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Effects of particle characteristics on the shear strength of calcareous sand
Pham Huu Ha Giang, P. O. Van Impe, W. F. Van Impe, Patrick Menge, Veerle Cnudde, Wim Haegeman, 2017, original scientific article

Abstract: The paper presents a 3D analysis (3DA) to evaluate the particle shape and size of silica and calcareous sands. The particles of calcareous sand are found to be less spherical than those of silica and crushed calcareous sands. Furthermore, the results indicate that the average sphericity (SPH) holds an inverse relationship to the particle size. However, in each sample the larger particles have higher SPHs than the smaller particles. In addition, the 3DA yields smaller particles than the sieve analysis (SA). Owing to a variety of particle shapes, causing particle interlocking, especially for calcareous sand, the particles cannot pass through the sieves by their shortest dimension. This paper discusses the effects of particle characteristics on the shear strength properties. Although the calcareous sand shows higher peak and residual shear strength properties, it tends to reach a lower shear strength at a small shear strain and a lower dilation than the silica sand. Moreover, the findings prove that the residual shear strength increases with the mean particle size. The sample with smaller particles shows less dilation under low vertical stress, while high vertical stress yields less compression. The relationship between the particle shape and shear strength properties is discussed based on the 3DA results.
Keywords: shear strength, sphericity, particle shape, calcareous sand
Published: 18.06.2018; Views: 440; Downloads: 46
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The dry fraction of unsaturated soils
Julio César Leal Vaca, Gustavo Gallegos Fonseca, Eduardo Rojas González, 2015, original scientific article

Abstract: An equation to account for the shear strength of unsaturated soils is proposed in this paper. This equation is defined as the equivalent stress, and is an extension of Murray’s equation. This approach applies to the general case of bi-modal structured soils showing a macrostructure and microstructure. The theoretical development considers the existence of a dry fraction in addition to the saturated and unsaturated fractions of the soil. These different fractions are included in a porous model, which allows an evaluation of the parameters of the equivalent stress equation. Finally, the paper includes a comparison between theoretical and experimental results. The comparison shows that the proposed equation can be used to estimate the shear strength of unsaturated soils.
Keywords: unsaturated soil, shear strength, equivalent stress, water retention curve
Published: 15.06.2018; Views: 688; Downloads: 39
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Atterberg limits in relation to other properties of fine-grained soils
Bojana Dolinar, Stanislav Škrabl, 2013, original scientific article

Abstract: In soil mechanics the Atterberg limits are the most distinctive and the easiest property of fine-grained soils to measure. As they depend on the same physical factors as the other mechanical properties of soils, the values of the liquid and plastic limits would be a very convenient basis for their prediction. There are many studies concerning the use of the Atterberg limits in soil mechanics; however, their results vary considerably and are not generally applicable. This paper explains the main reasons for the different conclusions in these studies, which do not take into account the following: a) the water in fine-grained soils appears as interparticle and interaggregate pore water as well as adsorbed water onto the surfaces of clay minerals; b) the physical properties of fine-grained soils depend on the quantity of pore water only, because the adsorbed water is tightly tied on the clayʼs external and internal surfaces and thus cannot influence to them; c) the quantity of adsorbed water on the external surfaces of the clay minerals in soils depends mostly on the size and the quantity of the clay minerals, while the interlayer water quantity depends mostly on the quantity and the type of the swelling clay minerals in the soil composition and their exchangeable cations. From this it follows that for swelling and non-swelling soils, the uniform relationships between the Atterberg limits (which represent the total quantity of pore water and the adsorbed water onto the external and internal surfaces of clay minerals) and other physical properties does not exist. This paper presents some possibilities for the use of the Atterberg limits in predicting the soilʼs other properties for non-swelling and limited-swelling soils.
Keywords: Atterberg limits, specific surface area, undrained shear strength, compressibility, hydraulic conductivity
Published: 14.06.2018; Views: 397; Downloads: 48
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Influence of geosynthetic reinforcement on the shear strength characteristics of two-layer sub-grade
Mehrad Kamalzare, Reza Ziaie-Moayed, 2011, original scientific article

Abstract: Due to the low bearing capacity of soft clayey soils in places that because of economic, military or geological conditions we are oblige to build a structure on, geosynthetics will be used to reinforce the soil and improve its bearing capacity. Particularly, A good example is roadways, where geosynthetics are placed between the interface of the granular materials and the soft-soil sub-grade to improve the bearing capacity of the composite layers. In previous research the behavior of one-layer soils that were reinforced with different kinds of geosynthetics were studied by experimental and analytical methods and some numerical models have been developed. In this paper the behavior of two-layer soils (granular base and clayey sub-grade) that were reinforced with some geosynthetics are investigated. Large-scale direct shear tests were performed on unreinforced and reinforced samples with different geosynthetics. The results show that depending on the characteristics of the geosynthetics, the inclusion of these materials may increase or decrease the shear strength parameters of the interface of two-layered soils. It implies that the geosynthetic-reinforced soils in the sub-base layer of roads are so sensitive to the characteristics of geosynthetics and will perform better than non-reinforced soils and consequently the load-carrying capacity of the basement will improve only if the appropriate geosynthetics are used. However, geogrid shows more reinforcement efficiency under higher vertical stresses. Increasing the relative density of the clayey sub-grade would also cause the geogrid reinforcement to be more effective.
Keywords: shear strength, geosynthetic, large scale direct shear test, soft clay, subgrade
Published: 13.06.2018; Views: 412; Downloads: 43
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Relationship between the undrained shear strength, water content, and mineralogical properties of fine-grained soils
Ludvik Trauner, Bojana Dolinar, Miha Mišič, 2005, original scientific article

Abstract: The relationship between the undrained shear strength of fine-grained soils and the water content can be described with a nonlinear function in which the type of soil is determined by two parameters. It is well known that these parameters depend mainly on the mineral compositions of soilsč these relationships, however, have not yet been investigated. The findings describedin this paper define those mineralogical properties of soils which determine the values of both parameters. Experimentally obtained results suggest that the parameters primarily depend on the size of the clay minerals,their quantity in soil composition, and the interlayer water quantityin the expanding clay minerals. As this dependence is well defined, the parameters, and thus the undrained shear strength at different water content, can be defined from knowledge of these mineralogical soil properties.
Keywords: soil mechanics, clays, fine-grained soils, shear strength, water content, mineralogy
Published: 01.06.2012; Views: 2079; Downloads: 96
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The impact of structure on the undrained shear strength of cohesive soils
Bojana Dolinar, Ludvik Trauner, 2007, original scientific article

Abstract: The relationship between the undrained shear strength and the water content ofcohesive soils can be described with a two parameter non-linear function. Parameter a is the water content at the undrained shear strength su=1 kPa, andb is the slope of the linear function which represents the ratio between the water content logarithm and the undrained shear strength logarithm. These parameters depend mainly on the type and amount of clay minerals in the soils,the particle sizes and shapes, their arrangements, the forces between the clay particles, and the chemical composition of the pore water. The impactof quantity, type and size of clay grains on the water content at a uniform undrained shear strength in different soils has been studied previously, whilst the impact of structure is less understood. Particle associations and arrangements (i.e. fabric), and the interparticle forces determine the structure of soil. This paper focuses on an investigation of therelationship between water content and undrained shear strength in kaolinite samples with different structures. The various arrangements of clay particles that resulted from the changed of interparticle forces were obtainedby salt addition (NaCl). Microfabrics of wet kaolinite samples were studied using a field emission scanning electron microscope. The results showed that clay structure exerts a strong influence on the relationship between the quantity of water and undrained shear strength. This was reflectedin the values of both soil-dependent parameters, a and b. Values of parameter a varied between 39.16% and 62.96%, and b between 0.100 and 0.139, for well crystallized kaolinite with salt concentrations of 0- 175 mmol/l. Forpoorly crystallized kaolinite with salt concentrations of 0-300 mmol/l, thevalues of a range between 46.96% and 100.30%, and b between 0.090% and 0.148%.
Keywords: geomechanics, clay, kaolonite, structure, fabric, undrained shear strength
Published: 31.05.2012; Views: 1630; Downloads: 83
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