scholarly journals Cut-Through Fractured Seepage Properties and Numerical Simulation of Sandstone after Different Temperature Treatments

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Haopeng Jiang ◽  
Annan Jiang
Keyword(s):  
Fracture Surface ◽  
Shear Failure ◽  
Failure Surface ◽  
Confining Pressure ◽  
Theoretical Formula ◽  
Negative Exponential Function ◽  
Damage Degree ◽  
Different Temperatures ◽  
Negative Exponential ◽  
Fractured Sandstone

To explore the seepage characteristics of cut-through fractured rocks after different temperatures, sandstone in the Hunan area was selected as the research object. First, the influence degree of different temperatures on the permeability of fractured sandstone was studied, and the permeability variation of fractured sandstone with net confining pressure was revealed. The test data was nonlinearly fitted to prove that the relationship between permeability and net confining pressure conforms to the characteristics of the negative exponential function. Second, the macroscopic fractured state of sandstone after different temperature treatments was analyzed, and it is concluded that the inclination angle of the fracture surface decreases with the applied thermal temperature, the fracture surface gradually develops into a single shear failure surface, and the damage degree becomes more and more serious. Finally, the theoretical formula for the calculation of fractured seepage was introduced, and the FLAC3D embedded fish language was used to compile the seepage-stress coupling calculation program of the fractured sandstone after different temperature treatments. Numerical calculations were carried out based on samples with different fracture angles of fractured sandstone, and the calculated values were in good agreement with the test results. The research results can provide guiding significance for the research on the influence of high temperature in fire tunnel on the evolution of permeability of surrounding rock fissures.

scholarly journals Investigation on the Influence of Temperature and Confining Pressure on the Hydraulic Conductivity of the Integrated and Fractured Jurassic Conglomerates

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Dingyang Zhang ◽  
Wanghua Sui ◽  
Jiawei Liu
Keyword(s):  
Hydraulic Conductivity ◽  
Shear Failure ◽  
Negative Relationship ◽  
Confining Pressure ◽  
Regression Equations ◽  
Intact Sample ◽  
Triaxial Cell ◽  
Different Temperatures ◽  
Confining Pressures ◽  
Constant Head

This paper presents an experimental investigation on the properties of hydraulic conductivity and permeability of conglomerates under different temperatures and confining pressures with integrated samples and samples with shear failure. Constant head tests were carried out in a temperature-controlled triaxial cell with samples obtained from the Zhuxianzhuang Coal Mine. Five levels of temperatures (10°C, 20°C, 28°C, 35°C, and 50°C) and three levels of confining pressures (3 MPa, 5 MPa, and 7 MPa) were chosen for the tests. The results show that there is a negative relationship between hydraulic conductivity and confining pressure with both original and shear failure samples. An inflection point of 35°C is found in the relationship between the flow rate and temperature. However, with increasing temperature conditions, hydraulic conductivity first increases and then decreases at 50°C with the intact sample, while hydraulic conductivity first decreases from 20°C and then increases with the shear failure sample. Finally, nonlinear regression equations of hydraulic conductivity and temperature were obtained under different confining pressures.

scholarly journals Study on the Permeability of Weakly Cemented Sandstones

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-14 ◽  
Author(s):  
XianZhou Lyu ◽  
Zenghui Zhao ◽  
Xiaojie Wang ◽  
Weiming Wang
Keyword(s):  
Fracture Surface ◽  
Permeability Coefficient ◽  
Confining Pressure ◽  
Theoretical Formula ◽  
Single Fracture ◽  
Hydraulic Pressure ◽  
Test Results ◽  
Rock Masses ◽  
Heterogeneous Rock ◽  
Two Sides

Fractured rocks are a type of complex media that widely exist in various projects including energy, hydraulic, and underground space engineering, whose permeability properties are a hotspot in current rock mechanics domain. Aiming at investigating the seepage characteristics of the fracture surfaces in different rock strata, uniaxial compressive test and permeability test were performed on single-fracture homogenous and heterogeneous rocks. Specifically, rock’s physical and mechanical parameters were measured in uniaxial tests while the initial width of the single fracture was determined through CT scanning. In combination with test results and the calculation model of the displacement of single-fracture heterogeneous rock under triaxial stress condition, the calculation formula of the permeability coefficient of single-fracture heterogeneous rock was derived. Results show that hydraulic pressure in the fracture can affect the permeability coefficient of the fractured rock. Hydraulic fracturing effect occurred with the increase of hydraulic pressure in the fracture, which then generates slight normal deformations of the rock masses on both two sides of the fracture surface, decreases the contact area in the fracture, and leads to the increases of both fracture width and permeability coefficient. For single-fracture rock, the lithological properties of the rock masses on both two sides of the fracture surface impose significant effects on the permeability coefficient. Under same hydraulic pressure and confining pressure, the permeability coefficient of single-fracture coarse sandstone is greatest, followed by that of single-fracture heterogeneous rock, and finally by single-fracture fine sandstone. Theoretical calculation results agree well with the test results, suggesting that the derived theoretical formula can adequately describe the variation tendencies of permeability coefficient with confining pressure and hydraulic pressure in the fracture.

scholarly journals Experimental Investigation on the Post-Peak Short-Term and Creep Behavior of Fractured Sandstone

Energies ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 598
Author(s):  
Yijiang Zong ◽  
Lijun Han ◽  
Yuhao Jin ◽  
Weisheng Zhao ◽  
Lingdong Meng
Keyword(s):  
Mechanical Behavior ◽  
Failure Modes ◽  
Shear Failure ◽  
High Stress ◽  
Confining Pressure ◽  
Short Term ◽  
Creep Failure ◽  
Creep Tests ◽  
Differential Stress ◽  
Fractured Sandstone

Short-term and creep tests of fractured sandstone with different degrees of damage prepared using pre-peak and post-peak unloading tests on intact sandstone were carried out using a servo-controlled rock mechanics system. Based on our experimental results, the influence of confining pressure and damage on short-term mechanical behavior of fractured sandstone with different degrees of damage was first analyzed. The results show that the peak strength, residual strength, elastic modulus, and secant modulus of fractured sandstone increase linearly with increasing confining pressure, but decrease with increasing damage. The short-term failure modes depend on the damage and change from typical shear failure modes to multiple shear failure modes with increasing damage. Then, the influence of the differential stress, confining pressure, and the degree of damage on the creep mechanical behavior of fractured specimens was further investigated. The axial instantaneous strain and creep strain increase linearly with increasing differential stress, and the specimens exhibit significant time-dependent behavior under high stress. The steady creep rate increases with increasing stress, but it decreases with increasing confining pressure and damage. However, the long-term strength and creep failure strength of fractured specimens increase linearly with increasing confining pressure, but they decrease linearly with increasing damage. The creep failure modes of fractured specimens are also the main shear failure modes, which are similar to the short-term failure modes.

scholarly journals An Extension Strain Type Mohr–Coulomb Criterion

2021 ◽  
Author(s):  
Manfred Staat
Keyword(s):  
Failure Modes ◽  
Peak Stress ◽  
Fracture Initiation ◽  
Failure Surface ◽  
Confining Pressure ◽  
Biaxial Compression ◽  
Simple Extension ◽  
Strain Criterion ◽  
Shear Component ◽  
Extension Strain

AbstractExtension fractures are typical for the deformation under low or no confining pressure. They can be explained by a phenomenological extension strain failure criterion. In the past, a simple empirical criterion for fracture initiation in brittle rock has been developed. In this article, it is shown that the simple extension strain criterion makes unrealistic strength predictions in biaxial compression and tension. To overcome this major limitation, a new extension strain criterion is proposed by adding a weighted principal shear component to the simple criterion. The shear weight is chosen, such that the enriched extension strain criterion represents the same failure surface as the Mohr–Coulomb (MC) criterion. Thus, the MC criterion has been derived as an extension strain criterion predicting extension failure modes, which are unexpected in the classical understanding of the failure of cohesive-frictional materials. In progressive damage of rock, the most likely fracture direction is orthogonal to the maximum extension strain leading to dilatancy. The enriched extension strain criterion is proposed as a threshold surface for crack initiation CI and crack damage CD and as a failure surface at peak stress CP. Different from compressive loading, tensile loading requires only a limited number of critical cracks to cause failure. Therefore, for tensile stresses, the failure criteria must be modified somehow, possibly by a cut-off corresponding to the CI stress. Examples show that the enriched extension strain criterion predicts much lower volumes of damaged rock mass compared to the simple extension strain criterion.

Patterns of roof runoff contamination and their potential implications on practice and regulation of treatment and local infiltration

1996 ◽  
Vol 33 (6) ◽  
pp. 39-48 ◽  
Author(s):  
Jürgen Förster
Keyword(s):  
Heavy Metals ◽  
Metal Surfaces ◽  
Precipitation Event ◽  
Pollution Level ◽  
Runoff Water ◽  
Roof Runoff ◽  
Negative Exponential Function ◽  
Subsequent Decrease ◽  
First Flush Effect ◽  
Negative Exponential

Roof runoff water was sampled from an experimental roof system and from house roofs in the city of Bayreuth, Germany. Samples were analysed for organic micropollutants, heavy metals and sum parameters. The pollution level and the shape of the runoff profiles are dependent on the individual properties of the precipitation event and the roof, but patterns with high concentrations at the beginning of the event and a subsequent decrease (first flush effect) are very typical. For dissolved substances, the profile can often be well described by a negative exponential function. Metal surfaces on the roofs cause extreme runoff pollution with heavy metals (Cu, Zn) that constitutes an environmental hazard. It is concluded that there is a need for the development of flexible drainage strategies for surface runoff and that metal surfaces should be avoided on roofs.

scholarly journals A Computational Model for Oxygen Depletion Hypothesis in FLASH Effect

2021 ◽  
Author(s):  
Ankang Hu ◽  
Rui Qiu ◽  
Zhen Wu ◽  
Hui Zhang ◽  
Wei Bo Li ◽  
...  
Keyword(s):  
Computational Model ◽  
Dose Rate ◽  
Oxygen Concentration ◽  
Microvessel Density ◽  
Oxygen Depletion ◽  
Oxygen Distribution ◽  
Resistance Level ◽  
Negative Exponential Function ◽  
Normal Tissues ◽  
Negative Exponential

Experiments have reported low normal tissue toxicities during FLASH irradiation, but the mechanism has not been elaborated. Several hypotheses have been proposed to explain the mechanism. One hypothesis is oxygen depletion. We analyze the time-dependent change of oxygen concentration in the tissue to study the oxygen depletion hypothesis using a computational model. The effects of physical, chemical and physiological parameters on oxygen depletion were explored. The kinetic equation of the model is solved numerically using the finite difference method with rational boundary conditions. Results of oxygen distribution is supported by the experiments of oxygen-sensitivity electrodes and experiments on the expression and distribution of the hypoxia-inducible factors. The analysis of parameters shows that the steady-state oxygen distribution before irradiation is determined by the oxygen consumption rate of the tissue and the microvessel density. The change of oxygen concentration after irradiation has been found to follow a negative exponential function, and the time constant is mainly determined by the microvessel density. The change of oxygen during exposure increases with dose rate and tends to be saturated because of oxygen diffusion. When the dose rate is high enough, the same dose results in the same reduction of oxygen concentration regardless of dose rate. The analysis of the FLASH effect in the brain tissue based on this model does not support the explanation of the oxygen depletion hypothesis. The oxygen depletion hypothesis remains controversial because the oxygen in most normal tissues cannot be depleted to radiation resistance level by FLASH irradiation.

Microstructural and Fractographic Analysis of CuAlNi Shape Memory Alloy before and after Heat Treatment

2020 ◽  
Vol 405 ◽  
pp. 100-106
Author(s):  
Ivana Ivanić ◽  
Mirko Gojić ◽  
Stjepan Kožuh ◽  
Borut Kosec
Keyword(s):  
Heat Treatment ◽  
Shape Memory Alloy ◽  
Fracture Surface ◽  
Shape Memory ◽  
Fractographic Analysis ◽  
Before And After ◽  
Different Temperatures ◽  
The Difference ◽  
Type Of Fracture ◽  
Scanning Electron

The paper presents comparison of microstructure and fracture surface morphology of the CuAlNi shape memory alloy (SMA) after different heat treatment procedures. The investigation was performed on samples in as-cast state and heat treated states (solution annealing at temperatures of 850 °C / 60’ / H2O and 920 °C / 60’ / H2O along with tempering at two different temperature 150 °C / 60’ / H2O and 300 °C / 60’ / H2O). The microstructure of the samples was examined by optical (OM) and scanning electron microscope (SEM) equipped with device for EDS analysis. The obtained fracture surfaces were examined by SEM. Optical and scanning electron microscopy showed martensitic microstructure in all investigated samples. However, the fractographic analysis of samples after tensile testing reveals significant changes in fracture mechanism. In both solution annealed states the results shows transgranular type of fracture, but after tempering at two different temperatures the difference is obvious. After tempering at 150 °C, along with transgranular type of fracture appear some areas with intergranular type of fracture. After tempering at 300 °C, fracture surface reveals completely intergranular type of fracture.

Fracture Behavior of an AlMgMnSc Alloy at Different Temperatures

2021 ◽  
Vol 1016 ◽  
pp. 292-296
Author(s):  
Yuliya Igorevna Borisova ◽  
Diana Yuzbekova ◽  
Anna Mogucheva
Keyword(s):  
Tensile Strength ◽  
Ultimate Tensile Strength ◽  
Brittle Fracture ◽  
Fracture Surface ◽  
Strain Rate ◽  
Fracture Behavior ◽  
Fine Grained ◽  
Angular Pressing ◽  
Different Temperatures ◽  
Elongation To Failure

An Al-4.57Mg-0.35Mn-0.2Sc-0.09Zr (wt. %) alloy was studied in the fine-grained state obtaining after equal channel angular pressing. The mechanical behavior of alloy at the temperatures 173 K, 298 K and 348 K and at strain rate 1×10–3 s–1 is studied. Increase of the temperature testing from 173 K to 348 K decreases the yield stress by 80 MPa, the ultimate tensile strength by 60 MPa while elongation-to failure increases by a factor of 1.4. It was found that at temperatures of 298 and 173 K, the studied alloy mainly demonstrates the mode of ductile fracture, and at a temperature of 348 K the mechanism can be described as mixed ductile-brittle fracture. It was also established that of the studied alloy is the temperature dependence of the size of the dimples on the fracture surface. The formation of smaller dimples in the samples deformed at 298 K was observed.

scholarly journals The meso-fracturing mechanism of marble under unloading confining pressure paths and constant axial stress

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Linna Sun ◽  
Liming Zhang ◽  
Yu Cong ◽  
Yaduo Song ◽  
Keqiang He
Keyword(s):  
Shear Failure ◽  
Axial Stress ◽  
Confining Pressure ◽  
Particle Flow Code ◽  
Shear Cracks ◽  
Confining Pressures ◽  
Tension Cracks ◽  
Trial And Error Method ◽  
Unloading Confining Pressure ◽  
Fracturing Mechanism

AbstractFailure tests on marble during unloading confining-pressure under constant axial stress and simulations with the particle flow code were performed. The influence mechanism of the unloading rate of the confining pressure, initial unloading stress, and confining pressure on the failure characteristics of, and crack propagation in, marble was studied. By using the trial-and-error method, the conversion relationship between the unloading rates of confining pressures in laboratory tests and numerical simulations was ascertained. Micro-cracks formed in the unloading process of confining pressure are dominated by tension cracks, accompanied by shear cracks. The propagation of shear cracks lags that of tension cracks. As the confining pressure is increased, more cracks occur upon failure of the samples. The proportion of shear cracks increases while that of tension cracks decreases. The failure mode of samples undergoes a transition from shear-dominated failure to conjugated shear failure.

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