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.

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 Mechanical Characteristics of Coal Samples under Triaxial Unloading Pressure with Different Test Paths

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Yang Zhang ◽  
Yongjie Yang ◽  
Depeng Ma
Keyword(s):  
Axial Strain ◽  
Triaxial Compression ◽  
Axial Loading ◽  
Peak Stress ◽  
Friction Angle ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Compression Tests ◽  
Leading Role ◽  
Unloading Rate

In order to understand the influence of unloading path on the mechanical properties of coal, triaxial unloading confining pressure tests with different initial confining pressure and different unloading rate were carried out. The test results show that the triaxial unloading strength of coal samples under different test conditions is lower than conventional triaxial tests, but the brittleness characteristics are more obvious. This result indicates that the coal samples are easily damaged under unloading conditions. In the axial loading stage of the confinement unloading tests, the axial strain plays a leading role. However, during the confining pressure unloading stage, the circumferential deformation is large, which is the main deformation in this stage. Higher unloading rates of confining pressure are associated with shorter times between the peak stress position and sample complete failure. This shows that samples are more easily destroyed under higher unloading rates and the samples are more difficultly destroyed under lower unloading rates. In addition, with increasing unloading rate, the peak principal stress difference and confining pressure at failure decrease gradually, whereas the confining pressure difference at failure increases gradually. Compared with conventional triaxial compression tests, the cohesion of coal is reduced and the internal friction angle is increased under the condition of triaxial unloading test.

scholarly journals Study on the variation of physical and mechanical characteristics under freeze-thaw condition

2020 ◽  
Vol 165 ◽  
pp. 03021
Author(s):  
Tian Yanzhe
Keyword(s):  
Compressive Strength ◽  
Elastic Modulus ◽  
Axial Strain ◽  
Triaxial Compression ◽  
Physical And Mechanical Properties ◽  
Peak Stress ◽  
Friction Angle ◽  
Confining Pressure ◽  
Freeze Thaw ◽  
Triaxial Compressive Strength

Subjected to freeze-thaw cycles, the deformation of physical and mechanical properties is the main cause of engineering disasters. Based on the analysis of the results of triaxial compression test after different freeze-thaw cycles, conclusions are drawn that: under the certain freeze-thaw cycles conditions, with the increase of confining pressure, the triaxial compressive strength, elastic modulus and the axial strain increase gradually, indicating that the failure of rock changes from brittle failure to plastic failure; in the case of same confining pressure, with the increase of the number of freeze-thaw cycles, the triaxial compressive strength,elastic modulus of rock decreases and the axial strain corresponding to peak stress gradually increase. With the increase of the number of freeze-thaw cycles, the cohesion of grit is in the form of exponentially decays to reduce,the internal friction angle changes very little.

scholarly journals Microcracking and the failure of polycrystalline ice under triaxial compression

1992 ◽  
Vol 38 (128) ◽  
pp. 65-76 ◽  
Author(s):  
P. Kalifa ◽  
G. Ouillon ◽  
P. Duval
Keyword(s):  
Triaxial Compression ◽  
Peak Stress ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Strain History ◽  
Compression Tests ◽  
Brittle Transition ◽  
Polycrystalline Ice ◽  
Strain Components

AbstractTriaxial and uniaxial compression tests have been carried out at –10°C on granular ice in order to study the role of microcracking on failure in the ductile-brittle transition zone. In the triaxial tests, the effect of confining pressure and strain rate on the crack population, as well as on strength and strain at the peak stress, was investigated. In the uniaxial tests, we measured the evolution of elastic and non-elastic components of deformation with the stress-strain history. The concept of effective stress, with a single scalar damage variable, was used to calculate the effect of microcracking on the strain components.

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.

Small-strain behavior of frozen sand in triaxial compression

1995 ◽  
Vol 32 (3) ◽  
pp. 428-451 ◽  
Author(s):  
Glen R. Andersen ◽  
Christopher W. Swan ◽  
Charles C. Ladd ◽  
John T. Germaine
Keyword(s):  
High Pressure ◽  
Strain Rate ◽  
Yield Stress ◽  
Axial Strain ◽  
Triaxial Compression ◽  
Strain Curve ◽  
Confining Pressure ◽  
Stress Strain ◽  
Strain Behavior ◽  
Frozen Sand

The stress–strain behavior of frozen Manchester fine sand has been measured in a high-pressure low-temperature triaxial compression testing system developed for this purpose. This system incorporates DC servomotor technology, lubricated end platens, and on-specimen axial strain devices. A parametric study has investigated the effects of changes in strain rate, confining pressure, sand density, and temperature on behavior for very small strains (0.001%) to very large (> 20%) axial strains. This paper presents constitutive behavior for strain levels up to 1%. On-specimen axial strain measurements enabled the identification of a distinct upper yield stress (knee on the stress–strain curve) and a study of the behavior in this region with a degree of precision not previously reported in the literature. The Young's modulus is independent of strain rate and temperature, increases slightly with sand density in a manner consistent with Counto's model for composite materials, and decreases slightly with confining pressure. In contrast, the upper yield stress is independent of sand density, slightly dependent on confining pressure (considered a second order effect), but is strongly dependent on strain rate and temperature in a fashion similar to that for polycrystalline ice. Key words : frozen sand, high-pressure triaxial compression, strain rate, temperature, modulus, yield stress.

scholarly journals Method Improvement and Effect Analysis of Triaxial Compression Acoustic Emission Test for Coal and Rock

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Yan Zhou ◽  
Chuanxiao Liu ◽  
Depeng Ma
Keyword(s):  
Acoustic Emission ◽  
Rock Mechanics ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Outer Wall ◽  
Test System ◽  
Test Method ◽  
Effect Analysis ◽  
High Confining Pressure ◽  
Ae Signals

In the study of the acoustic emission (AE) characteristics of rock samples or coal samples under triaxial compression conditions, most scholars carry out relevant experiments by placing the AE detector on the outer wall of the triaxial chamber of the rock mechanics test system. Owing to the continuous obstruction of AE signals by hydraulic oil in the triaxial chamber and the frequent interference of external noises, the final experimental data cannot objectively and truly reflect the essential characteristics of AE of rock or coal under triaxial compression conditions. It is difficult to scientifically guide and accurately predict precursory information of rock’s or coal’s rupture and instability. Based on this, a series of improvements and optimizations were made to the original triaxial compression AE test method, which is based on the modification of the communication interface of the rock mechanics test system, a test head which can put the AE detector into the triaxial chamber and withstands high confining pressure, in order to obtain the true, comprehensive, and reliable AE signals. It is of considerable significance to the scientific determination of the precursory characteristics of rock’s or coal’s rupture and instability.

Effects of Confining Pressure on Gas and Water Permeabilities of Rocks

2000 ◽  
Vol 663 ◽  
Author(s):  
M. Zhang ◽  
M. Takeda ◽  
T. Esaki ◽  
M. Takahashi ◽  
H. Endo
Keyword(s):  
Rock Specimen ◽  
Pulse Method ◽  
Confining Pressure ◽  
Great Depth ◽  
Test System ◽  
Saturated Rock ◽  
Underground Disposal ◽  
High Confining Pressure ◽  
Confining Pressures ◽  
The Difference

ABSTRACTKnowledge of the permeability of hydraulically-tight rock at great depth is crucially important for the design and/or assessment of facilities associated with underground disposal of radioactive nuclear wastes. This paper presents a recently developed laboratory permeability test system capable of testing low permeability rocks either by using air as a permeant or by the transient-pulse method under high confining pressure conditions that simulate ground pressures at depths. The new system was used to test Shirahama sandstone and Inada granite, which are two types of rock widely available in Japan. To investigate the effects of heterogeneity on rock permeability, specimens cored parallel to and perpendicular to bedding for sandstone, and specimens cored in the direction perpendicular to Rift Plane, Grain Plane and Hardway Plane for granite, were used. The results of this study showed that: 1) gas permeabilities of a dried rock specimen tested by air permeation are almost the same values as water permeabilities of the same saturated rock specimen tested by the transient-pulse method; 2) the intrinsic permeabilities of Shirahama sandstone and Inada granite range from about 8.33E-16 to 7.38E-17 m2 and from 1.86E-17 to 6.94E-20 m2, respectively. They decrease monotonously with increase in effective confining pressure (defined as the difference between the confining and pore pressures), while the rate of decrease diminishes at higher confining pressures. The reduction in permeabilities is due to the closure of microcracks that control fluid flow at low confining pressures; and 3) Inada granite is a heterogeneous and isotropic material. Its hydraulic heterogeneity is more significant in Rift Plane than in Hardway and Grain Planes.

scholarly journals A Strain-Based Percolation Model and Triaxial Tests to Investigate the Evolution of Permeability and Critical Dilatancy Behavior of Coal

Processes ◽  
2018 ◽  
Vol 6 (8) ◽  
pp. 127 ◽  
Author(s):  
Dongjie Xue ◽  
Jie Zhou ◽  
Yintong Liu ◽  
Sishuai Zhang
Keyword(s):  
Axial Strain ◽  
Triaxial Compression ◽  
Sudden Change ◽  
Volumetric Strain ◽  
Confining Pressure ◽  
Percolation Model ◽  
Triaxial Tests ◽  
Transition Behavior ◽  
Orthogonal Experiments ◽  
Stress Dependent

Modeling the coupled evolution of strain and CH4 seepage under conventional triaxial compression is the key to understanding enhanced permeability in coal. An abrupt transition of gas-stress coupled behavior at the dilatancy boundary is studied by the strain-based percolation model. Based on orthogonal experiments of triaxial stress with CH4 seepage, a complete stress-strain relationship and the corresponding evolution of volumetric strain and permeability are obtained. At the dilatant boundary of volumetric strain, modeling of stress-dependent permeability is ineffective when considering the effective deviatoric stress influenced by confining pressure and pore pressure. The computed tomography (CT) analysis shows that coal can be a continuous medium of pore-based structure before the dilatant boundary, but a discontinuous medium of fracture-based structure. The multiscale pore structure geometry dominates the mechanical behavior transition and the sudden change in CH4 seepage. By the volume-covering method proposed, the linear relationship between the fractal dimension and porosity indicates that the multiscale network can be a fractal percolation structure. A percolation model of connectivity by the axial strain-permeability relationship is proposed to explain the transition behavior of volumetric strain and CH4 seepage. The volumetric strain on permeability is illustrated by axial strain controlling the trend of transition behavior and radical strain controlling the shift of behavior. A good correlation between the theoretical and experimental results shows that the strain-based percolation model is effective in describing the transition behavior of CH4 seepage in coal.

Laboratory Measurement of Low-Permeability Rocks With a New Flow Pump System

1997 ◽  
Vol 506 ◽  
Author(s):  
Ming Zhang ◽  
Manabu Takahashi ◽  
Tetsuro Esaki
Keyword(s):  
Pore Pressure ◽  
Fluid Pressure ◽  
Confining Pressure ◽  
Test System ◽  
Low Permeability ◽  
Specific Storage ◽  
Pump System ◽  
The Difference ◽  
Host Rocks ◽  
Flow Pump

ABSTRACTNearly impermeable host rocks have been recognized as favorable media for many kinds of underground utilization such as radioactive nuclear waste disposal, storage of oil and LP gas, and CAES. To properly evaluate the ability of a geologic medium to retard transmission of fluids, it is necessary to accurately measure its hydraulic properties, most notably the permeability and specific storage. This paper presents a new flow pump permeability test system capable of testing low-permeability rocks under high confining and high pore pressure conditions, which simulate ground pressures at large depths. The new system was used to test the Inada Granite from Japan. The results of present study show that: 1) both permeability and specific storage of the rock are dependent not only on the confining pressure but also on the pore pressure. They decrease with the increment of the effective confining pressure, i.e., the difference between confining and pore pressures; 2) the permeability and specific storage of Inada Granite range from 10−11 to 10−12 cm/s and 10−6 to 10−7 1/cm, respectively. The flow pump technique with its rigorous theoretical analysis can be used to effectively obtain such low permeabilities within several tens of hours; 3) the storage capacity of flow pump system itself decreases with the increment of fluid pressure within the permeating system.

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