WEBJun 1, 2020 · In the loadingunloading tests, the PER value was calculated based on the initial porosity and the relative increment in the volumetric strain during the whole loadingunloading process. A lower ...
WEBFeb 1, 2019 · the pressure loading and unloading process was explained theoretically based on a tight fourparticle packing unit, whic h provides a reasonable explanation for the experimental results
WEBApr 1, 2017 · In underground operations, the coal cutter cut the coal seam, and large coal blocks were cut off from the coal wall. Then, the coal blocks were transported to the laboratory and processed into cylindrical specimens with diameters of 50 mm and lengths of 100 mm in accordance with the ISRM standard (Fairhurst and Hudson, 1999).The .
WEBApr 28, 2017 · During the postpeak loading and unloading process, the flow rate of the coal sample will decrease with the loading of confining pressure but increase with the unloading of confining pressure, and ...
WEBJun 1, 2019 · The fitting formulas of coal sample axial and radial permeability values under three loading/unloading cycles are shown in Table 5. In Table 5, subscripts A and R respectively denote the axial and radial permeability of coal samples; L and U denote loading and unloading, respectively; and 1, 2, and 3 refer to the number of .
WEBAug 1, 2022 · In the cyclic loading and unloading process, the load ing and unloading elastic modulus of coal samples experi ences a rapid increase at the beginning stage of the cyclic
WEBAs the coal body has a hysteresis effect during the unloading process, it cannot be unloaded to 0 when unloading, and the minimum unloading level was set for the four kinds of samples; that is, after unloading to 2% σ c, the loading was performed until the sample was destabilized.
WEBIn the excavation process, the coal pillar will undergo shear failure due to repeated loading and unloading from mining stress. Meanwhile, plastic flow will occur after shear failure. The permeability change of the coal pillar under plastic flow is closely related to the loading path. Through a permeability test of the coal sample after shear yielding under .
WEBJun 1, 2015 · Fig. 3 (a) compares the deviatoric stress–strain complete process in coal I under both constant and unloading confining pressures. Fig. 3 (b) plots the complete process of coal II under only unloading confining pressure. Firstly, the deviatoric stress–strain complete process is observed to be almost identical before the loading .
WEBMar 7, 2021 · In coal mining activities, the abutment stress of the coal has to undergo cyclic loading and unloading, affecting the strength and seepage characteristics of coal; additionally, it can cause ...
WEBFeb 20, 2020 · Loading and Unloading Elastic Modulus. Coal is a porous medium that is affected by the geologic environment during the formation process. Coal contains a large number of primary pores and microcracks, resulting in coal being a .
WEBMar 16, 2023 · Research on the mechanical properties and damage evolution of coal during true triaxial cyclic loading and unloading is of great significance for maintaining the longterm safety and stability of underground engineering structures in coal mines. In this paper, firstly, the deformation, strength and fracturing characteristics of coal during true triaxial .
WEBNov 20, 2022 · The paper represents a test investigation of the mechanical properties and acoustic emission (AE) characteristics of lowstrength coal specimens subjected to cyclic loading and unloading. From the lab tests, the following conclusions can be obtained: (1) The axial strain is very well linear with the loading–unloading cycle number, and the .
WEBNov 1, 2023 · Coalrock combinations is a composite structure often encountered in mining engineering. At present, the research on coalrock combinations mainly focuses on the loading mechanical properties. However, when mining engineering involves excavation, the mechanical characteristics of the coalrock combination during unloading are very .
WEBMar 20, 2023 · In the process of coal formation, the internal structure is different from the occurrence of primary cracks. As a result, the new crack generation and primary crack development of different samples are affected to different degrees during loading and unloading. Energy characteristics under true triaxial loading and unloading
WEBFeb 8, 2019 · Rock burst is a astrophic dynamic disaster caused by sudden failure and instability of coal, loading paths play an important role in the failure of coal, the coal failure process is associated with charge exception information. Hence, violent coal failure mechanics and time–frequency domain distribution of charge signal such as rock burst .
WEBSep 24, 2022 · Effect of Cyclic Loading and Unloading on the Deformation and Damage Properties of Sandstone from Beizao, a Coal Mine underneath the Bohai Sea in China September 2022 Geofluids 2022(3):111
WEBMay 14, 2024 · This study investigates the stability of an artificial dam used in an underground reservoir in a coal mine under periodic weighting imposed by overlying rock strata. For this purpose, cyclic loading and unloading tests with different stress amplitudes were designed. Differences in the mechanical performance of the artificial dam with and .
WEBJun 1, 2019 · (3) During the loadingunloading process of confining pressure, the permeability of coal containing gas is damaged to a certain extent and this damage can be represented by the maximal damage rate ...
WEBJan 7, 2023 · By testing permeability during the loading and unloading process of coal samples, key parameters of the fractional permeability model were obtained to enter specific values into the model to ...
WEBThe permeability characteristics of a broken coal mass under repeated loading and unloading conditions exert significance on spontaneous combustion of coal in goaf during the mining of coal seam groups. Considering this, by using the seepage test system for broken coalrock mass, seepage tests under cyclic loading and unloading .
WEBIn actual mining situations, the advancing speed of the working face is usually accelerated, which may affect the failure and seepage characteristics of gasbearing coal, and may even induce dynamic disasters. In order to discover the effects of such accelerated advancement of the working face, an experimental study on the failure and seepage .
WEBJun 1, 2020 · As the coal body has a hysteresis effect during the unloading process, it cannot be unloaded to 0 when unloading, and the minimum unloading level was set for the four kinds of samples; that is, after unloading to 2% σ c, the loading was performed until the sample was destabilized.
WEBJan 9, 2017 · various loading conditions, an ultrasonic test system f or the deformation and fracture of coal rock was used and a cyclic loading and unloading pattern is adopted.
WEBJan 23, 2021 · On the premise that the point of the maximum abutment pressure is the demarion point of gas migration, an experimental research was conducted on gasbearing coal by using a thermofluid–solid coupling test system. The research results demonstrate that irreversible strain and elastic modulus increase with increase in .
WEBFeb 1, 2024 · In the process of coal seam mining, the coal is disturbed by periodic pressure. This disturbance can be simplified to the loading process under different stress environments [5], [9], [10], [45], and the characteristics of the mining stress path are different under different advancing speeds [46]. Fig. 3 shows the loading path of the .
WEBSep 19, 2023 · This paper presents two experimental schemes, graded cyclic loading and unloading, and variable lower limit cyclic loading and unloading, to investigate the energy evolution and acoustic emission characteristics of rocks under different cyclic loading and unloading paths. The experiments were conducted using a WAW300B microcomputer .
WEBApr 5, 2021 · For example, in the loading and unloading process, much elastic energy accumulates in the coal and rock mass with increasing elastic deformation. Under unloading, elastic energy is released. In the test process, the total energy density and elastic energy density of the coal mass can be expressed as Formulas ( 2 ) and ( 3 ).
WEBSep 1, 2018 · However, the loading and unloading rates have an important influence on the mechanical properties of the coal, and are closely related to the excavation steps of the working face. During an actual excavation process in a coal mine, the coal miners often reduce the excavation steps in order to prevent coal and gas outburst.
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