Shear strength, interparticle locking, and dilatancy of granular materials

2007 ◽  
Vol 44 (5) ◽  
pp. 579-591 ◽  
Author(s):  
Peijun Guo ◽  
Xubin Su
Keyword(s):  
Granular Materials ◽  
Stress Ratio ◽  
Peak Stress ◽  
Friction Angle ◽  
Substantial Effect ◽  
Triaxial Tests ◽  
Ottawa Sand ◽  
Confining Pressures ◽  
Limestone Sand ◽  
Crushed Limestone

The effect of particle angularity on the strength and dilation of granular materials is investigated through a series of laboratory tests on two materials, Ottawa standard sand (Sand O) and crushed limestone (Sand L), that are made up of rounded and angular particles, respectively. Triaxial tests on both materials at different confining pressures and initial void ratios show that particle angularity has a substantial effect on both the peak friction angle ϕp and the mobilized friction angle at the onset of dilation, ϕf. It is found that ϕf is smaller than the critical friction angle ϕcv for Ottawa sand; nevertheless ϕf is larger than ϕcv for Sand L owing to interparticle locking induced by particle angularity. The experimental results clearly show the contributions to shear resistance from both dilation and interlocking, with interlocking still largely existing at the peak stress ratio but not at the critical state. Suggestions are made to modify the stress–dilatancy formulations for sand to take into account the effect of interparticle locking associated with particle angularity.Key words: granular material, dilatancy, interlocking, and particle shape.

scholarly journals Undrained Behavior of Microbially Induced Calcite Precipitated Sand with Polyvinyl Alcohol Fiber

2019 ◽  
Vol 9 (6) ◽  
pp. 1214 ◽  
Author(s):  
Sun-Gyu Choi ◽  
Tung Hoang ◽  
Sung-Sik Park
Keyword(s):  
Hydraulic Conductivity ◽  
Polyvinyl Alcohol ◽  
Friction Angle ◽  
Triaxial Tests ◽  
Calcite Precipitation ◽  
Environment Friendly ◽  
Ottawa Sand ◽  
Polyvinyl Alcohol Fiber ◽  
Constant Head ◽  
Undrained Behavior

Microbially induced calcite precipitation can cement sand and is an environment-friendly alternative to ordinary Portland cement. In this study, clean Ottawa sand was microbially treated to induce calcite contents (CCs) of 0%, 2%, and 4%. Polyvinyl alcohol fiber was also mixed with the sand at four different contents (0%, 0.2%, 0.4%, and 0.6%) with a constant CC of 4%. A series of undrained triaxial tests was conducted on the treated sands to evaluate the effects of the calcite treatment and fiber inclusion. Their hydraulic conductivity was also determined using a constant head test. As the CC increased from 0% to 4%, the friction angle and cohesion increased from 35.3° to 39.6° and from 0 to 93 kPa, respectively. For specimens with a CC of 4%, as the fiber content increased from 0% to 0.6%, the friction angle and cohesion increased from 39.6° to 42.8° and from 93 to 139 kPa, respectively. The hydraulic conductivity of clean Ottawa sand decreased by a factor of more than 100 as the CC increased from 0% to 4%. The fiber inclusion had less effect on the hydraulic conductivity of the specimen with 4% CC.

scholarly journals Experimental study on the thermal damage characteristics of cement stone

2020 ◽  
pp. 317-317
Author(s):  
Feng Xu ◽  
Bowen Qian ◽  
Ling Tan ◽  
Jianqiang Xu ◽  
Shengchuan Tang ◽  
...  
Keyword(s):  
Strain Curve ◽  
Horizontal Wells ◽  
Friction Angle ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Cement Stone ◽  
Different Temperatures ◽  
Confining Pressures ◽  
Southwest Region ◽  
Sealing Failure

Aiming at the problem of cement ring sealing failure during deep high-temperature shale gas exploitation, comprehensively considering the influence of the characteristics of multi-cluster fracturing of multiple horizontal wells and formation temperature, the cementing cement the southwest region is taken as the research object. After exposure to different temperatures (95?C and 135?C) and for different times (5, 10 and 20 times), axial and triaxial tests with different confining pressures (0, 5 MPa, 15 MPa and 30 MPa) were carried out. The research shows that: (1) the stress-strain curve of cement stone after heat treatment can be divided into four stages: compaction, elastic, yield and post-peak stage. As the confining pressure increases, the compaction phase disappears, the yield phase increases, and we see the transition from brittle to ideal plasticity after the peak; (2) as the temperature and number of thermal cycles increase, the cohesive force decreases significantly, and the internal friction angle shows a slight increase. The elastic modulus and the peak strength decreased.

scholarly journals The Bearing Capacity of Circular Footings in Sand: Comparison between Model Tests and Numerical Simulations Based on a Nonlinear Mohr Failure Envelope

2012 ◽  
Vol 2012 ◽  
pp. 1-10 ◽  
Author(s):  
Sven Krabbenhoft ◽  
Johan Clausen ◽  
Lars Damkilde
Keyword(s):  
Bearing Capacity ◽  
Yield Criterion ◽  
Friction Angle ◽  
Triaxial Tests ◽  
Test Results ◽  
Finite Element Program ◽  
Model Foundation ◽  
Element Program ◽  
Confining Pressures ◽  
Good Agreement

This paper presents the results of a series of triaxial tests with dry sand at confining pressures varying from 1.5 kPa to 100 kPa at relative densities of 0.20, 0.59, and 0.84. The results, which are in reasonable accordance with an equation given by Bolton, show that the friction angle is strongly dependent on the stress level and on the basis of the test results, a nonlinear Mohr failure criterion has been proposed. This yield criterion has been implemented in a finite element program and an analysis of the bearing capacity of a circular shaped model foundation, diameter 100 mm, has been conducted. Comparisons have been made with results from 1g model scale tests with a foundation of similar size and a good agreement between numerical results and test results has been found.

scholarly journals Triaxial Test and Mechanical Analysis of Rock-Soil Aggregate Sampled from Natural Sliding Mass

2015 ◽  
Vol 2015 ◽  
pp. 1-14 ◽  
Author(s):  
Shuling Huang ◽  
Xiuli Ding ◽  
Yuting Zhang ◽  
Wei Cheng
Keyword(s):  
Mechanical Behavior ◽  
Large Scale ◽  
Mechanical Response ◽  
Strain Curve ◽  
Friction Angle ◽  
Mechanical Analysis ◽  
Soil Aggregate ◽  
Hydropower Plant ◽  
Triaxial Tests ◽  
Confining Pressures

Rock-soil aggregate, as a specific geomaterial, exhibits complicated mechanical behavior. The rock-soil aggregate sampled from the deep layer of sliding mass at Jinpingzi area of Wudongde hydropower plant on Yangtze River is investigated to understand its mechanical behavior. Large-scale laboratory triaxial tests are conducted considering different gradations, stone contents and confining pressures. The results show that variation of stone content and gradation considerably affects the mechanical characteristics of rock-soil aggregate. Further, the influences of stone content, and gradation variation on stress-strain curve, Mohr-Coulomb criterion based shear strength parameters, Duncan-Chang model based deformation parameters, and internal friction angle are analyzed. A modified Rowe’s stress-dilatancy equation describing the mechanical response of rock-soil aggregate is then suggested.

scholarly journals Critical State Model of Sand-Tire Derived Aggregate Mixtures Based on Triaxial Tests

2021 ◽  
pp. 036119812199783
Author(s):  
Adolfo Foriero ◽  
Nima Ghafari
Keyword(s):  
Critical State ◽  
Axial Strain ◽  
Friction Angle ◽  
Critical State Model ◽  
State Model ◽  
Triaxial Tests ◽  
Experimental Program ◽  
Modified Cam Clay ◽  
Tire Derived Aggregate ◽  
Confining Pressures

This study is part of an environmental experimental program on the use of scrap automobile tires for geotechnical applications. Different types of laboratory tests were conducted to determine the elastic, plastic, and creep parameters of tire derived aggregate (TDA)-sand granulated mixtures. However, this paper emphasizes the plasticity parameters via the development of a critical state model based on the results of triaxial tests. This was attained by considering loose sand specimens, at a predetermined TDA volumetric content, subject to three different confining pressures under a constant axial displacement rate. The calculated deviatoric stress versus axial strain curves, obtained via the modified Cam Clay model, captured the non-linear elastoplastic response obtained in the tests. Results indicated that the level of the shear strength is highly dependent on critical state friction angle which in turn depends on the TDA content. For the loose TDA-sand mixtures used in the present study, the effect of the TDA content demonstrates a reinforcement of the sand matrix. However this reinforcement diminishes as the TDA content increases.

scholarly journals Testing and Micromechanical Modelling of Rockfill Materials Considering the Effect of Stress Path

2016 ◽  
Vol 2016 ◽  
pp. 1-14 ◽  
Author(s):  
Wang Feng ◽  
Chi Shichun ◽  
Li Shijie ◽  
Jia Yufeng
Keyword(s):  
Stress Ratio ◽  
Volumetric Strain ◽  
Stress Path ◽  
Complex Stress ◽  
Triaxial Tests ◽  
Rockfill Material ◽  
Rockfill Materials ◽  
Deformation Properties ◽  
Confining Pressures ◽  
Improved Model

We have extended the micromechanics-based analytical (M-A) model to make it capable of simulating Nuozhadu rockfill material (NRFM) under different stress paths. Two types of drained triaxial tests on NRFM were conducted, namely, the stress paths of constant stress ratio (CSR) and the complex stress paths with transitional features. The model was improved by considering the interparticle parameter variation with the unloading-reloading cycles and the effect of the stress transition path. The evolution of local dilatancy at interparticle planes due to an externally applied load is also discussed. Compared with Duncan-Chang’s E-u and E-B models, the improved model could not only better describe the deformation properties of NRFM under the stress path loading, but also present the volumetric strain changing from dilatancy to contractancy with increasing transitional confining pressures. All simulations have demonstrated that the proposed M-A model is capable of modelling the mechanical behaviour of NRFM in the dam.

Effect of End Restraint on High Pressure Tests of Granular Materials

1971 ◽  
Vol 8 (4) ◽  
pp. 579-588 ◽  
Author(s):  
M. Roy ◽  
K. Y. Lo
Keyword(s):  
High Pressure ◽  
Granular Materials ◽  
Volume Change ◽  
Triaxial Tests ◽  
Stress Strain ◽  
End Conditions ◽  
Pressure Tests ◽  
Confining Pressures ◽  
End Restraint ◽  
Distribution Of Stress

Comparative drained triaxial tests at high confining pressures were carried out on a strong- and weak-grained granular material with 'rough' and 'lubricated' ends. The results indicated that the stress-strain relationships are significantly influenced by the end conditions. The use of 'lubricated' ends for high pressure tests results in much more uniform distribution of stress, strain, volume change, and crushing of particles throughout the samples.

scholarly journals Mechanical Characteristics of Coal Samples under Triaxial Unloading Pressure with Different Test Paths

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Yang Zhang ◽  
Yongjie Yang ◽  
Depeng Ma
Keyword(s):  
Axial Strain ◽  
Triaxial Compression ◽  
Axial Loading ◽  
Peak Stress ◽  
Friction Angle ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Compression Tests ◽  
Leading Role ◽  
Unloading Rate

In order to understand the influence of unloading path on the mechanical properties of coal, triaxial unloading confining pressure tests with different initial confining pressure and different unloading rate were carried out. The test results show that the triaxial unloading strength of coal samples under different test conditions is lower than conventional triaxial tests, but the brittleness characteristics are more obvious. This result indicates that the coal samples are easily damaged under unloading conditions. In the axial loading stage of the confinement unloading tests, the axial strain plays a leading role. However, during the confining pressure unloading stage, the circumferential deformation is large, which is the main deformation in this stage. Higher unloading rates of confining pressure are associated with shorter times between the peak stress position and sample complete failure. This shows that samples are more easily destroyed under higher unloading rates and the samples are more difficultly destroyed under lower unloading rates. In addition, with increasing unloading rate, the peak principal stress difference and confining pressure at failure decrease gradually, whereas the confining pressure difference at failure increases gradually. Compared with conventional triaxial compression tests, the cohesion of coal is reduced and the internal friction angle is increased under the condition of triaxial unloading test.

scholarly journals Numerical Determination of RVE for Heterogeneous Geomaterials Based on Digital Image Processing Technology

Processes ◽  
2019 ◽  
Vol 7 (6) ◽  
pp. 346 ◽  
Author(s):  
Lanlan Yang ◽  
Weiya Xu ◽  
Qingxiang Meng ◽  
Wei-Chau Xie ◽  
Huanling Wang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Image Processing ◽  
Digital Image Processing ◽  
Digital Image ◽  
Color Image ◽  
Friction Angle ◽  
Triaxial Tests ◽  
Random Samples ◽  
Confining Pressures

Representative volume element (RVE) is an important parameter in numerical tests of mechanical properties of heterogeneous geomaterials. For this study, a digital image processing (DIP) technology was proposed for estimating the RVE of heterogeneous geomaterials. A color image of soil and rock mixture (SRM) with size of 400 × 400 mm2 taken from a large landslide was used to illustrate the determination procedure of the SRM. Six sample sizes ranging from 40 × 40 mm2 to 240 × 240 mm2 were investigated, and twelve random samples were taken from the binarized image for each sample size. A connected-component labeling algorithm was introduced to identify the microstructure. After establishing the numerical finite difference models of the samples, a set of numerical triaxial tests under different confining pressures were carried out. Results show that the size of SRM sample affects the estimation of the mechanical properties, including compressive strength, cohesion, and internal friction angle. The larger the size of the samples, the less variability of the estimated mechanical properties. The coefficient of variation (CV) was applied to measure the variability of mechanical properties, and the RVE of the SRM was determined easily with a predefined acceptance threshold of the CV. The results show that a DIP-based modeling method is an effective method got the RVE determination of heterogeneous geomaterials.

scholarly journals Influence of Soil Fabrics and Stress State on the Undrained Instability of Overconsolidated Binary Granular Assemblies

2018 ◽  
Vol 40 (2) ◽  
pp. 96-116 ◽  
Author(s):  
Youcef Mahmoudi ◽  
Abdellah Cherif Taiba ◽  
Leila Hazout ◽  
Wiebke Baille ◽  
Mostefa Belkhatir
Keyword(s):  
Friction Angle ◽  
Confining Pressure ◽  
Silty Sand ◽  
Triaxial Tests ◽  
Loading Conditions ◽  
Fines Content ◽  
Applied Loading ◽  
Granular Assemblies ◽  
Static Liquefaction ◽  
Confining Pressures

AbstractThe instability of saturated granular soils in field conditions generates drastic collapse in terms of runoff deformation because of its failing to sustain naturally applied loading conditions such as earthquakes, wave actions and vibrations. The objective of this laboratory investigation is to study the effects of the depositional methods, overconsolidation ratio (OCR) and confining pressure on the undrained instability shear strength of medium dense (Dr = 52%) sand–silt mixtures under static loading conditions. For this purpose, a series of undrained monotonic triaxial tests were carried out on reconstituted saturated silty sand samples with fines content ranging from 0% to 40%. Three confining pressures were used (P’c = 100, 200 and 300 kPa) in this research. The sand–silt mixture samples were prepared using two depositional methods, dry funnel pluviation (DFP) and wet deposition (WD), and subjected to two OCRs (1 and 2). The obtained instability lines and friction angles indicate that the funnel pluviated samples exhibit strain hardening compared to the wet deposited samples and that normally consolidated and overconsolidated wet deposited clean sandy samples were very sensitive to static liquefaction. The test results also indicate that the instability friction angle increases with the increase in the OCR expressing soil dilative character tendency increase. The instability friction angle decreases with the increase in the fines content for DFP and the inverse tendency was observed in the case of WD.

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