Laboratory characterisation of anisotropic and heterogeneous damage of rock sample using acoustic emission and ultrasonic monitoring technologies

Abstract In order to understand the rupture mechanism of rock and coal samples with holes, the acoustic emission (AE) tests of rock and coal samples with holes under uniaxial compression are done. Through the AE tests, the basic mechanical and AE variation rule of two samples in the total rupture process are obtained, the dynamic rupture process was observed and finally the spatial evolution and multi-fractal characteristic of AE are analyzed. The results show that the variation rule of AE events of two samples are coincident with the variation rule of stress. The uniaxial compressive strength of a rock sample with a hole is about five times than that of a coal sample with a hole, and the maximum AE pulsing counts (AEPC) of a rock sample with a hole is much larger than that of a coal sample with a hole. Due to the variation of lithology, the dynamic rupture process and the spatial evolution rule of AE events of rock and coal samples with holes are obviously different. But the distributions of the three-dimensional locations of the two samples are coincident with the macroscopic rupture morphology. Both of them have multi-fractal characteristic in the process of rupture, the multi-fractal spectrum width Δf(α) at the time of rupture is smaller than that before rupture and the Δf(α) before rupture is smaller than that after rupture. This indicates that the energy (E) before and after rupture is smaller than that at the time of rupture, the E after rupture is smaller than that before rupture and the E of a coal sample with a hole in each stage is less than that of the corresponding stages of a rock sample with a hole.

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Influence of the Disturbance in the Orthogonal Direction on the Kaiser Effect Using Discrete Element Method

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.361-363.139 ◽

2011 ◽

Vol 361-363 ◽

pp. 139-143

Author(s):

Hai Jun Wang ◽

Xu Hua Ren ◽

Ran Ran Tao

Keyword(s):

Acoustic Emission ◽

Rock Sample ◽

Peak Stress ◽

Particle Flow Code ◽

Underground Engineering ◽

Orthogonal Direction ◽

Design Work ◽

Kaiser Effect ◽

Rock Cores ◽

Rectangular Specimen

When a rock sample is subjected to cyclic loadings, acoustic emission (AE) events increase sharply when the peak stress value applied previously is attained. This phenomenon is called Kaiser effect (KE). One important application of the KE is to determine the in situ stress, the knowledge of which is critical for the design work for underground engineering. Compared to the traditional methods, the acoustic emission (AE) method based on KE is done in the laboratory with special loadings on the rock cores and thus very economical. However, one fundamental question needs to be answered is the influence of the damage introduced by many factors during the period of the coring and samples preparation and so on. In this paper, we explore the influence by a series of loadings on samples in the direction perpendicular to the direction of the previous peak stress. Cyclic uniaxial compressions on the rectangular specimen and cyclic Brazilian tests were carried out based on the contact model in the particle flow code. The results demonstrate that, the disturbance in the orthogonal direction cannot influence Kaiser effect of the rock sample.

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Creep Structure Effect of Layered Rock Mass Based on Acoustic Emission Characteristics

Shock and Vibration ◽

10.1155/2021/7419741 ◽

2021 ◽

Vol 2021 ◽

pp. 1-14

Author(s):

Huichen Xu ◽

Yong Zhang ◽

Chengwei Zhao ◽

Chengyu Miao ◽

Xiaoming Sun

Keyword(s):

Acoustic Emission ◽

Rock Mass ◽

Inclination Angle ◽

Stress Level ◽

Rock Sample ◽

Structural Effect ◽

Emission Characteristics ◽

Structural Effects ◽

Layered Rock ◽

Layered Rock Mass

Investigating the creep structural effect of layered rock mass is of great practical and theoretical significance. In this paper, taking the Muzhailing tunnel as an example, structure effect of layered rock mass based on acoustic emission characteristics has been analyzed. The study shows that creep parameters of layered rock mass are significantly influenced by structural effects, and the overall creep variable is small. The creep deformation of layered rock mass includes transient creep and steady-state creep at a low stress level. At a higher stress level, when the long-term strength of the rock sample is reached, the deformation increases rapidly, and the accelerated creep occurs in a very short period of time. The creep equation of the structural effects of layered rock mass was established based on the experimental results. Acoustic emission characteristics are analyzed during creep experiment; the study shows that the energy released at the time of initial loading and destruction accounted for most of the total energy. The initial energy release increased first and then decreased with the increase in inclination angle; as the inclination angle increased, the cumulative energy when the rock sample was damaged first decreased and then increased. The structural effect on the main frequency value at the time of failure mainly reflected in the trend that the main frequency value first increased and then decreased as the inclination angle increased. Based on the above analysis, we can recognize the structural effects of layered rock mass and provide the necessary parameters for on-site support.

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Research on the Impact of Different Force Directions on the Mechanical Properties and Damage Evolution Law of Sandstone with Different Hole Diameters

Advances in Civil Engineering ◽

10.1155/2021/4247027 ◽

2021 ◽

Vol 2021 ◽

pp. 1-14

Author(s):

Fukun Xiao ◽

Renhe Li ◽

Le Xing

Keyword(s):

Mechanical Properties ◽

Acoustic Emission ◽

Energy Conversion ◽

Rock Sample ◽

Strain Curve ◽

Hole Diameter ◽

Stress Strain Curve ◽

Rock Samples ◽

The Impact ◽

Vertical Hole

In this research, a uniaxial acoustic emission experiment was conducted on rock samples with different positions and diameters of the hole, and an analysis was made on the impact of different hole positions and diameters on the mechanical properties, failure, energy conversion, and acoustic emission-caused damage characteristics and laws of the rock samples. The results reveal as follows: first, due to the existence of holes in rocks, the stress-strain curve changes at each stage, accompanied by multiple stress drops. And the peak strength gradually reduces with the increase in hole diameter. At different hole positions, the duration that the rock sample passes through at each stage of the stress-strain curve varies, and the peak strength of the rock with the vertical hole is greater than that of the rock with the horizontal hole. This indicates that the bearing capacity and stability of the rock sample with the vertical hole are greater than those of the rock sample with the horizontal hole of the same diameter. Second, by making a comparison on the failure characteristics of rock samples, it is found that the intact rock shows brittle failure. For the rock sample with the horizontal hole, symmetrical tensile cracks initially appear in the upper and lower parts of the hole and finally form shear failure. As for the rock sample with the vertical hole, Y-shape failure originally presents and eventually forms N-shape failure with the increase in hole diameter. Over a comparison with the failure pattern of an intact rock sample, it is demonstrated that the final failure pattern and crack expansion trend on the rock sample vary with the change in the hole position and diameter. Third, as obtained by comparing and analyzing the energy conversion of the rock with different diameters of the hole, the energy conversion in the rock is changed due to the existence of holes, and the increase in hole diameter causes a gradual decrease in the elastic energy stored in the rock and gradual increase in the dissipated energy. And by comparing the energy conversion of the rock with different positions of the hole, it is acquired that the elastic energy conversion ratio of the rock with the vertical hole is higher than that of the rock with the horizontal hole. Furthermore, an explanation was made on the difference in the failure processes of the two types of rocks from the perspective of energy conversion.

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Acoustic Emission Characteristics of Graded Loading Intact and Holey Rock Samples during the Damage and Failure Process

Applied Sciences ◽

10.3390/app9081595 ◽

2019 ◽

Vol 9 (8) ◽

pp. 1595 ◽

Cited By ~ 5

Author(s):

Xiaofei Liu ◽

Huajie Zhang ◽

Xiaoran Wang ◽

Chong Zhang ◽

Hui Xie ◽

...

Keyword(s):

Acoustic Emission ◽

Rock Mass ◽

Large Scale ◽

Rock Sample ◽

Axial Stress ◽

Failure Process ◽

Dynamic Monitoring ◽

Rock Samples ◽

General Law ◽

Ae Counts

Rock burst is the result of the development and extension of micro-cracks during the loading process of large-scale rock mass in underground space engineering. Dynamic monitoring results by acoustic emission (AE) can accurately perceive the inner fracture evolution of rock mass and effectively warn about its induced disasters early. By contrastive testing the AE parameters in the whole fracture process of the intact and holey rock samples under graded loading, their spatiotemporal evolution rules were analyzed in this paper, and the damage model of rock samples based on AE localization events was established to analyze the relationship between rock damage and loads. The results show that: (1) Under the condition of grading loading, AE parameter increases with the increase of axial stress and show three states, respectively, which are slow-growth, stabilization and rapid increasing; meanwhile, the damage of the sample has a cumulative effect with time. (2) The AE counts and energy are highly correlated with the fracture of the sample that the more severe the damage of the sample, the faster the crack propagation as well as the higher the acoustic emission counts and the energy amplitude. The damage state of granite sample can be accurately judged by two parameters to character the damage evolution process and fracture mechanism. (3) Compared with the intact rock sample, due to the pressure relief effect of the hole, the rock sample containing the hole takes a long time in the compaction stage and with higher load stress level. Although the AE counts and energy were lower in the damage process, the general law of their response during damage and instability process still exists.

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Estimation of Rock In-Situ Stress by Acoustic and Electromagnetic Emission

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.13-14.357 ◽

2006 ◽

Vol 13-14 ◽

pp. 357-362 ◽

Cited By ~ 4

Author(s):

Yasuhiko Mori ◽

P. Sedlak ◽

Josef Sikula

Keyword(s):

Acoustic Emission ◽

Simultaneous Measurement ◽

Rock Sample ◽

Electromagnetic Emission ◽

In Situ Stress ◽

New Method ◽

Acoustic Emission Activity ◽

Kaiser Effect ◽

Emission Activity

The Kaiser Effect in acoustic emission is often used for an estimation of the stress to which rocks have been subjected. However, there are cases in which the Kaiser Effect is not clear, since the noises due to the contact and/or the stick slip between the pre-induced fracture surfaces are measured during the reloading process. In such cases, estimation of previous stress is difficult by the conventional method which is based on the acoustic emission activity observed under reloading process. In the tests for the Kaiser Effect on rocks, therefore, the noises must be eliminated from the acoustic emission generated from newly created cracks during the second loading process. Such techniques as analysis of the difference between the acoustic emission activity observed in the first and second reloading and the analysis of the change in the slope of the acoustic emission amplitude distribution have been proposed. In this paper we present a new method by which the maximum previous stress in rocks can be directly estimated without any post signal analysis. In the new method, simultaneous measurement of acoustic and electromagnetic emission during loading test of rock sample is employed. The electromagnetic emission in the deformation of rock sample generates only when the fresh surfaces due to cracking are created in the material, and the source of electromagnetic emission is the electrification between the fresh crack surfaces. This paper describes the simultaneous measurement of acoustic and electromagnetic emission useful for estimating the rock in-situ stress.

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Acoustic Emission in Friction

10.1016/s0167-8922(07)x8019-2 ◽

2007 ◽

Keyword(s):

Acoustic Emission

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