scholarly journals Mechanical Characteristics of Coal and Rock in Mining under Thermal-Hydraulic-Mechanical Coupling and Dynamic Disaster Control

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Haifeng Ma ◽  
Lingjie Wang ◽  
Xin'gang Niu ◽  
Fanfan Yao ◽  
Kexue Zhang ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Temperature Gradient ◽  
Coal Mine ◽  
Coal Sample ◽  
Deformation Modulus ◽  
Peak Stress ◽  
Confining Pressure ◽  
Peak Strain ◽  
Lateral Expansion ◽  
Mechanical Coupling

In order to reduce the risk of coal and rock dynamic disasters in the coal mine production process, the coupling mechanics characteristics of coal and rock produced in the process of coal mining in the Dingji Coal Mine are taken as the research object, and the experimental study on the deformation characteristics and the variation rule of mechanical parameters of raw coal under multifield coupling (temperature, gas, and stress coupling) was carried out. The results show that the elastic modulus, peak strain, and peak stress of raw coal samples under the thermal-hydraulic-mechanical coupling have the same change law in the test temperature range and all of them show a linear decreasing law as the temperature increases. Under the same temperature gradient increasing condition, the elastic modulus, peak strain, and peak stress show a nongradient decreasing trend as the temperature increases. Both the deformation modulus and the lateral expansion coefficient show a linear increase as the temperature increases, while the deformation modulus and the lateral expansion coefficient show a nongradient increase trend as the temperature increases under the same temperature gradient increasing condition. Under the action of the thermal-hydraulic-mechanical coupling, unloading confining pressure obviously accelerated the yield process of the coal sample, and the confining capacity of confining pressure on transverse strain of the coal sample decreased. To prevent the occurrence of coal and gas outburst, it is necessary to take specific prevention measures according to the change law of triaxial compression mechanics of a raw coal specimen under the action of the thermal-hydraulic-mechanical coupling.

scholarly journals Study on Mechanical Failure and PermeabilityCharacteristicsof Porous Gas-Bearing Coal under Triaxial Stress

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Xue-bo Zhang ◽  
Wen-yuan Wang ◽  
Ming Yang ◽  
Hang-hang Cai ◽  
Jia-jia Liu ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Elastic Modulus ◽  
Coal Sample ◽  
Confining Pressure ◽  
Gas Pressure ◽  
Peak Strength ◽  
Triaxial Stress ◽  
Peak Strain ◽  
Permeability Characteristics ◽  
Gas Bearing

To explore the mechanical failure and permeability characteristics of porous gas-bearing coal under triaxial stress, the triaxial compression experiment was carried out for porous and conventional gas-bearing coal samples based on the triaxial creep-seepage experiment system and sound emission signal acquisition system. Acoustic emission testing was carried out at the same time of loading failure. The experimental results showed that (1) under fixed gas pressure but changing confining pressure, the porous gas-bearing coal sample had higher peak strength and elastic modulus but lower peak strain; under changing gas pressure but fixed confining pressure, the porous gas-bearing coal sample had lower peak strength and peak strain but higher elastic modulus. When either confining pressure or gas pressure was changed, the mechanical properties of the two kinds of gas-bearing coal samples showed a good consistency, but the mechanical parameters differed greatly, with the peak strength, peak strain, and elastic modulus of porous coal samples are reduced by 1/4, 2/3, and 3/4, respectively. (2) When either the confining pressure or gas pressure was changed, the permeability of the porous gas-bearing coal sample was larger than that of the conventional gas-bearing coal sample. However, the change rules of permeability characteristics of the two were basically the same, except that there was a large difference in permeability value that the porous gas-bearing coal sample increases nearly twice as much as that of the conventional gas-bearing coal sample. (3) In the whole stress-strain process, the acoustic emission characteristics of the porous gas-bearing coal sample differed significantly from those of the conventional gas-bearing coal sample. The maximum ringdown count of the porous gas-bearing coal sample can be reduced by one-third at most, the maximum energy can be reduced by nearly half at most, and the maximum amplitude changes little with only 1–3 dB reduction. The research results have important guiding significance for the prediction of failure and instability of coal tunnel and the development of relevant protective techniques.

scholarly journals SHPB Testing and Analysis of Bedded Shale under Active Confining Pressure

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
Guoliang Yang ◽  
Jingjiu Bi ◽  
Xuguang Li ◽  
Jie Liu ◽  
Yanjie Feng
Keyword(s):  
Mechanical Properties ◽  
Elastic Modulus ◽  
Strain Rate ◽  
Peak Stress ◽  
Confining Pressure ◽  
Dynamic Mechanical Properties ◽  
Dynamic Elastic Modulus ◽  
Peak Strain ◽  
Dynamic Mechanical ◽  
Bedding Angle

Shale gas is the most important new energy source in the field of energy, and its exploitation is very important. The research on the dynamic mechanical properties of shale is the premise of exploitation. To study the dynamic mechanical properties of shale from the Changning-Weiyuan area of Sichuan Province, China, under confining pressure, we used a split Hopkinson pressure bar (SHPB) test system with an active containment device to carry out dynamic compression tests on shale with different bedding angles. (1) With active confining pressure, the shale experiences a high strain rate, and its stress-strain curve exhibits obvious plastic deformation. (2) For the same impact pressure, the peak stress of shale describes a U-shaped curve with an increasing bedding angle; besides, the peak stress of shale with different bedding angles increases linearly with rising confining pressure. The strain rate shows a significant confining pressure enhancement effect. With active confining pressure, the peak strain gradually decreases as the bedding angle increases. (3) As a result of the influence of different bedding angles, the dynamic elastic modulus of shale has obvious anisotropic characteristics. Shale with different bedding angles exhibits different rates of increase in the dynamic elastic modulus with rising confining pressure, which may be related to differences in the development of planes of weakness in the shale. The results of this study improve our understanding of the behavior of bedded shale under stress.

Experimental Study on Mechanical Characteristics of Deformation of Red Sandstone

2011 ◽  
Vol 261-263 ◽  
pp. 1234-1238
Author(s):  
Rui Hong Wang ◽  
Yu Zhou Jiang ◽  
Jing Guo ◽  
Shi Yi Wen
Keyword(s):  
Rock Mass ◽  
Elastic Modulus ◽  
Mechanical Characteristics ◽  
Deformation Modulus ◽  
Strain Curve ◽  
Confining Pressure ◽  
Peak Strain ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Red Sandstone

For geotechnical engineering, it has great significance to research the mechanical characteristics of rock mass under three dimensional stresses. Through triaxial compression failure test, the characteristics of stress-strain curve and deformation of red sandstone from Sichuan under different confining pressures has been analyzed. The results show that: with the increment of confining pressure, the failure mode of rock mass changes from brittle failure to ductile failure gradually, and an obvious yield platform appears near the peak strength of stress-strain curve; the elastic modulus, deformation modulus, peak strain and residual strain of rock sample increase with the increment of confining pressure, the elastic modulus and deformation modulus are not a fixed value, and the relation between deformation parameter and confining pressure can be fit through quadratic curve.

scholarly journals Experimental Study on Biaxial Dynamic Compressive Properties of ECC

Materials ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1257
Author(s):  
Shuling Gao ◽  
Guanhua Hu
Keyword(s):  
Strain Rate ◽  
Lateral Pressure ◽  
Deformation Modulus ◽  
Strain Curve ◽  
Peak Stress ◽  
Pressure Level ◽  
Strain Rates ◽  
Peak Strain ◽  
Stress Strain Curve ◽  
Toughness Index

An improved hydraulic servo structure testing machine has been used to conduct biaxial dynamic compression tests on eight types of engineered cementitious composites (ECC) with lateral pressure levels of 0, 0.125, 0.25, 0.5, 0.7, 0.8, 0.9, 1.0 (the ratio of the compressive strength applied laterally to the static compressive strength of the specimen), and three strain rates of 10−4, 10−3 and 10−2 s−1. The failure mode, peak stress, peak strain, deformation modulus, stress-strain curve, and compressive toughness index of ECC under biaxial dynamic compressive stress state are obtained. The test results show that the lateral pressure affects the direction of ECC cracking, while the strain rate has little effect on the failure morphology of ECC. The growth of lateral pressure level and strain rate upgrades the limit failure strength and peak strain of ECC, and the small improvement is achieved in elastic modulus. A two-stage ECC biaxial failure strength standard was established, and the influence of the lateral pressure level and peak strain was quantitatively evaluated through the fitting curve of the peak stress, peak strain, and deformation modulus of ECC under various strain rates and lateral pressure levels. ECC’s compressive stress-strain curve can be divided into four stages, and a normalized biaxial dynamic ECC constitutive relationship is established. The toughness index of ECC can be increased with the increase of lateral pressure level, while the increase of strain rate can reduce the toughness index of ECC. Under the effect of biaxial dynamic load, the ultimate strength of ECC is increased higher than that of plain concrete.

Experimental Study on Mechanical Property of Thermo-Mechanical and Hydro-Mechanical Coupling Condition for a Sandstone

2006 ◽  
Vol 326-328 ◽  
pp. 1797-1800 ◽  
Author(s):  
Qing Chun Zhou ◽  
Hai Bo Li ◽  
Chun He Yang ◽  
Chao Wen Luo
Keyword(s):  
Pore Pressure ◽  
Deformation Modulus ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Underground Engineering ◽  
Coupling Condition ◽  
West China ◽  
Mechanical Coupling ◽  
North Water ◽  
Confining Pressures

The mechanical properties of rock under high temperature, high geostress and high pore pressure are the basic and important information to assess the safety of underground engineering in west China. Based on the environmental conditions of the west route of south-to-north water transfer project in west China, a series of triaxial tests at confining pressures (0 to 60MPa) and temperatures (25°C to 70°C) as well as pore pressure (0 to 10MPa) have been conducted for a sandstone. It is reported that under the temperatures varying from 25°C to 70°C, the strength of the rock increases with the increment of confining pressure, while the deformation modulus of the rock doesn’t change distinctly with the increment of confining pressures. It is also indicated under the temperatures condition in the experiments, when the confining pressure is lower than 40MPa, the strength of the rock increases with the increment of temperature, whereas when the confining pressure is higher than 40MPa, the strength of rock tend to decrease with increment of temperature. It is further shown that the strength decreases with increasing pore pressure, and the decreasing rates tend to decrease with the increment of confining pressures.

scholarly journals Experimental Study on the Mechanical Behavior of Yunnan Limestone in Natural and Saturated States

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Xutao Zhang ◽  
Mingyang Ren ◽  
Zhaobo Meng ◽  
Baoliang Zhang ◽  
Jinglong Li
Keyword(s):  
Elastic Modulus ◽  
Mechanical Behavior ◽  
Water Content ◽  
Failure Modes ◽  
Shear Failure ◽  
Mechanical Response ◽  
Deformation Modulus ◽  
Confining Pressure ◽  
Hyperbolic Function ◽  
Test Results

Rock material is a kind of mineral assemblage with complex structural heterogeneity, whose mechanical behavior is strongly affected by water or moisture content. In this work, we carried out a series of laboratory tests to investigate the mechanical response (e.g., deformation, strength, and failure characteristics) of Yunnan limestone in natural and saturated states. Our test results show that (1) after saturation, the stiffness and strength of Yunnan limestone degenerate considerably. Compared with the natural condition, the elastic modulus, deformation modulus, and tensile modulus decrease by about 30% on average, and uniaxial compressive strength and tensile strength also decrease by about 15% and 20%, respectively. While Poisson’s ratio is less affected by water content, it can be regarded as a constant; (2) the elastic modulus and deformation modulus of Yunnan limestone are significantly affected by confining pressure, and the relationship between them and confining pressure satisfies the law of hyperbolic function; (3) the peak strength envelope of Yunnan limestone has significant nonlinear characteristics, which can be well described by generalized Hoek-Brown strength criterion. However, the generalized Hoek-Brown criterion does not apply to the residual strength, which shows a linearly increasing trend with the increasing confining pressure; (4) the failure modes of Yunnan limestone are significantly dependent on confining pressure but insensitive to water content. With the increasing confining pressure, the failure modes of Yunnan limestone transform from splitting failure, tension-shear mixed failure, single inclined plane shear failure to Y-shaped or X-shaped conjugated shear failure. The test results can provide important experimental data for the establishment of the constitutive model of Yunnan limestone, which will contribute to obtain more reliable results for stability assessment of Xianglu Mountain Tunnel.

scholarly journals Mechanical Properties and Uniaxial Compression Stress—Strain Relation of Recycled Coarse Aggregate Concrete after Carbonation

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2215
Author(s):  
Tian-Wen Chen ◽  
Jin Wu ◽  
Guo-Qing Dong
Keyword(s):  
Elastic Modulus ◽  
Coarse Aggregate ◽  
Concrete Structures ◽  
Peak Stress ◽  
Peak Strain ◽  
Stress Strain ◽  
Carbonation Depth ◽  
Aggregate Concrete ◽  
Recycled Coarse Aggregate ◽  
Stress Strain Relation

The application of recycled coarse aggregate (RCA) made from waste concrete to replace natural coarse aggregate (NCA) in concrete structures can essentially reduce the excessive consumption of natural resources and environmental pollution. Similar to normal concrete structures, recycled concrete structures would also suffer from the damage of carbonation, which leads to the deterioration of durability and the reduction of service life. This paper presents the experimental results of the cubic compressive strength, the static elastic modulus and the stress–strain relation of recycled coarse aggregate concrete (RAC) after carbonation. The results show that the cubic compressive strength and the static elastic modulus of carbonated RAC gradually increased with the carbonation depth. The uncarbonated and fully carbonated RAC show smaller static elastic modulus than natural aggregate concrete (NAC). As the carbonation depth increased, the peak stress increased, while the peak strain decreased and the descending part of the curves gradually became steeper. As the content of RCA became larger, the peak stress decreased, while the peak strain increased and the descending part of the curves gradually became steeper. An equation for stress–strain curves of RAC after carbonation was proposed, and it was in good agreement with the test results.

scholarly journals Mechanical Characteristics of Frozen Sandstone under Lateral Unloading: An Experimental Study

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Shuai Liu ◽  
Gengshe Yang ◽  
Xihao Dong ◽  
Yanjun Shen ◽  
Hui Liu
Keyword(s):  
Failure Modes ◽  
Rock Sample ◽  
Triaxial Compression ◽  
Radial Strain ◽  
Peak Stress ◽  
Confining Pressure ◽  
Test System ◽  
Peak Strain ◽  
Rate Of Increase ◽  
Unloading Rate

The lateral unloading strength and deformation of surrounding frozen rock are the key parameters for safety evaluation of frozen shaft construction. A low-temperature and high-pressure rock triaxial test system was used to simulate freezing construction, and a constant axial pressure unloading confining pressure test was carried out on frozen sandstone. The effects of freezing temperature, initial confining pressure, and unloading rate on the strength, deformation, and failure modes of frozen sandstone are studied. The main results of the study are as follows: (1) under the initial confining pressure of 20 MPa, the temperature of the sandstone decreases from 20°C to –5°C, and the peak stress and elastic modulus of triaxial compression increase by approximately 3 times. Under lateral unloading conditions, the peak stress of frozen sandstone is about 2∼3 times that of 20°C sandstone, and the peak strain of 20°C sandstone is smaller than that of frozen sandstone. The temperature of frozen sandstone decreases and the rate of increase in the peak stress of triaxial compression is slightly less than the rate of increase in the peak stress of lateral unloading. (2) The initial confining pressure of frozen sandstone increases, the growth rate of axial and radial strain increases, the radial strain dominates the failure process, and the lateral unloading strength decreases significantly. (3) The lateral unloading rate of frozen sandstone increases, the peak strength increases, and the axial and radial strain decrease. At a low unloading rate, partial creep deformation occurs. (4) The frozen rock sample undergoes tensile splitting failure under lateral unloading. According to the stress-strain curve of the frozen rock sample, the relationship between changes in the deformation modulus and changes in the confining pressure unloading amount during the unloading process of the rock sample is obtained.

scholarly journals The Scale Effect of Coarse-Grained Materials by Triaxial Test Simulation

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Xiaotao Ai ◽  
Guangjin Wang ◽  
Xiangyun Kong ◽  
Bo Cui ◽  
Bin Hu ◽  
...  
Keyword(s):  
Scale Effect ◽  
Triaxial Test ◽  
Failure Process ◽  
Deformation Modulus ◽  
Peak Stress ◽  
Friction Angle ◽  
Confining Pressure ◽  
Coarse Grained ◽  
Strength Parameters ◽  
And Migration

The scale effect is an unavoidable problem in the laboratory test of coarse-grained materials. By combining the self-developed cellular automaton program with laboratory experiments, a method of simulating the triaxial test of coarse-grained materials was proposed in this paper, and a triaxial test numerical specimen that can characterize the discontinuous, nonuniform, and heterogeneous characteristics of bulk geotechnical materials was established. The parallel grading method was adopted to create six grading curves for numerical simulation based on one in situ grading curve. The failure process and the scale effect on the strength and deformation of coarse-grained materials were analyzed and discussed. The results showed that under the same confining pressure, the peak stress and initial deformation modulus E i increased with the increase of the maximum particle size d max , while the degree of shear shrinkage and Poisson’s ration υ decreased. As the confining pressure increased, the scale effect of coarse-grained materials would be magnified. If particle breakage and migration were assumed to be neglected, the internal friction angle φ and d max would be roughly proportional, the cohesive force c fluctuated with the increase of d max , and the empirical relations between d max and c and φ were established, respectively, which provides a reference for estimating the actual shear strength parameters of coarse-grained materials on-site. The research results can provide a way of thinking for the study of the scale effect of coarse-grained materials and also have certain reference significance for inferring the strength parameters of the original-graded coarse-grained materials.

scholarly journals Sealing Performance of New Solidified Materials: Mechanical Properties and Stress Sensitivity Characterization of Pores

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Chao Zhang ◽  
Gaohan Jin ◽  
Chao Liu ◽  
Shugang Li ◽  
Junhua Xue ◽  
...  
Keyword(s):  
Coal Sample ◽  
Axial Strain ◽  
Triaxial Compression ◽  
Peak Stress ◽  
Confining Pressure ◽  
Stress Sensitivity ◽  
Test System ◽  
Sample Material ◽  
Sealing Material ◽  
The Difference

Borehole-sealing solidified material plays a significant role in improving sealing quality and enhancing gas drainage performance. In this study, the MTS815 electro-hydraulic triaxial servo test system and MR-60 NMR test system were adopted to conduct triaxial compression control experiment on the coal sample material, concrete material, and new solidified sealing material, respectively. This paper aims to analyze the difference of support effects, porosity, and stress sensitivity between those materials. Experimental results show that under the same stress condition, the stiffness of traditional concrete solidified material is the largest, while the new solidified material is the second, and the coal sample material is the smallest. Compared with the traditional concrete solidified material, the new solidified sealing material has better strain-bearing capacity and volumetric expansion capacity under each confining pressure in the experiment. The axial strain and volume increment of new solidified material is higher than those of the traditional concrete solidified material at the peak stress. Meanwhile, the confining pressure has a certain hysteresis effect on the postpeak stress attenuation. Fracture has the strongest stress sensitivity in three pore types, and its T2 map relaxation area has a larger compression than adsorption pore and seepage pore under the same pressure. The relative content of seepage pore and fracture in the new solidified material is less than that of coal and concrete samples, and the stress sensitivity of the new solidified materials is weaker than that of coal and concrete materials, thence, new solidified material will have better performance in borehole sealing. Outcomes of this study could provide guidance on the selection of the most effective sealing materials for sealing-quality improvement.

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