The Experts below are selected from a list of 11487 Experts worldwide ranked by ideXlab platform
Maosong Huang - One of the best experts on this subject based on the ideXlab platform.
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dem study of the three dimensional effect of soil arching in piled embankments
Civil Infrastructures Confronting Severe Weathers and Climate Changes Conference, 2018Co-Authors: Maosong HuangAbstract:Soil arching plays an important role in the design of piled-embankments of transportation facilities. This paper aims to study the three dimensional effect of soil arching in piled-embankments by discrete element simulation. The results show the formation of soil arching and the Stress transfer mechanism. The evolution of the Stress ratio of pile cap and subsoil was obtained, and the overestimation of the arching effect in plane strain condition was revealed. According to the movements of soil particles, the 3D uneven settlement pattern characteristic was plotted and clearly shows the formation of soil arching. The direction of Major Principal Stress in three typical sections clearly shows the 3D effect of Stress transfer mechanism. The obtained results are useful for the deformation calculation of high-speed railway piled embankment.
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influences of loading direction and intermediate Principal Stress ratio on the initiation of strain localization in cross anisotropic sand
Acta Geotechnica, 2018Co-Authors: Xilin Lu, Maosong Huang, Jiangu QianAbstract:Since cross-anisotropic sand behaves differently when the loading direction or the Stress state changes, the influences of the loading direction and the intermediate Principal Stress ratio (b = (σ 2 − σ 3)/(σ 1 − σ 3)) on the initiation of strain localization need study. According to the loading angle (angle between the Major Principal Stress direction and the normal of bedding plane), a 3D non-coaxial non-associated elasto-plasticity hardening model was proposed by modifying Lode angle formulation of the Mohr–Coulomb yield function and the Stress–dilatancy function. By using bifurcation analysis, the model was used to predict the initiation of strain localization under plane strain and true triaxial conditions. The predictions of the plane strain tests show that the Major Principal strain at the bifurcation points increases with the loading angle, while the Stress ratio decreases with the loading angle. According to the loading angle and the intermediate Principal Stress ratio, the true triaxial tests were analyzed in three sectors. The Stress–strain behavior and the volumetric strain in each sector can be well captured by the proposed model. Strain localization occurs in most b value conditions in all three sectors except for those which are close to triaxial compression condition (b = 0). The difference between the peak shear strength corresponding to the strain localization and the ultimate shear strength corresponding to plastic limit becomes obvious when the b value is near 0.4. The influence of bifurcation on the shear strength becomes weak when the loading direction changes from perpendicular to the bedding plane to parallel. The bifurcation analysis based on the proposed model gives out Major Principal strain and peak shear strength at the initiation of strain localization; the given results are consistent with experiments.
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strength criterion for cross anisotropic sand under general Stress conditions
Acta Geotechnica, 2016Co-Authors: Maosong Huang, Jose E AndradeAbstract:By incorporating the fabric effect and Lode’s angle dependence into the Mohr–Coulomb failure criterion, a strength criterion for cross-anisotropic sand under general Stress conditions was proposed. The obtained criterion has only three material parameters which can be specified by conventional triaxial tests. The formula to calculate the friction angle under any loading direction and intermediate Principal Stress ratio condition was deduced, and the influence of the degree of the cross-anisotropy was quantified. The friction angles of sand in triaxial, true triaxial, and hollow cylinder torsional shear tests were obtained, and a parametric analysis was used to detect the varying characteristics. The friction angle becomes smaller when the Major Principal Stress changes from perpendicular to parallel to the bedding plane. The loading direction and intermediate Principal Stress ratio are unrelated in true triaxial tests, and their influences on the friction angle can be well captured by the proposed criterion. In hollow cylinder torsional shear tests with the same internal and external pressures, the loading direction and intermediate Principal Stress ratio are related. This property results in a lower friction angle in the hollow cylinder torsional shear test than that in the true triaxial test under the same intermediate Principal Stress ratio condition. By comparing the calculated friction angle with the experimental results under various loading conditions (e.g., triaxial, true triaxial, and hollow cylinder torsional shear test), the proposed criterion was verified to be able to characterize the shear strength of cross-anisotropic sand under general Stress conditions.
Chandong Chang - One of the best experts on this subject based on the ideXlab platform.
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true triaxial strength and deformability of the german continental deep drilling program ktb deep hole amphibolite
Journal of Geophysical Research, 2000Co-Authors: Chandong Chang, Bezalel HaimsonAbstract:We designed and fabricated a true triaxial loading system and used it to determine deformational and strength characteristics of the amphibolite penetrated by the superdeep hole drilled in the Bohemian massif of southeastern Germany under the German Continental Deep Drilling Program (KTB). Amphibolite is found between 3200 and 7300 m and thus the dominant rock in this 9100-m boring. Our loading system enables the application of three unequal Principal Stresses to a rectangular prismatic rock specimen. During a test we maintained the least Principal (σ3) and the intermediate (σ2) Stresses constant and increased the Major Principal Stress (σ1) until brittle failure occurred, in the form of a fracture steeply dipping in the σ3 direction. Typically, for the same σ3 level the amphibolite compressive strength increased substantially with the magnitude of σ2, demonstrating the inadequacy of Mohr-like failure criteria that ignore the effect of the intermediate Principal Stress on rock strength. We found that a general criterion for the amphibolite could be expressed in the form of a power function relating the octahedral shear Stress at failure to the mean normal Stress acting on the plane containing the fracture. With respect to deformation, we established that for the same σ3 the onset of dilatancy increases significantly with the magnitude of σ2. Thus the intermediate Principal Stress appears to extend the elastic range of the Stress-strain behavior for a given σ3 and hence to retard the onset of the failure process. Scanning electron microscopy observations of the failure process reveal that microcracks develop mainly parallel to σ2 direction, as the intermediate Stress grows beyond σ3, localizing in close proximity of the eventual main fracture.
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a new true triaxial cell for testing mechanical properties of rock and its use to determine rock strength and deformability of westerly granite
International Journal of Rock Mechanics and Mining Sciences, 2000Co-Authors: Bezalel Haimson, Chandong ChangAbstract:Abstract A new true triaxial cell has been designed, fabricated, calibrated, and successfully tested. Its main feature is very high loading capability in all three orthogonal directions, enabling the testing to failure of hard crystalline rocks subjected to large least and intermediate Principal Stresses. All three Principal Stresses applied to rectangular prismatic specimens, 19×19×38 mm in size, are servo controlled. The cell was used to conduct an extensive series of tests in Westerly granite. A new true triaxial strength criterion for the rock was obtained that takes into account the effect of the intermediate Principal Stress. This turns out to be so significant that it raises serious questions about the suitability of criteria such as those named after Mohr, Coulomb, Griffith, and others. Measurements of strain in all three Principal directions revealed that the onset of dilatancy relative to the Major Principal Stress at failure rises substantially as the intermediate Principal Stress increases. The true triaxial tests also demonstrate that for the same least horizontal Stress the main fracture dip angle in Westerly granite increases as a function of the intermediate Principal Stress, suggesting a strengthening effect. Limited thin section and SEM study shows that microcrack propagation, crack localization, and main fracture characteristics are basically similar to those observed in common triaxial tests.
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a new true triaxial cell for testing mechanical properties of rock and its use to determine rock strength and deformability of westerly granite
International Journal of Rock Mechanics and Mining Sciences, 2000Co-Authors: Bezalel C Haimson, Chandong ChangAbstract:Abstract A new true triaxial cell has been designed, fabricated, calibrated, and successfully tested. Its main feature is very high loading capability in all three orthogonal directions, enabling the testing to failure of hard crystalline rocks subjected to large least and intermediate Principal Stresses. All three Principal Stresses applied to rectangular prismatic specimens, 19×19×38 mm in size, are servo controlled. The cell was used to conduct an extensive series of tests in Westerly granite. A new true triaxial strength criterion for the rock was obtained that takes into account the effect of the intermediate Principal Stress. This turns out to be so significant that it raises serious questions about the suitability of criteria such as those named after Mohr, Coulomb, Griffith, and others. Measurements of strain in all three Principal directions revealed that the onset of dilatancy relative to the Major Principal Stress at failure rises substantially as the intermediate Principal Stress increases. The true triaxial tests also demonstrate that for the same least horizontal Stress the main fracture dip angle in Westerly granite increases as a function of the intermediate Principal Stress, suggesting a strengthening effect. Limited thin section and SEM study shows that microcrack propagation, crack localization, and main fracture characteristics are basically similar to those observed in common triaxial tests.
Reiko Kuwano - One of the best experts on this subject based on the ideXlab platform.
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change in mechanical behaviour of gap graded soil subjected to internal erosion observed in triaxial compression and torsional shear
Geomechanics for Energy and the Environment, 2021Co-Authors: Reiko Kuwano, Luisa Fernanda Santa Spitia, Mehdi Bedja, Masahide OtsuboAbstract:Abstract Internal erosion can be a cause of failure in hydraulic structures such as levees, dikes and embankment dams. Suffusion is a type of internal erosion in which the fine particles migrate through the voids between the coarse particles under seepage flow, leaving behind the coarse skeleton. In this study the impacts of suffusion on the mechanical properties of soil in triaxial compression and torsional shear were investigated using a gap-graded soil mix of Silica sand No.5 and non-plastic silt. It was found that the erosion process varied depending on the initial density of the soil and higher density specimens showed relatively lower rates of erosion, degree of erosion, and compressive straining during erosion as compared with loose specimens. Effects on the mechanical behaviour of the soil were also dependent on the initial density of the specimen, with changes in the small strain stiffness, secant stiffness degradation, yield loci, small strain peak strength and medium strain strength in both drained and undrained conditions. In triaxial loading, force chains of coarse particles’ skeleton reinforced by fines developed in the suffusion process in the direction of Major Principal Stress, then the stiffness at small strain increased. On the other hand, in torsional shear testing, the reinforced soil skeleton established by the erosion did not resist against shear loading. Increase in stiffness at small strain range was not observed.
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dem analysis on the Stress wave response of spherical particle assemblies under triaxial compression
Computers and Geotechnics, 2021Co-Authors: Masahide Otsubo, Reiko KuwanoAbstract:Abstract It is challenging to understand the Stress wave response of cohesionless particle assemblies including compression and shear wave velocities ( V p and V s ) due to complicated particle-scale interactions particularly during a loading process. This contribution adopts the discrete element method to simulate triaxial compression experiments using spherical particles. Four samples are isotropically confined at various initial packing densities and then sheared monotonically up to the critical state. Small-amplitude wave propagation simulation is performed during shearing along the axis of loading. The results reveal that V p is affected by the Major Principal Stress and the coordination number contributing to the vertical direction rather than horizontal direction, while V s is more influenced by the geometric mean Stress and the mean coordination number. The wave velocity ratio ( V p / V s ) is well correlated with the fabric anisotropy, having a linear relationship. This enables prediction of microscopic change in fabric from macroscopic wave velocity values. Besides, a material-specific relationship between Stress levels and wave velocities is found at the critical state with a unique fabric anisotropy, independent of initial packing. V s in the isotropic state is found to be always larger that at the critical state under an equivalent Stress level.
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effect of shearing history on Stress wave velocities of sands observed in triaxial compression tests
Soils and Foundations, 2021Co-Authors: Troyee Dutta, Masahide Otsubo, Reiko KuwanoAbstract:Abstract For the accurate design of geotechnical structures subjected to static and dynamic loadings, precise estimation of elastic wave velocities and hence, small strain stiffness of soil is essential. However, the interpretation of elastic wave velocities propagating in deformed/sheared soil has not been comprehensively explored. In this research, shear (Vs) and compression wave velocity (Vp) measurements have been undertaken on three kinds of uniformly graded sands during drained triaxial compression by keeping minor Principal Stress constant. Planar piezoelectric transducers have been used to overcome the limitations associated with the more commonly used bender elements, such as distortion of transducers during specimen shearing. This technical note reveals that the increase of Major Principal Stress in the wave propagation direction has a more significant influence on Vp in comparison to Vs. The axial strain (ea) at which peak Vs is noted is comparable to the ea at which specimen dilation or phase transformation takes place. The Vs values show a substantial drop after phase transformation, although there is an increase in the mean Stress level. However, Vp increases even after specimen dilation takes place, and it is the Major Principal Stress that dictates its evolution during triaxial compression. Moreover, for a given material and initial Stress level, elastic wave velocities of specimens prepared at different initial densities approach one another during shearing and later merge at a large ea.
Jose E Andrade - One of the best experts on this subject based on the ideXlab platform.
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strength criterion for cross anisotropic sand under general Stress conditions
Acta Geotechnica, 2016Co-Authors: Maosong Huang, Jose E AndradeAbstract:By incorporating the fabric effect and Lode’s angle dependence into the Mohr–Coulomb failure criterion, a strength criterion for cross-anisotropic sand under general Stress conditions was proposed. The obtained criterion has only three material parameters which can be specified by conventional triaxial tests. The formula to calculate the friction angle under any loading direction and intermediate Principal Stress ratio condition was deduced, and the influence of the degree of the cross-anisotropy was quantified. The friction angles of sand in triaxial, true triaxial, and hollow cylinder torsional shear tests were obtained, and a parametric analysis was used to detect the varying characteristics. The friction angle becomes smaller when the Major Principal Stress changes from perpendicular to parallel to the bedding plane. The loading direction and intermediate Principal Stress ratio are unrelated in true triaxial tests, and their influences on the friction angle can be well captured by the proposed criterion. In hollow cylinder torsional shear tests with the same internal and external pressures, the loading direction and intermediate Principal Stress ratio are related. This property results in a lower friction angle in the hollow cylinder torsional shear test than that in the true triaxial test under the same intermediate Principal Stress ratio condition. By comparing the calculated friction angle with the experimental results under various loading conditions (e.g., triaxial, true triaxial, and hollow cylinder torsional shear test), the proposed criterion was verified to be able to characterize the shear strength of cross-anisotropic sand under general Stress conditions.
Masahide Otsubo - One of the best experts on this subject based on the ideXlab platform.
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change in mechanical behaviour of gap graded soil subjected to internal erosion observed in triaxial compression and torsional shear
Geomechanics for Energy and the Environment, 2021Co-Authors: Reiko Kuwano, Luisa Fernanda Santa Spitia, Mehdi Bedja, Masahide OtsuboAbstract:Abstract Internal erosion can be a cause of failure in hydraulic structures such as levees, dikes and embankment dams. Suffusion is a type of internal erosion in which the fine particles migrate through the voids between the coarse particles under seepage flow, leaving behind the coarse skeleton. In this study the impacts of suffusion on the mechanical properties of soil in triaxial compression and torsional shear were investigated using a gap-graded soil mix of Silica sand No.5 and non-plastic silt. It was found that the erosion process varied depending on the initial density of the soil and higher density specimens showed relatively lower rates of erosion, degree of erosion, and compressive straining during erosion as compared with loose specimens. Effects on the mechanical behaviour of the soil were also dependent on the initial density of the specimen, with changes in the small strain stiffness, secant stiffness degradation, yield loci, small strain peak strength and medium strain strength in both drained and undrained conditions. In triaxial loading, force chains of coarse particles’ skeleton reinforced by fines developed in the suffusion process in the direction of Major Principal Stress, then the stiffness at small strain increased. On the other hand, in torsional shear testing, the reinforced soil skeleton established by the erosion did not resist against shear loading. Increase in stiffness at small strain range was not observed.
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dem analysis on the Stress wave response of spherical particle assemblies under triaxial compression
Computers and Geotechnics, 2021Co-Authors: Masahide Otsubo, Reiko KuwanoAbstract:Abstract It is challenging to understand the Stress wave response of cohesionless particle assemblies including compression and shear wave velocities ( V p and V s ) due to complicated particle-scale interactions particularly during a loading process. This contribution adopts the discrete element method to simulate triaxial compression experiments using spherical particles. Four samples are isotropically confined at various initial packing densities and then sheared monotonically up to the critical state. Small-amplitude wave propagation simulation is performed during shearing along the axis of loading. The results reveal that V p is affected by the Major Principal Stress and the coordination number contributing to the vertical direction rather than horizontal direction, while V s is more influenced by the geometric mean Stress and the mean coordination number. The wave velocity ratio ( V p / V s ) is well correlated with the fabric anisotropy, having a linear relationship. This enables prediction of microscopic change in fabric from macroscopic wave velocity values. Besides, a material-specific relationship between Stress levels and wave velocities is found at the critical state with a unique fabric anisotropy, independent of initial packing. V s in the isotropic state is found to be always larger that at the critical state under an equivalent Stress level.
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effect of shearing history on Stress wave velocities of sands observed in triaxial compression tests
Soils and Foundations, 2021Co-Authors: Troyee Dutta, Masahide Otsubo, Reiko KuwanoAbstract:Abstract For the accurate design of geotechnical structures subjected to static and dynamic loadings, precise estimation of elastic wave velocities and hence, small strain stiffness of soil is essential. However, the interpretation of elastic wave velocities propagating in deformed/sheared soil has not been comprehensively explored. In this research, shear (Vs) and compression wave velocity (Vp) measurements have been undertaken on three kinds of uniformly graded sands during drained triaxial compression by keeping minor Principal Stress constant. Planar piezoelectric transducers have been used to overcome the limitations associated with the more commonly used bender elements, such as distortion of transducers during specimen shearing. This technical note reveals that the increase of Major Principal Stress in the wave propagation direction has a more significant influence on Vp in comparison to Vs. The axial strain (ea) at which peak Vs is noted is comparable to the ea at which specimen dilation or phase transformation takes place. The Vs values show a substantial drop after phase transformation, although there is an increase in the mean Stress level. However, Vp increases even after specimen dilation takes place, and it is the Major Principal Stress that dictates its evolution during triaxial compression. Moreover, for a given material and initial Stress level, elastic wave velocities of specimens prepared at different initial densities approach one another during shearing and later merge at a large ea.
