Failure characteristics and stress distribution of pre-stressed rock specimen with circular cavity subjected to dynamic loading

Overlapped residual coal pillars, together with the surrounding rock strata, play a combined bearing role in ultra-close multiple seam mining. Global stability of the whole bearing system is significant for the mining design, construction, and operation. Laboratory uniaxial compressive experiments for different kinds of sandwiched coal-rock specimens are carried out to investigate the progressive failure characteristics and mechanisms. Results show that: (1) The mechanical behavior of the sandwiched coal-rock specimen is mainly divided into four stages during the failure process. The response of the electrical resistivity and the evolution of acoustic emission (AE) energy are in good agreement with the mechanical behaviors at different stages, which are a reflection of the global failure characteristics of sandwiched specimens. (2) The distribution of AE events and the development of local strain can provide further insight into the local failure characteristics of coal elements or rock elements in sandwiched specimens. AE events are more likely to be generated in coal elements, which can propagate across coal-rock interfaces and induce damage to rock elements in a certain area. Similarly, the unbalanced deformation characteristics of coal elements and rock elements are apparently revealed in the progressive failure process. (3) Progressive failure of a sandwiched coal-rock specimen is closely associated with the interactions between the coal elements and rock elements. Initial failure usually appears in the coal elements. At this process, the recovery of elastic deformation and the output of strain energy are observed in the rock elements, which can accelerate the rupture of coal elements. In turn, the dynamic fracture energy generated in the rupture process of coal elements can propagate into rock elements and induce damage to rock elements a certain area. (4) The experimental results are helpful for maintaining the long-term stability of a sandwiched coal-rock system in ultra-close multiple seam mining.

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Stress redistribution of dynamic loading incident with arbitrary waveform through a circular cavity

International Journal for Numerical and Analytical Methods in Geomechanics ◽

10.1002/nag.2897 ◽

2019 ◽

Vol 43 (6) ◽

pp. 1279-1299 ◽

Cited By ~ 16

Author(s):

Ming Tao ◽

Zhanwen Li ◽

Wenzhuo Cao ◽

Xibing Li ◽

Chengqing Wu

Keyword(s):

Dynamic Loading ◽

Stress Redistribution ◽

Circular Cavity ◽

Arbitrary Waveform

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A case study of floor failure characteristics under fully mechanised caving mining conditions in extra-thick coal seams

Journal of Geophysics and Engineering ◽

10.1093/jge/gxaa031 ◽

2020 ◽

Vol 17 (5) ◽

pp. 813-826

Author(s):

Pingsong Zhang ◽

Yuanchao Ou ◽

Binyang Sun ◽

Chang Liu

Keyword(s):

Stress Distribution ◽

Western China ◽

Monitoring Method ◽

Thick Coal Seam ◽

Failure Characteristics ◽

Engineering Research ◽

Object A ◽

Working Face ◽

Floor Failure ◽

Inclined Boreholes

Abstract To determine the failure characteristics and evolution regularity of the floor strata during fully mechanised top-coal cave mining in typical deep and extra-thick seams in western China, the 61303 working face of an Ordos mine was selected as the engineering research object. A comprehensive monitoring method combining a BOTDR (Brillouin Optical Time-Domain Reflection) distributed fiber strain test and a borehole resistivity CT (Computerised Tomography) test was adopted. The results show that floor stress distribution of the deep-buried and extra-thick coal seam is significantly affected by the different depths of rock lithology. At the interface of the rock strata with a large difference in the elastic modulus, phenomena such as the asynchronism of strata movement and obvious differences in failure easily occur. The failure depth of the floor strata in the 61303 working face is approximately 15.90 m, and the influence depth of the floor disturbance is approximately 32.70 m. Under the influence of the mining pressure, floor stress distribution and crack evolution have obvious spatial and temporal effects. In different inclined boreholes, the data captured by the cable have different values and the fracture locations of the cable also differ. Compared with a single borehole, multiple boreholes with different inclinations, directions and locations can provide more comprehensive and reliable data trends. The knowledge obtained by this monitoring can provide reference information for the study of floor damage under similar conditions and the formulation of technical measures such as those that prevent mine water disasters.

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Study on the Failure Characteristics of Coal Wall Spalling in Thick Coal Seam with Gangue

Advances in Civil Engineering ◽

10.1155/2020/6668458 ◽

2020 ◽

Vol 2020 ◽

pp. 1-10

Author(s):

Guosheng Li ◽

Zhenhua Li ◽

Feng Du ◽

Zhengzheng Cao

Keyword(s):

Stress Distribution ◽

Coal Seam ◽

Internal Stress ◽

External Stress ◽

Theoretical Research ◽

Risk Area ◽

Thick Coal Seam ◽

Failure Characteristics ◽

Coal Wall ◽

Stress Environment

Coal wall spalling is one of the main factors restricting the safe and efficient mining of thick coal seam, and the gangue has an important impact on the coal wall spalling. To obtain the failure characteristics of coal wall spalling in thick coal seam containing gangue, numerical calculation and theoretical research were used to analyze the morphological differences of coal wall spalling with different gangue positions. Besides, the damage depth, width, and stress environment of coal wall panel caused by the position of gangue were mainly studied, and the failure mechanics model of coal seam containing gangue was established by using the stability theory of pressure bar. The results show that, compared with coal wall spalling in coal seam without gangue, coal seam with the lower and middle gangue has a significant weakening effect on the wall spalling, and coal seam with the upper gangue has little effect on the wall spalling. In the case of coal seam with gangue, the upper gangue has the highest risk area of coal wall spalling with the maximum depth and width of 2.0 m and 2.3 m. For coal seam with the upper gangue, the dangerous areas of coal wall spalling are mainly distributed in the vicinity of the gangue; for coal seam without the gangue, they are mainly distributed in the middle of the coal seam. The gangue cannot change the law of the external stress distribution of the coal seam, but it has an obvious impact on the internal stress distribution of the coal seam. With the different positions of the gangue, the stress distribution in the coal seam has a great difference, and the maximum difference is 1.8 MPa. This shows that the stress environment of the coal seam containing gangue has the following typical characteristics: “the external stress is controlled by the overburden fracture, and the internal stress environment is controlled by the gangue.” Through the mechanical analysis of the coal seam containing gangue, it is further verified that the coal seam containing gangue is more prone to spalling at the position of gangue.

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DYNAMIC STRESS DISTRIBUTION IN A MODEL OF IMPLANTED MANDIBLE: NUMERICAL ANALYSIS OF VISCOELASTIC BONE

Journal of Mechanics in Medicine and Biology ◽

10.1142/s0219519415500505 ◽

2015 ◽

Vol 15 (04) ◽

pp. 1550050 ◽

Cited By ~ 2

Author(s):

H. MOTALLEBZADEH ◽

M. TAFAZZOLI-SHADPOUR ◽

M. M. KHANI

Keyword(s):

Finite Element ◽

Stress Distribution ◽

Cortical Bone ◽

Dynamic Loading ◽

Viscoelastic Behavior ◽

Element Model ◽

Von Mises Stress ◽

Dental Implantation ◽

Trabecular Bones ◽

Von Mises

To determine the success of dental implants, mechanical stress distribution in the implant-bone interface is considered to be a determinant. Many researchers have used finite element modeling of implant-bone through applying static loading on the implant; however, dynamic loading has not extensively been investigated specially considering viscoelastic behavior of the bone. The aim of this study is to analyze effects of viscoelasticity of bone and dynamic loading comparable to mastication conditions on stress distribution in an implanted mandible. A three-dimensional finite-element model of an implanted mandible in the first molar region was constructed from computerized tomography data. Effects of several parameters, such as material properties including viscoelastic behavior of the cortical and trabecular bones, load amplitude, duration and direction on the instantaneous and long-term von Mises stress distribution of an implanted mandible were evaluated. In all loading conditions, the maximum von Mises stress occurred in cortical bone surrounding the neck of implant. Stress distribution was not noticeably affected by viscoelastic behavior during the first loading cycles, however, after 100 s periodic loading, the differences between stress magnitudes (especially in the cortical bone) became noticeable. In addition, sensitivity analysis showed that both cortical and trabecular bones were more sensitive to axial load than buccalingual and mesiodistal forces. The results of this study contribute to analysis of parameters involved in success of dental implantation.

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