scholarly journals Research on Coal Mechanical Properties Based on True Triaxial Loading and Unloading Experiment

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Yanyan Peng ◽  
Haoxiang Deng ◽  
Minghong Xing ◽  
Pengfei Guo ◽  
Chun Zhu
Keyword(s):  
Mechanical Properties ◽  
Acoustic Emission ◽  
Principal Stress ◽  
Coal Mine ◽  
Test System ◽  
Intermediate Principal Stress ◽  
Mine Safety ◽  
Triaxial Loading ◽  
True Triaxial ◽  
Loading And Unloading

To study the safety issues caused by coal mine excavation, self-developed simulation of earth interior atmosphere and sound test system was used to perform true triaxial loading and unloading tests of coal. An acoustic emission detection system was used to record the damage evolution trend of coal under different intermediate principal stress states. The experimental results show that in the true triaxial unloading test, as the intermediate principal stress increases, the failure state of coal changes from shear failure to partial shear tension failure, finally leading to overall yield failure. In the stress-strain curves, with the increase in intermediate principal stress, the strain in the direction of intermediate principal stress gradually changes from compression to expansion, and typical expansion occurs. The Mogi–Coulomb strength criterion better reflects the strength failure characteristics of coal during unloading. The stress-acoustic emission diagrams show that the increase in intermediate principal stress causes the internal cracks of the coal to grow unsteadily and exponentially, and the increase in intermediate principal stress makes the coal lose its ability to continue to bear the load. Studying the influence of the intermediate principal stress on the mechanical properties of coal has practical significance for coal mine safety production.

scholarly journals Mechanical and Coal Burst Breeding Mechanism of Coal Samples under True Triaxial Loading and Unloading

2019 ◽  
Vol 2019 ◽  
pp. 1-15
Author(s):  
Wei Shen ◽  
Lin-ming Dou ◽  
Hu He
Keyword(s):  
Acoustic Emission ◽  
High Speed ◽  
High Energy ◽  
Exponential Relationship ◽  
Burst Source ◽  
Time Curve ◽  
Triaxial Loading ◽  
True Triaxial ◽  
Unloading Rate ◽  
Loading And Unloading

A true triaxial loading and unloading experiment entailing “y-direction stress loading, z-direction stress unloading, and x-direction displacement fixing” of coal samples was conducted. Through analysis of the stress characteristics, fracture characteristics, and energy evolution in coal samples, the mechanical and coal burst breeding mechanisms of coal samples under true triaxial loading and unloading were revealed. The experiment found that the yield stress and peak stress of coal samples were not only affected by the initial loading and unloading of lateral stress but also had a negative exponential relationship with the ratio of the unloading rate and the loading rate (RURLR), thereby establishing the stress equation of coal samples under a true triaxial loading and unloading. There was a yield turning point in the stress-time curve of coal samples, and the difference in triaxial stress and acoustic emission before, and after, yield was significant. It was found that a high unloading rate and high initial stress are precursors to coal sample bursting. During loading and unloading, the high-energy area expanded, but its location was always fixed to within a certain area. The energy in this area was rapidly released to form a burst source when the sample was subjected to high-speed unloading. The nonbursting coal samples and the burst coal samples showed characteristic slabbing and bursting behaviours, respectively: the former corresponding to the acoustic emission energy value being two orders of magnitude lower than the latter. The research results can provide a reference for the study of mechanical behaviours and coal burst criteria in the rock surrounding a coal roadway excavation.

Study on the Mechanical Properties of Backfill Cream-Body during Coal Mining

2012 ◽  
Vol 170-173 ◽  
pp. 533-536 ◽  
Author(s):  
Shao Jie Chen ◽  
Wei Jia Guo ◽  
Hai Long Wang ◽  
Yi Tao Zhong
Keyword(s):  
Mechanical Properties ◽  
Coal Mine ◽  
Surface Mining ◽  
Test System ◽  
Control Surface ◽  
Ecological Environment ◽  
Uniaxial Compression Test ◽  
Mechanical Parameters ◽  
Test Results ◽  
Different Ages

In order to research the mechanical properties of the backfill cream-body under engineering conditions in the coal mine, the uniaxial compression test of backfill cream-body with different ages abtained from the filling locale of Daizhuang coal mine is conducted with MTS815.03 rock test system. The characteristics of backfill cream-body in the limited space and a certain environment are studied. Research shows that, the strength of backfill cream-body is high, but coagulability is bad and the discreteness of mechanical properties is different; Uniaxial compressive strength is 2.3 ~ 13.17 MPa and the average is 5.436 MPa; The elastic modulus is very low ,which is only 53.66 ~ 2614.35 MPa and the average is 645.14 MPa. The deformation is bigger when absorbing load; Poisson's ratio is low, which is only 0.0001 ~ 0.2112 and the average is 0.0265, which indicates that the backfill cream-body doesn't need the space of transverse deformation when bearing compression deformation; The mechanical parameters of backfill cream-body with different ages are fitted and regressed. Test results is important to control surface mining subsidence effectively, liberate the coal resources under buildings, railways and waterbodies and protect the ecological environment.

The Changing Rule of Rock Strength under True Triaxial Condition

2014 ◽  
Vol 522-524 ◽  
pp. 1410-1413
Author(s):  
Ze Kang Wen ◽  
Ke Min Wei ◽  
Jia Quan Hu ◽  
You Ling Fang
Keyword(s):  
Principal Stress ◽  
Rock Strength ◽  
Quadratic Function ◽  
Intermediate Principal Stress ◽  
Stress Effect ◽  
True Triaxial Test ◽  
True Triaxial ◽  
Minimum Principal Stress ◽  
Stress Coefficient ◽  
Intermediate Principal Stress Effect

The intermediate principal stress effect of the rock has been demonstrated. By analyzing true triaxial test results of Dunham dolomite and Mizuho trachyte, we studied relationship between minimum principal stress and the rock strength under the same intermediate principal stress coefficient, and the relationship between intermediate principal stress and the rock strength under the same minimum principal stress condition. Research shows that the minimum principal stress has a linear relation with the rock strength, the intermediate principal stress coefficient of a quadratic function relation with the rock strength. And the mathematic expression of the intermediate principal stress effect function was calculated.

scholarly journals The suction,yield and strength characteristics of unsaturated intact loess based on true tri-axial tests

2019 ◽  
Vol 7 (3) ◽  
Author(s):  
Jinjin Fang
Keyword(s):  
Principal Stress ◽  
Stress Ratio ◽  
Shear Failure ◽  
Confining Pressure ◽  
Intermediate Principal Stress ◽  
True Triaxial ◽  
Yield Stress Increase ◽  
Isotropic Consolidation ◽  
The Relationship ◽  
Intact Loess

To simulate the failure of loess under undrained condition in the actual engineering,a series of isotropic consolidation and shear tests with different intermediate principal stress ratio b under constant water content were performed on intact loess with various initial suctions using the true tri-axial apparatus for unsaturated soil. The relationship between the saturations and initial suctions,the characteristics of yield,suction and strength of unsaturated intact loess were studied. The results show that the initial suctions and the suctions after the isotropic consolidation decrease with the increase of saturations. The suctions increase with the increase of the intermediate principal stress ratio b at the true triaxial shear failure. The net mean yield stress increase with the increase of the initial suction. The yield suction is a constant,but not always equal to the maximum suction that the soil specimen experienced in the history. The strength of soil increase with the increase of the net confining pressure,initial suction and the intermediate principal stress ratio b.

scholarly journals Seepage Flow Properties of a Columnar Jointed Rock Mass in a True Triaxial Experiment

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-18
Author(s):  
Yanxin He ◽  
Zhende Zhu ◽  
Wenbin Lu ◽  
Yunjin Hu ◽  
Xinghua Xie ◽  
...  
Keyword(s):  
Rock Mass ◽  
Principal Stress ◽  
Jointed Rock ◽  
Jointed Rock Mass ◽  
Intermediate Principal Stress ◽  
True Triaxial ◽  
Minimum Principal Stress ◽  
Baihetan Hydropower Station ◽  
Columnar Jointed Rock Mass ◽  
Seepage Characteristics

A columnar jointed rock mass is a type of rock mass with strong geometric anisotropy and high interface permeability. Its seepage characteristics pose new challenges to the construction and maintenance of the Baihetan Hydropower Station on the Jinsha River. The research object in this study is the columnar jointed rock mass (basalt) in the dam area of Baihetan Hydropower Station. Similar-material model samples of the columnar jointed rock mass with different column dip angles ( α = 0 ° ~90°) were prepared following a similar principle. A true triaxial seepage–stress coupling test was conducted to evaluate the seepage characteristics of similar-material samples with different dip angles under intermediate principal stress and minimum principal stress. The experimental results showed that the columnar jointed rock mass exhibited apparent seepage anisotropy. The relationship curve between the volume flow rate Q and the pressure gradient − d P / d L of the samples with different dip angles showed evident nonlinear seepage under intermediate principal stress, which could be well expressed using the Forchheimer equation. It shows the characteristics of a typical linear Darcy flow under minimum principal stress. The law of variations in the permeability of the samples with different dip angles under intermediate principal stress can be well expressed using the one-dimensional quadratic function equation k = a + b σ 2 + c σ 2 2 , and the law of variations in the permeability of the samples with different dip angles under minimum principal stress can be well expressed using the logarithmic function k = a + b ln σ 3 . The permeabilities of the columnar jointed rock mass with dip angles of 0°, 15°, 30°, and 60° were most sensitive to changes in stress, and the seepage characteristics increased in complexity after changes in stress.

Mechanical Properties and Failure Behavior of Dry and Water-Saturated Anisotropic Coal Under True-Triaxial Loading Conditions

2019 ◽  
Vol 53 (11) ◽  
pp. 4799-4818 ◽  
Author(s):  
Yubing Liu ◽  
Guangzhi Yin ◽  
Minghui Li ◽  
Dongming Zhang ◽  
Gun Huang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Failure Behavior ◽  
Loading Conditions ◽  
Triaxial Loading ◽  
True Triaxial ◽  
Water Saturated

scholarly journals Three dimensional statistical damage constitutive model of rock based on Griffith strength criterion

2021 ◽  
Author(s):  
Song Chen ◽  
Xiuling Cao ◽  
Zhao Yang
Keyword(s):  
Constitutive Model ◽  
Principal Stress ◽  
Damage Mechanics ◽  
Brittle Materials ◽  
Strength Criterion ◽  
Intermediate Principal Stress ◽  
True Triaxial ◽  
Damage Constitutive Model ◽  
Two Parameters ◽  
The Relationship

Abstract According to the damage mechanics theory and Lemaitre strain equivalence theory, because most rock materials are brittle materials, Griffith strength criterion has good applicability to describe the fracture failure of brittle materials from the perspective of energy. Using a new method to describe the rock micro-element strength based on Griffith strength criterion, and assuming the micro-element strength obeys the Weibull distribution, a true triaxial constitutive model of damage softening reflecting the whole process of rock failure is established. On this basis, the influence of the two parameters in the model on the curve of the constitutive model is analyzed, and the relationship between the two parameters and the intermediate principal stress in the model is established, and the model is revised reasonably. Finally, a true triaxial damage constitutive model of rock is established. The results are in good agreement with the experimental curve, which verifies its validity and rationality. At the same time, the relationship between the damage evolution and the strain and stress is discussed, and the influence of the size of the intermediate principal stress on the relationship is analyzed in detail.

Fractal characteristics of acoustic emission of gas-bearing coal subjected to true triaxial loading

Measurement ◽  
2021 ◽  
Vol 169 ◽  
pp. 108349 ◽  
Author(s):  
Ran Zhang ◽  
Jie Liu ◽  
Zhanyou Sa ◽  
Zaiquan Wang ◽  
Shouqing Lu ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Triaxial Loading ◽  
True Triaxial ◽  
Fractal Characteristics ◽  
Gas Bearing
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