نشریه روش های تحلیلی و عددی مهندسی معدن
پیاپی 35 (Summer 2023)

Mines have a considerable role in polluting the environment. Greenhouse gases and wastes mainly cause pollution. In this regard, trucks that carry ores in a mine are a primary source of these pollutants. Selecting trucks with low fuel consumption can help to reduce pollution. The present research seeks to evaluate the effects of the objectives (Cost objectives, Production objectives, and Environmental objectives) in mines on the type of trucks to select and the routes they take, as well as the effect of the duration of stone transportation on pollution. The study's data were obtained from the Chadormalu iron mine in Yazd Province. As the results showed, the objectives set in the mine affect the CO2 level, and the goals followed with human health concerns induce lower CO2 emissions. It found that the time ores are transported by trucks affects the CO2 level. However, only the objective type affects the waste level resulting from tailings, not the speed of trucks. It is recommended that the duration of truck loading and unloading and the time the trucks waste waiting in lines be reduced to the extent possible to lower CO2 emission.

This paper considers the non-associated flow rule to propose an analytical solution to calculate the ground reaction curve at the crown of a circular tunnel. This solution is based on the Mohr-Coulomb failure criterion and the dilation angle has been considered as a function of two factors of rock mass quality and confining stress. The results show that if the radial displacements are not controlled, a loosening zone is produced in the tunnel crown (cohesion=0.2 MPa and friction angle=25°). Moreover, based on the trend of the ground reaction curve at the tunnel crown, three new concepts “minimum required support pressure”, “maximum allowable strain”, and “safety factor based on the maximum allowable strain” was presented. Considering the interaction between the support characteristics curve and ground reaction curves, the efficiency of the associated flow rule to the non-associated flow rule was investigated. Results state that the use of the associated flow rule causes some sort of computational errors in determining the maximum allowable strain (too high) and consequently, the design accuracy of the support system is very low. Moreover, taking into account the associated flow and non-associated flow rules at the sidewall and tunnel crown, the interaction between the support characteristics curve and ground reaction curve was investigated. Based on the results, it was suggested that to design an optimal support system, it is necessary to calculate the safety factor based on the maximum allowable strain by considering the interaction between the support characteristics curve and the ground reaction curve at the tunnel crown. Finally, a procedure was presented for the design of the support system.

Sand production is a complex mechanism that reduces oil and gas production and leads to wellbore instability, tubing erosion, and even erosion of surface installations. The hydrodynamic action of the flow on the surface leads to the breakup of solid particles from the surface. This is one of the main sources of sand production. The sand production may be affected by the combination of flow rate and the stress regime around the wellbore. In this paper, sand production in a vertical wellbore is numerically studied. A 3D finite element model in various stress regimes (i.e., normal, strike-slip, and reverse based on Anderson's classification) presenting various conditions of reservoirs was used. A typical drawdown pressure was chosen to simulate the production in the wellbore. The numerical model uses a sand production criterion based on the velocity of the fluid flow, the porosity of formation, transport concentration, and sand production coefficient to determine the initiation of sand production. The sand production volume was determined for a duration of a week in all cases. The most erosion of materials in all models occurred near the junction of the wellbore and perforation. This is an expected result since based on rock mechanics, the junction of the wellbore and perforation is also the location of the most stress concentration. It was concluded that the collaboration of high-stress concentration and high-pressure drawdown caused the excessive sanding problem. The results of the paper provide insight into the effect of stress regimes and orientation of perforation on the volume of sand production.

Abdasht chromite mine is located in the ultramafic complex of southern Iran, which has abundant chromite reserves such as Soghan, Esfandagheh, Faryab, etc. The main purpose of this study was to investigate the capability of Hyperion in the alteration mapping related to chromite mineralization in the Abdasht area, south of Kerman Provine, Iran.  Since serpentine and magnesite have been observed associated with chromite in this area, mapping of these minerals can be used for the exploration of chromite. For this purpose, atmospheric correction/calibration was performed on the Hyperion images. The representative samples collected from the outcrops in the area were tested in the laboratory of the Iranian Space Agency and the spectra of serpentine and magnesite were extracted. Serpentine and magnesite were mapped, using Spectral Angle Mapper (SAM) and Matched Filtering (MF) methods. In order to verify and control the results, a field visit has been made to the area. The obtained classification accuracy for serpentine obtained from MF and SAM methods were 87% and 81%, respectively.  Magnesite map showed an overall accuracy of 65% and 60% for MF and SAM methods, respectively. The lower accuracy of magnesite can be attributed to its small extent in the field. It is suggested that due to the power of Hyperion images in the detection of chromite-bearing serpentine rocks, these images can be used for the exploration of chromite.

Assessment of strength anisotropy has been one of the most challenging subjects in rock mechanics and civil engineering. The orientation of the discontinuity plane, the aggregate distribution, and the specimen size have a significant influence on the mechanical properties of rock and cementitious materials. This study aims to evaluate the effect of anisotropy on uniaxial compressive strength, elastic constants, and destruction-specific energy using physical modeling. For this purpose, different concrete blocks were produced in which aggregate sizes of 9.5, 12.5, and 19 mm were used. Different cylindrical specimens with diameters of 45, 69, and 94 mm were prepared. A suite of laboratory testing was performed on prepared concrete samples as a function of discontinuity plane angle (α=30°,45°, and 60°), including uniaxial compressive strength and deformability tests. The results obtained have shown that the mechanical properties of cementitious materials have different values concerning the banding plane, aggregate size, and specimen volume. It was shown that the uniaxial compressive strength and tangent modulus of elasticity show the highest values in low discontinuity plane angle than those obtained in the other directions. However, in concrete mixtures with a grain size of 0-19 mm, an increasing-decreasing trend of strength behavior was observed with ascending the orientation of the discontinuity plane from 30° to 60°. The findings presented indicated that with increasing aggregate size, strength properties descend due to the rise in heterogeneities that affect failure modes. Finally, it was revealed that when specimen size increases from 69 to 94 mm in diameter, led to significant rises in the values of compressive strength and elasticity modulus in cementitious materials.

One of the greatest issues regarding Iranian concrete dams is the lack of consideration for increasing our knowledge about them and their performance in times of accidents such as floods, earthquakes, and impact load caused by explosion waves. Some of the most significant objectives of this research are an investigation of the effect of TNT content and its distance from the concrete dam, the identification of critical points of the dam, and the impact of fluid on the amount of damage caused by the explosion to the concrete dam under impact load. The analysis used in this research is straightforward. It should be noted that the discovery of the critical points of the dam in the event of an accident, such as an explosion with complex behavior, can minimize human and financial losses. The LBE method was employed in this study. The interaction between the dam and the water behind it is one of the very considerable parameters that influence the deformation of the dam due to the hydrodynamic pressure of the water behind the dam. It is demonstrated by the results that doubling and tripling the amount of TNT leads to an increase in the pressure on the crest of the full dam by 46.63% and 64.68% respectively; besides, by multiplying the amount of TNT by four and five, the mentioned pressure increases by 70% and 75.58%, respectively.