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Impoundments of tailings and active surface subsidence zones induced by ore mining were the major environmental problems. The aim of this study was to investigate the technical feasibility of impoundment of tailings using active surface subsidence zones. The self-designed scaled physical model was conducted to investigate the movement laws of tailings under different heights of granular media and tailings, and then drawing ore in these experiments was performed to simulate the mining process. The experimental results showed that the isolated extraction zone and stoping sequence had a primary influence on the doping process of tailings. Besides, when the height of granular media was more than that of the isolated movement zone, the uniform mode of drawing ore could be decreased the amounts of tailings drawn from drawpoints. Meanwhile, the doping process was not impacted by continuously emission of tailings to active surface subsidence zones. Thus, the field test was employed in the Dabeishan Iron Mine and the mining schemes were put forward based on the experimental data. The results showed that the recovery ratio and dilution ratio were 80.9% and 24.3% respectively, and that the scheme established in this paper could be used in practice. [ABSTRACT FROM AUTHOR]

To study the damage evolution laws of red sandstone samples with prefabricated cracks under cyclic uniaxial compression, physical tests were conducted. In this research, the stress–strain curve characteristics, failure process characteristics, strength, and deformation properties of the cracked sandstone specimens were studied under different cracked geometric parameters (α, β) and cyclic loads. The experimental results revealed that the elasticity modulus, deformation modulus, residual strength, and peak strength increased linearly with the number of loading cycles. Additionally, the failure modes of the samples transition from brittle failure under a small number of loading cycles to ductile failure under a high number of loading cycles. The elastic modulus and peak strength of all the specimens under cyclic loading showed a "strengthening" phenomenon. With increasing crack dip angle (α), the peak strength and crack initiation stress first increased and then decreased. However, with the increase in the crack bridge inclination angle (β), the peak strength and crack initiation stress first decreased and then increased. By using the fitting analysis of the damage evolution equation, it was proven that the damage variable method is suitable for describing the damage evolution characteristics of cracked sandstone. [ABSTRACT FROM AUTHOR]

In this paper, the slope rock mass is numerically characterized by considering hydraulic and mechanical properties using two distinct element models. The flow rate and permeability are calculated from localized fluxes through rock masses with varied fracture orientations and scales. Flow models suggest that rock mass permeability is predominantly controlled by fracture size. High rock mass permeability is simulated when the fractures are enlarged. Hydraulic anisotropy is captured when the difference in the fracture size is amplified. The mechanical properties of the slope rock mass are characterized through numerical shearing tests. In general, high permeability corresponds to low shearing resistance of the rock mass. The fractures obliquely distributed to shearing direction lead to additional shearing resistance. Enlarged fractures reflect high conductivity of the rock mass structure and decrease the shearing resistance. Mechanical anisotropy of the rock mass is also captured and attributed to the difference in the fracture size. The relations between hydraulic and mechanical properties are examined, and negative exponential relations are fitted between rock mass cohesion and permeability. The research introduces permeability as reference to slope rock mass characterization and provides reliable methods to this challenging issue. [ABSTRACT FROM AUTHOR]

The assessment of rock mass cavability is a key research topic when mines intend to adopt block caving mining during the feasibility stages. However, cavability assessment is a multi-index and non-linear complex process in system engineering, and uncertainty exists in the assessment process. In this situation, it is important for cavability assessments to minimize the subjectivity of human judgements and consider the factors that influence cavability and their interrelationships. In this study, we introduce a new approach that combines fuzzy comprehensive assessment (FCA) with rock engineering system (RES). First, the FCA was applied to establish an assessment model based on a conversion function, membership function, and fuzzy assessment matrix. Second, the RES was used to determine the weights of influential factors by applying an interaction matrix. Third, rock mass cavability was analysed based on the assessment model and the factor weights. The results of the cavability assessment were for a partial rock mass due to the discontinuity of the cavability assessment index value in space. Therefore, geostatistics and block models were adopted to establish a regionalized model of rock mass cavability, and the spatial distribution of cavability was obtained. Based on the Luoboling copper-molybdenum mine as a case study, FCA and the RES were applied, and a regionalized model of cavability was established. The results can provide a basis for studies of block caving mining and mine design. [ABSTRACT FROM AUTHOR]

In practice, a damage zone is generally formed after tunnel excavation in jointed rock mass. This damage zone is closely related to rock mass properties and requires careful examination in order for cost effective supporting designs. In this research, a synthetic rock mass (SRM) numerical method is applied for characterizations of the jointed rock mass and excavation damage zone (EDZ) near underground tunnels in 3D. The SRM model consists of bonded particles and simulates deformation and crack propagation of the rock mass through interactions between these particles. The effects of joint stiffness and distribution on the rock mass properties are systematically examined by comparing the numerical data with an empirical geological strength index (GSI) system and an associated Hoek-Brown strength criterion. The numerical results suggest that rock mass properties are comparable to the empirical GSI/Hoek-Brown system only when inclined joints are simulated in the rock mass subjected to axial loading. The rock mass is strengthened and the empirical GSI/Hoek-Brown characterization becomes inappropriate when the joints are less favorable to shear sliding. The SRM method is then applied for characterizations of tunnel EDZ. It appears that the depth and location of the EDZ are a function of the tunnel orientation, joints, and in situ stresses. The EDZ depth is expected to be higher when inclined joints are simulated. The EDZ area is reduced when the joints in the rock mass are horizontally and vertically distributed. [ABSTRACT FROM AUTHOR]

The soils are often distributed in a stratified structure. When an earthquake occurs, there are always risks of liquefaction for stratified soils which can cause serious consequences. The research aims to investigate the liquefaction and post-liquefaction deformation of saturated sand with stratified structure. The influences of liquefaction and post-liquefaction deformation were analyzed by varying the thickness, position, and layers of powdery sands. The findings showed that the correlations between the times taken to reach liquefaction for cyclic loading and the thicknesses of the powdery sandy interlayer are non-linear. With the optimal thickness, the powdery sand interlayer can effectively prevent the transfer of power water pressure. And two-layer powdery interlayer in the sample was more favorable to resist pore water pressure than that with single layer. The strength of post-liquefaction deformation and failure patterns are closely related to the distribution of powdery layer. The work provides new research evidence on the liquefaction and failure mechanism of saturated sands with stratified structure under cyclic loading which often happen during earthquakes. [ABSTRACT FROM AUTHOR]

The crushing degree of caved ore-rock is one of the key factors influencing the success of block caving mines. The secondary rock failure in granular media is a major link which influences the crushing degree of ore-rock. Rolling Resistance Linear (granules) and Flat-Joint Model (rocks) of discrete element software were used to establish a mathematical model of rocks in granular media. Failure characteristics in granular media of rocks with different mechanical properties were studied. The crushing rules of ore-rock were also analyzed. The study results show that, when the ratio of compressive strength and vertical stress of rocks (ky) is smaller than 1.37, the compressive strength plays a major role in rock failure. The generated cracks are mainly shear cracks. At this very moment, rocks can be broken into small-size granules. When ky is larger than 1.37, the tensile strength plays a major role in rock failure. Further, when the ratio of tensile strength and vertical stress (kl) is smaller than 0.32, generated cracks are mainly tensile cracks. At this very moment, rocks can be broken into big-size granules. When kl is larger than 0.32, rocks basically suffer no failure. [ABSTRACT FROM AUTHOR]