Accurate characterization and visualization of the complex inner structure and stress distribution of rocks are of vital significance to solve a variety of underground engineering problems. In this paper, we incorporate several advanced technologies, such as CT scan, three-dimensional(3D) reconstruction, and 3D printing, to produce a physical model representing the natural coal rock that inherently contains complex fractures or joints. We employ 3D frozen stress and photoelastic technologies to characterize and visualize the stress distribution within the fractured rock under uniaxial compression. The 3D printed model presents the fracture structures identical to those of the natural prototype. The mechanical properties of the printed model,including uniaxial compression strength, elastic modulus,and Poisson's ratio, are testified to be similar to those of the prototype coal rock. The frozen stress and photoelastic tests show that the location of stress concentration and the stress gradient around the discontinuous fractures are in good agreement with the numerical predictions of the real coalsample. The proposed method appears to be capable of visually quantifying the influences of discontinuous,irregular fractures on the strength, deformation, and stress concentration of coal rock. The method of incorporating3 D printing and frozen stress technologies shows a promising way to quantify and visualize the complex fracture structures and their influences on 3D stress distribution of underground rocks, which can also be used to verify numerical simulations.
Yang JuHeping XieZemin ZhengJinbo LuLingtao MaoFeng GaoRuidong Peng
Traditional coal mining and utilisation patterns are severely detrimental to natural resources and environments and significantly impede safe, low-carbon, clean, and sustainable utilisation of coal resources. Based on the idea of in situ fluidized coal mining that aims to transform solid coal into liquid or gas and transports the fluidized resources to the ground to ensure safe mining and low-carbon and clean utilisation, in this study, we report on a novel in situ unmanned automatic mining method. This includes a flexible, earthworm-like unmanned automatic mining machine (UAMM) and a coal mine layout for in situ fluidized coal mining suitable for the UAMM. The technological and economic advantages and the carbon emission reduction of the UAMM-based in situ fluidized mining in contrast to traditional mining technologies are evaluated as well. The development trends and possible challenges to this design are also discussed. It is estimated that the proposed method costs approximately 49% of traditional coal mining costs. The UAMM-based in situ fluidized mining and transformation method will reduce CO2 emissions by at least 94.9% compared to traditional coal mining and utilisation methods. The proposed approach is expected to achieve safe and environmentally friendly coal mining as well as lowcarbon and clean utilisation of coal.
Yang JuYan ZhuHeping XieXiaodong NieYong ZhangChang LuFeng Gao
Accurate knowledge of the influence of rock deformation on the permeability of fluid flow is of great significance to a variety of engineering applications, such as simultaneous extraction of coal and gas, oil/gas exploitation, CO2 geological sequestration, and underground water conservation. Based on the CT representation of pore structures of sandstones, a LBM(Lattice Boltzmann Method) for simulating CH4 flow in pore spaces at microscale levels and a parallel LBM algorithm for largesize porous models are developed in this paper. The properties of CH4 flow in porous sandstones and the effects of pore structure are investigated using LBM. The simulation is validated by comparing the results with the measured data. In addition, we incorporate LBM and FEM to probe the deformation of microstructures due to applied triaxial forces and its influence on the properties of CH4 flow. It is shown that the proposed method is capable of visually and quantitatively describing the characteristics of microstructure, spatial distribution of flow velocity of CH4,permeability, and the influences of deformation of pore spaces on these quantities as well. It is shown that there is a good consistency between LBM simulation and experimental measurement in terms of the permeability of sandstone with various porosities.
