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.

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.

scholarly journals Experimental Study on Shear Strength of Saturated Remolded Loess

2021 ◽  
Author(s):  
Jie Lai ◽  
Yun Liu ◽  
Yuzhou Xiang ◽  
Wei Wang ◽  
Jiangbo Xu ◽  
...  
Keyword(s):  
Shear Strength ◽  
Shear Rate ◽  
Strain Curve ◽  
Confining Pressure ◽  
Cohesive Force ◽  
Dry Density ◽  
Stress Strain ◽  
Loess Area ◽  
Confining Pressures ◽  
Homogeneous Composition

Abstract Loess has the characteristic of macropore, loose structure, homogeneous composition and collapsibility. It is easy to saturate when it encounters heavy rainfall and irrigation, resulting in landslides, roadbed subsidence and dam instability in the loess area. To study the influence of dry density and shear rate on shear strength of saturated remolded loess, an SLB-6A stress-strain controlled triaxial shear penetration tester was used to conduct Consolidated Undrained(CU) test in the Yan'an area. During the test, three variables of shear rate, confining pressure and dry density were controlled. The dry densities of the samples were 1.5g/cm3, 1.6g/cm3 and 1.7g/cm3 respectively. The CU test of the saturated remolded loess at a confining pressure of 100kPa, 150kPa, and 200kPa was performed at a shear rate of 0.04mm/min, 0.08mm/min, 0.16 mm/min, and 0.4mm/min respectively. It is found that the stress-strain curve of saturated remolded loess gradually moves up with the increase of dry density. When the dry density is equal to ρd=1.5g/cm3, the deviatoric stress under different confining pressures there is a tendency to increase first and then decrease with increases of shear rate. When the dry density is equal to ρd=1.6g/cm3 and ρd=1.7g/cm3, the deviational stress under different confining pressures shows the trend of increasing first, decreasing and then increasing with the increase of shear rate, which is different from that at the dry density ρd =1.5g/cm3 at a shear rate v=0.4mm/min. When the dry density ρd=1.5g/cm3, the cohesive force decreases first and then increases with the increase of shear rate. When the dry density ρd=1.6g/cm3 and ρd=1.7g/cm3, the cohesive force first increases at 0.08 mm/min, and then decreases with the increase of shear rate. The cohesion and internal friction angles tend to increase as the dry density 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.

scholarly journals Acoustic Emission Simulation on Coal Specimen Subjected to Cyclic Loading

2020 ◽  
Vol 2020 ◽  
pp. 1-17
Author(s):  
Huiqiang Duan ◽  
Depeng Ma
Keyword(s):  
Numerical Simulation ◽  
Acoustic Emission ◽  
Cyclic Loading ◽  
Confining Pressure ◽  
Rock Masses ◽  
Coal Specimen ◽  
Cycle Number ◽  
Confining Pressures ◽  
Unloading Rate ◽  
Ae Counts

The damage and failure state of the loaded coal and rock masses is indirectly reflected by its acoustic emission (AE) characteristics. Therefore, it is of great significance to study the AE evolution of loaded coal and rock masses for the evaluation of damage degree and prediction of collapse. The paper mainly represents a numerical simulation investigation of the AE characteristics of coal specimen subjected to cyclic loading under three confining pressures, loading-unloading rates, and valley stresses. From the numerical simulation tests, the following conclusions can be drawn: (1) The final cycle number of coal specimen subjected to cyclic loading is significantly influenced by the confining pressure, followed the valley stress. With the increase in confining pressure or valley stress, the cycle number tends to increase. However, the loading-unloading rate has a little influence on it. (2) The AE counts of coal specimen subjected to cyclic loading are greatly influenced by the confining pressure and the valley stress. With the increase in the confining pressure, the cumulative AE counts at the 1st cycle tend to increase but decrease at a cycle before failure; with the decrease in the valley stress, the cumulative AE counts per cycle increase in the relatively quiet phase. However, the loading-unloading rate has a little influence on it. (3) The failure mode of coal specimen subjected to cyclic loading is significantly influenced by the confining pressure. Under the uniaxial stress state, there is an inclined main fractured plane in the coal specimen, under the confining pressures of 5 and 10 MPa, the coal specimen represents dispersion failure. The loading-unloading rate and valley stress have little influence on it. (4) The AE ratio is proposed, and its evolution can better reflect the different stages of coal specimen failure under cyclic loading. (5) The influence of confining pressure on the broken degree of coal specimen subjected to cyclic loading is analyzed, and the higher the confining pressure, the more broken the failed coal specimen.

“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).

Fatigue Life Prediction in Rapid Die Casting

2008 ◽  
Author(s):  
Chuan Huat Ng ◽  
Karl-Heinrich Grote ◽  
Ru¨diger Ba¨hr
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Fatigue Life ◽  
Experimental Testing ◽  
Die Casting ◽  
Life Time ◽  
Casting Process ◽  
Simulation Software ◽  
Stress Strain ◽  
Fracture Models

During a die casting process, it is very difficult to achieve efficient and correct casting tooling endurance results by the casting designer and foundry man. However, it is very costly and time consuming to predict the tooling endurance with a trial and error method based on expertise and experience. After an extensive fatigue design study, it was possible to develop specimen design models for the simulation of the time and temperature dependent stress-strain and fracture models to determine the thermal fatigue prediction. In this research, stress-strain approach, heat transfer concept and life time calculation methods were used to predict the casting tool endurance by a computer simulation. The thermal stress and heat transfer behaviour analysis were performed using RWP casting numerical simulation software. It is shown that numerical simulation techniques can simulate stress concentration on the specimen surface to thermal behaviour. Furthermore, the result from the specimen based simulation model associated with fracture indicators permits the construction of a life time design curve independent of time and temperature. The fatigue life predicted by simulation based models and the results from experimental testing on real components are very similar. The simulation results showed that they match the experimental results, including a design safety factor.

scholarly journals Shaft Resistance of Long (Flexible) Piles Considering Strength Degradation

2021 ◽  
Vol 27 (3) ◽  
pp. 54-66
Author(s):  
Aysar Hassan Subair ◽  
Ala Nasir Aljorany
Keyword(s):  
Soil Structure ◽  
Frictional Resistance ◽  
Confining Pressure ◽  
Strength Degradation ◽  
Analysis Tool ◽  
Shaft Resistance ◽  
Model Pile ◽  
High Confining Pressure ◽  
Confining Pressures ◽  
Shear Strength Degradation

Soil-structure frictional resistance is an important parameter in the design of many foundation systems. The soil-structure interface area is responsible for load transferring from the structure to the surrounding soil. The mobilized shaft resistance of axially loaded, long slender pile embedded in dense, dry sand is experimentally and numerically analyzed when subjected to pullout force. Experimental setup including an instrumented model pile while the finite element method is used as a numerical analysis tool. The hypoplasticity model is used to model the soil adjacent to and surrounding the pile by using ABAQUS FEA (6.17.1). The soil-structure interface behavior depends on many factors, but mainly on the interface soil's tendency to contract or dilate under shearing conditions. To investigate this tendency, three piles with different surface roughness and under different confining pressures are used. A dilation behavior is observed in the relation of the average shaft resistance with the axial displacement for piles with rough and medium roughness surfaces, while contraction behavior is noticed when shearing piles with smooth surfaces. A large shear strength degradation of about (10%) reduction in the shaft resistance is observed under low confining pressure compared to a lesser reduction value of about (2%) under high confining pressure. Good agreement is obtained between the experimental and the numerical results.

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.

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