scholarly journals Undrained monotonic triaxial loading behaviors of a type of iron ore fines

2018 ◽  
Vol 55 (9) ◽  
pp. 1349-1357 ◽  
Author(s):  
Hailong Wang ◽  
Junichi Koseki ◽  
Fei Cai ◽  
Tomoyoshi Nishimura
Keyword(s):  
Iron Ore ◽  
Initial Conditions ◽  
Triaxial Compression ◽  
Axial Loading ◽  
Sandy Soils ◽  
Peak Stress ◽  
Confining Pressure ◽  
Compression Tests ◽  
Static Liquefaction ◽  
Iron Ore Fines

Concerning the static liquefaction properties of an industrial cargo, i.e., iron ore fines (IOF), undrained monotonic behaviors of a type of IOF are revealed through conducting triaxial compression tests. It is found that IOF exhibit some similar behaviors as those of common sandy soils, while some very unusual behaviors are also observed. All IOF specimens with compaction degree of 84%–95% and confining pressure of 50–200 kPa exhibit dilative behavior from the beginning of axial loading until the deviator stresses reach their peaks (qpk). Then the dilative behavior transforms to a contractive behavior, and the contractive behavior continues until reaching the residual stress without observation of phase transformation and quasi steady state. These behaviors are not usually observed for common sandy soils based on extensive previous works. More studies may be necessary as these unusual behaviors imply that flow failure, similar to the undrained monotonic behavior of very loose sand, may be triggered regardless of the density of IOF. In addition, this study also establishes the relationships of IOF between its initial conditions, peak stress conditions, and residual conditions by employing classical knowledges developed for sandy soils.

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 Microcracking and the failure of polycrystalline ice under triaxial compression

1992 ◽  
Vol 38 (128) ◽  
pp. 65-76 ◽  
Author(s):  
P. Kalifa ◽  
G. Ouillon ◽  
P. Duval
Keyword(s):  
Triaxial Compression ◽  
Peak Stress ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Strain History ◽  
Compression Tests ◽  
Brittle Transition ◽  
Polycrystalline Ice ◽  
Strain Components

AbstractTriaxial and uniaxial compression tests have been carried out at –10°C on granular ice in order to study the role of microcracking on failure in the ductile-brittle transition zone. In the triaxial tests, the effect of confining pressure and strain rate on the crack population, as well as on strength and strain at the peak stress, was investigated. In the uniaxial tests, we measured the evolution of elastic and non-elastic components of deformation with the stress-strain history. The concept of effective stress, with a single scalar damage variable, was used to calculate the effect of microcracking on the strain components.

scholarly journals Analysis of Failure Characteristics and Strength Criterion of Coal-Rock Combined Body with Different Height Ratios

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Tuo Wang ◽  
Zhanguo Ma ◽  
Peng Gong ◽  
Ning Li ◽  
Shixing Cheng
Keyword(s):  
Shear Failure ◽  
Underground Mining ◽  
Triaxial Compression ◽  
Peak Stress ◽  
Strength Criterion ◽  
Confining Pressure ◽  
Experimental Results ◽  
Compression Tests ◽  
Rock Body ◽  
Coal Rock

In underground mining and roadway support engineering of coal mine, the coal and rock layers bear loads together; therefore, the deformation and mechanical characteristics of the coal-rock combined bodies are not the same as those of the pure coal or rock bodies. In this paper, conventional triaxial compression tests of coal-rock combined bodies with different height ratios were conducted. And the stress and deformation characteristics of coal-rock combined body were studied and the experimental results were analyzed with different strength criteria. The results show that the peak stress, elastic modulus, and strength reduction coefficient of coal-rock combined body are negatively correlated with the ratio of coal to coal-rock combination height and positively correlated with the confining pressure; the coal-rock combination shows obvious ductility under 10 MPa confining pressure. Under the conventional triaxial condition, the shear failure was the main cause of the lateral deformation of the coal body in the coal-rock combination, which was much larger than that of the rock body. The circle deformation value, volume strain value, and the deformation rate in the postpeak stage of coal-rock combination are much higher than those in the prepeak stage. Mohr–Coulomb and general Hoek–Brown strength criterion fit the experimental results well.

scholarly journals Permeability evolution of unloaded coal samples at different loading rates

2014 ◽  
Vol 18 (5) ◽  
pp. 1497-1504 ◽  
Author(s):  
Ze-Tian Zhang ◽  
Zhang Ru ◽  
Jian-Feng Liu ◽  
Xiao-Hui Liu ◽  
Jia-Wei Li
Keyword(s):  
Triaxial Compression ◽  
Axial Loading ◽  
Peak Stress ◽  
Initial Permeability ◽  
Differential Method ◽  
Permeability Evolution ◽  
Compression Tests ◽  
Evolution Law ◽  
Loading Rates ◽  
Conventional Triaxial Compression

As coal mass is often at unloading status during mining process, it is of great significance to push on the research on permeability evolution of unloaded coal samples at different loading rates. A series of triaxial unloading experiments were conducted for initially intact coal samples using an improved rock mechanics testing system, and the permeability was continuously measured by the constant pressure differential method for methane. Permeability evolution law of unloaded coal samples and the influence mechanism of loading rates on that were studied. The results of triaxial unloading experiments indicate that the permeability of coal samples increases throughout the whole testing process without a descent stage, which is different from the permeability evolution law in conventional triaxial compression tests. The maximum permeability of unloaded coal sample, which is 4 to 18 times to its initial permeability, often appears before reaching the peak stress and increases with the decrease of axial loading rate. Stress state corresponding to the surge point of permeability of the unloaded coal samples is also discussed.

scholarly journals Microcracking and the failure of polycrystalline ice under triaxial compression

1992 ◽  
Vol 38 (128) ◽  
pp. 65-76 ◽  
Author(s):  
P. Kalifa ◽  
G. Ouillon ◽  
P. Duval
Keyword(s):  
Triaxial Compression ◽  
Peak Stress ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Strain History ◽  
Compression Tests ◽  
Brittle Transition ◽  
Polycrystalline Ice ◽  
Strain Components

AbstractTriaxial and uniaxial compression tests have been carried out at –10°C on granular ice in order to study the role of microcracking on failure in the ductile-brittle transition zone. In the triaxial tests, the effect of confining pressure and strain rate on the crack population, as well as on strength and strain at the peak stress, was investigated. In the uniaxial tests, we measured the evolution of elastic and non-elastic components of deformation with the stress-strain history. The concept of effective stress, with a single scalar damage variable, was used to calculate the effect of microcracking on the strain components.

scholarly journals Fatigue Characteristics of Limestone under Triaxial Compression with Cyclic Loading

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Yongjie Yang ◽  
Huiqiang Duan ◽  
Luyi Xing ◽  
Shan Ning ◽  
Jiakun Lv
Keyword(s):  
Cyclic Loading ◽  
Damage Evolution ◽  
Triaxial Compression ◽  
Peak Stress ◽  
Confining Pressure ◽  
Primary Phase ◽  
Fatigue Properties ◽  
Dissipated Energy ◽  
Loading Frequency ◽  
Compression Tests

This paper presents an experimental investigation of the fatigue properties of limestone subjected to triaxial compression with axial cyclic loading. Tests were conducted on intact limestone samples with a loading frequency of 0.5 Hz and a confining pressure of 10 MPa. The test results show the following five points. (1) Under triaxial conditions, the axial and circumferential deformations at the failure point induced by cyclic loading are slightly larger than the corresponding deformations at the peak stress achieved by conventional compression tests. (2) The first level cyclic loading process has a strong influence on rock deformation in the primary phase during subsequent level cyclic loading. A smaller difference in stress amplitude between the two loading stress levels leads to less deformation during the latter. (3) Circumferential and volumetric changes are more sensitive to fatigue failure in terms of deformation and strain rate than axial changes. (4) The three phases of dissipated energy evolution are consistent with a sample’s deformation such that the energy dissipation characteristics reflect the fatigue damage evolution process. (5) A new damage formula is proposed that can concisely describe a rock’s zero-cycle damage and damage evolution.

scholarly journals Permeability Characteristic and Failure Behavior of Filled Cracked Rock in the Triaxial Seepage Experiment

2019 ◽  
Vol 2019 ◽  
pp. 1-12
Author(s):  
Xinyu Liu ◽  
Zhende Zhu ◽  
Aihua Liu
Keyword(s):  
Growth Rate ◽  
Rock Mass ◽  
Failure Modes ◽  
Peak Stress ◽  
Confining Pressure ◽  
Strength Characteristics ◽  
Failure Behavior ◽  
Compression Tests ◽  
Secondary Cracks ◽  
Safety And Stability

Filling is commonly found in natural cracked rock mass. As the weakest part of the rock, the filling properties directly affect the rock deformation and strength, permeability, and so on and affect the safety and stability of the rock mass engineering. In this study, a single slit has been preset in sandstones and filled with different physical properties materials. Based on the laboratory triaxial seepage test, the permeability and strength characteristics of filled cracked sandstones are analyzed, and the failure modes are obtained. The main findings of this study are as follows: (1) The permeability coefficient peak value of the filled cracked rock appears before the stress peak. (2) At the same confining pressure growth rate, the peak stress growth rate of the filled cracked rock is generally higher than that of the intact rock and the strength growth rate of the cracked rock increases with the length of the fracture. The strength characteristics of the filling in the uniaxial compression tests and triaxial seepage tests are significantly affected by the hydraulic properties. (3) The strength and permeability coefficients of cracked rock filled with cement mortar are more sensitive to the change of confining pressure, while under the same condition, the ones of cracked rock filled with gypsum mortar are stable. (4) According to the failure mechanism, under the seepage stress, the secondary cracks can be divided into 3 types and the failure modes can be divided into 2 types.

scholarly journals Triaxial Testing of Geosynthetics Reinforced Tailings with Different Reinforced Layers

Materials ◽  
2020 ◽  
Vol 13 (8) ◽  
pp. 1943
Author(s):  
Fu Yi ◽  
Changbo Du
Keyword(s):  
Triaxial Compression ◽  
Friction Angle ◽  
Confining Pressure ◽  
Test Results ◽  
Compression Tests ◽  
Strength Index ◽  
Stress Strain ◽  
High Confining Pressure ◽  
Zhang Model ◽  
Triaxial Compression Tests

To evaluate the shear properties of geotextile-reinforced tailings, triaxial compression tests were performed on geogrids and geotextiles with zero, one, two, and four reinforced layers. The stress–strain characteristics and reinforcement effects of the reinforced tailings with different layers were analyzed. According to the test results, the geogrid stress–strain curves show hardening characteristics, whereas the geotextile stress–strain curves have strain-softening properties. With more reinforced layers, the hardening or softening characteristics become more prominent. We demonstrate that the stress–strain curves of geogrids and geotextile reinforced tailings under different reinforced layers can be fitted by the Duncan–Zhang model, which indicates that the pseudo-cohesion of shear strength index increases linearly whereas the friction angle remains primarily unchanged with the increase in reinforced layers. In addition, we observed that, although the strength of the reinforced tailings increases substantially, the reinforcement effect is more significant at a low confining pressure than at a high confining pressure. On the contrary, the triaxial specimen strength decreases with the increase in the number of reinforced layers. Our findings can provide valuable input toward the design and application of reinforced engineering.

Influence of Curing Pressure on Unconfined Compressive Strength of Cemented Clay

2018 ◽  
Vol 928 ◽  
pp. 263-268 ◽  
Author(s):  
Anuchit Uchaipichat
Keyword(s):  
Compressive Strength ◽  
Unconfined Compressive Strength ◽  
Cement Content ◽  
Soft Clay ◽  
Peak Stress ◽  
Confining Pressure ◽  
Compression Tests ◽  
Unconfined Compression ◽  
Soil Cement ◽  
Curing Pressure

The soil-cement columns are generally installed and cured in the soft clay layers under confining pressure. The strength of the soil-cement columns may be influenced by confining pressure during curing period. In this study, the main objective was to study the influence of curing pressure on unconfined compressive strength of cemented clay. A series of unconfined compression tests was performed on a cement admixed clay sample cured under pressure values of 0 kPa (atmospheric pressure), 25kPa, 50kPa and 100 kPa using a typical unconfined compression equipment. The test samples with values of cement content of 0.5, 1.0 and 2.0 percent were cured for 28 days.The stress-strain curves obtained from all tests show a peak value of stress. The unconfined compressive strength or peak stress obviously increased with increasing cement content for all curing pressure conditions. It can be observed that the strength of samples gradually increased with curing pressure for cement content of 0.5 percent. For cement contents of 1.0 and 2.0 percent, the strengths of samples cured under pressures of 25 kPa dramatically increased from the strength of samples cured without pressure (0 kPa), however, the strengths of samples for curing pressures of 25, 50 and 100 kPa were not clearly different.

scholarly journals Experimental Investigation and Micromechanical Modeling of Elastoplastic Damage Behavior of Sandstone

Materials ◽  
2020 ◽  
Vol 13 (15) ◽  
pp. 3414
Author(s):  
Chaojun Jia ◽  
Qiang Zhang ◽  
Susheng Wang
Keyword(s):  
Damage Evolution ◽  
Triaxial Compression ◽  
Damage Model ◽  
Confining Pressure ◽  
Micromechanical Modeling ◽  
Compression Tests ◽  
Integration Algorithm ◽  
Damage Behavior ◽  
Plastic Strain Increment ◽  
Elastoplastic Damage

The mechanical behavior of the sandstone at the dam site is important to the stability of the hydropower station to be built in Southwest China. A series of triaxial compression tests under different confining pressures were conducted in the laboratory. The critical stresses were determined and the relationship between the critical stress and confining pressure were analyzed. The Young’s modulus increases non-linearly with the confining pressure while the plastic strain increment Nϕ and the dilation angle ϕ showed a negative response. Scanning electron microscope (SEM) tests showed that the failure of the sandstone under compression is a coupled process of crack growth and frictional sliding. Based on the experimental results, a coupled elastoplastic damage model was proposed within the irreversible thermodynamic framework. The plastic deformation and damage evolution were described by using the micromechanical homogenization method. The plastic flow is inherently driven by the damage evolution. Furthermore, a numerical integration algorithm was developed to simulate the coupled elastoplastic damage behavior of sandstone. The main inelastic properties of the sandstone were well captured. The model will be implemented into the finite element method (FEM) to estimate the excavation damaged zones (EDZs) which can provide a reference for the design and construction of such a huge hydropower project.

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