نشریه روش های تحلیلی و عددی مهندسی معدن
پیاپی 17 (Winter 2019)

Slope stability analysis of jointed rocks has been the focus of many studies. The presence of joints and discontinuities in rock environments intensifies instability along with the development of block movements. Many analytical and numerical methods have been proposed and applied to analyze the stability of jointed rock slopes. Computation complexity, incapability of presenting a reliable safety factor to be used for developing a proper design operation and improper analysis speed are the known challenges of these methods. This paper has developed the well-known analytical Key Group Method (KGM) to Toppling-Free fall-Sliding Key Group (TFS_KGM) version. To this end, toppling and free fall failure are added to the existing method in order to have a better analysis of jointed rock slopes. In this method, unstable key blocks participate in creating groups which may rotate or free fall besides sliding. The new TFS_KGM computes stability conditions and final safety factors based on the most unstable sliding, rotating and free fall movements with consideration of in situ stresses. Results of using this method in jointed rock slopes and the comparison with DEM numerical, KBM and KGM analytical methods show that the method is very effective particularly when the geometrical conditions of the jointed rocks make the toppling and free fall failures potentially possible. The method demonstrates a simple computation method along with a proper analysis speed. It also provides accurate design safety factors and much more optimized critical failure areas than previous methods.

This paper focuses on some fracture toughness tests performed on the pre-cracked Brazilian specimens of rock-like materials. Also the effect of rock fracture filling on the fracture toughness was considered experimentally.  Fracture toughness is a key parameter for studying the crack propagation and fragmentation processes in rock structures. Fracture mechanics is an applicable tool to improve the mechanical performance of materials and components. It is a comparatively general phenomenon that rock fractures are naturally filled with gouging material, but the impact of fillings on rock fracture toughness has not yet been considered precisely. In the present study, an experimental investigation was made to evaluate the effect of rock fracture fillings on the crack propagation mechanism and fracture toughness of some rock like specimens. For this purpose, several molds are used for preparation of Brazilian disks with straight central crack. In the next stage, three different ratios of ingredients have been used for preparation of three model materials to fill the central pre-crack of the specimen. Diametrical compression load with a rate of 0.3 mm/min in different directions respect to the central crack orientation is applied to the Brazilian disk specimens and the failure loads corresponding to the each test are recorded. Result of laboratory tests indicates that fracture fillers strongly affect the value of rock fracture toughness while fracture filler has no influence on the failure mode of CSCBD specimens. Also the impact of filler cohesion on mode II fracture toughness is more than its impact on mode I fracture toughness.

Selecting a suitable pillar recovery method is one of the most important issues in the room and pillar mining. The main purpose of this study is to compare two methods for pillar recovery in Tabas central coal mine (TCM). Among the existing methods, the two methods, “Modified split and fender” and “Shortwall” are chosen for the numerical modeling. The three dimensional finite difference method (FLAC3D software) is used to model these methods. In the next step, the vertical stress and displacement, the plastic zone condition and the safety factor during each stage of pillar recovery were compared for each method. The results of this modeling show that the percentages of coal recovery for two methods of “modified split and fender” and “shortwall” are around 70% and 82% respectively. Comparing the percentage recovery of coal for these two methods, exhibits that the shortwall method is more suitable than modified split and fender, for this mine.

Remnant magnetization causes a change in the direction and intensity of the magnetization vector. If inversion is performed regardless of remnance, in some cases it may have unreliable and misleading results. For inversion with respect to remnant magnetization, several solutions have been proposed so far, one of which is to convert the data of total magnetic field into data that is independent of the direction of magnetization. In this study, the transformation of Total Field Anomaly (TFA) into Total Magnitude Anomaly (TMA) is used. The inversion algorithm is based on improving compact inversion method and is just two-dimensional. In compact inversion, anomalies may concentrate on the surface of the earth, and thus the response is unreliable. To solve this problem, a combination of matrices and weighting functions have been used, including elements such as magnetic susceptibility and depth function. The resulting model can be smooth or compact (with sharp edges) based on changing compactness factor. The method has been tested using several synthetic and real data. The synthetic data are a 2D tabular prism, of which the top buried-depth is 20 m and the length and width are 40 to 20 m, a dipping prism with a vertical tabular nearby. The real example is magnetic data over Galinge iron-ore deposit in Qinghai province of China, and the data of four profiles have been considered for 2D inversion. Inversion even smooth or sharp, have been conducted with all models, and especially sharper models are consistent with the known geologic attributes of the magnetic sources.

Application of micro-piles to stabilize unstable slopes has been widely considered in recent years. A micro-pile is a small-diameter (typically less than 300 mm), drilled, and grouted as non-displacement pile that is typically reinforced. The main objective of this study is to evaluate the influence of the micro-pile group on increasing safety factor as well as finding the optimum position of micro-piles across the embankments slopes. In this study, numerical analyses were performed to investigate the efficiency of micro piles on the behavior of embankments using ABAQUS Finite Element code. The analyses have been carried for plane strain conditions and under earthquake loads. Based on acquired results, it was implied that using micro pile groups on the lower part of embankment slope is the optimal approach to reinforce embankments. This can increase the embankment safety factor by 33% in static mode and by 34% in dynamic mode. The impacts of the parameters of micro pile inclination angle, diameter, length, micro-pile spacing, and the type of soil on safety factor in dynamic mode have been investigated. Results show that increasing the length and diameter of the micro piles increase the safety factor. By increasing the micro pile angle in respect to vertical axis up to 30°, safety factor increases but any additional increase of the angle decreases the factor. Furthermore, by increasing the spacing of micro piles up to 4 times the diameter, causes improving the safety factor, but more space has a negative impact. By strengthening the type of the adhesive soil (simultaneous increase of embankment adhesion from 8 KPa to 16 KPa and elasticity module from 30 MPa to 60 MPa), embankment safety factor increases by 40%. Furthermore, by strengthening the sandy soil (simultaneous increase of internal friction angle from 32 to 40 and soil elasticity module from 20 MPa to 45 MPa), the safety factor of embankment increases by 41 percent.

Increasing efficiency does not necessarily require the use of expensive technologies. Sometimes implementing properly management and engineering principles, employing skilled and efficient manpower, planning appropriately, and identifying effective priorities can increase efficiency and reduce costs. Conveyor belt equipment pieces are category components which carry heavy materials in factories and mines. Downtime of the pieces have many costs for the factory. Identification of parts of conveyor belts, taking preventative and repair measures and prioritizing measures in order to increase efficiency and reduce cost for downtime conveyor belt are important. In this study, using fuzzy TOPSIS technique to prioritize the preventative and repair measures of conveyor belt equipment pieces factory in the pelletizing plant of GolGohar mining and industrial company have been discussed. In this regard,  the main and ten other parts of conveyor belt along with their practical roles are identified from viewpoint of engineers and technicians who deal with them. Besides, intended preventative and repair measures are identified according to previous records. Then maintenance repair parts and expert opinions are discussed to prioritize the preventative measures. Finally, recommendations are provided for increasing efficiency of conveyor belt and reducing cost and repair time.

One of the factors affecting overbreak or slough of the roof and walls of underground stopes, causing unplanned dilution is blast vibration. The amount of damage caused by earth vibration can be measured in terms of peak particle velocity (PPV). In this study, in order to investigate the effects of blast vibration on the occurrence of unplanned dilution, 72 three-component records acquired upon 24 blasts were obtained at underground Venarch Manganese Mines. Once finished with data analysis, scale distance was used to propose an exponential equation for predicting PPV based on the cubic root of the charge weight per delay. Then, the effect of blast vibration on walls and roof of the stope was examined on 24 different explosions, dilution values were recorded at various scaled distances to the face, and the relationship between them was determined. Equivalent linear overbreak/slough (ELOS) was used to determine dilution, with cavity monitoring system (CMS) being used to calculate it. Then a practical diagram was presented to predict the boundary of the dilution area from the explosion. Finally, The relationship between the amount of ELOS against the PPV was presented and it was determined if the PPV was fewer than or equal to 6.73 mm / s, the dilution will not occur.