Shear Strength Of Sand Research Articles

Influence of Particle Size on the Friction and Interfacial Shear Strength of Sands of Similar Morphology

Size and morphological characteristics of particles play vital role on the shear and interfacial shear strength of sands. Often, effects of these parameters are merged and cannot be easily separated. Effect of size of the particles on the shear and interfacial shear strength of sands is presented in this paper through direct shear and interface direct shear tests complemented with image analyses and surface roughness studies. To eliminate the effect of morphological characteristics, three sands of different particle sizes with similar morphological characteristics like angularity, roundness, sphericity and roughness were selected for the study. These morphological characteristics for all three sands were determined from the analysis of scanning electron microscope images and were found to be similar for all three sands. It was observed from the symmetric direct shear tests that the particle size has no effect on the peak friction angle when the tests were carried out at same void ratio. However, ultimate friction angles were affected by the particle size. Shear band thickness was estimated from image segmentation analysis of the profiles of colored sand columns during shear and the same was correlated to the particle size. Interface direct shear tests were carried out on sand–geomembrane interfaces to study the effect of particle size on the interfacial shear strength. Microscopic images of geomembranes were captured after the interface shear tests to understand the change in surface roughness of the geomembrane due to particle indentations. Surface roughness studies on geomembrane samples after the tests confirmed that the plowing and groove formation on geomembranes during interface shear tests depend on the particle size as well as the relative roughness of the sand particles with respect to the membrane. Sand of medium particle size showed highest interfacial strength because of more number of effective contacts per unit area of the interface.

Application of Wood to Sand-slag and its Effect on Soil Strength

In certain situations, sand is required to have extra shear strength to provide more safety, stability and support for structures. Shear strength in sand arises from friction and resistance between particles. The most common means of increasing the shear strength of sand is the cementation method. Another practice is using an additive such as slag. Some studies show that wood has also been used to improve soil strength, mostly for soft and expansive soil. However, there is limited information available on sand. Therefore, the purpose of this research is to determine whether the shear strength of a sand-slag mixture is affected by the addition of wood. Baldivis sand, a locally sourced material, was used in the experiment because it has been widely used in construction and geotechnical projects in Western Australia. The shear strength of the sand-slag-wood material was determined using an automated direct shear testing machine. There were a number of variations in test conditions, including as the amount of wood introduced into the sand-slag, the percentage of slag in the sand, the gaps between the wood, and wood orientation. The results showed that the shear strength of the sand-slag mixture tended to be enhanced by the presence of wood. The sand-slag mixture containing wood seemed to be stronger than the sand-slag without wood or the pure sand. The position of the wood also contributed to the improvement in shear strength. Placing the wood vertical to the shear direction resulted in greater strength than when the wood was positioned horizontally. From these results, it can be concluded that wood is another potential means of enhancing the shear strength of sand-slag mixture. The quantity of wood and the way it is arranged, such as distance and direction, may result in different levels of improvement to the shear strength of the sand-slag.

Experimental investigation of shear strength of sands with inherent fabric anisotropy

Loading direction-dependent strength of sand has been traditionally characterized in the principal stress space as a direct extension of the Mohr–Coulomb criterion. A recent study found that it is more appropriate to define anisotropic strength of sand on failure/shear planes, but this proposition has only been demonstrated with discrete element method (DEM) simulations. The present study experimentally investigates anisotropic shear strength of sands in this new framework. Three granular materials with distinct grain characteristics ranging from smooth and rounded particles to flaky and angular particles are tested with the bedding plane inclination angle ψ b varying over the full range of 0°–180°. The main objective is to study how the peak friction angle ϕ p of sand is affected by the ψ b angle and how the ψ b–ϕ p relationship evolves with the change of characteristics of constituent sand particles. We find that the general trend of ψ b–ϕ p curves for real sands resembles what was predicted by DEM in a previous study, whereas rich anisotropic strength behavior is revealed by the laboratory data. The effects of normal stress and initial density, as well as shear dilation behavior at different shear directions, are also studied.

Influence of fines content on liquefied strength of silty sands

Critical state soil mechanics is a useful framework to understand sand behavior. In this paper, a relationship is developed for estimating undrained critical shear strength of sands based on the critical state framework. The relationship is validated by comparison with laboratory test results and sand liquefied strength from field liquefaction failure case histories. Using this relationship, the influence of fines content on undrained critical shear strength is studied for different combinations of effective stress and density. The parametric study indicates that depending on soil void ratio, effective stress, and the shape and mineralogy of the fine particles, undrained critical strength may increase, remain the same, or decrease as the amount of fines content increases. Both the susceptibility to liquefaction and the severity of strain-softening are affected by adding fines. It is suggested that the critical state parameter is inadequate for describing the behavior of liquefiable sands and sand shearing-compressibility should be taken into account in liquefaction analysis.

Influence of state and compressibility on liquefied strength of sands

Critical-state soil mechanics is a useful framework to understand sand behavior. In this paper, a relationship is developed for estimating undrained critical shear strength of sands based on the critical-state framework. The application of this relationship is demonstrated by comparison with laboratory test results and sand liquefied strength from field liquefaction flow failure case histories. Using this relationship, the effects of effective stress variation and density on undrained critical shear strength are studied for different combinations of critical-state line parameters corresponding to several reference sands. The parametric study indicates that depending on sand void ratio, undrained critical shear strength may increase, remain the same or decrease as sand shearing–compressibility (represented by the slope of the critical-state line) increases. The underlying mechanisms of field failures in dense sands and reverse behavior of compressible sands are explained through this relationship. It is suggested that the critical-state parameter alone is insufficient for describing the behavior of liquefiable sands and sand shearing–compressibility should be also taken into account for estimating undrained shear strength corresponding to the changes in density and effective confining stress.

Shear strength of microfine cement grouted sands

Unconsolidated–undrained (single and multi-stage) triaxial compression tests were conducted to evaluate the shear strength of microfine cement grouted sands. Microfine cements of three different types were obtained by pulverising ordinary cements produced in Greece. Multi-stage triaxial compression tests can be used dependably for determination of the shear strength parameters of cement grouted sands. It has been observed that the Mohr–Coulomb failure criterion represents adequately the behaviour of the grouted sands. Grouting with microfine cement suspensions improves the strength of sands significantly, and the improvement is primarily controlled by the water-to-cement (W/C) ratio of the suspensions. The positive effect of microfine cement grouting on the shear strength of sands is mainly the addition of cohesion, which is substantial even at a distance of 1·2 m from the injection point. Grouting with suspension, using W/C = 1 provides the sand with cohesion of about 2·6 MPa. The shear strength parameters vary with axial strain, and cohesion attains a maximum value well before failure.

Shear Strength Evaluation of Lower Sand in Nakdong River Delta

An empirical method of estimating the shear strength of deep sands from the Nakdong River Delta was developed. The piezocone penetration test (CPT/CPTu) and sampling of disturbed sand at several depths were performed at two sites. A total of 39 isotropically consolidated–drained triaxial tests on reconstituted samples provided by a slurry displacement method were conducted to estimate the shear strengths. The sand deposits are classified into three types based on the physical properties and the soil behavior type index (Ic). The six existing empirical formulas considered in the present study, which are based on the overburden stress and cone resistance, either underestimate or overestimate the shear strengths of the sands obtained from the triaxial tests. By contrast, the newly developed empirical formula, which accounted for the types of sands in addition to the two other factors, matches well with the triaxial results.

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.

Interfacial shear strength of silty sand–geogrid composite

This study has been carried out to investigate the interface shear strength of sand reinforced by high-density polyethylene cogged geogrid, with variation in fines content from 0 to 45%. To this end, a set of large direct shear tests (30 × 30 × 15 cm) was systematically conducted. The behaviour of sand and silty sand reinforced with a special type of cogged geogrid is studied in terms of interfacial shear strength of the soil. An analysis of test results indicates that the reinforcement improved the shearing behaviour of the sand and silty sand samples. Attaining the peak strength at greater shear strain due to reinforcement and lowering the post-peak loss of strength of specimens with higher silt content, compared to the specimens with lower silt content, are the indications implying that the reinforcement and increasing the silt content tend to transform the shearing behaviour of sand and silty sand specimens from a brittle to a ductile manner. The results also indicated that as the silt content increases up to 35%, the combined shear strength decreases. Further increase in the silt content made no significant change to the combined shear strength of the soil samples.

The Consequence of Particle Crushing in Engineering Properties of Granular Materials

This paper presents experimental investigation for particles breakage for natural sand. The particle breakage was induced by subjecting the sample to one dimensional compression. Grain size analyses were performed before and after induced breakage. Thereafter, the sand shear strength parameters were assessed using direct shear box tests and the coefficient of permeability was assessed using constant head permeameter. Examining the obtained results revealed that the amount of breakage due to one dimensional compression was of order higher than the amount occurring during direct shear test. Peak shear strength parameters decreased with the particles breakage increasing. Moreover, dilation angle of shear strength pronouncedly decreases with the amount of particles breakage increasing. Crushing has obvious effect on the evaluated coefficient of permeability.

Shear Strength of Sands Reinforced with Polypropylene Fibers

The inclusion of oriented or randomly distributed discrete elements, such as fibers, to reinforce soil has recently attracted increasing attention in geotechnical engineering. The present paper studies the shear strength parameters of reinforced sands, consisting of different mean grain sizes. The polypropylene fiber volumetric content of the sands ranges from 0.1 to 0.5 %. Specifically, a series of direct shear tests were conducted to determine the peak and residual shear strength parameters of unreinforced and reinforced sands. Laboratory results showed that fiber reinforcement substantially improved the residual strength of fine sands of medium dense state. On the contrary, reinforced sands of high dense state appeared to exhibit negligible strength increment. Based on the experimental results, a non-linear regression analysis was performed to correlate the shear strength of reinforced sand with some descriptor variables.

Effect of grading characteristics on the undrained shear strength of sand: review with new evidences

In this paper, the shear strength of saturated pure sand and sand-silt mixture is evaluated by monotonic un- drained triaxial tests that were carried out on reconstituted specimens at same relative densities and a constant confin- ing pressure (σ30300 kPa). The test results were used to conclude on the effect of low non-plastic contents (0-20 %) and grading characteristics on the liquefaction resistance of the sand. The test results indicate that the undrained residual strength reduced with the increase of non-plastic fine con- tent. Also, shear strength of gap-graded sand mixed with low non-plastic fine content increases with decrease in ef- fective size (D50). In other words, in this state, we can use the D50 as a parameter to control of silty sand's undrained resistance. Besides, the undrained residual strength of pure sand specimens with same effective size increases due to increase of coefficient of uniformity (Cu).

휴대용콘의 선단저항값을 이용한 모래의 상대밀도 및 내부마찰각 추정

Sand is one of the essential materials used for social infrastructure construction such as embankment, landfill and backfill. It was known that mechanical properties and shear strength of sand are closely related to relative density. Therefore it is very important to determine accurate relative density. In this study, Portable Cone Penetration Tester (PCPT) was used to estimate the relative density and the internal friction angle of sand. PCPT cone-tip resistance (<TEX>$q_c$</TEX>) was measured changing the relative density of the two soil samples.Standard sand (JMJ) and Busan sand (BS). Also, a direct shear test was performed to investigate relationship between relative density and internal friction angle. The size and shape of soil particles were confirmed by using Scanning Electron Microscope (SEM). As a result, the log value of <TEX>$q_c$</TEX> was linearly correlated with relative density and internal friction angle. In particular, the internal friction angle of BS sample was greater than that of JMJ, which was due to difference of the shape and mean size of particles. This result shows that it is important to determine the shape and size of particles as well as relative density to define mechanical property of sand. Through this study, it can be more effectively and conveniently to investigate relative density and shear strength of sand by using PCPT in situ.

Relationships between Shape Characteristics and Shear Strength of Sands

In the Mohr-Coulomb criterion, the shear strength of sands is typically characterized by the internal friction angle, which depends on many factors such as grain size and distribution, the mineralogical origin of the particles, particle shape, unit weight, geological history, cementation, saturation, and overburden pressure. In this study, the empirical relationships among three particle shape indices, different fractal dimension definitions, and internal friction angles were investigated. Within this context, direct shear tests were conducted on 38 different types of sands from different origins and with various grain sizes. For each type of sand, image analyses were performed to find out the roundness, sphericity, regularity parameters belonging to individual grains. Additionally, several statistics of these parameters for different types of sands were determined. The results revealed that particle shape has a limited effect on the friction angle of sands in comparison to grain size distribution. Furthermore, it was found that decreasing regularity in particle shape caused an increase in the internal friction angle of uniform sands. These findings agree with the empirical relationship between the internal friction angle and particle shape suggested in the literature.

Direct Shear Tests on Waste Tires–Sand Mixtures

Waste tires are used in some engineering applications and thereby reduce the potential impact on the environment, for example, as lightweight materials in geotechnical engineering projects. This paper presents a brief literature review on geotechnical applications of processed waste tires, and a laboratory study on the effect of tire shreds on the physical properties of two different sands (fine angular sand and coarse rotund sand). Each type of sand was mixed four different percentages of rubber particles; 5, 10, 20 and 50% by dry weight. Direct shear tests were employed to investigate the effect of rubber particles on the shear strength of sands and internal friction angle. The addition of shredded waste rubber particles slightly decreased both the internal angle of friction and the shear strengths of the sands within the tested stress and strain levels. Additionally, a prediction model using stepwise regression (SR) method is proposed to calculate the shear strength of sands with the increasing rubber content. The performance of accuracies of proposed SR models are quite satisfactory. The proposed SR models are presented as relatively simple explicit mathematical functions for further use by researchers.

Modelling the scale effect of granular media for strength and bearing capacity

This paper investigates a method of analysis for the scale effect on shear strength of sands – a fundamental problem of considerable importance to soil mechanics. The phenomena of scale effect for direct shear box tests and footing bearing capacity tests are briefly described and the available analytical methods are discussed. First, the couple-stress theory is reviewed and its extension to a Drucker–Prager type is illustrated. Subsequently, material constants are discussed. Attention is then focused on the internal length of sand, which is shown to be the key parameter for scale effect for granular soil. Then, the predicted results are compared with experimental results on two sands. The main observations of the comparison for the scale effect are sketched and its limitations are discussed.

Triaxial compression behavior of sand and tire wastes using neural networks

Tire waste additions to sand enhance the shear strength of sand for embankments. Granular and fiber shape tire wastes and their mixture with sand under drained and undrained conditions were tested in triaxial compression apparatus and modeled using neural networks (NN). In the experimental study, tire crumb and tire buffings inclusions were used at varying contents as soil reinforcement. Both quick tests and consolidated drained (CD) triaxial tests were performed to analyze the effects of tire content, tire shape, and tire aspect ratio on the shear strength of sand. Then, this extensive experimental database obtained in laboratory was used in training, testing, and prediction phases of three neural network-based soil models. The input variables in the developed NN models are tire wastes content, tire wastes type, test type, effective stress, and axial strain, and the output is the deviatoric stress. The accuracy of proposed models seems to be satisfactory. Furthermore, the proposed models are also presented as simple explicit mathematical functions for further use by researchers.

Influence of tire fiber inclusions on shear strength of sand

ABSTRACT: Reinforcement of soils with natural and synthetic fibers is a viable technique for increasing the soil strength. The objective of this study is to reinforce sand with tire waste inclusions. In this study, two different experimental programs were performed. In the first program, sand, tire crumb and tire crumb–sand mixtures were tested in the standard direct shear test equipment to observe the optimum content for modifying the shear strength properties of the sand. In the second program, large-scale direct shear tests were performed to observe the shear strength improvement imparted by tire waste inclusions. Two different processed tire wastes were used: tire crumb (TC) and fiber-shaped tire buffings (TB). The tire buffings were divided into two parts for representing different aspect ratios (TB1 and TB2). The following factors were studied to evaluate the influence of TC, TB1 and TB2 inclusions on the shear strength: normal stress, tire waste type, aspect ratio, and tire waste content. Three factors were found to significantly affect the shear strength values: normal stress, aspect ratio, and tire waste content. Also, it is seen that increasing the aspect ratio of the fibers increases the shear strength of the mixture.

Dilatancy and Shear Strength of Sand at Low Confining Pressures

Sand dilates with shearing at a rate that increases with increasing relative density DR and decreases with increasing effective confining stress c. The peak friction angle of a sand depends on its critical-state friction angle and on dilatancy. In this paper, we develop a simple correlation between peak friction angle, critical-state friction angle, and dilatancy based on triaxial compression and plane-strain compression test data for sand for a range of confining pressures from very low levels to approximately 196 kPa. DOI: 10.1061/ASCEGT.1943-5606.0000237 CE Database subject headings: Sand, Soil type; Stress; Dilatancy; Shear strength; Friction. Author keywords: Sand; Low confining stress; Dilatancy; Shear strength; Friction angle.

Experimental study of the overconsolidation and saturation effects on the mechanical characteristics and residual strength of Chlef river sandy soil

This paper presents a laboratory study of the influence of the saturation evaluated in terms of Skempton´s pore pressure coefficient (B) and overconsolidation ratio (OCR) on the behavior of Chlef sand. The study is based on drained and undrained triaxial compression tests which were carried out for Skempton´s pore pressure coefficient varying between 13 and 90% and OCR varying between 1 and 8. Tests were conducted on medium dense sand samples having an initial relative density Index Id = 0.5 at an effective stress of 100 kPa. The paper is composed of two parts. The first one presents the characteristics of the sand used in this study, the second provides an analysis of the experimental results and discusses the influence of Skempton´s pore pressure coefficient (B) and OCR on the mechanical characteristics of the sand. The tests show that the increase in the Skempton´s pore pressure coefficient (B) reduces the soil dilatancy and amplifies the phase of contractancy and reduces the frictional and characteristic angle of the sand. The increase of OCR improves the stiffness of sand and accelerates the appearance of dilatancy; and increases frictional and characteristic angle of the sand. Moreover, the present study focuses on the effect of saturation and overconsolidation on the residual shear strength of sand.