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 Study of statistical damage constitutive model of layered composite rock under triaxial compression

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Yong-Sheng Liu ◽  
Zhuan-Zhuan Qiu ◽  
Xue-Cai Zhan ◽  
Hui-Nan Liu ◽  
Hai-Nan Gong
Keyword(s):  
Constitutive Model ◽  
Axial Strain ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Layered Composite ◽  
Model Parameters ◽  
Compression Tests ◽  
Fitting Method ◽  
Confining Pressures ◽  
Curve Fitting Method

Abstract The layered composite rock was subjected to triaxial compression tests under constant confining pressure and the stress–strain curves under different confining pressures were obtained. Based on the continuous damage theory and statistical strength theory, it is assumed that the strength of rock microelements obeys Weibull distribution by taking the defects such as random micro-cracks in the rock into account. The statistical constitutive model of layered composite rock with damage correction is established by taking the axial strain of rock as a random distribution variable of microelement strength. The model parameters were determined by the curve fitting method and referring to some test parameters. By comparing the experimental data and the constitutive model curve, the rationality and feasibility of the model are verified.

Assessment of Inherent Anisotropy and Confining Pressure Influences on Mechanical Behavior of Anisotropic Foliated Rocks Under Triaxial Compression

2015 ◽  
Vol 49 (6) ◽  
pp. 2155-2163 ◽  
Author(s):  
Davood Fereidooni ◽  
Gholam Reza Khanlari ◽  
Mojtaba Heidari ◽  
Ali Asghar Sepahigero ◽  
Amir Pirooz Kolahi-Azar
Keyword(s):  
Mechanical Behavior ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Inherent Anisotropy

Mechanical behaviour of powders using a medium pressure flexible boundary cubical triaxial tester

2003 ◽  
Vol 217 (3) ◽  
pp. 233-241 ◽  
Author(s):  
F Li ◽  
V M Puri
Keyword(s):  
Shear Modulus ◽  
Mechanical Behaviour ◽  
Triaxial Compression ◽  
Three Dimensional ◽  
Volumetric Strain ◽  
Confining Pressure ◽  
Alumina Powder ◽  
Medium Pressure ◽  
Mean Pressure ◽  
Confining Pressures

A medium pressure (<21 MPa) flexible boundary cubical triaxial tester was designed to measure the true three-dimensional response of powders. In this study, compression behaviour and strength of a microcrystalline cellulose powder (Avicel® PH102), a spray-dried alumina powder (A16SG), and a fluid-bed-granulated silicon nitride based powder (KY3500) were measured. To characterize the mechanical behaviour, three types of triaxial stress paths, that is, the hydrostatic triaxial compression (HTC), the conventional triaxial compression (CTC), and the constant mean pressure triaxial compression (CMPTC) tests were performed. The HTC test measured the volumetric response of the test powders under isostatic pressure from 0 to 13.79MPa, during which the three powders underwent a maximum volumetric strain of 40.8 per cent for Avicel® PH102, 30.5 per cent for A16SG, and 33.0 per cent for KY3500. The bulk modulus values increased 6.4-fold from 57 to 367MPa for Avicel® PH102, 3.7-fold from 174 to 637 MPa for A16SG, and 8.1-fold from 74 to 597MPa for KY3500, when the isotropic stress increased from 0.69 to 13.79 MPa. The CTC and CMPTC tests measured the shear response of the three powders. From 0.035 to 3.45MPa confining pressure, the shear modulus increased 28.7-fold from 1.6 to 45.9MPa for Avicel® PH102, 35-fold from 1.7 to 60.5MPa for A16SG, and 28.5-fold from 1.5 to 42.8MPa for KY3500. In addition, the failure stresses of the three powders increased from 0.129 to 4.41 MPa for Avicel® PH102, 0.082 to 3.62 MPa for A16SG, and 0.090 to 4.66MPa for KY3500, respectively, when consolidation pressure increased from 0.035 to 3.45MPa. In addition, the shear modulus and failure stress values determined from the CTC test at 2.07, 2.76, and 3.45MPa confining pressures are consistently greater than those from the CMPTC test at the same constant mean pressures. This observation demonstrates the influence of stress paths on material properties. The CTT is a useful tool for characterizing the three-dimensional response of powders and powder mixtures.

scholarly journals Triaxial Compressive Failure Characteristics and Constitutive Model Study of Jurassic-Cretaceous Weakly Cemented Sandstone

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Jinlong Cai ◽  
Wei Zou
Keyword(s):  
Constitutive Model ◽  
Residual Strength ◽  
Triaxial Compression ◽  
Volumetric Strain ◽  
Ductile Failure ◽  
Mathematical Expression ◽  
Confining Pressure ◽  
Mining Area ◽  
Peak Strength ◽  
Correction Coefficient

A conventional triaxial compression test of Jurassic-Cretaceous typical weakly consolidated sandstone from a mining area in Ordos, China, was conducted using an MTS816 tester. Results showed that, before the peak, the rock had a distinct yield stage. When the specimen reached its peak strength, the strength decreased rapidly and showed an obvious brittle failure. When the confining pressure was increased to 15 MPa, the decrease of strength was slow and the rock tended toward ductile failure. With the increase of confining pressure, the cyclic strain initially increased slightly, whereas the volumetric strain increased greatly and the rock sample was in a compression state. When the load reached a critical value, the curve was reversely bent, resulting in volume expansion, whereas the peak strength, residual strength, and elastic modulus increased with confining pressure, and Poisson’s ratio decreased with the confining pressure. In the model based on macroscopic failure rock, the expression of the relationship between fracture angle and confining pressure provided a solid theoretical basis for the direction and failure mode of the macroscopic crack. Based on the rock strength theory and Weibull random distribution assumption of rock element strength, the damage variable correction coefficient was introduced when the residual strength was considered. Then, the mathematical expression of the 3D damage statistical constitutive model was established. Finally, the theoretical curve of the established constitutive model was compared with the triaxial test curve, which showed a high degree of coincidence.

scholarly journals Mechanical Properties and Numerical Analyses of Basalt Fiber Crumb Rubber Mortars in Soft Rock Roadways

2019 ◽  
Vol 2019 ◽  
pp. 1-13 ◽  
Author(s):  
Jun-Ling Qin ◽  
Wei-Guo Qiao ◽  
Deng-Ge Lin ◽  
Shuai Zhang ◽  
Ji-Yao Wang
Keyword(s):  
Constitutive Model ◽  
Triaxial Compression ◽  
Basalt Fiber ◽  
Soft Rock ◽  
Crumb Rubber ◽  
Compression Tests ◽  
Confining Pressures ◽  
Roadway Support ◽  
Uniaxial Compressive Stress ◽  
Triaxial Compression Tests

The strength of crumb rubber mortars can be improved by the addition of basalt fibers. However, limited studies have been conducted on basalt fiber crumb rubber mortars (BF-CRM), and the constitutive model is still very immature. In this paper, uniaxial compressive stress-strain curves are obtained for several groups of BF-CRM specimens with different contents. By comparison with the GZH model, modified GZH parameters that can be used in a BF-CRM constitutive model are obtained. Then, taking the support scheme of the main substation of a mine as the background, FLAC3D is used to simulate the roadway support, BF-CRM replaces the ordinary mortars in the original support, and triaxial compression tests are performed at different confining pressures. In this way, the application of BF-CRM in roadway support is studied and analyzed.

scholarly journals The Effect of Confining Pressure on the Mechanical Properties of Sand–Ice Materials

1973 ◽  
Vol 12 (66) ◽  
pp. 469-481 ◽  
Author(s):  
Bernard D. Alkire ◽  
Orlando B. Andersland
Keyword(s):  
Axial Strain ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Silica Sand ◽  
Creep Tests ◽  
Ice Volume ◽  
Coulomb Failure ◽  
Confining Pressures ◽  
Sand Material ◽  
Cylindrical Samples

Cylindrical samples containing 0.59 mm to 0.84 mm diameter silica sand at about 97% and 55% ice saturation (the ratio of ice volume to sand pore volume) were tested at a temperature of −12° C in triaxial compression. Both constant axial strain-rate tests and step-stress creep tests provide information on the influence of confining pressure on the shear strength and creep behavior of the sand–ice material. Changes in the degree of ice saturation help show the influence of the ice matrix versus the sand material on the mechanical behavior. Data are discussed in terms of the Mohr–Coulomb failure law and creep theories. It is shown that the cohesive component of strength depends on response of the ice matrix, whereas the frictional component of strength responds in a manner very similar to unfrozen sand tested at high confining pressures. Experimental data show that creep rates decrease exponentially and creep strength increases with an increase in confining pressure.

scholarly journals Ice triaxial deformation and fracture

1994 ◽  
Vol 40 (135) ◽  
pp. 305-318 ◽  
Author(s):  
M.A. Rist ◽  
S.A.F Murrell
Keyword(s):  
Shear Fracture ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Maximum Principal Stress ◽  
Brittle Strength ◽  
Independent Evidence ◽  
Polycrystalline Ice ◽  
Confining Pressures ◽  
Pressure Independent ◽  
Ice Failure

AbstractAn experimental investigation into the mechanical behaviour of polycrystalline ice in triaxial compression has been conducted using conditions generally favourable to brittle fracture and microcracking. Under triaxial stresses at high strain rate, ice failure occurs by abrupt shear fracturing, generally inclined at about 45° to the maximum principal stress. At −20°C, such failure is suppressed by the imposition of a small confining pressure, allowing a transition to ductile-type flow accompanied by distributed microcracking, but at —40°C shear fracture persists under confinement of up to at least 50 MPa. For low confining pressures (< 10 MPa), brittle strength is strongly pressure-dependent; above this it is pressure-independent. Evidence is presented that suggests this may reflect a change from a fracture process influenced by friction to fracture initiated by localized yielding. Ductile yield strength is found to be little influenced by confining pressure despite the inhibition of cracking that leads to greatly contrasting observed crack densities. Flow conforms to the well-known power law for ice withQ= 69 J mol−1andn= 4.2 over the temperature range −20° to −4-5° C Under these conditions, microcracking in ice appears to remain remarkably stable and non-interacting.

scholarly journals Investigation on the relationship between CT numbers and marble failure under different confining pressures

2021 ◽  
Vol 60 (1) ◽  
pp. 846-852
Author(s):  
Yang Yan-Shuang ◽  
Li Kai-Yue ◽  
Zhou Hui ◽  
Tian Hao-Yuan ◽  
Cheng Wei ◽  
...  
Keyword(s):  
Damage Mechanics ◽  
Triaxial Compression ◽  
Ct Scanning ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Compression Tests ◽  
Ct Number ◽  
Confining Pressures ◽  
Loading Tests ◽  
Rock Specimens

Abstract Computed tomography (CT) scanning technology is helpful in investigating rock materials as it can demonstrate the micro structure of rock clearly. Conventional triaxial compression tests and the corresponding graded triaxial loading tests were carried out to investigate the complex failure mechanism of the marble at the Jinping Hydropower Station. After that CT-scanning tests were done on the loaded marble specimens. The test results show that (1) the CT numbers of the specimens have a certain statistical regularity, that is, the CT numbers of the specimens under different confining pressures satisfy the Weibull distribution, as the confining pressure increases, the mean values rise while variances decrease; (2) in the two groups of tests, the average CT numbers corresponding to the conventional triaxial tests are higher than those corresponding to the graded loading tests, but the CT number variances are lower than those of the graded loading tests; and (3) according to meso-damage mechanics, the damage variables of the rock specimens were established based on the definition of CT numbers. The calculation results show that the damage variables decrease with the increase in confining pressure, the damage variables of the rock specimens in the graded loading tests are higher than those in the conventional triaxial test, and the differences between the two loading tests have grown with the increase in confining pressure.

scholarly journals A Parabolic Failure Criterion for Transversely Isotropic Rock: Modification and Verification

2019 ◽  
Vol 2019 ◽  
pp. 1-12
Author(s):  
Ding-Jian Wang ◽  
Huiming Tang ◽  
Peiwu Shen ◽  
Yi Cai
Keyword(s):  
Experimental Data ◽  
Failure Criterion ◽  
Triaxial Compression ◽  
Transversely Isotropic ◽  
Confining Pressure ◽  
Prediction Errors ◽  
Compression Tests ◽  
Predictive Capacity ◽  
Data Set ◽  
Transversely Isotropic Rock

It is of great significance to develop a failure criterion that can describe the orientation-dependent behavior of transversely isotropic rocks. This paper presents a simplified parabolic model that is successful in predicting the strengths of rocks under different confining pressures and bedding angles. The model is a modified version of the normal parabolic criterion for intact rocks. The two orientation-dependent parameters (σcβ and kβ) in the model show trigonometric relationships with the bedding angle, and they can be readily determined through uniaxial and triaxial compression tests. The shape of the failure envelope is determined by kβ, and σcβ only affects the level of rock strength. With application to 446 experimental data, the predicting results by the parabolic criterion are highly consistent with the experimental data, and the predictive capacity of the proposed criterion is better than those of the McLamore-Gray and Tien-Kuo criteria. Besides, the prediction errors for the high confining pressure condition and the bedding-sliding failure mode are smaller than those for the low confining pressure and the non-bedding-sliding failure. Moreover, the prediction error almost remains steady with the decrease of data set, indicating that the proposed criterion is of high precision even if the experimental data are limited.

scholarly journals Disturbance Evolution Behavior of Loess Soil under Triaxial Compression

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Yali Xu ◽  
Panpan Guo
Keyword(s):  
Triaxial Compression ◽  
Deformation Modulus ◽  
Loess Soil ◽  
Confining Pressure ◽  
Compression Tests ◽  
Structural Effects ◽  
Moisture Contents ◽  
Confining Pressures ◽  
Evolution Behavior ◽  
Disturbance Function

This paper presents an investigation into the evolution law of the structural effects of Xi’an loess soil, based on the disturbed state concept. First, a series of consolidated and drained triaxial compression tests were performed on undisturbed and remoulded loess samples prepared at five different moisture contents and tested at four different confining pressures. Second, two disturbance functions with different parameters were proposed to quantify mathematically the structural effects of loess. Finally, the proposed disturbance functions were validated against documented test results by other researchers. The results indicated that the single-parameter disturbance function, with the deformation modulus as its parameter, provides convenience for application but takes no account of the respective contributions of deviatoric stress and mean stress to the disturbance evolution behavior of loess. The double-parameter disturbance function, with the shear and bulk moduli as its parameters, is capable of distinguishing these respective contributions and reflects well the disturbance evolution behavior of loess under various moisture contents and confining pressures. The effects of moisture content and confining pressure on the parameters of the disturbance functions were found to be unsteady. The proposed disturbance functions lay the foundation for establishing a constitutive model for loess accounting for the structural effect.

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