scholarly journals Mechanical Properties and Acoustic Emission Properties of Rocks with Different Transverse Scales

2017 ◽  
Vol 2017 ◽  
pp. 1-8
Author(s):  
Xi Yan ◽  
Li Jun ◽  
Liu Gonghui ◽  
Guo Xueli
Keyword(s):  
Mechanical Properties ◽  
Acoustic Emission ◽  
Uniaxial Compression ◽  
Compression Strength ◽  
Petroleum Engineering ◽  
Uniaxial Compression Strength ◽  
Emission Properties ◽  
Aspect Ratios ◽  
Transverse Scale ◽  
The Stability

Since the stability of engineering rock masses has important practical significance to projects like mining, tunneling, and petroleum engineering, it is necessary to study mechanical properties and stability prediction methods for rocks, cementing materials that are composed of minerals in all shapes and sizes. Rocks will generate acoustic emission during damage failure processes, which is deemed as an effective means of monitoring the stability of coal rocks. In the meantime, actual mining and roadway surrounding rocks tend to have transverse effects; namely, the transverse scale is larger than the length scale. Therefore, it is important to explore mechanical properties and acoustic emission properties of rocks under transverse size effects. Considering the transverse scale effects of rocks, this paper employs the microparticle flow software PFC2D to explore the influence of different aspect ratios on damage mechanics and acoustic emission properties of rocks. The results show that (1) the transverse scale affects uniaxial compression strength of rocks. As the aspect ratio increases, uniaxial compression strength of rocks decreases initially and later increases, showing a V-shape structure and (2) although it affects the maximum hit rate and the strain range of acoustic emission, it has little influence on the period of occurrence. As the transverse scale increases, both damage degree and damage rate of rocks decrease initially and later increase.

THE INFLUENCE OF CLASSIFICATION PARAMETERS UNCERTAINTY ON ROCK MASS QUALITY ASSESSMENT

2020 ◽  
Author(s):  
Ahmed Mušija ◽  
Kenan Mandžić
Keyword(s):  
Rock Mass ◽  
Uniaxial Compression ◽  
Compression Strength ◽  
Working Environment ◽  
Uniaxial Compression Strength ◽  
Adequate Model ◽  
Geotechnical Characteristics ◽  
Road Tunnels ◽  
The Stability

The construction of underground objects is a very complex task that takes into account a large number of input parameters that affect the process of building and stability of underground objects during the exploatation. Engineering geological and geotechnical characteristics of the rock mass represent the basic input data for the development of an adequate model and assessment of the quality of the rock mass, and thus the assessment of the primary support that will ensure the stability of the rock mass during construction. In order to more clearly define the quality of rock mass as a working environment, various classifications have been developed in the world that analyze the influencing factors and give an assessment of the quality of rock mass. Uniaxial compression strength and the influence of groundwater appear as parameters in the RMR classification of rock mass. The paper presents the problems of adequate definition of uniaxial compression strength parameters and influence of groundwater in construction of road tunnels.

scholarly journals Mechanical Properties and Acoustic Emission Characteristics of Karst Limestone under Uniaxial Compression

2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
Author(s):  
Jianxun Chen ◽  
Qingsong Wang ◽  
Jiaqi Guo ◽  
Yanbin Luo ◽  
Yao Li ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Acoustic Emission ◽  
Water Content ◽  
Uniaxial Compression ◽  
Wave Velocity ◽  
Brittle Failure ◽  
Shear Failure ◽  
Testing Machine ◽  
Natural State ◽  
Saturated State

Firstly, I-RPT ultrasonic detector was used to test the wave velocity of karst limestone with different initial microstructure and water content. Then, RMT-150B rock testing machine and DS2-16B acoustic emission system were used to test the acoustic emission (AE) under uniaxial compression. Mechanical properties and AE characteristics were obtained during rock failure. The detailed relationship between stress-strain and AE characteristics was studied in this paper. Research results indicated the following: (1) For samples with many primary fissures and defects, wave velocity in dry state was larger than that in its natural state. From natural state to saturated state, the wave velocity tended to increase. For samples with good integrity, wave velocity increased with increasing of water content. (2) In the dry state, the samples presented tension failure. In saturated state, the samples presented tension-shear failure. For samples with cracks and good integrity, samples showed brittle failure. For samples with many corrosion pores which showed ductile damage under natural and saturated state, the spalling phenomenon was enhanced under saturated state. (3) With increasing of water content, the peak stress and AE peak reduced dramatically. In brittle failure, AE peak could be considered a sign of failure. In ductile failure, AE activity decreased gradually with the decrease of stress. (4) The mechanical properties and AE characteristics corresponding to four main fracture propagation types were also discussed.

scholarly journals Specific Energy of Hard Coal Under Load

2015 ◽  
Vol 37 (1) ◽  
pp. 9-16 ◽  
Author(s):  
Anna Bogusz ◽  
Mirosława Bukowska
Keyword(s):  
Kinetic Energy ◽  
Total Energy ◽  
Uniaxial Compression ◽  
Specific Energy ◽  
Compression Strength ◽  
Longitudinal Strain ◽  
Full Range ◽  
Dissipated Energy ◽  
Uniaxial Compression Strength ◽  
Recoverable Energy

Abstract The article presents results of experimental tests of energy parameters of hard coals under loading, collected from research sites located within five main geologic structures of Upper Silesian Coal Basin (GZW) - Main Trough, Main Anticline, Bytom Trough, Rybnik Trough and Chwałowice Trough. Coals from12 mines were analysed, starting with seams of group 200, through groups 400, 500, 600 and, finally, seams of group 700. Coal of each of the groups of seams underwent uniaxial compression stress of the energy parameters, in a servo-controlled testing machine MTS-810NEW, for the full range of strain of the tested coal samples. Based on the tests the dependence of different types of specific energy of longitudinal strain of coals on the value of uniaxial compression strength was determined. The dependence of the value of dissipated energy and kinetic energy of coals on the uniaxial compression strength was described with a linear function, both for coals which due to their age belong to various bed sand for various lithotypes of coal. An increase in the value of dissipated energy and in kinetic energy was observed, which was correlated with an increase in uniaxial compression strength of coal. The share of dissipated energy is dominant in the total energy of strain. Share of recoverable energy in the total energy of strain is small, independent of the compression strength of coals and is at most a few per cent high. In coals of low strength and dominant share of dissipated energy, share of recoverable energy is the biggest among the tested coals. It was shown that following an increase in compression strength the share of recoverable energy decreases, while the share of dissipated energy in the total energy increases. Further studies of specific energy of longitudinal strain of rocks in the full-range strain will be the next step inperfecting methodology of research into natural rock burst susceptibility of Carboniferous rock mass and changes in the susceptibility resulting from mining activity.

scholarly journals Investigation of the Effect of Bedding Layer Angle and Tunnel Number on the Stability of Tunnel under Uniaxial Compression Using PFC2D

2021 ◽  
Author(s):  
Vahab Sarfarazi ◽  
Kaveh Asgari ◽  
Mahdiyah Azizian
Keyword(s):  
Mechanical Properties ◽  
Uniaxial Compression ◽  
Dominant Mode ◽  
Two Dimensions ◽  
Particle Flow Code ◽  
Concrete Layer ◽  
Tunnel Diameter ◽  
Tunnel Number ◽  
Crack Growth Path ◽  
The Stability

In this paper the effect of bedding layer angle on the stability of tunnel under uniaxial compression have been investigated using particle flow code in two dimensions (PFC2D). For this purpose, numerical rectangle models with dimension of 100*100 mm have been prepared. These models consist of layers with different mechanical properties i.e., concrete layer and gypsum layer. The angle of these layers related to horizontal axis change from 0° to 90° with increment of 15°. These models are consisting of one, two and three tunnel. The diameter of tunnel change based on the tunnel number. The tunnel diameter was 6 m, when one tunnel exists in the model. The tunnel diameter was 3 m, when two tunnels exist in the model. The tunnel diameter was 2 m, when three tunnels exist in the model. These models were subjected to uniaxial compression. The results show that tensile cracks are dominant mode of fracture occurred in the models. The joint angle and tunnel number have important effect on the failure pattern and failure strength. Also, the mechanical properties of beddings control the crack growth path. The crack grows through the weak layers when bedding angle was equal to 45° and 60°, but it intersects the layer for any other bedding angels.

scholarly journals Dual role of microcracks: toughening and degradation

2001 ◽  
Vol 38 (2) ◽  
pp. 427-440 ◽  
Author(s):  
G M Nagaraja Rao ◽  
C RL Murthy
Keyword(s):  
Mechanical Properties ◽  
Acoustic Emission ◽  
Uniaxial Compression ◽  
Inelastic Strain ◽  
Dual Role ◽  
Compression Tests ◽  
Defective Structure ◽  
Heating And Cooling ◽  
Thermally Treated

One of the methods of improving the mechanical properties of ceramics is to introduce a defective structure that acts as a restraint for the propagation of cracks. In the present study a detailed investigation was carried out by introducing a defective structure in rock to determine if there is any improvement in properties similar to ceramics. Granite was chosen for the investigation, and the microcracks were introduced by a heating and cooling cycle. Uniaxial compression tests have shown that granite thermally treated to 200°C shows the highest strength, and the strength of granite treated to 400°C is comparable to that of unheated granite. Both ultrasonic images and acoustic-emission monitoring show that for thermally treated samples the stress-induced microcrack and macrocrack nucleation and their growth are retarded. The variations in mechanical properties are explained based on the concept of toughening and degradation. Uniaxial compression tests on unheated and thermally treated granite samples have clearly established the dual role of microcracks, which operate in the toughening and degradation mechanisms.Key words: thermal treatment, microcrack, inelastic strain, ultrasonic C-scan imaging, acoustic emission, toughening.

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