scholarly journals Investigation on Triaxial Dynamic Model Based on the Energy Theory of Bedding Coal Rock under Triaxial Impact Compression

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Yang Xue ◽  
Xiaohui Liu ◽  
Rui Zhao ◽  
Yu Zheng ◽  
Xin Gui
Keyword(s):  
Constitutive Model ◽  
Confining Pressure ◽  
Strain Rates ◽  
Peak Strain ◽  
Dynamic Failure ◽  
Impact Compression ◽  
Failure Characteristics ◽  
Confining Pressures ◽  
Coal Rock ◽  
Energy Theory

To investigate the dynamic failure characteristics of bedding rocks in depth, a series of dynamic impact compression tests on parallel and vertical bedding coal rocks were conducted by the split Hopkinson pressure bar test system at 10–103 s−1 strain rates and 0, 4, 8, and 12 MPa confining pressures. According to the experiments, the mechanical properties and energy characteristics of bedding coal rock under different confining pressures and strain rates were obtained, and a triaxial dynamic constitutive model of bedding coal rock was established based on the energy theory of rock failure. The results show that the compressive strength, peak strain, incident energy, dissipated energy, and dynamic strength increase factor gradually increase with increase in strain rate, but the increase in peak strain weakens as confining pressure rises. The influence of bedding structure on strength and energy is not obvious in the uniaxial state, while it gradually enhances as confining pressure increases. The obvious difference in DIF and the energy dissipation ratio of bedding coal rocks gets obvious in SHPB tests. Considering the influence of confining pressure, strain rate, and bedding on the dynamic failure characteristics, the dynamic constitutive model of bedding coal rock was established by introducing the comprehensive influence factor K and the DIF. Comparing with test results, the model parameters are almost confirmed, and the correctness of the model is further verified by analysing the law of K value. Meanwhile, the stress-softening characteristics of coal rock in postpeak are well simulated by the dynamic constitutive model. The results can provide reference value for dynamic issues such as high-efficiency rock breaking, prevention of rock burst, and surrounding rock support in deep rock masses.

scholarly journals The energy evolution characteristics of coal under different dynamic strain rates and confining pressures

2019 ◽  
Vol 23 (3 Part A) ◽  
pp. 1409-1416
Author(s):  
Yi-Qiang Lu ◽  
Xiao-Hui Liu ◽  
Jing Xie ◽  
Zhi-Qiang He ◽  
Cong Li
Keyword(s):  
Split Hopkinson Pressure Bar ◽  
Confining Pressure ◽  
Tensile Failure ◽  
Dynamic Strain ◽  
Strain Rates ◽  
Strengthening Effect ◽  
Peak Strain ◽  
Energy Evolution ◽  
Evolution Characteristics ◽  
Confining Pressures

Coal specimens from baijiao coal mine were impacted by a split Hopkinson pressure bar to study its dynamic mechanical behavior under different confining pressures (0-12 MPa) and different strain rates (20-250 s-1). The performances and the energy evolution characteristics of the coal specimens were analyzed. The results show that the strengthening effect and toughening effect of rock are gradually enhanced with the increase of confining pressure. At the same time, the coal failure gradually transitions and develops from tensile failure to compression-shear failure under the action of confining pressure. The peak strength and peak strain of coal rock show significant strain rate correlation and strong confining pressure effect with the change of confining pressures and strain rates. The dynamic strength growth factor of coal is approximately linear with the increasing of strain rates. The energy density and energy absorption density increase linearly with the increase of strain rates, and the energy consumption ratio has a logarithmic growth relationship with the strain rates.

scholarly journals Mechanical Properties of Rock–Coal–Rock Composites at Different Inclined Coal Seam Thicknesses

2022 ◽  
Vol 9 ◽  
Author(s):  
Bo Ma ◽  
Feng Wang ◽  
Hongyang Liu ◽  
Dawei Yin ◽  
Zhiguo Xia
Keyword(s):  
Mechanical Properties ◽  
Coal Seam ◽  
Failure Modes ◽  
Peak Stress ◽  
Confining Pressure ◽  
Seam Thickness ◽  
Peak Strain ◽  
Confining Pressures ◽  
Coal Rock ◽  
Coal Seam Thickness

A comprehensive understanding of the mechanical properties of coal and rock sections is necessary for interpreting the deformation and failure modes of such underground sections and for evaluating the potential dynamic hazards. However, most studies have focused on horizontal coal–rock composites and the mechanical properties of inclined coal–rock composites have not been considered. To explore the influence of different confining pressures and inclined coal seam thicknesses on the mechanical properties and failure characteristics of rock–coal–rock (RCR) composites, a numerical model based on the particle flow code was used to perform simulations on five inclined RCR composites at different confining pressures. The results show that the mechanical properties and failure characteristics of the RCR composites are affected considerably by the inclined coal seam thickness and the confining pressure. (1) When the inclined coal seam thickness is constant, the elasticity modulus of the inclined RCR composite increases nonlinearly with the confining pressure at first, and then remains constant. At the same confining pressure, the elasticity modulus of the inclined RCR composite decreases nonlinearly with the inclined coal seam thickness. (2) When the confining pressure is constant, the peak stress of the inclined RCR composite decreases with the increase of the inclined coal seam thickness. When the inclined coal seam thickness is constant, the peak stress increases with the confining pressure. (3) As the inclined coal seam thickness increases, the peak strain of the inclined RCR composite first decreases rapidly, and then remains constant when there is no confining pressure. When the confining pressure is between 5 and 20 MPa, the peak strain of the inclined RCR composite gradually increases. (4) In the absence of confining pressure, there are few microcracks in the rock at an inclined coal seam thickness of 10 mm, whereas all the other cracks are in the coal section. When the confining pressure ranges between 5 and 20 MPa, the failure modes of the RCR composite can be divided into Y- and X-types.

scholarly journals A Nonlinear Statistical Damage Constitutive Model for Porous Rocks

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Yue Pan ◽  
Zhiming Zhao ◽  
Liu He ◽  
Guang Wu
Keyword(s):  
Constitutive Model ◽  
Solid Skeleton ◽  
Porous Rocks ◽  
Different Types ◽  
Confining Pressures ◽  
Damage Constitutive Model ◽  
Statistical Damage Constitutive Model ◽  
Energy Theory ◽  
Water Contents ◽  
Statistical Damage

In the current paper, the deformation behaviours of rocks during compression are studied by testing 10 groups of sandstone samples with different porosity characteristics. According to the energy theory, the rock material was divided into two parts: solid skeleton and voids. A statistical damage-based approach was adopted to establish a nonlinear statistical damage constitutive model. The validity of the statistical damage constitutive model is verified by the test data. The statistical damage constitutive model performs well in each stage of rock compression before failure. For different types of rocks, different confining pressures, and different water contents, the statistical damage constitutive model fits well. This model can be applied to most types of rocks and in most engineering environments.

scholarly journals Mechanical Properties of Grouted Crushed Coal with Different Grain Size Mixtures under Triaxial Compression

2018 ◽  
Vol 2018 ◽  
pp. 1-13 ◽  
Author(s):  
Yuhao Jin ◽  
Lijun Han ◽  
Qingbin Meng ◽  
Suresh Sanda ◽  
Haizhi Zang ◽  
...  
Keyword(s):  
Grain Size ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Peak Strain ◽  
Compression Tests ◽  
Reinforcement Effect ◽  
Confining Pressures ◽  
Mechanical Behaviours ◽  
Ultimate Failure ◽  
Different Grain Size

To have a better understanding of the reinforcement effect on the crushed zone after grouting in coal mining extraction work, a self-designed grouting apparatus was used to study the effects of the grain size mixtures (distribution) and the stress state on the mechanical behaviours of grouted crushed coal specimens. From the various grouting tests, triaxial compression tests and scanning electron microscopy (SEM) observations of grouted specimens with different grain size mixtures, it was found that, for the same grain size mixture, the peak (σp) and residual (σr) strengths of the grouted specimens increased with an increase in confining pressure. It was found that the average slope values of the σp-σ3 curves for the grouted specimens with different grain size mixtures were all larger than those of the σr-σ3 curves. It was observed that the peak strain (εp) of the grouted specimens with different grain size mixtures increased overall with increasing confining pressure. For constant confining pressure, the peak and residual strengths both gradually increased approximately linearly as the grain size mixtures varied from small to large, but at higher confining pressures, the influence of the grain size mixture on the peak (or residual) strength increased. These mechanical behaviours of the grouted crushed coal specimens were strongly dependent on the variation in the grain size mixtures and in the confining pressure, which can be explained by the crack evolution process within the grouted specimen under triaxial compression, to a certain extent. Ultimate failure of the grouted specimen occurred just after propagation and coalescence of the cracks through the entire grouted specimen. Moreover, there were three major microscopic diffusion modes for the grouts flowing in most of the crushed coal specimens. Based on these test results, it was found that the reinforcement effect of the grouted specimen related to the splitting grouting mode (occurring in most of the large specimens) seems to be better than that of the penetrating (filling) grouting mode (in most of the small specimens).

Laboratory Testing and Consitiutive Modeling of Coal Including Anisotropy

1992 ◽  
Vol 296 ◽  
Author(s):  
Dar-Hao Chen ◽  
Musharraf M. Zaman ◽  
Anant R. Kukreti
Keyword(s):  
Constitutive Model ◽  
Triaxial Compression ◽  
High Capacity ◽  
Ground Surface ◽  
Transversely Isotropic ◽  
Confining Pressure ◽  
Inherent Anisotropy ◽  
Deformation Response ◽  
Young’S Moduli ◽  
Confining Pressures

AbstractIn this study, the stress-deformation response of coal in the laboratory under threedimensional (3-D) loading conditions similar to those existing in an actual coal mine is investigated, and a constitutive model, including the effects of anisotropy, is developed. The coal samples were obtained from a mine in LeFlore County, Oklahoma, at a depth of approximately 25–30 ft below the ground surface. A High Capacity Cubical Device with servo-controlled independent loading along three axes of a cubical specimen and a computerized data acquisition and monitoring system were used to conduct the tests. A total of 21 tests under 4 different confining pressures and 5 different stress paths were conducted. The influence of the degree of anisotropy was investigated by comparing the transversely isotropic and isotropic idealizations for different stress paths (Triaxial Compression, Triaxial Extension and Simple Shear) at different confining pressures (1,600, 3,200 and 5,600 psi). The experimental results demonstrated that the coal exhibits inherent anisotropy and that it can be treated approximately as a transversely isotropic material. Also, the Young's moduli were found to be dependent on the confining pressure. The experimental data were used to evaluate the material constants associated with the elasto-plastic constitutive model developed in the study.

scholarly journals Experimental Study on Coupling Influence of Temperature and Confining Pressure to Deformation and Strength Characteristics of Rock-like Material with Pre-Existing Crack

Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7572
Author(s):  
Hongwei Wang ◽  
Yongyan Wang ◽  
Xi Fu
Keyword(s):  
Young’S Modulus ◽  
Failure Mode ◽  
Young's Modulus ◽  
Confining Pressure ◽  
Strength Characteristics ◽  
Peak Strain ◽  
Influence Of Temperature ◽  
Confining Pressures ◽  
Initial Cracks ◽  
Deformation And Strength Characteristics

In this paper, destructive compression tests under the coupled influence of temperatures (20–60 °C) and confining pressures (0–7 MPa) were carried out on rock-like material with pre-existing crack to explore the deformation and strength characteristics. The stress–strain curves of rock-like material under the coupled influence of temperatures and confining pressures were obtained. Meanwhile, the correlations of peak stress, peak strain, and average Young’s modulus with temperatures and confining pressures were obtained. The results of the experiments indicate that, firstly, the compressive strength decreased and the deformation increased due to the influence of pre-existing cracks; the combined effect of initial cracks, temperature, and confining pressure gave rise to a more complicated mechanism of soft rock deformation. Secondly, the deformation of rock-like material was affected by initial cracks, confining pressures, and temperatures, but the influence of temperature was lower than that of confining pressure and initial crack. The failure mode of rock-like material was brittle at the confining pressure of 0 and 1 MPa and plastic at the confining pressure of 5 and 7 MPa. The critical confining pressure value of failure mode for rock-like material was 3 MPa. Thirdly, the peak strength and peak strain of rock-like material increased with confining pressure. Temperature had less influence on the rock-like material strength and peak strain than confining pressure. Lastly, Young’s modulus decreased with temperature and confining pressure.

scholarly journals Experimental Study on Mechanical Properties of Deep Buried Granite under Different Confining Pressures

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Jun Zhao ◽  
Tan Zhang
Keyword(s):  
Cyclic Loading ◽  
Confining Pressure ◽  
Surrounding Rock ◽  
Underground Engineering ◽  
Failure Characteristics ◽  
Deformation And Failure ◽  
Cyclic Loading And Unloading ◽  
Confining Pressures ◽  
Crack Damage Stress ◽  
Loading And Unloading

Brittle failure of hard rock poses a serious threat to the stability of surrounding rock in deep underground engineering. In order to study the deformation and failure characteristics of deep buried granite under high confining pressure cyclic loading and unloading, MTS815 electro-hydraulic servo rock test system was used to conduct cyclic loading and unloading tests under confining pressures of 15 MPa, 35 MPa, 45 MPa, and 55 MPa, and the corresponding stress-strain curves and deformation failure characteristic curves were obtained. The experimental results show the follows: (1) under the same confining pressure, the peak strength, crack initiation stress, crack damage stress, and Poisson’s ratio of the specimens under cyclic loading and unloading are larger than those under conventional triaxial loading and unloading, and the unloading elastic modulus is smaller than that, under conventional triaxial compression; (2) the results show that, under different confining pressures, the granite samples show obvious brittle failure characteristics, the elastic modulus and crack initiation stress increase first and then decrease with the confining pressure, the peak strength and crack damage stress of the samples increase linearly with the confining pressure, and Poisson’s ratio increases first and then remains unchanged with the confining pressure; (3) under the two kinds of stress conditions, the macroscopic failure of the samples is mainly shear failure. The deformation and failure law of granite samples revealed in this study has significant reference value for the selection of rock mass mechanical model of surrounding rock stability of underground engineering, the formulation of surrounding rock support countermeasures, and the evolution law of mechanical parameters with damage variables.

scholarly journals A Constitutive Model of Sandy Gravel Soil under Large-Sized Loading/Unloading Triaxial Tests

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Pengfei Zhang ◽  
Han Liu ◽  
Zhentu Feng ◽  
Chaofeng Jia ◽  
Rui Zhou
Keyword(s):  
Constitutive Model ◽  
Large Scale ◽  
Confining Pressure ◽  
Peak Strength ◽  
Triaxial Tests ◽  
Model Parameters ◽  
Sandy Gravel ◽  
Cumulative Volume ◽  
Gravel Soil ◽  
Confining Pressures

Based on large-scale triaxial tests of sandy gravel materials, the strength and deformation characteristics under loading/unloading conditions are analyzed. At the same time, the applicability of the hyperbolic constitutive model to sandy gravel is studied using experimental data. The results indicate that sandy gravel under low confining pressures (0.2 and 0.4 MPa) shows a weak softening trend; the higher the confining pressure, the more obvious the hardening tendency (0.6 and 0.8 MPa) and the greater the peak strength. During unloading tests, strain softening occurs, and the peak strength increases with increasing confining pressure. During loading tests, dilatancy appears when the confining pressure is low (0.2 MPa). With increasing confining pressure (0.4, 0.6, and 0.8 MPa), the dilatancy trend gradually weakens, and the cumulative volume tric strain increases, which reflects the relevance of the stress paths. Through research, it is found that the hyperbolic constitutive model has good applicability to sandy gravel soils, and the corresponding model parameters are obtained.

scholarly journals Long-term creep behavior of deep-buried marble under different confining pressures

2019 ◽  
Vol 23 (Suppl. 3) ◽  
pp. 653-660
Author(s):  
Ersheng Zha ◽  
Ru Zhang ◽  
Zetian Zhang ◽  
Li Ren ◽  
Wenju Zhang ◽  
...  
Keyword(s):  
Creep Behavior ◽  
Shear Failure ◽  
Confining Pressure ◽  
Tensile Failure ◽  
Creep Failure ◽  
Failure Characteristics ◽  
Underground Caverns ◽  
Confining Pressures ◽  
Term Creep

To explore the long-term creep behavior of deep rock, the long-term tri-axial creep mechanical behavior of the rock under different confining pressures has been carried out. The results show that the instantaneous strain and creep strain of the high confining pressure specimen are significantly higher than that of the low confining pressure specimen under high deviatoric stress. By analyzing the failure characteristics of different confining pressure specimens, it is found that with the increase of the confining pressure, the creep failure characteristics of the marble transforms from tensile failure to shear failure. These research results have certain reference significance for the long-term stability analysis of the deep underground caverns.

scholarly journals Experimental Study on Triaxial Unloading Failure of Deep Composite Coal-Rock

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Xin Li ◽  
Hao Li ◽  
Zhen Yang ◽  
Zhongxue Sun ◽  
Jiayu Zhuang ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Failure Criterion ◽  
Confining Pressure ◽  
Exponential Relationship ◽  
Partial Fracture ◽  
Triaxial Compressive Strength ◽  
Confining Pressures ◽  
Unloading Rate ◽  
Coal Rock ◽  
And Control

With the deep mining of coal, the phenomenon of high ground stress is more likely to cause dynamic disaster. In view of the above problems, this paper takes the unloading process of coal mining as the background to study the effects of mining rates under different conditions on the mechanical properties and triaxial failure criterion of composite coal-rock, so as to provide a theoretical basis for the prevention and control of dynamic disasters in coal mines. The composite coal-rock models with a composite ratio of 1 : 1 : 1 were tested under different unloading rates or confining pressures. The results show that the triaxial unloading process of coal-rock can be divided into five stages: compaction, single elasticity, elastic-plastic unloading, partial fracture, and complete fracture. In this paper, the failure criterion of composite coal-rock triaxial unloading is derived. The unloading rate has an exponential relationship with the triaxial compressive strength, and the relationship between initial confining pressure and compressive strength is linear. The triaxial compressive strength is determined by both. The peak strains ε of all samples under different unloading conditions were around 0.01. And initial confining pressure had an influence on the strain variation trend during the unloading of composite coal-rock. The higher the initial confining pressure, the greater the elastic modulus. In addition, an increase of initial confining pressure led to the increase of the total energy converted into dissipated part in the process of fracture and caused the obvious increase of the rebound characteristics of the curve. However, the unloading rate had no influence on the strain trend.

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