فصلنامه مهندسی معدن
پیاپی 53 (زمستان 1400)

Investigation of first weighting process due to greater caving span and higher induced stresses when compared to the periodic ones is imperative in the planning stage of a longwall coal mining project. Hence, a reliable prediction of caving span and abutment pressure during this process has major role in stability analysis of operation. This paper presents the results of numerical simulation intended to examine stress distribution in terms of peak abutment pressures during first weighting process in longwall mining. Longwall mining was simulated by incorporating Universal Distinct Element Code (UDEC) to investigate the effects of five critical parameters included roof strata uniaxial compressive strength, immediate roof height, spacing of bedding planes and mining depth and in-situ stresses ratio on vertical and horizontal peak abutment pressures. The results showed that relationships between all critical parameters with the exception of in-situ stresses ratio and front and rear abutment pressures in vertical and horizontal directions are the same. In addition, it was concluded that all parameters have a direct relationship with the rear and front abutment pressures whereas this relationship is indirect for the immediate roof height and the extraction height.

Injection as a conventional method is used to seal permeable dams and tunnel walls. Faults, joints, and layering surfaces exist as open discontinuities of varying degrees in all rocks. Discontinuities can be completely closed or open, affecting the strength and permeability of the rocks. The injection is the process by which the material is injected into the seams and crevices and porous spaces of rocks and soils, improving physical and strength properties and reducing the permeability of the organization. In the last two decades, the use of nanoparticles in engineering, medical sciences, etc has been very significant. In recent years, the addition of silica nano-particles and iron nano-particles to concrete, cement, and all construction materials has been growing rapidly due to increased efficiency and improvement of important and essential parameters in this industry. The purpose of this study was to analyze by a cylinder under high-pressure superfine cement injection press with additive silica nano-particles with different W/C ratios. Simulation of broken rock environments, single-seam or one-sided, has been performed by laboratory blades with dimensions of 40, 50, 60, 80, 100, 150 and 200 microns in laboratory conditions. The results of super-fine cement injection operations with silica nanoparticles indicate that the best and most effective injection operations are W/C: 3/2, 3/1, 1/0.7 and 1/1 ratios in the blade filter.

Identification of the element dispersion patterns and relating them to the geochemical anomalies is one of the exploration tools, especially in the semi-detailed and detailed phases. Methods that can simultaneously analyze samples and elements are recommended for this purpose. In this paper, two methods namely, correspondence cluster analysis (CCA) and density-based clustering algorithm (DENCLUE) and the geochemical data of Khoynaroud region have been used. Clustering of 165 soil samples, along with the results of the 7 elements analysis associated to the porphyry copper-gold mineralization, namely As, Au, Cu, Hg, Pb, S and Zn, shows that four A, B, C and D areas are visible with mineralization potential in the study area. In CCA method, the data are divided into 6 clusters. These clusters contain S with 57 samples, 61 samples, Pb with 16 samples, Cu with 8 samples, As with 7 samples and Au, Hg and Zn with 17 samples, respectively. While in DENCLUE method include 5 clusters in the form of S with 66 samples, 43 samples, Pb and Zn with 38 samples, Au and Cu with 10 samples and As and Hg with 8 samples, respectively. Part C2 of area C and part D2 of area D are proposed as the best areas with the possibility of porphyry mineralization and as well as area A with the possibility of hydrothermal vein mineralization. Area B and part D1 with the possibility of vein mineralization and the need for additional exploration are also likely to be the next proposals. The results also show the better clustering of the elements, better adaptation of the proposed areas for mineralization with multi-element geochemical anomalies and geological conditions of the study area are the advantages of DENCLUE algorithm. Therefore, this algorithm can be used to relate the element dispersion pattern with their geochemical anomaly.

The phenomenon of dilution is one of the undesirable consequences of mining that is caused by the unwanted mixing of tailings and minerals. Adverse effects of dilution include increased costs of extraction, transportation, processing, mining grade, and environmental degradation. Dilution control requires identifying the causes of the dilution. Field surveys of the East Azerbaijan Sungun copper mine, which is extracted by the open-pit method, show that factors such as dyke infiltration, contact of tailings blocks and mineral at the borders, sample error Vector and Murphy's errors (human error) are the factors influencing the dilution. In this study, in order to estimate the amount of external dilution (dilution due to dykes) of Sungun copper mine, geostatistical modeling (index kriging) was used. The external dilution rate of the mine (11.3%) was calculated. The amount of external dilution seemed to be higher than the maximum initial estimate of dilution in open-pit mines with mass reserves, but this number is reasonable given the presence of dykes. To reduce the external dilution due to the penetration of the dykes, it was suggested to use the XRF model 7000. Statistical data available before and during the use of the XRF device showed that when using the device, the daily average (actual) grade obtained is closer to the predicted grade. Also, the amount of external dilution due to dykes has decreased.

lead and zinc mine of Gole zard is located in ALigudarz city of Lorestan province and the grade of galena and sphalerite minerals in this sulfide ore is 5.4% and 23.7%, respectively. Research has shown that lead in ores is complexed by chlorine ions. For this purpose direct lead leaching was performed on the ore of this mine by mixing hydrochloric acid and NaCl solution and the effect of each of the parameters of temperature, time, pulp density, stirring and hydrochloric acid concentration on lead leaching was investigated. The results showed that the parameters of hydrochloric acid concentration, pulp density and time had the most effect and pulp stirring time and temperature had the least effect on lead recovery and finally under optimal conditions of 60 minutes, temperature 50 ° C, pulp density 10%, hydrochloric acid concentration 15% and the stirring speed 1000 rpm, the lead recovery was obtained about 91.7%.

Due to the increasing number of accidents while working in the mines, studies related to maintaining the safety and health and improving safety management are expanding today. To reduce accidents and injuries, risk assessment should be performed continuously in the mines. For this purpose, two gold mines of Ardestan Dareh Ashki and Isfahan Moteh were examined. In the first stage of risk assessment, information on hazards in the mines was collected and in the second stage, the probability of occurrence and severity of its effect were evaluated. The two gold mines were then developed using methods similar to the ideal option and fuzzy logic to assess the risks The total hazards of the ore mining and concentrating operations in these mines were 136, which were classified into 8 groups. Finally, after completing the necessary calculations, several groups with different risks were obtained. The first group with the highest risk included unpredictable explosions, non-standard explosives, tailings dam failure, cyanide leakage, people falling into the tailings dam, electrocution while working with equipment, slipping or slipping, not wearing safety clothing, unauthorized entry It was in the area of ​​extraction and explosion during firefighting. Based on the obtained results, it is possible to plan and take appropriate action to prevent the occurrence of undesirable results.

Given the high importance of hydraulic failure in the oil and gas industry in order to stimulate and increase the capacity of oil reservoirs, the analysis of crack propagation in these environments during this process is very important. Although the amount of porosity in such reservoirs may be low, but these porosities and cracks, are considered as weaknesses and discontinuities of the environment and a determining factor in the number and propagation path of the cracks. In the present paper, using the linear elastic fracture mechanics, initiation, propagation and spread of cracks in porous samples are modeled by the finite element method (XFEM) developed in Abacus software, based on the criterion of the maximum principle stress and the criterion of independent of the failure. In order to validate the proposed method,, the results were compared with the KGD method and with an error of 0.04% in the maximum crack opening size and 4.87% in the maximum crack length, an acceptable agreement was obtained. The results showed that the use of spring elements as elastic support to simulate the elastic properties of the environment can be useful and effective. The hydraulic fracture modeling process is performed on microscopy-CT scan images of three real sandstone samples and the crack growth path is analyzed. Also, the amount of energy absorbed per unit length in each sample is calculated and the final path of crack propagation with increasing injection pressure is presented. Then, by calculating the percentage of empty space before and after failure in each sample, absolute and relative failures in each case are calculated and the results are compared with each other. The results show that due to compression and reduction of porosity, the absorbed energy per unit length decreases and a lower level of the sample is affected by hydraulic failure.