Experimental Study of the Multiple Fractalisation of Coal and Rock Failure Subjected to the Coupled Effects of Water, Temperature and Dynamic Loads
Tingxu Jin,
Xiaoyuan Sun,
Kai Liu
et al.
Abstract:The mechanical properties of water-rich coal and rock in a subzero environment are very different from those at room temperature, which causes many unexpected hazards for projects. In this study, coal and rock samples subjected to the coupled effects of water, temperature, and dynamic loads were taken as the research object, and the discussion was shaped around their mechanical properties. The crack evolution trend and different gradient impact velocities were determined using a split-Hopkinson pressure bar (S… Show more
“…Yao et al [21] studied the effect of inclusions on the fracture evolution and mechanical properties of mortar structure, and analyzed the deformation characteristics using DIC technology. Based on the multi-fractal of high-speed digital image correlation (HS-DIC) technology and quality screening method, Jin et al [22] investigated the evolution trend of surface cracks during crushing and the distribution characteristics of sample fragments after crushing from the perspective of a fractal. Martin et al [23] analyzed the effect of four different tension levels on the strain/stress of the hole specimen based on the DIC system calibration procedure.…”
In order to study the hydration absorption behaviors and characteristics of sandstone in Mogao Grottoes in China, the pressure-less hydration absorption experiment on the outcrop porous sandstone of Mogao Grottoes was carried out by using the self-developed real-time monitoring experimental system. The hydration absorption was measured and the curve of hydration absorption with time was drawn. At the same time, the digital image correlation method (DIC) was used to measure the full-field deformation, and the speckle pattern of the sample was analyzed using Match ID, and the displacement field and strain field of the sandstone sample at different hydration absorption moments were computed. Moreover, the sparse area and dense area of sandstone are used as regions of interest (ROI) for DIC analysis. According to the test results, it is concluded that the hydration absorption of sandstone increases rapidly in the initial stage, and gradually tends to be stable with the change of time. This corresponds well with the deformation characteristics of sandstone analyzed using DIC. In the initial stage, the deformation of sandstone increases rapidly. With the change in time, the deformation of sandstone samples gradually slows down. When the hydration adsorption reaches saturation, the sandstone continues to deform for a period of time before stopping hydration absorption. The results of the mercury injection test and the XRD test show that the porosity of the sparse area is larger than that of the dense area and the particle content of the dense area is lower. When the sandstone is saturated with water, the liquid is immersed in the pores between the solid particles, which makes the sparse area more prone to stress concentration, and the deformation in the sparse area is larger. Therefore, when analyzing the hydration absorption deformation of sandstone, the porosity should be considered.
“…Yao et al [21] studied the effect of inclusions on the fracture evolution and mechanical properties of mortar structure, and analyzed the deformation characteristics using DIC technology. Based on the multi-fractal of high-speed digital image correlation (HS-DIC) technology and quality screening method, Jin et al [22] investigated the evolution trend of surface cracks during crushing and the distribution characteristics of sample fragments after crushing from the perspective of a fractal. Martin et al [23] analyzed the effect of four different tension levels on the strain/stress of the hole specimen based on the DIC system calibration procedure.…”
In order to study the hydration absorption behaviors and characteristics of sandstone in Mogao Grottoes in China, the pressure-less hydration absorption experiment on the outcrop porous sandstone of Mogao Grottoes was carried out by using the self-developed real-time monitoring experimental system. The hydration absorption was measured and the curve of hydration absorption with time was drawn. At the same time, the digital image correlation method (DIC) was used to measure the full-field deformation, and the speckle pattern of the sample was analyzed using Match ID, and the displacement field and strain field of the sandstone sample at different hydration absorption moments were computed. Moreover, the sparse area and dense area of sandstone are used as regions of interest (ROI) for DIC analysis. According to the test results, it is concluded that the hydration absorption of sandstone increases rapidly in the initial stage, and gradually tends to be stable with the change of time. This corresponds well with the deformation characteristics of sandstone analyzed using DIC. In the initial stage, the deformation of sandstone increases rapidly. With the change in time, the deformation of sandstone samples gradually slows down. When the hydration adsorption reaches saturation, the sandstone continues to deform for a period of time before stopping hydration absorption. The results of the mercury injection test and the XRD test show that the porosity of the sparse area is larger than that of the dense area and the particle content of the dense area is lower. When the sandstone is saturated with water, the liquid is immersed in the pores between the solid particles, which makes the sparse area more prone to stress concentration, and the deformation in the sparse area is larger. Therefore, when analyzing the hydration absorption deformation of sandstone, the porosity should be considered.
The stability of coal and rock masses in water-rich mines is affected by both mine water erosion and dynamic disturbances. Thus, it is necessary to study the dynamic mechanical response and failure characteristics of coal and rock under the combination of saltwater and a high strain rate. To this end, a split Hopkinson pressure bar device was employed to investigate the effects of impact velocity, water content, and immersion liquid on the dynamic mechanical behaviours of coal and rock. The results revealed that the weakening effect of saltwater on the dynamic mechanical properties of coal and rock is much greater than that of distilled water. With increasing moisture content, the dynamic compressive strength of the coal specimens decreases monotonically, while that of the rock shows a trend of first increasing and then decreasing. The failure process and destruction of coal and rock are comprehensively affected by both the external impact load and the physical and mechanical properties of the material. The degree of damage of the coal and rock specimens increases with increasing impact velocity and water content. Moreover, the influence of various factors on the impact fracture mechanism of coal and rock under saltwater immersion conditions was revealed. These findings are highly important for the design and maintenance of underground coal and rock building structures.
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