Particle damage observed in ring shear tests on sands

2010 ◽  
Vol 47 (5) ◽  
pp. 497-515 ◽  
Author(s):  
Abouzar Sadrekarimi ◽  
Scott M. Olson
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Normal Stress ◽  
Size Distribution ◽  
Constant Volume ◽  
Engineering Properties ◽  
Shear Tests ◽  
Ring Shear ◽  
Particle Damage ◽  
Ring Shear Tests

In this paper, particle damage of three test sands with different mineralogical compositions is studied using stress–displacement response measured in ring shear tests, particle-size distributions of the original sand prior to shear and from the shear band after shear, and by examining particle shape changes determined by scanning electron microscope. Particle damage during shearing produced a wider particle-size distribution, and damage typically continued until the normal stress was small (about 28 kPa) in constant volume ring shear tests and the internal stresses were distributed among sufficient particle contacts such that damage practically ceased. The dominant damage mechanism (typically either particle abrasion and shearing-off asperities or particle splitting) depended strongly on the soil response (i.e., contraction or dilation), particle hardness, and particle-size distribution, but both mechanisms produced particles that were more angular and rougher than the original sand particles. The magnitude of particle damage observed in the ring shear tests was influenced by the consolidation normal stress, shear displacement, particle mineralogy, particle-size distribution, drainage conditions, and soil fabric (in constant volume tests). Lastly, the influence of particle damage on engineering properties including hydraulic conductivity, liquefaction resistance, stress–strain response, friction angle, and critical state are briefly discussed.

scholarly journals The effect of particle shape on the deformation and stress reduction of a gravel soil due to wetting

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Reza Mahinroosta ◽  
Vahid Oshtaghi
Keyword(s):  
Particle Size ◽  
Shear Stress ◽  
Particle Size Distribution ◽  
Normal Stress ◽  
Size Distribution ◽  
Stress Reduction ◽  
Particle Shape ◽  
Particle Breakage ◽  
Direct Shear ◽  
Particle Shapes

AbstractThis paper investigates the effect of particle shape on the stress reduction and collapse deformation of gravelly soil using a medium-scale direct shear test apparatus under different relative densities, normal stress, and shear stress levels. A new method based on the Micro-Deval test was introduced to produce sub-angular particles from angular particles. Therefore, two series of soil specimens were obtained with the same rock origin, particle size distribution, and relative density but different particle shapes. In addition to traditional direct shear tests on dry and wet specimens, a specific test procedure was applied to explore the stress reduction and collapse of soil specimens due to wetting. The results of the tests, including shear stress–shear displacement and vertical displacement-shear displacement, were compared. The results showed that the stress reduction and settlement due to wetting increased with vertical and shear stress levels in both types of particle shapes, with higher values in angular particle shapes. The particle breakage of the soil specimens was also studied quantitatively using the change in the particle size distribution before and after the test. It was shown that the wetting of the samples had more impact on the particle breakage in angular gravel than sub-angular gravel, which increased linearly with the normal stress.

scholarly journals Shear rate effect on the residual strength characteristics of saturated loess

2019 ◽  
Author(s):  
Baoqin Lian ◽  
Jianbing Peng ◽  
Qiangbing Huang
Keyword(s):  
Shear Strength ◽  
Shear Rate ◽  
Normal Stress ◽  
Rate Effect ◽  
Shear Tests ◽  
Residual Shear Strength ◽  
Shear Rates ◽  
Ring Shear ◽  
Ring Shear Tests ◽  
The Difference

Abstract. Residual shear strength of soils is an important soil parameter for assessing the stability of landslides. To investigate the effect of the shear rate on the residual shear strength of loessic soils, a series of ring shear tests were carried out on loess from three landslides at two shear rates (0.1 mm/min and 1 mm/min). Naturally drained ring shear tests results showed that the shear displacement to achieve the residual stage for specimens with higher shear rate was greater than that of the lower rate; both the peak and residual friction coefficient became smaller with increase of shear rate for each sample; at two shear rates, the residual friction coefficients for all specimens under the lower normal stress were greater than that under the higher normal stress. The tests results revealed that the difference in the residual friction angle фr at the two shear rates, фr (1)–фr (0.1), under each normal stress level were either positive or negative values. However, the difference фr(1)–фr (0.1) under all normal stresses was negative, which indicates that the residual shear parameters reduced with the increasing of the shear rate in loess area. Such negative shear rate effect on loess could be attributed to a greater ability of clay particles in specimen to restore broken bonds at low shear rates.

Engineering Properties of Soils as Related to Mineralogy and Particle-Size Distribution

1984 ◽  
Vol 48 (5) ◽  
pp. 978-982 ◽  
Author(s):  
W. G. Harris ◽  
L. W. Zelazny ◽  
J. C. Parker ◽  
J. C. Baker ◽  
R. S. Weber ◽  
...  
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Engineering Properties

scholarly journals Breakage Characteristics of Quartz Sand Based on Ring Shear Tests: Implications for the Fragmentation Processes of Rock Avalanches

2022 ◽  
Vol 2022 ◽  
pp. 1-12
Author(s):  
Xinxin Zheng ◽  
Ruichen Chen ◽  
Jian Chen ◽  
Song Chen ◽  
Lulu Shi
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Quartz Sand ◽  
Shear Tests ◽  
Rock Avalanches ◽  
Ring Shear ◽  
Study Results ◽  
Dry Granular Flow ◽  
Ring Shear Tests

To investigate the effects of internal shear fragmentation on dry granular flow, in this study a series of ring shear tests were performed on quartz sand samples under different normal stresses (100 kPa, 200 kPa, and 300 kPa), shear displacements (3 m, 5 m, 10m, 15 m, and 20 m), and shear rates (30 deg min−1, 60 deg min−1, and 90 deg min−1). Next, the grain-size distributions, fractal dimensions, and microcharacteristics of the quartz sand before and after the experiments were compared and analyzed. The study results show that grain breakage under shearing preferentially occurs at the edges of the particles and forms a bimodal distribution in frequency grain-size distribution curves, which is consistent with observations of rock avalanches. The fine particles prevent the coarse particles from breaking, in turn leading to the ultimate grain-size distribution and stable fractal dimension (2.61) of quartz sand at relatively small shear displacements compared with the travel distance of rock avalanches. The results of this study suggest that the fragmentation of rock avalanches during the shear spread stage may be far less significant than previously believed. Therefore, the fragmentation effect is not considered to be a major factor of the hypermobility in the late stage of rock avalanches.

scholarly journals Functional Relationships Between the Content of Particles Smaller than 0.05 mm. and 0.002 mm. in Size, and the Plasticity Index of Soils

1969 ◽  
Vol 52 (4) ◽  
pp. 343-350
Author(s):  
M. A. Lugo López ◽  
Raúl Pérez Escolar
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Plasticity Index ◽  
Engineering Properties ◽  
Mathematical Approach ◽  
Functional Relationships ◽  
Laborious Work ◽  
Fair Degree

A mathematical approach is presented herein to determine the plasticity index of soils on the basis of the percentage of particles smaller than 0.05 mm in size. The particle-size distribution can be determined easily and quickly, and then, with a few calculations, the plasticity index can be estimated with fair degree of precision. The laboratory determination of plasticity index requires more laborious work. The equation developed is exponential, as follows:Plasticity index = —0.052394 + 3.1538e0.029284X, where e= 2.71828 and X is the percentage of particles smaller than 0.05 mm. in size.The correlation coefficient obtained was on the order of 0.92. On the basis of the percentage of particles smaller than 0.05 mm., about 85 percent of the variability of the plasticity index values was explained. The plasticity index is one of the more useful engineering properties of soils.

scholarly journals Shear rate effect on the residual strength characteristics of saturated loess in naturally drained ring shear tests

2020 ◽  
Vol 20 (10) ◽  
pp. 2843-2856
Author(s):  
Baoqin Lian ◽  
Xingang Wang ◽  
Jianbing Peng ◽  
Qiangbing Huang
Keyword(s):  
Shear Strength ◽  
Shear Rate ◽  
Normal Stress ◽  
Rate Effect ◽  
Shear Tests ◽  
Residual Shear Strength ◽  
Shear Rates ◽  
Ring Shear ◽  
Ring Shear Tests ◽  
The Difference

Abstract. Residual shear strength of soils is an important soil parameter for assessing the stability of landslides. To investigate the effect of the shear rate on the residual shear strength of loessic soils, a series of naturally drained ring shear tests were carried out on loess from three landslides at two shear rates (0.1 and 1 mm min−1). Experimental results showed that the shear displacement to achieve the residual stage for specimens with higher shear rate was greater than that of the lower rate; both the peak and residual friction coefficient became smaller with increase in shear rate for each sample; at two shear rates, the residual friction coefficients for all specimens under the lower normal stress were greater than those under the higher normal stress. Moreover, specimens with almost the same low fraction of clay (CF) showed a similar shear rate effect on the residual friction coefficient, with normal stress increasing, whereas specimens with high CF (24 %) showed a contrasting tendency, indicating that such an effect is closely associated with CF. The test results revealed that the difference in the residual friction angle ϕr at the two shear rates, ϕr(1)−ϕr(0.1) under each normal stress level are either positive or negative values, of which the maximum magnitude is about 0.8∘. However, the difference ϕr(1)−ϕr(0.1) determined under all normal stress levels was negative, which indicates that the residual shear parameters reduced with the increasing of the shear rate in the loess area. Such a negative shear rate effect on loess could be attributed to a greater ability of clay particles in specimens to restore broken bonds at low shear rates.

scholarly journals The Effect of Particle Size Distribution And Shape On The Microscopic Behaviors of Loess Via DEM

2021 ◽  
Author(s):  
Xi-An Li ◽  
Jianqiang Sun ◽  
Hongyu Ren ◽  
Tuo Lu ◽  
Yongbiao Ren ◽  
...  
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Contact Force ◽  
Engineering Properties ◽  
Dry Density ◽  
Normal Contact ◽  
Clay Particles ◽  
Normal Contact Force ◽  
Sand Particles

Abstract Loess has loose metastable structure, which is not difficult to be destroyed under load. As the core and soul of loess structure, it is part of the main research directions of loess engineering properties at present to study its microscopic behaviors and then realize the interpretation and prediction of macroscopic mechanical properties. In this study, based on the analysis of the basic physical properties of loess samples from seven different places, each sample was scanned by X-ray with continuous slice CT, and the three-dimensional microstructure of loess samples was established. According to the computer graphics method, each particle is equivalent to an ellipsoid, and the flattening rate and elongation rate of particles in each sample are quantitatively counted. Taking the particle size distribution (PSD) and shape parameters (flatness and elongation) of each sample as the control factors for generating discrete element method (DEM) samples, a series of triaxial compression simulation tests were carried out, and the microscopic behaviors of each sample were studied within the whole test framework. Comparing the results of seven different samples, it is shown that both PSD and particle shape have effects on stress-strain relationship, dry density and the normal contact force of loess samples. Most of the sand particles (> 0.075mm) are flat particles, while the clay particles (< 0.005mm) are mainly near spheres. When the volume fraction of sand particles is large, the dry density of the sample is the lowest. However, when the content of near spherical clay particles is large and the particle size distribution is good, and the average coordination value is large, which shows that it has strong normal contact force, and thus higher shear strength.

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