Summary of collapsible behaviour of artificially structured loess in oedometer and triaxial wetting tests

2012 ◽  
Vol 49 (10) ◽  
pp. 1147-1157 ◽  
Author(s):  
Mingjing Jiang ◽  
Haijun Hu ◽  
Fang Liu
Keyword(s):  
Water Content ◽  
Experimental Studies ◽  
Stable State ◽  
Confining Pressure ◽  
Triaxial Apparatus ◽  
Stress Point ◽  
High Confining Pressure ◽  
Interparticle Bonding ◽  
Oedometer Tests ◽  
Natural Loess

This paper summarizes experimental studies on wetting-induced collapsibility in loess using single-oedometer, double-oedometer, and triaxial wetting tests. Artificially structural loess samples with interparticle bonding calcite (CaCO3) and a large void ratio were tested in the laboratory to avoid sampling disturbance of natural loess. The comparison between the single- and double-oedometer tests confirms that the wetting-induced deformation is independent of the sequence of wetting and loading. The conventional triaxial apparatus was enhanced for investigating the collapse deformation in response to different water content increments when subjected to different stress levels. The wetting-induced strain subjected to high confining pressure develops in two steps. It increases with increasing water content and reaches a relatively stable plateau, and then increases rapidly again until a final stable state is reached. The initial collapse surface was found by plotting the wetting-induced strain vectors observed in triaxial wetting tests. The wetting-induced strain is negligible when a specimen is wetted at a stress point inside this surface, while it becomes significant when wetted beyond this surface.

scholarly journals A novel triaxial apparatus to evaluate the effect of high temperature nitrogen injection concept and design

2021 ◽  
Vol 25 (6 Part B) ◽  
pp. 4527-4535
Author(s):  
Sheng-Cheng Wang ◽  
Ya-Nan Gao ◽  
Lan-Ying Huang ◽  
Hai-Jian Li ◽  
Shan-Jie Su
Keyword(s):  
High Temperature ◽  
Underground Mining ◽  
Confining Pressure ◽  
Maximum Pressure ◽  
Coal Seams ◽  
Nitrogen Gas ◽  
New Device ◽  
Nitrogen Injection ◽  
Triaxial Apparatus ◽  
High Confining Pressure

High temperature nitrogen, injection into coal seams is supposed to improve the per?meability and thus maintain the safety of underground mining. A novel triaxial appa?ratus is recently developed, aiming at providing the effective method to evaluate the effect of high temperature nitrogen injection. The main feature of this novel appara?tus is its high confining pressure, gas injection with high pressure as well as the high temperature. This new device can be either used for natural coal samples (e.g. intact or fractured) or the synthetic coal samples. A series of leakage tests were conducted to verify the feasibility of this instrument, the results of which have confirmed that the maximum pressure (i.e. 10 MPa) can be reached. In addition, the high temperature and pressure of nitrogen gas can also be sustain at the requested level. Based on the preliminary tests on the instrument, a large amount of tests were carried out to eval?uate the effect of nitrogen injection in enhancing the permeability of coking coal from the Pingdingshan coalfield, China, and the influence of high temperature nitrogen injection on mechanical parameters of coal was obtained.

Gas permeability of a compacted bentonite–sand mixture: coupled effects of water content, dry density, and confining pressure

2015 ◽  
Vol 52 (8) ◽  
pp. 1159-1167 ◽  
Author(s):  
Jiang-Feng Liu ◽  
Frédéric Skoczylas ◽  
Jean Talandier
Keyword(s):  
Water Content ◽  
Gas Permeability ◽  
Confining Pressure ◽  
Degree Of Saturation ◽  
Dry Density ◽  
Sand Mixture ◽  
Compacted Bentonite ◽  
High Confining Pressure ◽  
Confining Pressures ◽  
Gas Tightness

The gas-tightness of compacted bentonite–sand mixtures is important to the total sealing efficiency of geological repositories. The initial aim of this work was to determine whether the combination of a high confining pressure (Pc) and incomplete saturation could cause a bentonite–sand mixture to become gas-tight. The results show that the physical characteristics of the materials (degree of saturation, Sr; porosity, [Formula: see text]; and dry density, ρd) are very sensitive to changes in the applied confining pressures and their own swelling deformation (or shrinkage). The combination of these changes affects the sample’s effective gas permeability (Keff). For materials prepared at a relative humidity (RH) of 98%, Keff decreased from 10−16 to 10−20 m2 when Pc increased from 1 to 7 MPa. This means that gas-tightness can be obtained for a compacted bentonite–sand mixture when the materials experience a series of changes (e.g., w, Sr, [Formula: see text], and ρd). In addition, larger irreversible deformation (or hysteresis) was observed during the loading–unloading cycle for the sample with higher water content. This phenomenon may be attributed to larger interactions between the macrostructural and microstructural deformations and the decrease of preconsolidation pressure during hydration.

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

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.

Testing Study on the Effects of Water Content on Permeability for Coal

2014 ◽  
Vol 580-583 ◽  
pp. 201-204
Author(s):  
Chun Hui Zhang ◽  
Xiao Pan Xu
Keyword(s):  
Water Content ◽  
Pore Pressure ◽  
Coal Sample ◽  
Channel Wall ◽  
Confining Pressure ◽  
Liaoning Province ◽  
Air Drying ◽  
Slippage Effect

To obtain the effects of water content on the permeability of coal, briquette specimen were obtained from Wulong Mine, Liaoning Province. The permeability of the air drying, bounding water and saturating specimens were tested with self-made equipment respectively, and the effects of water content on permeability for coal were studied. The results showed that: (1)The permeability of specimens decreases with confining pressure increasing, and the air drying and bounding water specimens take on obvious slippage effect. However the saturated specimens never take on slippage effects. It is because the channels of saturated coal sample are occupied by water. When the gas goes through specimens, gas never is absorbed. Collision between gas and the channel wall decreases, and the slippage effect disappears. (2) With water content increasing, the permeability of specimens decreases. (3)The permeability of specimens increases when pore pressure increases.

scholarly journals Intragranular deformation mechanisms in calcite deformed by high-pressure torsion at room temperature

2020 ◽  
Vol 114 (2) ◽  
pp. 105-118
Author(s):  
Roman Schuster ◽  
Gerlinde Habler ◽  
Erhard Schafler ◽  
Rainer Abart
Keyword(s):  
High Pressure ◽  
Twin Boundary ◽  
Brittle Failure ◽  
Room Temperature ◽  
High Pressure Torsion ◽  
Confining Pressure ◽  
Temperature Deformation ◽  
Orientation Relationships ◽  
High Confining Pressure ◽  
Confining Pressures

AbstractPolycrystalline calcite was deformed to high strain at room-temperature and confining pressures of 1–4 GPa using high-pressure torsion. The high confining pressure suppresses brittle failure and allows for shear strains >100. The post-deformation microstructures show inter- and intragranular cataclastic deformation and a high density of mechanical e$$ \left\{01\overline{1}8\right\} $$011¯8 twins and deformation lamellae in highly strained porphyroclasts. The morphologies of the twins resemble twin morphologies that are typically associated with substantially higher deformation temperatures. Porphyroclasts oriented unfavorably for twinning frequently exhibit two types of deformation lamellae with characteristic crystallographic orientation relationships associated with calcite twins. The misorientation of the first deformation lamella type with respect to the host corresponds to the combination of one r$$ \left\{10\overline{1}4\right\} $$101¯4 twin operation and one specific f$$ \left\{01\overline{1}2\right\} $$011¯2 or e$$ \left\{01\overline{1}8\right\} $$011¯8 twin operation. Boundary sections of this lamella type often split into two separated segments, where one segment corresponds to an incoherent r$$ \left\{10\overline{1}4\right\} $$101¯4 twin boundary and the other to an f$$ \left\{01\overline{1}2\right\} $$011¯2 or e$$ \left\{01\overline{1}8\right\} $$011¯8 twin boundary. The misorientation of the second type of deformation lamellae corresponds to the combination of specific r$$ \left\{10\overline{1}4\right\} $$101¯4 and f$$ \left\{01\overline{1}2\right\} $$011¯2 twin operations. The boundary segments of this lamella type may also split into the constituent twin boundaries. Our results show that brittle failure can effectively be suppressed during room-temperature deformation of calcite to high strains if confining pressures in the GPa range are applied. At these conditions, the combination of successive twin operations produces hitherto unknown deformation lamellae.

scholarly journals Triaxial Testing of Geosynthetics Reinforced Tailings with Different Reinforced Layers

Materials ◽  
2020 ◽  
Vol 13 (8) ◽  
pp. 1943
Author(s):  
Fu Yi ◽  
Changbo Du
Keyword(s):  
Triaxial Compression ◽  
Friction Angle ◽  
Confining Pressure ◽  
Test Results ◽  
Compression Tests ◽  
Strength Index ◽  
Stress Strain ◽  
High Confining Pressure ◽  
Zhang Model ◽  
Triaxial Compression Tests

To evaluate the shear properties of geotextile-reinforced tailings, triaxial compression tests were performed on geogrids and geotextiles with zero, one, two, and four reinforced layers. The stress–strain characteristics and reinforcement effects of the reinforced tailings with different layers were analyzed. According to the test results, the geogrid stress–strain curves show hardening characteristics, whereas the geotextile stress–strain curves have strain-softening properties. With more reinforced layers, the hardening or softening characteristics become more prominent. We demonstrate that the stress–strain curves of geogrids and geotextile reinforced tailings under different reinforced layers can be fitted by the Duncan–Zhang model, which indicates that the pseudo-cohesion of shear strength index increases linearly whereas the friction angle remains primarily unchanged with the increase in reinforced layers. In addition, we observed that, although the strength of the reinforced tailings increases substantially, the reinforcement effect is more significant at a low confining pressure than at a high confining pressure. On the contrary, the triaxial specimen strength decreases with the increase in the number of reinforced layers. Our findings can provide valuable input toward the design and application of reinforced engineering.

Study on the strength of frozen clay at high confining pressure

2008 ◽  
Vol 2 (2) ◽  
pp. 240-242 ◽  
Author(s):  
Xiaoxiao Chang ◽  
Wei Ma ◽  
Dayan Wang
Keyword(s):  
Confining Pressure ◽  
High Confining Pressure ◽  
Frozen Clay

scholarly journals Macroscopic and Mesoscopic Mechanical Properties of Mine Tailings with Different Dry Densities under Different Confining Pressures

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Zhi-jun Zhang ◽  
Yao-hui Guo ◽  
Ya-kun Tian ◽  
Lin Hu ◽  
Xi-xian Wang ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Coordination Number ◽  
Mine Tailings ◽  
Confining Pressure ◽  
Simulation Software ◽  
Particle Flow ◽  
Dry Density ◽  
Stress Strain ◽  
High Confining Pressure ◽  
Confining Pressures

Particle flow numerical simulation software (PFC3D) was utilized to establish the consolidated-undrained triaxial compression test numerical models of mine tailings with different dry densities to deeply investigate the macroscopic and microscopic characteristics of mine tailings in a tailing pond in Hunan Province. Comparing the results of the simulation and the laboratory experiment, the mesoscopic parameters of the particle flow numerical simulation were obtained through continuously adjusting the mesoscopic parameter with the higher degree of agreement between the stress-strain curve, the peak strength, and the elastic modulus as the determining standard. The macroscopic and microscopic characteristics of mine tailings were studied from the perspectives of stress-strain, axial strain-volume strain, coordination number, particle velocity vector, and contact force between particles. After numerous numerical tests, it was found that the PFC3D simulation results are consistent with experiment results of the dry density tailing samples under different confining pressures; compared with the high confining pressure, the simulation test results at lower confining pressures were more with that of the laboratory tests; low density and high confining pressure both have inhibitory effect on the dilatancy characteristics of triaxial samples; with the same confining pressure, the dilatancy tendency of low dry density samples is suppressed comparing with the high dry density samples. The initial coordination number of the numerical model is large, which proves that the contact degree of the model is good to some extent.

“Deformation of Rocks under High Confining Pressures. I. Experiments at Room Temperature.” Journal of Geology, Vol. xliv, no. 5, pp. 541–577. By David T. Griggs. (1936).

Geophysics ◽  
1936 ◽  
Vol 1 (3) ◽  
pp. 378-379
Author(s):  
M. Mott‐Smith
Keyword(s):  
High Pressure ◽  
Hydrostatic Pressure ◽  
Room Temperature ◽  
Confining Pressure ◽  
Earth’S Crust ◽  
Differential Stress ◽  
High Confining Pressure ◽  
Confining Pressures ◽  
Earth's Crust

This article describes experiments on the flow and rupture of rocks under compression, tension, and torsion, while at the same time subjected to a high confining pressure supplied through a liquid surrounding the specimen. The hydrostatic pressure of this liquid could be measured very accurately and could be maintained constant. In addition, a “differential” stress was applied to the specimen, and the deformation was measured directly. By using the high pressure technique of P. W. Bridgman the confining pressure was carried up to 13,000 atmospheres, equivalent to a depth in the earth’s crust of 28 miles, and four times that available to F. W. Adams in his pioneering experiments (1901–1917).

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