scholarly journals Experimental Study of the Effect of High Temperature on the Mechanical Properties of Coarse Sandstone

2019 ◽  
Vol 9 (12) ◽  
pp. 2424 ◽  
Author(s):  
Sijiang Wei ◽  
Yushun Yang ◽  
Chengdong Su ◽  
Syabilla Rachmadina Cardosh ◽  
Hao Wang
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Rock Strength ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Temperature Threshold ◽  
Compression Tests ◽  
Fracture Angle ◽  
Different Temperatures ◽  
Actual Fracture

In order to study the effect of high temperature on the mechanical properties of rock, two groups of coarse sandstone samples were subjected to the uniaxial compression and triaxial compression test at room temperature of 25 °C and high temperatures of 100~1000 °C. The study comes to some conclusions: (1) With the increase of temperature, the longitudinal wave velocity gradually decreases, and the damage factor of temperature gradually increases. (2) For uniaxial compression tests at different temperatures, the high temperature action within 500 °C has a strengthening effect on the compression strength, and the high temperature effect has a weakening effect on the compression strength when temperatures exceed 500 °C; so 500 °C is the temperature threshold. (3) For triaxial compression tests at different temperatures, the rock strength is positively correlated with temperature and confining pressure when the temperature is lower than 800 °C and the confining pressure is lower than 15 MPa; the rock strength is negatively correlated with temperature and confining pressure when the temperature is over 800 °C and confining pressure is above 15 MPa, so 800 °C is the temperature threshold, and 15 MPa is the confining pressure threshold. (4) In the triaxial compression, the actual fracture angle of the sample after high temperature is basically the same as the theoretical calculation value, high temperature has little effect on the actual fracture angle of the sample, and the actual fracture angle is negatively correlated with the confining pressure.

scholarly journals Study on Mechanical Behavior of Jurassic Frozen Sandstone in Western China Based on NMR Porosity

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Maoyan Ma ◽  
Yishun Huang ◽  
Guangyong Cao ◽  
Jian Lin ◽  
Shiliang Xu
Keyword(s):  
Mechanical Properties ◽  
Growth Rate ◽  
Low Temperature ◽  
Rock Strength ◽  
Tracking System ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Western China ◽  
Compression Tests ◽  
Rock Mechanical Properties

Study of frozen rock mechanical properties is necessary for safe application of the artificial ground freezing method in excavation of Chinese western water-rich soft rock layers. Triaxial compression tests and NMR test for samples from the western Jurassic sandstone were performed to investigate rock mechanical properties affected by low temperature and confining pressure. The results show mechanical parameters such as peak strength, cohesion, internal friction angle, residual strength, and elasticity modulus increased with the decreasing temperature under stable pressure, and the above parameters increased with the increasing confining pressure at a certain temperature. In particular, the growth rate of the rock strength would decline when the temperature was below −10°C in this study. Strength attenuation coefficients increased with the decreasing temperature, which indicated higher brittleness, whereas plastic characters got more obvious with the increasing confining pressure at a stable temperature. Furthermore, during the first two freezing stages, porosity decreased sharply with obvious increase of pore (crack) ice content, while porosity varied little at the third stage, which was the reason for the growth rate of rock strength declining with continuous low temperature from microcosmic point of view.

scholarly journals A Thermal Damage Constitutive Model for Oil Shale Based on Weibull Statistical Theory

2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Guijie Zhao ◽  
Chen Chen ◽  
Huan Yan
Keyword(s):  
High Temperature ◽  
Constitutive Model ◽  
Oil Shale ◽  
Thermal Damage ◽  
Triaxial Compression ◽  
Strain Curve ◽  
Practical Significance ◽  
Compression Tests ◽  
Different Temperatures ◽  
Damage Constitutive Model

In this work, we first studied the thermal damage to typical rocks, assuming that the strength of thermally damaged rock microelements obeys a Weibull distribution and considering the influence of temperature on rock mechanical parameters; under the condition that microelement failure conforms to the Drucker–Prager criterion, the statistical thermal damage constitutive model of rocks after high-temperature exposure was established. On this basis, conventional triaxial compression tests were carried out on oil shale specimens heated to different temperatures, and according to the results of these tests, the relationship between the temperature and parameters in the statistical thermal damage constitutive model was determined, and the thermal damage constitutive model for oil shale was established. The results show that the thermal damage in oil shale increases with the increase of temperature; the damage variable is largest at 700°C, reaching 0.636; from room temperature to 700°C, the elastic modulus and Poisson’s ratio decrease by 62.66% and 64.57%, respectively; the theoretical stress-strain curve obtained from the model is in good agreement with the measured curves; the maximum difference between the two curves before peak strength is only 5 × 10−4; the model accurately reflects the deformation characteristics of oil shale at high temperature. The research results are of practical significance to the underground in situ thermal processing of oil shale.

Mechanical Properties of Bentonite-Sand Mixtures Under Triaxial Stress Condition

1994 ◽  
Vol 353 ◽  
Author(s):  
M. Umedera ◽  
A. Fujiwara ◽  
N. Yasufuku ◽  
M. Hyodo ◽  
H. Murata
Keyword(s):  
Mechanical Properties ◽  
Shear Strength ◽  
Water Content ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Strength Properties ◽  
Compression Tests ◽  
Optimum Water Content ◽  
Triaxial Compression Tests ◽  
Optimum Water

AbstractA series of triaxial compression tests is being conducted under the drained condition on bentonite and sand mixtures, known as buffer, in saturated and optimum water content states to clarify the mechanical properties of the buffer.It was found that the mechanical properties of bentonite and sand mixtures are strongly influenced by water and bentonite contents: shear strength in a saturated state is less than that in an optimum water content state; shear strength decreases rapidly with increasing bentonite content. Strength properties are much dependent on confining pressure.

IMPACT OF WATER AND CO2 ON THE MECHANICAL PROPERTIES OF LOW PERMEABLE ROCKS

2021 ◽  
Vol 7 (2) ◽  
pp. 130-146
Author(s):  
Anatolii A. KISLITSYN ◽  
Nikita V. Lipatov
Keyword(s):  
Mechanical Properties ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Strength Properties ◽  
Pore Fluid ◽  
Co2 Injection ◽  
Core Samples ◽  
Different Temperatures ◽  
Confining Pressures ◽  
Temporary Decrease

This article features experiments on triaxial compression of low-permeable dolomite samples with different confining pressures (2-20 MPa), different pore fluids (dry air, water, CO2), and different temperatures (25-150 °C). The authors have studied the effect of confining pressure, pore fluid and temperature on the strength properties of the studied samples. The results show an increase in the strength with grwoing confining pressure. When the confining pressure increases from 2 to 20 MPa, the compressive strength increases from 86 to 370 MPa. Temperature has a significant effect on rock strength under low confining pressure conditions. With the increasing confining pressure reaching 15 MPa, increasing temperature has little effect on the strength of dolomite samples. Under an effective confining pressure of 5 MPa, the temperature weakening occurs on the dolomite specimens when the temperature exceeds 90 °C. During compression, liquid diffusion occurs in the specimens. Higher water viscosity can cause a temporary decrease in effective confining pressure, which can increase the strength of the rock. More prominent fractures are observed in the samples, and more fluid is injected under CO2 injection conditions, which may be useful for increasing the permeability of the geothermal reservoir. Two groups of experiments have been performed on the samples in this study: the first group of experiments investigated the effect of confining pressure on the fracture stress of core samples, without pore fluid injection; the second group of experiments investigated the effect of water or CO2 and temperature on the mechanical properties of core samples.

scholarly journals Experimental Investigation on Failure Modes and Mechanical Properties of Rock-Like Specimens with a Grout-Infilled Flaw under Triaxial Compression

2019 ◽  
Vol 2019 ◽  
pp. 1-14
Author(s):  
Huilin Le ◽  
Shaorui Sun ◽  
Feng Zhu ◽  
Haotian Fan
Keyword(s):  
Mechanical Properties ◽  
Rock Mass ◽  
Epoxy Resin ◽  
Failure Modes ◽  
Shear Failure ◽  
Fractured Rock ◽  
Triaxial Compression ◽  
Friction Angle ◽  
Confining Pressure ◽  
Compression Tests

Flaws existing in rock mass are one of the main factors resulting in the instability of rock mass. Epoxy resin is often used to reinforce fractured rock mass. However, few researches focused on mechanical properties of the specimens with a resin-infilled flaw under triaxial compression. Therefore, in this research, epoxy resin was selected as the grouting material, and triaxial compression tests were conducted on the rock-like specimens with a grout-infilled flaw having different geometries. This study draws some new conclusions. The high confining pressure suppresses the generation of tensile cracks, and the failure mode changes from tensile-shear failure to shear failure as the confining pressure increases. Grouting with epoxy resin leads to the improvement of peak strengths of the specimens under triaxial compression. The reinforcement effect of epoxy resin is better for the specimens having a large flaw length and those under a relatively low confining pressure. Grouting with epoxy resin reduces the internal friction angle of the samples but improves their cohesion. This research may provide some useful insights for understanding the mechanical behaviors of grouted rock masses.

Experimental Research of Fine Sandstone Strength and Deformation Characteristics under Different Confining and Hydraulic Pressure

2013 ◽  
Vol 353-356 ◽  
pp. 562-570 ◽  
Author(s):  
Zai Bin Liu
Keyword(s):  
Rock Strength ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Hydraulic Pressure ◽  
Compression Tests ◽  
Exponential Relationship ◽  
Sandstone Rock ◽  
Strength And Deformation

In order to study sandstone rock strength and deformation parameters under pore water pressure conditions, triaxial compression tests of different hydraulic pressure were executed. Fitting equations of fine sandstone confining pressure and hydraulic pressure coupling effects were established. This research show that fine sandstone rock strength increases with confining pressure increases. Rock mass strength and cohesion have negative exponential relationship with hydraulic pressure. When the hydraulic pressure is 3MPa, elasticity and confining pressure fit to logarithmic relationship. Fine sandstone Elasticity modulus decreases with hydraulic pressure increases. Poisson’s ration and hydraulic pressure fit to linear relationship.

scholarly journals Experimental Study on Rock-Like Specimens with Single Flaw under Hydro-Mechanical Coupling

2019 ◽  
Vol 9 (16) ◽  
pp. 3234 ◽  
Author(s):  
Jinquan Xing ◽  
Cheng Zhao ◽  
Songbo Yu ◽  
Hiroshi Matsuda ◽  
Chuangchuang Ma
Keyword(s):  
Mechanical Properties ◽  
Shear Failure ◽  
Water Pressure ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Tensile Failure ◽  
Compression Tests ◽  
Cracking Behavior ◽  
Mechanical Coupling ◽  
High Confining Pressure

In order to study the mechanical characteristics and cracking behavior of jointed rock mass under hydro-mechanical coupling, a series of uniaxial compression tests and triaxial compression tests were carried out on cylinder gypsum specimens with a single pre-existing flaw. Under different confining pressures, water pressure was injected on the pre-existing flaw surface through a water injection channel. The geometrical morphology and tensile or shear properties of the cracks were determined by X-ray computed tomography (CT) and scanning electron microscope (SEM). Based on the macro and micro observation, nine types of cracks that caused the specimen failure are summarized. The results of mechanical properties and crack behavior showed that the confining pressure inhibited the tensile cracks, and shear failure occurred under high confining pressure. The water pressure facilitated the initiation and extension of tensile crack, which made the specimens prone to tensile failure. However, under the condition of high confining pressure and low water pressure, the lubrication effect had a significant effect on the failure pattern, under which the specimens were prone to shear failure. This experimental research on mechanical properties and cracking behavior under hydro-mechanical coupling is expected to increase its fundamental understanding.

scholarly journals Effects of Water and scCO2 Injection on the Mechanical Properties of Granite at High Temperatures

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Nao Shen ◽  
Qiang Zhang ◽  
Xiaochun Li ◽  
Bing Bai ◽  
Haixiang Hu
Keyword(s):  
Mechanical Properties ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Pore Fluid ◽  
Reservoir Rock ◽  
Working Fluid ◽  
Co2 Injection ◽  
Enhanced Geothermal Systems ◽  
Different Temperatures ◽  
The Impact

Geothermal energy is an important resource to substitute for traditional fossil fuels. The mechanical properties of reservoir rock under the conditions of water and scCO2 injection at different temperatures are crucial for the safety of Enhanced Geothermal Systems. However, the effects of working fluid on the mechanical properties of granite at in situ temperatures are still rarely reported. To reveal the impact mechanisms, conventional triaxial compression experiments were conducted on granite specimens with different confining pressures (2–20 MPa), different pore fluid (10 MPa water or CO2), and different temperatures (25–150°C) in the present study. SEM analyses were applied to the specimens to determine failure surface morphologies after the experiments. The experimental results show that the effective confining pressure, pore fluid, and temperature have significant effects on the strength of granite specimens. The strength of granite increases with the increase of effective confining pressure, with similar granite strength under the same effective confining pressure (dry, water, and CO2). Temperature strengthening of granite is limited by high confining pressure (∼15 MPa). Under the effective confining pressure of 5 MPa, temperature weakening occurs on granite specimens when temperature is higher than 90°C. There is fluid diffusion in the specimens during compression. The higher viscosity of water may cause a temporary decrease in effective confining pressure, which may increase the strength of granite. The growth or formation of cracks is mainly observed in quartz and feldspar grains without short-term chemical effects. More visible cracks are observed on the specimens and more volume of fluid is injected under CO2 injection conditions, which may be beneficial to increase the permeability of geothermal reservoir.

Mechanical Properties of Sandstone under Loading and Unloading Conditions

2014 ◽  
Vol 852 ◽  
pp. 441-446 ◽  
Author(s):  
Xing Xia Wang ◽  
Wen Juan Ma ◽  
Jian Wen Huang ◽  
Zai Yi Liao
Keyword(s):  
Mechanical Properties ◽  
Triaxial Compression ◽  
Deformation Modulus ◽  
Confining Pressure ◽  
Rock Deformation ◽  
Test Results ◽  
Compression Tests ◽  
Triaxial Compressive Strength ◽  
Unloading Confining Pressure ◽  
Triaxial Compression Tests

The mechanical properties of rock mass under unloading conditions are essentially different from that under loading conditions. Triaxial compression tests and unloading confining pressure tests are conducted, and test results show that unloading failure is more brittle, and rock samples suffer more damage under unloading failure. The larger the initial confining pressure is, the easier of unloading failure is occurred. The increasing or decreasing values of rock deformation modulus under unloading conditions are within 10% of rock triaxial compressive strength. Unloading failure leads to deterioration of rock deformation modulus, which decreases gradually with confining pressure decreasing, and the decrease rates get bigger and bigger with unloading ratio of confining pressure increasing. Deformation modulus is only 24-34% of that under loading condition when rock strength goes down to residual strength.

Influence of Clay Mineral Content on the Mechanical Properties and Microfabrics of Tailings

2021 ◽  
Author(s):  
Chao Zhang ◽  
Zhenkai Pan ◽  
Changkun Ma ◽  
Lei Ma ◽  
Xueting Li
Keyword(s):  
Mechanical Properties ◽  
Mechanical Behavior ◽  
Clay Minerals ◽  
Clay Mineral ◽  
Mineral Content ◽  
Triaxial Compression ◽  
Clay Content ◽  
Nitrogen Adsorption ◽  
Confining Pressure ◽  
Compression Tests

Abstract Clay mineral content has an important influence on the mechanical behavior of tailings, and the mechanical behavior of tailings directly affects the stability of tailings dams. XRF and XRD tests were carried out on tailings from three different regions. The chemical and mineral compositions of the tailings are analyzed. The strength and failure deformation of tailings were studied by carrying out laboratory triaxial compression tests. The effect of clay content on the stress path of tailings was investigated. The microfabric of tailings samples was examined with scanning electron microscopy (SEM) and nitrogen adsorption tests. The results show that the confining pressure corresponding to the samples exhibiting strain hardening increases with increasing clay mineral content in the tailings. The cohesion of tailings increases linearly, and the specific surface area decreases as the content of clay minerals increases. Nitrogen adsorption test results reveal from a microscopic point of view that changes in pore structure are associated with the content of clay minerals. The higher the content of clay minerals is, the higher the proportion of micropores (aggregated interior). Macroscopically, the overall porosity decreases and the fineness of the pores increases with clay content, which will directly affect the mechanical properties of tailings.

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