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).

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 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.

Experimental Study of Stress-Strain Characteristics of the Fly Ash Blended with Curing Agent

2010 ◽  
Vol 168-170 ◽  
pp. 1934-1942
Author(s):  
Zheng Shen ◽  
Lan Zong ◽  
Xiang Dong
Keyword(s):  
Fly Ash ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Uniaxial Stress ◽  
Curing Agent ◽  
Compression Tests ◽  
Growth Trend ◽  
Stress Strain ◽  
Confining Pressures ◽  
Triaxial Compression Tests

The stress-strain characteristics of the fly ash blended with curing agent was studied using uniaxial and triaxial compression tests. Curing agent JNS-2 was used as the stabilizing agents in sample preparation. Four curing agent JNS-2 contents of 3%, 6%, 9% and 12% were selected for sample preparation. UU triaxial compression tests were conducted in a range of confining pressures from 100 kPa to 300 kPa. The experimental results obtained from the laboratory tests showed that curing age, mixture ratio, compaction degree and confining pressures had significant influence on the shape of curves. Uniaxial stress-strain test results demonstrated that the latter strength and deformation characteristics of the fly ash blended with curing agent grew little and with the increase of curing agent amount and compaction factor, the curve of uniaxial stress-strain changed significantly. On the other hand, triaxial stress-strain test results indicted that the failure strain showed a partial negative growth trend with the increase of curing agent amount, and the failure stress showed a partial positive growth trend with the increase of curing agent amount. When the curve was at high confining pressure, it showed hardening type, when at low confining pressure it showed softening type.

Gravel Content Effect on the Shear Strength of Clay-Gravel Mixtures

2011 ◽  
Vol 71-78 ◽  
pp. 4685-4688 ◽  
Author(s):  
Chen Wang ◽  
Chuan Ni Zhan
Keyword(s):  
Shear Strength ◽  
Internal Friction ◽  
Triaxial Compression ◽  
Constant Strain Rate ◽  
Friction Angle ◽  
Confining Pressure ◽  
Internal Friction Angle ◽  
Compression Tests ◽  
Gravel Content ◽  
Confining Pressures

Gravel content is an important factor affecting the mechanical properties of clay-gravel mixtures. To study the effects of gravel content on the shear strength of clay-gravel mixtures, constant-strain-rate drained triaxial compression tests were conducted for various mixtures. The gravel contents were 30%, 40%, 50% and 70%. The confining pressures were varied from 50kPa to 300kPa. Test results indicate that the deviator stress at failure under the same confining pressure increases with the increase in gravel content. As the gravel content in the mixtures is between 30% and 50%, the shear strength is jointly attributed by clay and gravel. An increase in gravel content results in slight increases in both the cohesion intercept and internal friction angle. At gravel content of up to 70%, the shear strength of the mixture is controlled by that of the gravel, and the cohesion intercept and the internal friction angle increase sharply.

scholarly journals Mechanical Modeling of Frozen Coarse-Grained Materials Incorporating Microscale Investigation

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Shan-Zhen Li ◽  
Liang Tang ◽  
Shuang Tian ◽  
Xian-Zhang Ling ◽  
Yang-Sheng Ye ◽  
...  
Keyword(s):  
Strain Softening ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Coarse Grained ◽  
Peak Strain ◽  
Compression Tests ◽  
Engineering Structures ◽  
Softening Behavior ◽  
Coarse Grained Material ◽  
Predicted Values

In the cold regions of China, coarse-grained materials are frequently encountered or used as backfilling materials in infrastructure construction, such as dams, highways, railways, and mineral engineering structures. Effects of confining pressure (0.2, 0.5, and 1 MPa) and frozen temperature (−2, −5, −10, and −15°C) on the stress-strain response and elastic modulus were investigated using triaxial compression tests. Moreover, the microscale structures of a coarse-grained material were obtained by X-ray computed tomography. The coarse-grained material specimens exhibited strain-softening and significant dilatancy behaviors during shearing. A modified model considering microstructures of the material was proposed to describe these phenomena. The predicted values coincided well with the experimental results obtained in this study and other literatures. The sensitivity analysis of parameters indicated that the model can simulate the initial hardening and post-peak strain-softening behavior of soils. And the transition of volume strain from contraction to dilatancy can also be described using this model. The results obtained in this study can provide a helpful reference for the analysis of frozen coarse-grained materials in geotechnical engineering.

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.

Post-Critical Mechanical Properties Of Sedimentary Rocks In The Upper Silesian Coal Basin (Poland)

2015 ◽  
Vol 60 (2) ◽  
pp. 517-534 ◽  
Author(s):  
Mirosława Bukowska
Keyword(s):  
Triaxial Compression ◽  
Residual Deformation ◽  
Confining Pressure ◽  
Compression Tests ◽  
Functional Relationships ◽  
Conventional Triaxial Compression ◽  
Upper Silesian Coal Basin ◽  
Confining Pressures ◽  
Waste Rocks ◽  
Triaxial Compression Tests

AbstractIn this paper, we present the results of a study of the Upper Carboniferous sedimentary rocks of the Upper Silesian Coal Basin (USCB) in Poland. We examined the hard coals, which belong to various stratigraphic units of Upper Carboniferous coal-bearing strata, and waste rocks, i.e., sandstones, mudstones, claystones. We present the results of tests of their post-critical mechanical properties. These results are from tests of the post-critical modulus, residual stress and residual deformation from experiments using a servo-controlled testing machine (MTS) with uniaxial compression and conventional triaxial compression. We applied confining pressures of up to 50 MPa at a strain rate of 10−5− 10−1s−1(0.003-6.0 mm/sec). The confining pressure applied in the triaxial compression tests reflected the conditions of current and future mining activities in the USCB at depths exceeding 1.300 metres. The strain rate applied in the tests reflected the values observed in the rockmass surrounding the mine workings and the rate of certain geodynamic phenomena occurring in the Carboniferous rockmass in the USCB, e.g., rock bursts. We present the values of the sub-critical modulus of coals and waste rocks, the functional relationships between the post-critical modulus and uniaxial compression strength, which are described using an exponential function of high correlation coefficients of the given rocks, and an exponential relationship between the post-critical modulus and the longitudinal elasticity modulus (Young’s modulus). Based on the results of tests of the post-critical properties of the Carboniferous rocks under triaxial compression and at various strain rates, we devised the functional relationships between the properties of the rocks and the confining pressure. The dependence of the post-critical modulus of the sandstones and claystones on the confining pressure is described using a polynomial function of degree 2, and that of the coals is described using an exponential function. The relationship between the residual stress and residual deformation in the rocks and the confining pressure was described using a linear function. The obtained results of tests have a practical application in forecasting behaviour of rocks located deep, and designing safe exploitation of mineral deposits. Confining pressures of up to 50 MPa used in the conventional triaxial compression tests allowed us to predict the behaviour of the rock mass at large depths. These data provide general knowledge of the tendencies in behaviour of rocks at substantial depths and the ability to design safe methods of mining deposits of various raw materials, including energy sources. These deposits are mined from increasingly great depths as the reserves are gradually exhausted and collieries of the largest European coal basins are continuously reconfigured.

Particle Breakage of Gypsum Granular Materials in Triaxial Compression Tests

2011 ◽  
Vol 374-377 ◽  
pp. 2261-2264 ◽  
Author(s):  
Jian Wei Zhang ◽  
Chen Wang ◽  
Qi Wen Zheng
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Granular Materials ◽  
Grain Size Distribution ◽  
Triaxial Compression ◽  
Particle Breakage ◽  
Primary Study ◽  
Compression Tests ◽  
Confining Pressures ◽  
Triaxial Compression Tests

In order to study the particle breakage of granular materials during compression, a series of triaxial compression tests were conducted for gypsum granular materials. Meanwhile, the primary study on evolution laws of particle breakage was carried out. It was found that the deviator stress increases with the increase in confining pressures for gypsum granular materials at the same axial strain. The degree of particle breakage of gypsum granular materials increases with the increase in confining pressures. The relative breakage index can be adopted to denote the particle breakage degree and increases with the increase in confining pressures. When the initial grain size distribution of gypsum granular materials is fractal, the grain size distribution complies with fractal during compression under different confining pressures. The fractal dimension increases with the increase in confining pressures and can be adopted as a parameter for measuring the degree of particle breakage.

Experimental Investigation on Mechanical Properties of Soft Rock under Instantaneous Triaxial Compression

2012 ◽  
Vol 594-597 ◽  
pp. 218-221
Author(s):  
Yu Wang ◽  
Feng Liu
Keyword(s):  
Mechanical Properties ◽  
Shear Failure ◽  
Triaxial Compression ◽  
Deformation Modulus ◽  
Soft Rock ◽  
Confining Pressure ◽  
Test System ◽  
Compression Tests ◽  
Confining Pressures ◽  
Failure Angle

Using the RMT-150C rock mechanics test system, the instantaneous triaxial compression tests for muddy siltstone were carried out under different confining pressures, and the instantaneous mechanical properties of soft rock were obtained. The results show that the strength parameters of sample have a positive linear relation with the confining pressure, and the sensitivity of peak strength on the confining pressure is higher than that of residual strength. The elastic and deformation modulus of sample linearly increase with the confining pressure going up, and the elastic modulus is more sensitive to the confining pressure. The soft rock sample shows typical ductility failure characteristic, while the damage characteristic is mainly shear failure and the shear failure angle linearly decreases with the confining pressure going up.

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.

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