scholarly journals Research on Energy Conversion and Damage Features of Unloading Instability of Sandstone under High Stress

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Zhiyuan Hou ◽  
Chuanbo Hao ◽  
Fukun Xiao ◽  
Gang Liu
Keyword(s):  
Energy Conversion ◽  
Elastic Energy ◽  
Failure Process ◽  
High Stress ◽  
Confining Pressure ◽  
Dissipated Energy ◽  
Radial Deformation ◽  
Sandstone Sample ◽  
Surplus Energy ◽  
Unloading Confining Pressure

In order to explore the failure characteristics of sandstone under unloading conditions in deep zone with high stress, constant axial pressure and unloading confining pressure tests were conducted on a yellow sandstone sample under different initial confining pressures using the French ROCK600-50 triaxial tester, and the mechanical properties, energy conversion characteristics, and damage evolution law of sandstone failure under unloading conditions were obtained. The test results showed that the axial deformation, the confining pressure for failure, and the shear fracture energy during the failure process of sandstone under the unloading state were positively correlated with the initial confining pressure; the dilatancy amount and speed and the radial deformation were negatively correlated with the initial confining pressure, exhibiting the characteristics of dilatancy under low confining pressure and compression under high confining pressure. Before the unloading point, almost all the energy absorbed by the rock under low initial confining pressure was converted into elastic energy, while part of the energy absorbed under high initial confining pressure was converted into dissipated energy, and the higher the confining pressure, the greater the proportion of the dissipated energy converted. The higher the initial confining pressure, the greater the elastic energy, radial deformation energy, and dissipated energy at the rock fracture point. The larger the unloading confining pressure, the greater the postpeak failure energy and surplus energy of sandstone, and the greater the increase in the proportion of elastic energy converted into surplus energy. The higher the confining pressure, the larger the damage value at the unloading point; the damage speed in the unloading stage was significantly greater than that in the loading stage.

scholarly journals Experimental Investigation of Energy Evolution in Sandstone Failure during Triaxial Unloading Confining Pressure Tests

2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Rui Yang ◽  
Depeng Ma ◽  
Yongjie Yang
Keyword(s):  
Elastic Energy ◽  
Triaxial Compression ◽  
High Stress ◽  
Confining Pressure ◽  
Energy Evolution ◽  
Compression Tests ◽  
Sandstone Sample ◽  
Pressure Tests ◽  
Unloading Confining Pressure ◽  
Sample Damage

The deformation and failure of sandstone samples are closely related to energy changes in the material. To explore the energy evolution during the process of sandstone sample damage, loading and unloading tests with different test paths were conducted. The results show that more energy is stored and consumed before the stress reaches its peak, while after the peak stress, more energy is released and consumed. Energy dissipation increases internal cracking, leads to sample damage and lithologic deterioration, and reduces the bearing capacity of the sample. During triaxial unloading of the confining pressure, the higher the initial unloading confining pressure, the more the elastic energy stored, and the more the energy released when the sandstone sample fails, resulting in more severe damage. Therefore, during the excavation of high-stress rock masses, large amounts of elastic energy stored in sandstone can be rapidly released, leading to rock burst disasters. Additionally, during triaxial unloading confining pressure tests, the damage in sandstone when the sample is close to failure increases more rapidly than that during conventional triaxial compression tests because of the unloading effect of the confining pressure. This phenomenon also illustrates that the failure of sandstone induced by unloading is more sudden than that induced by loading.

scholarly journals Hydraulic properties and energy dissipation of deep hard rock under H-M coupling and cycling loads

2019 ◽  
Vol 23 (Suppl. 3) ◽  
pp. 935-942 ◽  
Author(s):  
Cheng-Han Zhang ◽  
Shuang You ◽  
Hong-Guang Ji ◽  
Fei Li ◽  
Hong-Tao Wang
Keyword(s):  
Acoustic Emission ◽  
Osmotic Pressure ◽  
Hydraulic Properties ◽  
Coupling Effect ◽  
High Stress ◽  
Confining Pressure ◽  
In Situ Stress ◽  
Dissipated Energy ◽  
Underground Engineering ◽  
Loading And Unloading

The permeability of deep rock is closely related to the stability and safety of underground engineering. The rocks in deep stratum are mostly with high stress and high osmotic pressure. Therefore, it is necessary to consider the coupling effect between porewater pressure and in situ stress on rock mass. A series of triaxial cyclic loading and unloading experiments under hydraulic-mechanics coupling conditions are carried out to studied the mechanical and hydraulic properties of granite in the depth of 1300 m to 1500 m. Especially, the effect of the disturbance on the permeability of fractured rocks are investigated by unloaded the confining pressure. Tests results presented that the stress-strain curves of deep granite showed typical brittle characteristics. The principal stress of granite exhibited a linear relationship under the high confining pressure of 34-40 MPa and high osmotic pressure of 13-15 MPa. Dissipated energy of the rock decreased to a relatively low level after 2-3 loading cycles and then slowly increased. Permeability showed a decreasing trend as the loading and unloading cycles increase. Finally, acoustic emission technology was used to monitor the fracture evolution in rocks, the acoustic emission signal released as the fractures develop and energy dissipated. The results would provide basic data for the exploitation and excavation in the deep galleries.

scholarly journals Fractal Characteristics of Coal and Sandstone Failure under Different Unloading Confining Pressure Tests

2020 ◽  
Vol 2020 ◽  
pp. 1-11 ◽  
Author(s):  
Tianran Ma ◽  
Depeng Ma ◽  
Yongjie Yang
Keyword(s):  
Fractal Dimension ◽  
Shear Failure ◽  
High Stress ◽  
Confining Pressure ◽  
Stress Conditions ◽  
Surface Cracks ◽  
Sandstone Rock ◽  
Pressure Tests ◽  
Fractal Characteristics ◽  
Unloading Confining Pressure

To analyze the fractal characteristics of coal rock failure under unloading conditions, triaxial unloading confining pressure tests were carried out on coal and sandstone rock samples under different unloading rates and initial confining pressures. We examined the distribution of the surface cracks and fragmentation of the coal and sandstone samples that failed under different triaxial unloading confining pressure tests. The results showed that the fractal dimension of the surface cracks in coal and sandstone decreased as the initial unloading confining pressure increased. Thus, shear failure is more obvious in coal or sandstone with high-stress conditions caused by unloading confining pressure than in coal or sandstone with low-stress conditions. However, the fractal dimension of the surface cracks increased with the unloading rates. Additionally, the fractal dimension of the fragmentation in the coal and sandstone samples had a negative correlation with the initial unloading confining pressure. When the initial confining pressure was relatively low, the samples underwent splitting and shear failure; when the initial confining pressure was higher, the failure mode was mostly shear failure and the fragmentation of the samples was less homogeneous. In contrast, the fractal dimension of the fragmentation in the coal and sandstone increased with higher unloading rates. The lithology had a significant effect on the fractal dimension of the surface cracks and on the fragmentation. Samples with more internal fissures had more surface cracks and the fragmentation was more homogeneous when the rock failed compared with samples with less fissures under the same experimental conditions.

scholarly journals Energy Evolution and Acoustic Emission Characteristics of Sandstone Specimens under Unloading Confining Pressure

2019 ◽  
Vol 2019 ◽  
pp. 1-9
Author(s):  
Tao Qin ◽  
Yanwei Duan ◽  
Hongru Sun ◽  
Honglei Liu ◽  
Lei Wang
Keyword(s):  
Acoustic Emission ◽  
Elastic Strain ◽  
Strain Energy ◽  
High Stress ◽  
Confining Pressure ◽  
Emission Characteristics ◽  
Energy Evolution ◽  
Peak Point ◽  
Unloading Confining Pressure ◽  
Rock Specimens

The acoustic emission characteristics of rock specimens under different initial unloading confining pressures were tested to obtain the damage and rupture characteristics of the sandstone unloading confining pressure path. The CT scan and three-dimensional reconstruction of the fractured rock specimens were carried out to study the differences of energy evolution and acoustic emission characteristics during the failure of sandstone under different initial unloading pressures. The results show that the unloading confining pressure has a significant influence on the deformation and failure of the rock. There is a significant yielding platform for the circumferential strain and the bulk strain at the peak of the unloading pressure. The larger the initial unloading pressure is, the greater the axial absorption strain energy, the dissipative energy, and the elastic strain energy are at the peak point. After the stress peak point, the elastic strain can be quickly converted into the dissipative energy for rock damage. The elastic energy released from the moment of rock failure under high confining pressure is more concentrated. The acoustic emission ringing and b value characteristic parameters of the rock have a good correlation with the internal energy evolution of the rock, which better reflects the progressive damage of the rock under low stress and the sudden failure of high-stress unloading.

scholarly journals Numerical simulation study on rheological failure characteristics of rock mass under high stress

2020 ◽  
Vol 192 ◽  
pp. 04003
Author(s):  
Liming Qiu ◽  
Xueqiu He ◽  
Dazhao Song ◽  
Zhenlei Li
Keyword(s):  
Numerical Simulation ◽  
Rock Mass ◽  
Failure Process ◽  
High Stress ◽  
Sudden Change ◽  
Confining Pressure ◽  
Simulation Software ◽  
The Body ◽  
Failure Characteristics ◽  
Rock Failure Process

This paper uses the RFPA numerical simulation software to establish a numerical model of the rheological failure of the rock mass under stress. Rheological failure characteristics of the body was researched, and the results shows: (1) The rupture sequence of rock rupture is from the corner to the middle. When the rock loses stability under pressure, the rock often ruptures from the corner. The corner gradually collapses and cracks. Then the cracks spread to the middle of the rock. Many cracks extending from the corners are in the rock. The central part intersects each other and eventually causes the rock to break. (2) Rock samples of different lithologies have different stress values when they break under the same confining pressure. From the experimental process, we know that granite>sandstone>mudstone. Therefore, the higher the strength of the rock, the harder the rock will be broken. (3) The weaker the plasticity at rupture, the stronger the brittleness and the stronger the sudden change of rupture. In the deep mining process, the greater the confining pressure, the more obvious the rheological characteristics of the rock, and the greater the total energy released during the rock failure process.

Energy Dissipation Analysis on Unloading Confining Pressure Failure Process of Rock Material

2012 ◽  
Vol 256-259 ◽  
pp. 398-401 ◽  
Author(s):  
Fu Jiang Chen ◽  
Hong Xia Li ◽  
Ze Qi Zhu
Keyword(s):  
Energy Dissipation ◽  
Rock Sample ◽  
Failure Process ◽  
Strain Curve ◽  
Confining Pressure ◽  
Rock Material ◽  
Test Machine ◽  
Lateral Deformation ◽  
Unloading Confining Pressure ◽  
Pressure Failure

The energy dissipation law of rock material are analyzed comprehensively by studying the energy exchange between test machine and rock sample in two typical stress-strain curve of unloading tests. The relationships between energy, deformation and confining pressure in unloading confining pressure failure process are expected to be found based on energy dissipation analysis. It shows that the energy dissipation is greatly related to the failure characteristic of rock material and confining pressure. Both two unloading tests show that energy dissipation has a nonlinear relationship with time and linear relationship with lateral deformation. The much the confining pressure is in unloading condition, the more the energy dissipation is under the same lateral deformation, and the obviously the rock sample suffers brittle failure.

scholarly journals Energy Evolution Analysis and Brittleness Evaluation of High-Strength Concrete Considering the Whole Failure Process

Crystals ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1099
Author(s):  
Ruihe Zhou ◽  
Hua Cheng ◽  
Mingjing Li ◽  
Liangliang Zhang ◽  
Rongbao Hong
Keyword(s):  
Release Rate ◽  
Elastic Energy ◽  
High Strength Concrete ◽  
Evaluation Method ◽  
Failure Process ◽  
High Strength ◽  
Confining Pressure ◽  
Brittleness Index ◽  
Energy Evolution ◽  
Strength Concrete

In this work, we aimed to solve the problems that exist in the brittleness evaluation method of high-strength concrete through a triaxial compression test of C60 and C70 high-strength concrete. Then, the relationship between the energy evolution of its elastic energy, dissipative energy, pre-peak total energy and additional energy and its axial strain, confining pressure, and concrete strength grade was analyzed. Taking the accumulation rate of pre-peak elastic strain energy and the dissipation rate of dissipative energy, and the release rate of post-peak elastic energy, as the evaluation indicators to characterize the brittleness of high-strength concrete. A brittleness evaluation method that reflects the whole failure process of high-strength concrete is proposed and verified by experiments. The results show that with the increase of the confining pressure, the proportion of elastic energy in the whole process of high-strength concrete failure gradually decreases. The storage rate of pre-peak elastic energy and the release rate of post-peak elastic energy are gradually reducing, the brittleness index gradually decreases, and the confining pressure inhibits the brittleness of high-strength concrete. Under the same confining pressure, the brittleness index of C70 concrete is greater than that of C60 concrete, which indicates that, with the increase of the strength grade, the brittleness level of concrete gradually increases and the ductility decreases. These findings have a certain theoretical significance for the scientific design of high-strength concrete structures and the improvement of their safety in the future.

scholarly journals Experimental Study on the Influence of Specimen Shape on Rockburst Proneness of Red Sandstone

2020 ◽  
Vol 2020 ◽  
pp. 1-17 ◽  
Author(s):  
Jiajun Yang ◽  
Fengqiang Gong ◽  
Dongqiao Liu ◽  
Zhixiang Liu
Keyword(s):  
Energy Storage ◽  
Energy Density ◽  
Elastic Energy ◽  
Failure Process ◽  
Dissipated Energy ◽  
Shape Effect ◽  
Energy Index ◽  
Red Sandstone ◽  
Linear Relationships ◽  
Specimen Shape

To investigate the specimen shape effect on rockburst proneness of rock materials, a string of conventional and single-cycle loading-unloading uniaxial compression tests was performed with cylindrical and cuboid red sandstone specimens. Despite similar development paths on stress-strain curves for the specimens with two shapes, the cuboid specimens generally show a higher uniaxial compressive strength than the cylindrical specimens. The energy evolution laws inside the two shaped specimens were explored. The results show that the input energy density (IED), elastic energy density (EED), and dissipated energy density (DED) of the two shaped specimens increased in a quadratic relationship with the increment of unloading level. Moreover, the linear relationships between the EED, DED, and IED were further confirmed for two shaped specimens, which were defined as the linear energy storage and dissipation laws, respectively. The energy storage coefficients and energy dissipation coefficients (the slopes of the linear relationships between the EED, DED, and IED, respectively) are almost independent of the specimen shape. According to the linear energy storage and dissipation laws, the peak EED and peak DED of every specimen can be calculated accurately. Finally, combining the failure process of rock specimens recorded by a high-speed camera, the elastic energy index (WET), the residual elastic energy index (AEF), and the far-field ejection mass ratio (MF) of each specimen were adopted to assess the rockburst proneness of the red sandstone sampled in cylindrical and cuboid. The results show that cuboid specimens exhibited stronger rockburst proneness than cylindrical ones, which favorably agreed with the actual failure phenomena.

scholarly journals Energy Evolution Characteristics and Distribution Laws of Rock Materials under Triaxial Cyclic Loading and Unloading Compression

2017 ◽  
Vol 2017 ◽  
pp. 1-16 ◽  
Author(s):  
Mingwei Zhang ◽  
Qingbin Meng ◽  
Shengdong Liu
Keyword(s):  
Cyclic Loading ◽  
Energy Density ◽  
Elastic Energy ◽  
Confining Pressure ◽  
Dissipated Energy ◽  
Energy Evolution ◽  
Elastic Energy Density ◽  
Evolution Characteristics ◽  
Storage Limit ◽  
Confining Pressures

To explore the influence of confining pressure on the energy evolution characteristics of loaded rocks, triaxial cyclic loading-unloading experiments on sandstones were carried out under 6 kinds of confining pressures using the axial loading and circumferential deforming control modes. Total energy density, elastic energy density, and dissipated energy density absorbed by rock specimens under different confining pressures were obtained. The confining pressure effect of the evolution process and distribution law in energy accumulation and dissipation was analyzed. Energy conversion mechanism from rock deformation to failure was revealed, and energy conversion equations in different stress-strain stages were established. The method of representing the rock energy accumulation, dissipation, and release behaviors by energy storage limit density, maximum dissipated energy density, and residual elastic energy density was established. The rock showed that, with the increase of confining pressure, the characteristic energy density of rock increased in the power exponent form, and the energy storage limit density increased faster than the maximum dissipated energy density. The greater the confining pressure was, the greater the proportion of elastic energy before peak was. It is indicated that the confining pressure increased the energy inputting intensity, improved the energy accumulating efficiency, and inhibited the energy releasing degree.

scholarly journals Damage Evaluation for Rock Burst Proneness of Deep Hard Rock under Triaxial Cyclic Loading

2018 ◽  
Vol 2018 ◽  
pp. 1-7 ◽  
Author(s):  
Shuang You ◽  
Hongguang Ji ◽  
Zijian Zhang ◽  
Chenghan Zhang
Keyword(s):  
Cyclic Loading ◽  
Rock Burst ◽  
Elastic Energy ◽  
Failure Process ◽  
Damage Zone ◽  
High Stress ◽  
Energy Index ◽  
Dissipation Energy ◽  
Deep Mining ◽  
Cyclic Loading And Unloading

High stress and strong excavation disturbance are the main causes of dynamic disasters, rock burst in deep hard rocks, and are more frequent and violent than those in shallow, which seriously restricts the deep mining. Given rock burst encountered in deep mining of Lingnan metal mines, the optimized triaxial cyclic loading and unloading tests are designed to characterize the performance of rock failure and to evaluate the rock burst proneness. The correlation between elastic energy index and damage evolution is built, and rock burst proneness in each status is analyzed; furthermore, the dissipation energy in the failure process of deep rocks is explicated. In this paper, the law that the elastic energy index via damage increases is drawn. In terms of the dynamic disaster conditions in the deep rock, the identification approach for the damage zone of the rock burst is established.

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