the intergranular void ratio of the CDG-fine sand mixture became equal to emax for plain CDG soil, was named as Transition Fine Sand Content (TFSC), which occurred at 20-30% fine sand content. Normalization of the critical state stresses showed that for the samples with low P/Pc between 0.58 and 0.65 (i.e. the CDG soil mixed with fine sand), the stress paths moved directly towards the critical state without passing through the boundary surface of the soil mixture, which revealed the impact of the fine sand addition to the CDG soil structure, reflecting an improvement in the soil strength behavior by developing a strong interlocking among the particles of the mixture. It was also observed that a small portion of stress paths could pass through the boundary of Hvorslev surface in the case of low fine sand content (≤ 10 %) and the boundary of Hvorslev surface observed clearly in the case of plain CDG soil. The friction angle increased at steady state from 28- 32.6, and the cohesion decreased from 15 to 8.3 kN/m 2 with increasing fine sand content. A comparison of critical state parameters and strength properties between weathered granite CDG soil from Malaysia and Hong Kong were also made and summarized in this study.

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.

Influence of inter-granular void ratio on monotonic and cyclic undrained shear response of sandy soils

Liquefaction of sandy soil deposits during earthquakes has been one of the most important problems in the field of geotechnical earthquake engineering. A major challenge is the assessment of the appropriate undrained shear strength of liquefied soils to be used in the study of liquefaction stability of different types of earth structures (embankments, earthdams, etc.). The objective of this laboratory investigation is to study the effect of the inter-granular void ratio on the phase transition state undrained shear strength of loose, medium dense and dense ( D r = 12 , 50, and 90%) sand–silt soil mixtures under monotonic loading and liquefaction potential under cyclic loading. For this purpose, we considered the matrix of sand with fines as a combination of two sub-matrices: a coarser grain matrix and a finer grain matrix. Moreover, series of undrained triaxial compression tests were carried out on reconstituted saturated silty sand samples with fines contents ranging from 0 to 50%. The results show that the global void ratio does not reflect the real behaviour of the soil and the undrained shear strength at the phase transition state can be correlated to the inter-granular void ratio of the sand–silt mixtures up to 50% fines content. Indeed, it decreases linearly with further increase in the inter-granular void ratio. The results of the undrained cyclic tests confirm this tendency.

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.