scholarly journals Experimental Study on Mesoscopic Shear Behavior of Calcareous Sand Material with Digital Imaging Approach

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Jianhua Shen ◽  
Xing Wang ◽  
Wenbai Liu ◽  
Poyu Zhang ◽  
Changqi Zhu ◽  
...  
Keyword(s):  
Shear Band ◽  
Normal Stress ◽  
Direct Shear ◽  
Particle Rotation ◽  
Calcareous Sand ◽  
Maximum Shear Strain ◽  
Lower Shear ◽  
Analysis Technique ◽  
Shear Process ◽  
Movement Mechanism

The study of the mesostructure of soil under loading is the basis for understanding its macromechanical properties and for establishing its constitutive model. In this study, a series of shear tests was performed on dry calcareous sand under constant normal stress by a modified direct shear apparatus. Digital images of the sample at different shear stages are obtained. The mesostructural parameters of the sample are then extracted and analyzed using an image analysis technique. The results show that the shear-band is located at the junction of the upper and lower shear boxes with a thickness of 0.79–1.59 mm. During shearing, the position of the maximum shear strain incremently shifted to the junctions between the two shear boxes. The azimuths of the particles prior to the test distribute symmetrically on both sides of 90°. After the test, the azimuths of the particles are mainly obtuse angles (150–180°) and the long axis of the particles generally points in the opposite direction from the shear-band. The sand particles undergo four stages: random arrangement during initial sample preparation, compaction under normal stress, particle rotation during shearing, and ordered alignment after shearing. The test results help to reveal the movement mechanism of calcareous sand at the mesoscopic level during the direct shear process.

Microscopic Analysis of Sand Shear Band in Direct Shear Test Based on Particle Flow Theory

2012 ◽  
Vol 170-173 ◽  
pp. 83-87
Author(s):  
Yang Liu ◽  
Jie Hu ◽  
Shun Chuan Wu
Keyword(s):  
Shear Band ◽  
Direct Shear Test ◽  
Shear Test ◽  
Displacement Vector ◽  
Particle Diameter ◽  
Average Particle ◽  
Direct Shear ◽  
Particle Rotation ◽  
Principal Stresses ◽  
Shear Process

In order to analyze the microscopic shear mechanics behavior of sands, a numerical simulation is carried out in sand direct shear test with commercial DEM software PFC2D. By compiling FISH function, PFC2D is able to visualize principal stresses and their inclination inside the sample. In the simulation, particle rotation gradient and particle displacement vector are observed to analyze the microscopic formation mechanism of shear band. The strain and deformation is concentrated in a band whose thickness is about 10 times of average particle diameter and the band is close to the shear plane. The porosity ratio in shear band is higher than other parts of the sample with shear process.

Shear strength and dilative characteristics of an unsaturated compacted completely decomposed granite soil

2010 ◽  
Vol 47 (10) ◽  
pp. 1112-1126 ◽  
Author(s):  
Md. Akhtar Hossain ◽  
Jian-Hua Yin
Keyword(s):  
Shear Strength ◽  
Normal Stress ◽  
Matric Suction ◽  
Water Retention Curve ◽  
Direct Shear ◽  
Normal Stresses ◽  
Soil Water Retention Curve ◽  
Strength Data ◽  
Decomposed Granite ◽  
Completely Decomposed Granite

Shear strength and dilative characteristics of a re-compacted completely decomposed granite (CDG) soil are studied by performing a series of single-stage consolidated drained direct shear tests under different matric suctions and net normal stresses. The axis-translation technique is applied to control the pore-water and pore-air pressures. A soil-water retention curve (SWRC) is obtained for the CDG soil from the equilibrium water content corresponding to each applied matric suction value for zero net normal stress using a modified direct shear apparatus. Shear strength increases with matric suction and net normal stress, and the failure envelope is observed to be linear. The apparent angle of internal friction and cohesion intercept increase with matric suction. A greater dilation angle is found at higher suctions with lower net normal stresses, while lower or zero dilation angles are observed under higher net normal stresses with lower suctions, also at a saturated condition. Experimental shear strength data are compared with the analytical shear strength results obtained from a previously modified model considering the SWRC, effective shear strength parameters, and analytical dilation angles. The experimental shear strength data are slightly higher than the analytical results under higher net normal stresses in a higher suction range.

scholarly journals Frictional properties between geocells filled with granular material

2021 ◽  
Vol 20 (2) ◽  
pp. 332-345
Author(s):  
Gökhan Altay ◽  
◽  
Cafer Kayadelen ◽  
Taha Taskiran ◽  
Baki Bagriacik ◽  
...  
Keyword(s):  
Granular Material ◽  
Normal Stress ◽  
Granular Materials ◽  
Direct Shear ◽  
Shear Tests ◽  
Direct Shear Tests ◽  
Frictional Properties ◽  
Geotechnical Structures ◽  
Series Of Experiments ◽  
Restricted Volume

The parameters concerning the interaction between geocell and granular materials is required for the design of many geotechnical structures. With this in mind, a series of experiments using simple direct shear tests are conducted in order to understand the frictional properties between geocells filled with granular materials. The 54 test samples are prepared by filling the geocell with granular materials having three different gradations. These samples are tested at three different relative densities under three different normal stress levels. As a result, it was observed that interface resistance between the geocells filled with granular material is found to be generally greater than in the samples without geocells. Additionally, these samples with geocells are found to be stiffer; this is due to the fact that the samples with geocell gained more cohesion because geocells confined the grains within a restricted volume.

Uncompacted Void Content of Fine Aggregate as Quality Indicator of Materials Used in Superpave Mixtures

2000 ◽  
Vol 1723 (1) ◽  
pp. 37-44 ◽  
Author(s):  
Jose Leomar Fernandes ◽  
Reynaldo Roque ◽  
Mang Tia ◽  
Lorenzo Casanova
Keyword(s):  
Shear Strength ◽  
Microscopic Analysis ◽  
Test Methods ◽  
Standard Test ◽  
Design System ◽  
Void Content ◽  
Fine Aggregate ◽  
Direct Shear ◽  
Lower Shear ◽  
Fine Aggregates

The uncompacted void content of fine aggregate, or fine aggregate angularity (FAA), was introduced in the Superpave mixture design system to screen smooth or rounded fine aggregates that may result in mixtures with low rutting resistance. The assumption is that fine aggregates with lower FAA values have lower shear strength (internal friction) and lower resistance to rutting. Continued implementation and evaluation of the Superpave system has led to numerous questions regarding the validity of this assumption and of the use of the FAA test in general. Nine fine aggregates were used to evaluate the FAA test and to determine whether it was a reliable indicator of fine aggregate shear strength. FAA tests were performed using three gradations and the three standard test methods (A, B, and C). Microscopic analysis was conducted to obtain independent visual measures of angularity and texture. Direct shear tests were performed at four confining stresses to determine shear strength parameters. Results indicated that FAA values were related to visual measures of texture and angularity. However, although FAA value contributed to shear strength, it appeared that other factors such as toughness, gradation, and packing characteristics of the fine aggregate overshadow its effect. For the fine aggregates tested, the FAA test rejected aggregates with high shear strength and accepted aggregates with low shear strength. It was concluded that FAA values alone may not be adequate to assess shear resistance of fine aggregate. Direct shear strength may be a better parameter, but additional work is required to evaluate its validity and feasibility.

Analysis of sand – woven geotextile interface shear behavior using discrete element method (DEM)

2020 ◽  
Vol 57 (3) ◽  
pp. 433-447 ◽  
Author(s):  
Shi-Jin Feng ◽  
Jie-Ni Chen ◽  
Hong-Xin Chen ◽  
Xin Liu ◽  
T. Zhao ◽  
...  
Keyword(s):  
Shear Band ◽  
Discrete Element Method ◽  
Coordination Number ◽  
Direct Shear Test ◽  
Shear Test ◽  
Discrete Element ◽  
Sliding Contact ◽  
Direct Shear ◽  
Interface Shear ◽  
Normal Anisotropy

The interaction between soil and geotextile is essential for the performance of reinforced soil. This study reveals the microscopic mechanism of interface shear between sand and geotextile based on the discrete element method (DEM). The surface characteristics of geotextile are simulated by overlapped particles. The micromechanical parameters of sand, geotextile, and interface are calibrated effectively using laboratory test results. Three types of shear tests on the sand–geotextile interface are simulated; namely, interface direct shear test (IDST), double-sided interface shear test (D_IST), and interface direct shear test with periodic boundary (PBST). For IDST, the results show that the thickness of shear band is 2.4∼3.0 times the average particle diameter (D50); the contact force, percentage of sliding contact, and contact normal anisotropy inside the shear band are larger than those outside the shear band, whereas the coordination number is smaller inside the shear band. The mechanical response of D_IST is similar to that of IDST. However, D_IST has a shear band thickness of 3.0D50, and greater coordination number, percentage of sliding contact, and contact normal anisotropy. The results of PBST indicate that the peak stress and the shear band no longer appear without boundary constraint and the contact distribution is uniform.

scholarly journals Effect of Rock Particle Content on the Mechanical Behavior of a Soil-Rock Mixture (SRM) via Large-Scale Direct Shear Test

2019 ◽  
Vol 2019 ◽  
pp. 1-16
Author(s):  
Longqi Liu ◽  
Xuesong Mao ◽  
Yajun Xiao ◽  
Qian Wu ◽  
Ke Tang ◽  
...  
Keyword(s):  
Shear Strength ◽  
Normal Stress ◽  
Large Scale ◽  
Direct Shear Test ◽  
Shear Test ◽  
Volumetric Strain ◽  
Direct Shear ◽  
Stress Strain ◽  
Particle Content ◽  
Rock Particle

The mechanical strength of the landslide deposits directly affects the safety and operation of the roads in the western mountainous area of China. Therefore, the research is aimed at studying the mechanisms of a landslide deposit sample with different rock particle contents by analyzing its characteristics of the stress-strain behavior, the “jumping” phenomenon, the volumetric strain, and the shear strength parameters via a large-scale direct shear test. Stress-strain results show that stress-strain curves can be divided into 3 different stages: liner elastic stage, yielding stage, and strain-hardening stage. The shear strength of SRM behaves more like “soil” at a lower rock particle content and behaves more like “rock joints” at a higher rock particle content. Characteristics of the “jumping” phenomenon results show that the “intense jumping” stage becomes obvious with the increasing rock particle content and the normal stress. However, the lower the rock particle content is, the more obvious the “jumping” phenomenon under the same normal stress is. Volumetric strain results show that the sample with a lower rock particle content showed a dilatancy behavior under the low normal stress and shrinkage behavior under the high normal stress. The dilatancy value becomes smaller with the increasing normal stress. The maximum shear stress value of the rock particle content corresponds to the maximum value of dilatancy or shrinkage. We also conclude that the intercept of the Mohr failure envelope of the soil-rock mixture should be called the “equivalent cohesion,” not simply called the “cohesion.” The higher the normal stress and rock particle content are, the bigger the equivalent cohesion and the internal friction angle is.

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.

Experimental Research on Strength Characteristics of Bulky Rock Material with Different Coarse Grain Content in Waste Pile of Mine

2012 ◽  
Vol 170-173 ◽  
pp. 295-300 ◽  
Author(s):  
Jun Du ◽  
Ke Peng Hou ◽  
Wei Liang
Keyword(s):  
Shear Modulus ◽  
Normal Stress ◽  
Friction Angle ◽  
Rock Material ◽  
Shear Displacement ◽  
Coarse Grain ◽  
Horizontal Loading ◽  
Shear Process ◽  
Main Basis ◽  
Rock And Soil

Bulky rock material of waste pile was composed of discarded rock and soil which was blasted and stripped from stope. It was characterized by dispersibility, complexity and variability. Shear strength index of bulky rock material was the main basis for analyzing slope stability of the waste pile. After the study on bulky rock material with different coarse grain content by indoor direct shear test, the results indicated that there was no obvious peak strength during the shear process, and variation of the shear displacement was slight in initial horizontal loading stage. Horizontal loading increased slowly and shear displacement had obvious change when shear displacement exceeded 5mm. Under the same normal stress, shear modulus G0.01 increased with the increase of coarse grain content when shear strain of specimen is 1/100. Shear modulus G0.01 of the specimen with same coarse grain content increased with the increase of normal stress, varying sensitive of G0.01 reduced when coarse grain content was larger. When the specimens with same coarse grain content were under failure, the shear modulus Gfailure was smaller than G0.01. Cohesive force c of the bulky rock material began to increase and then decrease with the increase of coarse grain content, and reached its maximum of 31.25KPa when the coarse grain content was 70%, internal friction angle increased with the increase of coarse grain content.

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