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.
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Compared with the axial loading rate, the hoop unloading rate is the main reason for the change of the rock failure mode . Ma et al. found that the rapid unloading intensified the damage of coal samples before and after rupture, resulting in a sharp increase in the damage curve. Therefore, in actual production, the excavation speed of coal and ...
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Coalburst is a violent dynamic failure of coal during underground mining. It is of significance to study failure pattern as well as energy evolution and transition during coalbursts and how they are influenced by preconfinement. This paper presents unloadinginduced coalburst simulations using the distinct element method via a combined staticdynamic loadingunloading strategy.
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Conventional and cyclic unloading tests with different unloading rates were conducted to study the influences of unloading patterns and rates on the deformation characteristics and mechanical properties of tectonic coal. The results demonstrate that, under continuous unloading, a lower unloading rate promotes an increase in the circumferential strain but inhibits increases in axial strain.
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Given the roadway deformation and surrounding rock control in the process of thin coal seam mining, the coalrock combination with inclination angles for 0°, 15°, 30°, 45°, and 60° was designed. The rock mechanic test machine was used to conduct a uniaxial compression test and a graded loading and unloading test on the coalrock combination; the failure characteristics of the two were ...
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The mining of coal resources causes the stress on the front and both sides of the working face to be in a complex loading and unloading process, and the gas contained in the coal body migrates, which can cause gasdynamic disasters in severe cases.
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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
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Mining under the sea is a challenging task in China. Affected by blasting, tunneling, and other engineering disturbance, surrounding rock is often in a state of cyclic loading and unloading stress. In this study, in order to investigate the effect of cyclic loading and unloading on the deformation and damage characteristics of sandstone underneath the Bohai Sea, the GCTS test machine is used ...
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The size effect of coalgangue mass after loading and unloading test is the reflection of its inherent structural complexity, which is due to the existence of fracture network system in rock mass and the joint influence of loading and unloading process. Coalgangue physical and mechanical properties and particle distribution, as well as defects ...
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Ship Cargo Handling, Loading, Unloading: A commercial ship is usually a link in a "trade route" between distant points. Goods flowing in the route must be transferred to and from the sea link; they must also be given care while aboard the ship, and in turn they must not be a hazard to the ship and its crew. Ancient cargo handling consisted almost exclusively of manually carrying cargo in ...
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Discussion on bulk carrier loading and unloading operations and freight safety for the owner's and master's responsibilities and ... Hu SP, Jin YX, et al. Performance simulation of the transportation process risk of bauxite carriers based on the Markov Chain and Cloud model. J Mar Sci Eng 2019; 7(4): 116. Crossref. Google Scholar. 7. ...
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To investigate the influence of loadingunloading paths as well as loading and unloading rates on the deformation and failure behavior of coal, laboratory experiments and numerical simulations of unloading under axial pressure and confinement were carried out. The effect of different axial loading rates and unloading rates on the deformation and failure behavior of coal under the unloading ...
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During the deformation process of coal under the combined highstatic confining pressure and axial disturbance loads, we found that the final instability failure of coal specimens, subjected to disturbance load, were more likely to occur in the disturbance loading and unloading stage, such as specimen SB1, and SD1.
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Experimental Device. The "gascontaining coal thermalfluidsolid coupling threeaxis servo seepage system" developed by Chongqing University (Fig. 2) was used to study the effect of variable confining pressure unloading rate on coal deformation and permeability characteristics during the alternate loading and unloading device has a maximum axial force of 1000 kN, a ...
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Unloading PRB coal cars with a Dravo rotary dumper
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In the unloading process, the fracture space in coal sample extends and expands passively, instead of the compression of fracture under stress loading. The microcracks and beddings in the coal sample gradually connect, the number of gas permeation channels increases, and the rate of gas transport within coal becomes faster.
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A scheme of the uniaxial cyclic loading and unloading tests is shown in Fig. 2b. The test process used the displacement control method, and the loading and unloading rate was mm/min, with 6 ...
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The process of loading and unloading can involve heavy equipment, moving machinery, and manual labor, which increases the risk of accidents and injuries. It is crucial to provide comprehensive training, enforce safety protocols, and use proper personal protective equipment to minimize these risks. 2. Damage to cargo and vessel.
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The residual strains has produced by the first loadingunloading of coal are 7 × 10 −5, × 10 −4, and × 10 −4, respectively. ... However, if the loadingunloading process was continued beyond this point, the residual strain reappeared. The occurrence of the nonresidual strain phenomenon was found to be directly related to the ...
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Thus, the axial stress in the experiment is equal to the confining stress. In this study, three loading and unloading seepage tests have been carried out to simulate the effect of three coal seams mining on the caving zone and the second and third loading and unloading stress paths are the same as the first loading and unloading stress path.
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Compared with the loading approaches mentioned above, the cyclic loadingunloading testament is an effective approach in revealing the mechanical response of coal and rock under repeated disturbance of excavation, 47, 50, 51 through parameters, such as peak strength, elastic modulus, and energy dissipation features. 33, 47, 48, 52 Though many ...
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The working process of the underground coal bunker was actually the loading or unloading of coal for the silo wall. And the stress environment of the silo wall and surrounding rock continually changes, resulting in the deformation of the silo wall under the inner lateral pressure. Stress Analysis
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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
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Scholars have examined the mechanical 22,23, the damage 24,25, and the energy characteristics 26,27 of coal under cyclic loading and unloading. In the process of cyclic loading, some scholars ...
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The rock mass in fault zones is frequently subjected to cyclic loading and unloading during deep resource exploitation and tunnel excavation. Research on the mechanical and hydraulic characteristics of fault rock during the cyclic loading and unloading is of great significance for revealing the formation mechanism of waterconducting pathways in fault and preventing water inrush disasters. In ...
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Fig. 3 presents the influences of gas pressure on coal permeability during gas loadingunloading processes at temperatures of 30 °C, 40 °C, 50 °C, 60 °C, and 70 °C, respectively. In the loading process, the coal permeability decreases gradually. As the pore pressure rises from MPa to MPa, the coal permeability decreases rapidly.
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To study the anisotropic mechanical properties and energy evolution of layered rock masses under the action of cyclic loading, uniaxial graded cyclic loading and unloading tests under different upper and lower stress limits were carried out on samples with different bedding angles (0°, °, 45°, °, and 90°) to explore the deformation and mechanical response characteristics of bedded ...
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Observing the whole unloading process, the unloading time is 133 s when the density of coal bulk is 1600 kg/m 3, the unloading time is s when the density is 1350 kg/m 3 and the unloading time is s when the density is 1100 kg/m 3, so the higher the particle density in the silo, the faster is the unloading speed.
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To further validate and promote the proposed damage constitutive model, the loadingunloading process of coal material is also simulated. Because energy is continuously transformed during loading, in the loadingunloading process, the damage variable is also defined by energy dissipation.
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The coils are then loaded either on a reel style or cradle style uncoiling system. Cradle style uncoilers are relatively easy to load, you basically lower your coil onto the cradle, position the sides guides to center the coil and your coil is ready to be released. On a reel type the process is not as easy. You have a large heavy object either ...
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In order to attain high efficiency, carefully matched loading and unloading terminals are necessary. In one example, a unit train transporting 17,400 tons per 1,200kilometre round trip from mine to plant has a turnaround time of 72 hours—including a 4hour loading and 10hour unloading and servicing time per train. Onhighway trucks
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