Search

A multi-step interpolation approach was proposed to model the three-dimensional grade distribution and to demarcate orebody in a thin and anfractuous bauxite seam. A pre-mining demonstration procedure was established to virtually perform fully mechanized longwall mining in the modelled bauxite seam. Meanwhile, a comprehensive evaluation function expressed by the sum of dilution and loss rates of bauxite was utilized to determine the optimal cutting heights (1.71–2.69 m) and a suitable diameter (1.5 m) for the cutting drums mounted on a double-drum shearer to achieve no-waste and high-recovery mining of the demarcated 106,026 m 3 bauxite orebody. In addition, a numerical model of strata containing geological defects (a karst cave and fault), discontinuities (joints and stratifications) and a mountain was established to simulate the discontinuous motion and overburden fracturing disturbed by the longwall mining in the modelled bauxite seam. The results indicated that the overburden presented reliable stability and impermeability, in which no large-scale caving in goaf, no water influx, no cave collapse, no fault slip, and no mountain slope landslide occurred. This was due to arched roofs above the Karst cave and the mining-induced fractured zone, the subcritical condition of the longwall panel in the dip section, and support from the protective pillar between two adjacent panels. [ABSTRACT FROM AUTHOR]

This study further develops the discontinuous deformation and displacement (DDD) method to model the nonlinear deformation and failure behaviors of jointed rock masses. The improved DDD (IDDD) method is then proposed to provide a unified formulation for solving the transformation of rock materials from continuum to discontinuum. By embedding finite elements into model blocks, the deformation ability and stress distribution within blocks are refined, and the fracture of an intact block is permitted. Namely, the rock blocks containing a number of finite elements are deformable and can be broken into several smaller parts during calculation. The edges of damaged elements are new joints and mechanical interaction between neighboring blocks along these new interfaces is therefore allowed. A series of numerical tests are conducted to validate the correctness and effectiveness of the IDDD model in terms of bending deformation, frictional contact, strength characteristics, crack propagation, etc. Meanwhile, the failure mode of a block system and flexural toppling of a jointed rock slope are further analysed. The results are in good agreement with the theoretical analyses, previous studies and experimental data. Overall, the proposed IDDD method is effective and reliable to model the nonlinear mechanical behaviors of jointed rock masses and it has shown particular advantages over the conventional numerical methods. [ABSTRACT FROM AUTHOR]

Abstract To investigate the dynamic Mohr-Coulomb and Hoek-Brown strength criteria under the low confining pressures at high strain rates, the dynamic uniaxial and triaxial compression tests of sandstone were conducted with a conventional and modified triaxial SHPB system, respectively. The confining pressures are 5.0 MPa, 7.5 MPa, 10.0 MPa, 12.5 MPa and 15.0 MPa, and the strain rates varied from approximately 40 s−1 to 160 s−1. The results show that the cohesion is a linear positive correlation with the logarithm of strain rate, and the internal friction angle is a linear negative correlation with the logarithm of strain rate. The change of cohesion is more obvious than that of the internal friction angle. The rock parameter m also exhibits a linear positive correlation with the logarithm of strain rate. Furthermore, the relationships between cohesion, internal friction angle and rock parameter m and strain rate were obtained. On this basis, the unified dynamic Mohr-Coulomb and Hoek-Brown strength criteria at high strain rates were established. According to the established dynamic strength criteria, the strength of sandstone under high strain rates and low confining pressures can be estimated theoretically. By comparing the theoretical curve and test data, it can be concluded that established dynamic Mohr-Coulomb and Hoek-Brown strength criteria of sandstone are appropriate for both high strain rates and low confining pressures. [ABSTRACT FROM AUTHOR]

Ore recovery and dilution in caving mines are strongly determined by the flow characteristics of broken rock, especially under inclined boundary conditions. A physical draw model was designed and used to investigate the gravity flow characterization of granular materials during longitudinal sublevel caving. The three-dimensional (3D) shapes of flow axis, isolated extraction zone (IEZ) and ore remnants under inclined walls were obtained using the discharged quantity method and 3Dmine software, which indicated that stope boundary conditions and orebody dip have an impact on the characteristics of gravity flow. The experimental results also showed that the gravity flow characteristics of 3D draw experiments under the inclined walls were significantly different from those of the two-dimensional (2D) draw experiments. The flow axis is a line segment and lies in the same plane and only the width of the IEZ can be displayed in 2D experiment. However, the flow axis is a space curve segment in 3D draw experiment. Since being cut off by the front and inclined upper walls simultaneously, the 3D IEZ is more complicated than the 2D IEZ and both the width and thickness of the draw body are displayed simultaneously in 3D state. The shape and location of ore remnants in 3D state are also different from that in 2D state. Therefore, the 3D IEZ is more consistent with the actual situation than 2D IEZ for sublevel caving stope. The 3D gravity flow presented may be used to determine the design of the extraction layout and improve ore recovery during longitudinal sublevel caving. [ABSTRACT FROM AUTHOR]