Impurity Effects on the Mechanical Properties and Permeability Characteristics of Salt Rock

Impure salt rock strata are extensively distributed in China, giving them great significance in the study of the physical properties of impure salt rock for the construction of underground gas storage in salt mines. To investigate the confining pressure and impurity effects on the mechanical properties and gas permeability characteristics of salt rock, permeability tests under hydrostatic confining pressure and conventional triaxial compression (CTC), on salt rock samples with different impurity contents, were carried out. The results demonstrate that the confining pressure effects cause an increase in triaxial compression strength, but a decrease in permeability. However, impurity enhances the bearing capacity and permeability of the salt rock; both rock strength and permeability increase with an increase in impurity content. Moreover, the broken salt rock specimens were analyzed after the CTC test using Computed Tomography (CT) equipment. To understand the relationships between pore volume and permeability, considering the confining pressure and impurity effects, the cracks were divided into four groups according to different crack diameter ranges: ~0.05 mm, 0.05–1 mm, 1–10 mm and ~10 mm. The CT analysis results show that while the pore volume of smaller cracks shows an “increasing–decreasing” trend by increasing confining pressure, the pore volume of large cracks gradually decreases, indicating that the rock permeability is highly related to macro-cracks. However, impurity has more complicated implications on rock permeability and cracks, and needs further investigation.

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Study on mechanical properties and damage evolution of carbonaceous shale under triaxial compression with acoustic emission

International Journal of Damage Mechanics ◽

10.1177/1056789521991193 ◽

2021 ◽

pp. 105678952199119

Author(s):

Kai Yang ◽

Qixiang Yan ◽

Chuan Zhang ◽

Wang Wu ◽

Fei Wan

Keyword(s):

Mechanical Properties ◽

Acoustic Emission ◽

Water Content ◽

Damage Evolution ◽

Damage Assessment ◽

Triaxial Compression ◽

Confining Pressure ◽

Damage Variable ◽

Natural State ◽

Carbonaceous Shale

To explore the mechanical properties and damage evolution characteristics of carbonaceous shale with different confining pressures and water-bearing conditions, triaxial compression tests accompanied by simultaneous acoustic emission (AE) monitoring were conducted on carbonaceous shale rock specimens. The AE characteristics of carbonaceous shale were investigated, a damage assessment method based on Shannon entropy of AE was further proposed. The results suggest that the mechanical properties of carbonaceous shale intensify with increasing confining pressure and degrade with increasing water content. Moisture in rocks does not only weaken the cohesion but also reduce the internal friction angle of carbonaceous shale. It is observed that AE activities mainly occur in the post-peak stage and the strong AE activities of saturated carbonaceous shale specimens appear at a lower normalized stress level than that of natural-state specimens. The maximum AE counts and AE energy increase with water content while decrease with confining pressure. Both confining pressure and water content induce changes in the proportions of AE dominant frequency bands, but the changes caused by confining pressure are more significant than those caused by water content. The results also indicate that AE entropy can serve as an applicable index for rock damage assessment. The damage evolution process of carbonaceous shale can be divided into two main stages, including the stable damage development stage and the damage acceleration stage. The damage variable increases slowly accompanied by a few AE activities at the first stage, which is followed by a rapid growth along with intense acoustic emission activities at the damage acceleration stage. Moreover, there is a sharp rise in the damage evolution curve for the natural-state specimen at the damage acceleration stage, while the damage variable develops slowly for the saturated-state specimen.

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Damage evolution and recrystallization enhancement of frozen loess

International Journal of Damage Mechanics ◽

10.1177/1056789517731138 ◽

2017 ◽

Vol 27 (8) ◽

pp. 1131-1155 ◽

Cited By ~ 21

Author(s):

Zhiwei Zhou ◽

Wei Ma ◽

Shujuan Zhang ◽

Cong Cai ◽

Yanhu Mu ◽

...

Keyword(s):

Mechanical Properties ◽

Strain Rate ◽

Damage Evolution ◽

Deformation Process ◽

Triaxial Compression ◽

Confining Pressure ◽

Recrystallization Process ◽

Frozen Soils ◽

Time Deformation ◽

Pressure Melting

A series of multistage triaxial compression, creep, and stress relaxation tests were conducted on frozen loess at the temperature of −6℃ in order to study the damage evolution and recrystallization enhancement of mechanical properties during deformation process. The effect of strain rate, confining pressure, and hydrostatic stress history in the degradation laws of mechanical properties is investigated further. The strain rate has a significant influence on the stress–strain curve which dominates the evolution trend of mechanical properties. The mechanical behaviors (strength, stiffness, and viscosity) of frozen loess all exhibit evident response for the consolidation and pressure melting phenomenon caused by the confining pressure. The multistage loading tests under different hydrostatic stresses are capable of differentiating the development characteristics of mechanical properties during axial loading and hydrostatic compression process, respectively. The testing results indicated that the recrystallization of the ice particle in the frozen soils is an important microscopic factor for enhancement behaviors of mechanical parameters during the deformation process. This strengthening degree of mechanical properties is determined by temperature, duration time, deformation degree, and stress state during the recrystallization process. The phase transformation led by pressure melting and ice recrystallization is a nonnegligible changing pattern of frozen soils microstructure, which has apparent role in the damage evolution of mechanical properties.

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Cracking Behaviors and Mechanical Properties of Rock-Like Specimens with Two Unparallel Flaws under Conventional Triaxial Compression

Advances in Civil Engineering ◽

10.1155/2019/5849703 ◽

2019 ◽

Vol 2019 ◽

pp. 1-15 ◽

Cited By ~ 1

Author(s):

Huilin Le ◽

Shaorui Sun ◽

Chenghua Xu ◽

Liuyang Li ◽

Yong Liu

Keyword(s):

Mechanical Properties ◽

Inclination Angle ◽

Failure Modes ◽

Shear Failure ◽

Triaxial Compression ◽

Confining Pressure ◽

Critical Value ◽

Tensile Failure ◽

Rock Bridge ◽

Bridge Length

Flaws existing in rock masses are generally unparallel and under three-dimensional stress; however, the mechanical and cracking behaviors of the specimens with two unparallel flaws under triaxial compression have been rarely studied. Therefore, this study conducted comprehensive research on the cracking and coalescence behavior and mechanical properties of specimens with two unparallel flaws under triaxial compression. Triaxial compressive tests were conducted under different confining pressures on rock-like specimens with two preexisting flaws but varying flaw geometries (with respect to the inclination angle of the two unparallel flaws, rock bridge length, and rock bridge inclination angle). Six crack types and eleven coalescence types in the bridge region were observed, and three types of failure modes (tensile failure, shear failure, and tensile-shear failure) were observed in experiments. Test results show that bridge length and bridge inclination angle have an effect on the coalescence pattern, but the influence of bridge inclination angle is larger than that of the bridge length. When the confining pressure is low, coalescence patterns and failure modes of the specimens are greatly affected by flaw geometry, but when confining pressure rose to a certain level, the influence of confining pressure is larger than the effect of flaw geometry. The peak strength of the specimens is affected by flaw geometry and confining pressure. There is a critical value for the bridge length. If the bridge length is larger than the critical value, peak strengths of the samples almost keep constant as the bridge length increases. In addition, as the bridge inclination angle increases, there is an increase in the probability of tensile cracks occurring, and with an increase in the confining pressure, the probability of the occurrence of shear cracks increases.

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Effect of Impurity Content on Elastic Modulus and Poisson Ratio of Salt Rock

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.204-208.467 ◽

2012 ◽

Vol 204-208 ◽

pp. 467-470

Author(s):

Xian Lei Zong ◽

Chun He Yang ◽

Jiang Jiang Zuo ◽

Jing Bin Xu ◽

Guo Dong Ji

Keyword(s):

Elastic Modulus ◽

Poisson Ratio ◽

Impurity Content ◽

Single Layer ◽

Confining Pressure ◽

Mechanical Parameters ◽

Salt Rock ◽

Estimation Formula ◽

Experimental Values ◽

Basic Features

The basic features of salt rock in China are as follows: thickness single layer, more layered distribution and impurities and others. The unstable mechanical parameters are caused by the different types and content of minerals in natural salt rock. Elastic modulus and Poisson ratio of natural samples from certain northern area in China which are compressed under different confining pressure is then analysed with the impurity content to get the relationship between them. Comparing the experimental values with the predicted calculated by Mori-Tanaka method, a linear estimation formula is proposed for the prediction of mechanical parameters suitable for practical engineering applications in this area.

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Mechanical Properties of Bentonite-Sand Mixtures Under Triaxial Stress Condition

MRS Proceedings ◽

10.1557/proc-353-307 ◽

1994 ◽

Vol 353 ◽

Cited By ~ 1

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.

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

Tyumen State University Herald Physical and Mathematical Modeling Oil Gas Energy ◽

10.21684/2411-7978-2021-7-2-130-146 ◽

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.

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

Shock and Vibration ◽

10.1155/2019/4909534 ◽

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.

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Prefabricated Structures Surface Marble Rheological Tests and Constitutive Model Analysis

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.501-504.419 ◽

2014 ◽

Vol 501-504 ◽

pp. 419-425

Author(s):

Qing Xu ◽

Jiang Da He ◽

Hong Qiang Xie ◽

Ming Li Xiao ◽

Jian Feng Liu

Keyword(s):

Mechanical Properties ◽

Rheological Properties ◽

Flow Rate ◽

Axial Stress ◽

Triaxial Compression ◽

Confining Pressure ◽

Rheological Parameters ◽

Structural Plane ◽

High Confining Pressure ◽

Confining Pressures

The mechanical properties of intact rock and rock containing structural plane are very different. From the diversion tunnel of Jinping deep rock site to retrieve the complete block of marble, after a high confining pressure triaxial compression simulation tectonic movements, the formation of structural plane, it represents the mechanical properties of the original rock. On the surface of the marble structure containing triaxial compression creep tests, the results showed: at low confining pressure, the weak marble surface as micro-damage accumulation, the emergence of non-uniform partial destruction, while at high confining pressure, creep curve better continuity and integrity; different confining pressures, marble initial rheology and stability both appear rheological phase, accelerated phase rheological obvious; different confining pressures, the same stage of the axial stress steady flow rate compared with the confining pressure increases, the axial steady state flow rate becomes smaller; marble under test showed the rheological properties, the use of Nishihara model can better demonstrate the rheological properties and determine the rheological parameters for other practical engineering reference.

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Experimental Investigation of the Influence of the Adsorption Gas on the Permeability Characteristics of the Coal Containing Gas

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.616-618.190 ◽

2012 ◽

Vol 616-618 ◽

pp. 190-196

Author(s):

Deng Ke Wang ◽

Jian Ping Wei ◽

Le Wei ◽

Heng Jie Qin

Keyword(s):

Coal Sample ◽

Gas Adsorption ◽

Triaxial Compression ◽

Axial Loading ◽

Experimental System ◽

Confining Pressure ◽

Gas Pressure ◽

Permeability Characteristics ◽

Gas Seepage ◽

Loading Case

A large number of laboratory experiments on the gas seepage characteristics by the self-developed gas-bearing coal triaxial compression experimental system and conducts the comparative analysis of the similarities and differences of the permeability among CO2, CH4 and N2. The results show that given the condition of constant gas pressure, the permeability of the coal sample decreases with the increase of the confining pressure; under the constant confining pressure, the permeability of the coal sample decreases with the increase of the gas pressure; gases of different adsorbabilities have different permeabilities. The stronger the gas adsorption is, the worse its permeability will be; in the axial loading case, the permeabilities of different gases all reduce firstly and increase afterward, showing the generally V-shaped variation law. The results are of certain theoretical values on the in-depth understanding of the migration law of the gas in coal seams.

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Gas Permeability Change with Deformation and Cracking of a Sandstone under Triaxial Compression

10.21203/rs.3.rs-392045/v1 ◽

2021 ◽

Author(s):

Yuan-Jian LIN ◽

Jiang-Feng LIU ◽

Tao CHEN ◽

Shi-Jia MA ◽

Pei-Lin WANG ◽

...

Keyword(s):

Gas Permeability ◽

Axial Stress ◽

Triaxial Compression ◽

Gas Injection ◽

Injection Pressure ◽

Confining Pressure ◽

Loading Path ◽

Permeability Evolution ◽

Axial Pressure ◽

Triaxial Cell

Abstract In this paper, a THMC multi-field coupling triaxial cell was used to systematically study the evolution of gas permeability and the deformation characteristics of sandstone. The effects of confining pressure, axial pressure and air pressure on gas permeability characteristics were fully considered in the test. The gas permeability of sandstone decreases with increasing confining pressure. When the confining pressure is low, the variation of gas permeability is greater than the variation of gas permeability at high confining pressure. The gas injection pressure has a significant effect on the gas permeability evolution of sandstone. As the gas injection pressure increases, the gas permeability of sandstone tends to decrease. At the same confining pressure, the gas permeability of the sample during the unloading path is less than the gas permeability of the sample in the loading path. When axial pressure is applied, the axial stress has a significant influence on the permeability evolution of sandstone. When the axial pressure is less than 30 MPa, the gas permeability of the sandstone increases as the axial pressure increases. At axial pressures greater than 30 MPa, the permeability decreases as the axial pressure increases. Finally, the micro-pore/fracture structure of the sample after the gas permeability test was observed using 3D X-ray CT imaging.

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