نشریه روش های تحلیلی و عددی مهندسی معدن
پیاپی 7 (بهار و تابستان 1393)

Select a support system of tunnels has an important role safety and economic status. This choice usually based on experience of designer engineers. But the question is always whether the best choice has been done?. In this study, Linear Assignment (LA) as the one of the most important method of multiple Attribute decision making (MADM), to select optimum support system of tunnels has been used. In this way the tunnel support system selection as a multi attribute decision making has been considered and the criteria for selection optimum support system include: support cost, safety factor, applicability, time installation, displacement and capable of mechanization. For this purpose, first, using the finite difference numerical method) FLAC2D (, various support systems based on technical parameters and stability of the tunnel has been identified. Then based on considered criteria, using the aforementioned optimum support system has been selected.

The most common feature of the sedimentary and metamorphic rocks is anisotropy playing a significant role in behaviour of this type of rocks under applied forces. Therefore many experimental investigations are done to consider the influence of anisotropy on mechanical behaviour and peak strength of these rocks. Numerical method and especially Distinct Element Method (DEM) can be used to simulate brittle failure of rocks under uniaxial and triaxial loading. In this study the mechanical behaviour of a transversely isotropic rock is investigated by PFC code. Thus, samples with varying bedding angle (from 0 to 90 degree) are loaded under different confining pressures. Comparison of numerical and experimental results revealed that PFC is an efficient tool for simulation of failure behaviour of transversely isotropic rocks. Also it’s indicated that the peak strength of transversely isotopic rock is varied by anisotropy orientation; then, a model is suggested to predict the peak strength of transversely isotropic rocks.

Ventilation is One of the vital issues in advancing tunnels of mine network, including mine No.1 of Parvadeh, because the various pollutants especially dusts and blasting gases are concentrated in the face which should be directed to the outside of tunnel. To provide a ventilation system in advancing tunnels, at first, the air flow quantity has to be calculated in viewpoints of fire damp, dusts, blasting gases(if needed) and respiration and then the maximum amount must be considered as a base for ventilation design. In order to ventilate the tunnel face with cross section area of 15 m2, the calculated air quantity is 6.75 m3/s. In addition, to perform the auxiliary ventilation, three duct types were compared which variance analysis proved that the duct with 900 mm in diameter had a significant effect on static pressure drop in probability level of 5%. Finally, to circulate the required air, different fans were studied and it was found that the blowing fan with rate of 12 m3/s and pressure of 7.4 kPa is suitable for ventilation of advancing tunnel in the mine.

Due to dipolar nature of magnetic anomaly, symmetric causative magnetic bodies located anywhere other than magnetic poles produce asymmetric anomaly, which causes complicated interpretation. Using RTP technique these asymmetric anomalies are converted to that are observed in magnetic poles. This technique is usually utilized in the frequency domain in which induces noise in dataset. Other limitation is restricting the application of the algorithm to regions with constant geomagnetic inclination and declination. Various algorithms have been devised to solve this problem. In this regard, the method based on Taylor’s series expansion of RTP data in mean value of inclination and declination in studied area has been devised. This method has been applied on magnetic data from Siriz Iron ore mine and their results are compared to the frequency domain RTP.

Ability of discrete element method to simulate initiation and propagation of cracks enables researchers to investigate different topics in the field of fracture mechanics, which is not possible with using finite element and boundary element methods. Study of micro-cracks and failure threshold in rocks with high compression strength help better understanding of brittle behavior under real conditions. PFC2D is based on discrete element method and its special features in modeling the propagation of cracks are compared with other numerical methods. The problems which researchers are faced with this software are mismatch in tensile strength and failure mode of numerical modeling in real samples with high compression strength. In this study, experimental results were used to calibrate numerical models. Petrographic thin sections and cubic samples of granite were prepared for SEM studies. Necessary information about the grain distribution and distribution of micro-cracks in rock samples with microscopic studies were obtained for using in numerical model. In addition, in this study, a clumping method was used. The clumps size is controlled by known influence radius to achieve correct failure pattern of models in accordance with lab samples. Using this type of clumping, showed that ratio of tensile to compressive strength decreases from a mount of 0.5 (without clumping) to less than 0.1 and the tensile strength in numerical models were almost equal to lab samples in high compressive strength.

Alishar index with high potential to Cu-Au mineralization is located in Urumieh-Dokhtar magmatic belt and in Arak province. Geological units of the area consists mainly of andesitic, Trachyandesitic-basaltic andesite lava, andesite to basaltic andesite tuff and rhyolitic to dacitic tuff which is affected by hydrothermal solutions so the igneous rock units display some kinds of alterations such as phyllic, propylitic, argilic and silicic alterations as well as iron oxide (hematite, goethite) and copper mineralization. Plentiful silicified and mineralized veins and veinlets is a favorable environment for gold mineralization. High correlation between Cu and Fe can be explained by the presence of chalcopyrite and correlation between Au, As and Bi are attributed to substitutions in Cu, Bi minerals and arsenopyrite. Multivariate statistical analyses have demonstrated three stages in mineralization in the area. The first stage shows: Cu, Au, Ag, Bi, Mn, Co and Zn; the second stage includes: Fe, Sb and the last stage comprises as, Cd and Mo enrichment. The evidences comprising host rock composition, ore minerals, alteration types, tectonic regime, geochemical analysis results and high correlation between Fe, Cu and Au and also elevation in concentration of these elements demonstrates that Alishar mineralization is similar to IOCG.

Inverting geophysical data due to their nonlinear nature is a very complex process, especially when a very high resolution in low depth is considered. In the past two decades, nonlinear inversion algorithms such as neural networks and genetic algorithms with significant growth for the interpretation of geophysical data have been used. In this study, geophysical inverting subsurface pipeline's data with high resolution is done. Thus, back-propagation network helped us to interpreting two-dimensional resistivity tomography data. Network parameters, including input and output data types, number of layers, number of neurons in each layer, network optimal learning rate, momentum coefficient and their impact on the value of the network error. After 20 iterations the error is reduced to 0.001. Robust pipeline (1000 ohm m) in a homogeneous half- space (100 Ohm m) by dipole-dipole array and one meter electrode spacing was modeled. 36 data sets that contained 207 components, were considered in this study, the 18 data sets in the training phase, 9 data sets in the evaluation phase and other data sets were assigned to a validation phase and the field data sets after the interpretation were compared with conventional inversion method. in this study, Comparing pseudo-sections interpreted by the artificial neural network method and conventional methods showed that although both methods lead to the detection pipeline but the artificial neural network method has a capability to separate two tube in pipelines that perched in 1.2 meter distance from each other and have 32 centimeter diameter and even can offer an approximately estimation of the diameter of the pipelines in pseudo-sections.

There are three notch displacement modes including the Mode I or opening mode where the notch displacement is perpendicular to the notch front, Mode II or shear mode where notch dimensions are displaced in the notch plane and the Mode III or tear mode where the notch dimensions are displaced in the notch plane parallel to the notch front. Some application areas of rock fracture mechanics can be listed as hydraulic fracturing, rock blasting, rock cutting, mechanized drilling, rock slope stability and comminution in mineral processing. The aim of the present study was to examine the effect parameter of width on the mode ICritical Stress Intensity Factor (Critical SIF) using a thick-walled hollow cylindrical marly specimen and the oil well environment was simulated in the laboratory. The marly specimens were prepared from the Bangestan formation in southern and southwestern Iran. To perform the tests, two artificial symmetrical notches with certain dimensions were created in specimens with an outer diameter (OD) of 73 mm, an inner diameter (ID) of 25 mm and a height of 150 mm. A triaxial stress was applied on the specimen and the pressure required for the propagation of the artificial notches was measured. Three tests were conducted to investigate the effect of notch width on the mode I Critical SIF. Two finite element software including ABAQUS 6.12 and ANSYS 14 were used for calculating I Critical SIF. Excel and SPSS softwares were used for investigating the effect of notch width on the mode I Critical SIF. By conducting three tests, it was concluded that with an increase of 50 percent of the notch width, mode I Critical SIF decreases 20 percent. Meanwhile, it was found that the mode I Critical SIF linearly decreased with an increase in the notch width.