Mechanical Analysis of Roof Subsidence Based on Rheological Properties of Solid Backfill Materials

To study the influence of the rheological properties of backfill materials on strata movement during solid backfill mining, Poyting-Thomson model was selected as the rheological model for the backfill materials based on their experimentally derived rheological properties. By regarding the roof as a thin elastic plate, a rheological mechanical model of the roof when using solid backfill mining, was established. According to the elastic-viscoelastic correspondence principle, the deflection of the roof at different times was obtained by use of the energy method. By taking the 7203W backfill mining panel of a coalmine in Zhaizhen town as an example, the subsidence of the roof over time was calculated. Results showed that the maximum subsidence was 205 mm, which was close to that measured in situ. Meanwhile, the observation of boreholes drilled into the roof evinced its integrity. Therefore, these results can provide a theoretical basis for predicting strata movement and surface subsidence during solid backfill mining

Compression of Aggregates of Acid-Leached Coal Gangues: Implications for Coal Mine Backfill

The compression mechanical properties of coal gangues subjected to acidic immersion were examined using a cylinder and a YAS-500 electrohydraulic servotesting system in order to investigate the effects of pH and particle size on its compaction stress-strain and stress-compaction relationships. The evolutionary trends of the leaching solution’s pH at various immersion times during the coal gangue corrosion process were analyzed. Then, inductively coupled plasma optical emission spectroscopy (ICP-OES) was performed on the leaching solutions to determine their chemical compositions and concentrations. An X-ray diffractometer (XRD) and X-ray fluorescence (XRF) spectroscopy also performed qualitative and quantitative analyses of the coal gangues samples. The mechanisms of hydrochemical corrosion in coal gangues were ultimately elucidated by analyzing these results, taking into consideration the chemical reactions of the acidic solutions and coal gangues. The results indicate that hydrochemical damage in coal gangues is more sensitive to small particle size and stronger acidity. The compressive mechanical properties of coal gangues that had been immersed demonstrated that their bearing capacity decreased as the particle sizes decreased and acidity increased. It was also established that acid leaching changes the mineral composition, particles, and pores of coal gangues, thus degrading their compressive mechanical properties

Random gravel model and particle flow based numerical biaxial test of solid backfill materials

Fully mechanized coal mining with backfilling (FMCMB) has become a major solution of “green mining”. The mechanical properties of backfill materials are key factors of ground control in FMCMB face. To study the strength behaviors of the solid backfill materials, we developed a method of generating random gravel model by using computational geometry algorithms, then coded the generating method into a program with MATLAB software, and implemented several numerical biaxial tests under different confining stresses by using a generated random gravel model and the Particle Flow Code PFC2d. Peak deviatoric stress, post-peak softening, initial contraction and dilation and the relations between them and confining stress can be observed. And the initial elastic modulus of the samples, Poisson’s ratio, frictional angle and cohesion can be derived from the numerical biaxial test results. The results indicate a good feasibility study of mechanical properties of the solid backfill materials by random gravel model and particle flow based numerical biaxial test. Keywords: Backfill mining, Backfill materials, Biaxial test, Numerical simulation, PF

Compression Characteristics of Solid Wastes as Backfill Materials

A self-made large-diameter compression steel chamber and a SANS material testing machine were chosen to perform a series of compression tests in order to fully understand the compression characteristics of differently graded filling gangue samples. The relationship between the stress-deformation modulus and stress-compression degree was analyzed comparatively. The results showed that, during compression, the deformation modulus of gangue grew linearly with stress, the overall relationship between stress and compression degree was approximately nonlinear, and the deformation of gangue was rather large during the initial portion of the test. Gangue sample mixed with Talbot Formula provides the best deformation resistance capacity, followed by fully graded and single-graded gangue samples. For applications, with adjustment of the gradation of filling materials and optimal design of compacting equipment, surface subsidence may be better controlled

Overview of Solid Backfilling Technology Based on Coal-Waste Underground Separation in China

China is the world’s largest coal producer country. However, large-scale coal mining has led to severe environmental pollution issues such as surface subsidence and gangue piling up. The gangue discharging amount has ranked the first in the world and coal mine enterprises are facing enormous discharging reduction pressure. This paper summarizes the research progress of the solid backfilling mining technology and then illustrates the realistic demands and significance of implementing underground coal-waste separation. It also focuses on the technical principles, systems and key equipment of the common underground coal-waste separation methods, such as the selective crushing method, the dense medium shallow groove method, the vibro-assisted jigging method and full-size water separation method and ray identification method. In addition, the selection steps of underground coal-waste separation method, the design process of large section separation chamber and the design principle of separation and backfilling system are proposed, finally, the mining-separating-backfilling + X for coal mining is put forward. By combining the technology of mining-separating-backfilling with other technologies, such as gob-side entry retaining with non-pillar mining, gas extraction, solid waste treatment, water protection mining, mining under buildings, railways and water bodies, the integrated mining methods, mining-separating-backfilling + setting pillars, gas drainage, treatment, protection and prevention methods are formed. It also introduced the ‘mining-separating-backfilling + gas extraction’ technology’s whole idea, system arrangement, separation equipment and practical engineering application effects based on the specific engineering case of pingmei no. 12 coal mine. The results indicate that the integration of underground coal-waste separation and solid backfilling technology could achieve gangue discharging reduction, underground washing and surface subsidence control. It is effective at realizing green mining