فصلنامه مهندسی معدن
پیاپی 40 (پاییز 1397)

Uncertainty in required parameters in analysis and design of structures is an important issue that is usually considered by rock engineers. This uncertainty is due to the developed relations and also rocks’ nature. Modulus of deformation is one of the geo-mechanical parameters that is widely utilized in design and analysis. But estimating this parameter according to the empirical relations is associated with uncertainty and this causes mistakes in decision making of engineers. Purpose of this paper is to develop a novel concept entitled uncertainty matrix for practical prediction of deformation modulus with high level of confidence. Therefore, modulus of deformation is obtained based on the uncertainty matrix and statistical methods. Later, using the uncertainty matrix and t distribution, a domain for variation of deformation modulus is determined. In order to do a case study and also defining the elements of uncertainly matrix, models that are function of rock mass rating and data sets of sand-stone slopes in Kahar formation are applied. Results indicate that, prediction of deformation modulus for rock mass according to the developed method in comparison with the general methods is more reliable. In addition, deformation modulus with the probability of 95% for the studied sand-slope is in the range 23.67 to 30.00(GPa).

Sehezar area is located in southern Tonokabon in Mazandaran province, north of Iran, near the Tarom – Hashdtjin belt. The existence of granitoid masses in the region can be important in terms of mineralization potential. The geological complex exposed in the area mainly consists of Paleozoic to Cenozoic lithologic units. In this study, a number of samples were used for microscopic and petrographic studies, as well as some samples of granites in the area for the classification of rocks. According to the studies performed on polished sections, minerals of pyrite, chalcopyrite and magnetite were observed. The textures found in thin sections are granular, Hyaloporphyritic, and Vitrophyric. The presence of porphyry textures indicates the simultaneous intrusions with volcanics and clastics originating from them. The major minerals in the region include quartz, K-feldspar, and plagioclase, and in some cases, hornblende, biotite, and pyroxene appear as the major mineral. The minor minerals found in the samples include sphene, pyroxene, iron oxides, apatite, and opaque minerals. Petrographic studies showed that the intrusive rocks of the region are of granite, granodiorite, syenite to quartz-syenite and quartz-monzonite. The magma in this area is in the domain of alkaline to calc-alkaline series and is a magnesian series and in the domain of metaluminous to peraluminous. The granites of the studied area are of peraluminous type and have a tectonic setting of the active continental margin and are I-type. Variogram studies showed that the spherical model is the best fitted model, and the spatial correlation range for the three elements of Au, Cu and Fe are approximately 350 m. Evaluating the results of geostatistics by calculating the root mean square error (RMSE) and calculating the mean absolute error (MAE) indicates the acceptable accuracy of variogram model. According to the Meinert diagrams and spatial correlation of the elements, it is concluded that these masses can be related to the deposits of iron-gold-copper.

The occupational and health hazards associated with working in coal mines are known as the main concerns despite the high importance of coal production in the economic development of countries. Irreparable damages to personal and financial losses can be avoided if the effective factors result in the occupational risks of underground coal mines are identified. In this research, these factors were initially identified in the case of underground coal mines in Iran. Then, the direct and interaction effects of the identified factors were evaluated and determined using fuzzy cognitive map approach that is based on the analysis of the cause and effect interaction between the identified effective factors. Results indicated that dust concentration, individual negligence and mistakes, inappropriate and inadequate ventilation, errors in design, planning, and execution, and the volume and concentration of methane gas are respectively determined the important factors caused the occupational hazards in the underground coal mines of Iran. The statistical study of the accidents occurred in Iran's underground coal mines, especially recent events, confirms the results of this research.

At the Gol-E-Gohar iron ore concentration plant and the Sarcheshmeh copper complex SAG mills with the diameter of 9 and 10 m and length of 2 and 4.9 m, respectively, are used to reduce the size of the ore. Monitoring of the operation in these two plants indicated that the tonnage of the Gol-E-Gohar mill was lower than the nominal value with large variations and the Sarcheshmeh mill experienced liner breakages which in turn increased the non-scheduled shutdowns. To simulate the charge trajectory KMPCDEM software which has been developed based on discrete element method (DEM) was used. The results of simulations using two different liner designs were verified with a 1-m diameter and 22-cm length model mill. The comparison indicated that at the worst case the difference between the shoulder and toe positions of the simulated and measured charges was found to be less than 4 degrees which was not significant. The simulations showed that cataracting particles do not impact toe rather they hit shell liners. In order to solve this problem, various liner designs at the plant operating conditions were simulated with the objective of reaching a state where the falling charge impact the toe region. To arrive at such a condition, for the Gol-E-Gohar SAG mill the release angle was increased from 7 to 30 degrees and for the Sarcheshmeh case the number of lifters was decreased from 60 to 40 and the release angle increased from 15 to 30 degrees. The proposed liner designs were constructed and installed in the industrial SAG mills. At Gole-E-Gohar, the feed rate increased by 17% and its variation reduced by 31% which indicated more stable operation. At Sarcheshmeh, on average the number of broken liners decreased from 4.2 to 1 and the variation of feed rate decreased by 30%.

Effect of discontinuities roughness including tooth-shaped asperity, rough undulating and smooth plane having different orientations respect to confining pressure on the strength of rock under triaxial stresses has been investigated in this research. 15 groups of specimens having three types of discontinuities roughness and five types of slope angles from 0 to 90 degrees have been successfully prepared and tested under triaxial stresses. The axial strength of rough undulating and tooth-shaped asperity discontinuities decreases a little with increasing slope angle from 30 to 45 degrees under constant confining pressure and in general the axial strength of smooth plane discontinuities having different orientations is less than the axial strength of rough undulating and tooth-shaped asperity discontinuities under the different confining pressures. For tooth-shaped asperity discontinuities having orientation angles 45 degrees, failure also occurred at the body of the specimens particularly with increasing the confining pressure. Sliding occurred at the one side of tooth-shaped asperities of discontinuity having orientation angles of 60 degree under uniaxial loading and displacement took place at the direction of discontinslopeuities. But tooth-shaped asperities were broken along the discontinuities under the higher confining pressures. The effect slope angle on the axial strength decreases with an increase of confining pressure and rate of reducing the axial strength increases with an increase of discontinuity roughness. As, the strength of specimens having very rough discontinuities under high confining pressures approaches to the strength of massive (intact) rock. The maximum axial strength to the minimum axial strength ratio (Rtriax) has high value for the zero confining pressure and it decreases sharply as a negative power function of confining pressure then approaches to a constant value.

The Esfordi phosphate concentrate with total assay of REE equal to 1.2 percent is one of the richest source of rare earth elements in Iran. It contains Ce(5608 ppm), La(1959ppm) and Nd(2227ppm). In this research, the effect of mechanical activation on the leaching of rare earth elements by nitric acid from Esfordi phosphate concentrate was investigated. For the investigation of mechanical activation effect on leaching of REE, a planetary ball mill was used with steel balls of diameter about 20 mm, ball to powder ratio of 15 and 2 and with a retention time of 90 minuts in dry situation and air atmosphere. Because of high and low leachability of fluorapatite and REE minerals by nitric acid, respectively, tow stage leaching methode was used. The first leaching stage residue, that contained about 99 % of REEs in initial phosphate concentrate, was activated mechanically at ball to powder ratio of 12 and then leached. Results showed that the mechanical activation had important influence on leaching of REE by nitric acid from phosphate concentrate and improved the leaching of Ce, La and Nd from about 1% (without mechanical activation) to 35.79, 42.61 and 30.34% , respectively. The amorphization degree increased to 1.2 and 57% after 90 min intensive milling with ball to powder ratio of 2 and 15 to 1, respectively. Also, the crystallite size and microstrain of Fluorapatite differed from 225 nm and 0.08 % for initial sample to 225 nm and 0.09 % and 81.8 nm and 0.63 % for mechanically activated samples with ball to powder ratio of 2 and 15 to 1 respectively.

Determination of ore body domain is the main step in the beginning of a mining project. The mine designing, mining and processing plant planning would be implemented based on this domain. Traditional methods characterize this domain graphically and would not concentrate error and uncertainty, but Geostatistics as a powerful tool is able to determine this domain using spatial statistics. Ore domain is a district variable that can be modeled by different simulation methods, such as Truncated Gaussian simulation (TGS). TGS simulates the domain according to the simulation of one Gaussian function and rock type rule. Furthermore, simple relations can be applied for determination of ore domain, for example, Distance Function (DF). DF defines the ore boundary by the Euclidian distance between each point and the nearest dissimilar point and the distance calibration.
Statistical and geostatistical validations are applied to find the best realization of TGS. The DF and TGS results are compared by assessing confusion matrices, overall error and precision of the modeled domains. Moreover, different plans, and section are qualitatively compared. Validation and comparisons indicate that TGS is a more efficient way to model the ore domain. Therefore, Gol Gohar mine was studied and after the implementation of both methods showed that TGS compared to DF results in more precise domain simulation. TGS algorithm is able to reproduce the small scale anisotropies versus, better results at large scale anisotropies using DF algorithm.
Key words: Geostatistics, Ore Domain, Truncated Gaussian simulation, Distance Function,

Design and selection of a proper machine and its performance prediction is a very delicate and important part for planning and estimation of project costs in mining and mechanized tunneling. Assessment of rock cuttability in mechanized excavation includes the study of rock behavior and rock-tool interaction. Accordingly, laboratory rock cutting test is the most reliable method to precisely evaluate the behavior of rock and tool in a close condition to real field situation. In this study, the small scale linear cutting machine was used for assessing the rock cuttability and its relationship with rock mechanical parameters. To do this, test specimens were selected from Qom Upper Red Sandstones. At the same time, standard tests were carried out for detailed rock characterization and determination of its physical and mechanical properties. Upon performing the tests, the cutting force and specific energy respectively showed linear and nonlinear relationship with the cutting depth. Also, the cutting speed didn't show a meaningful relation with cutting force and specific energy. The results obtained from rock cutting tests were compared with those from Evans rock cuttability model. Although the experiment is in good agreement with theory, more tests are underway to achieve more accurate results and develop a new model for determination of rock cuttability.

Over break phenomenon in the executive process of a tunneling project is always one of the most important issues. Nowadays, according to the progress of industry and entrance of new technologies to tunneling industry and gradual acceptance, the new methods are replaced instead of traditional methods (drilling and blast). Although, largely the issue of over break has been controlled by project implementers, but the existence of this major issue in tunnel projects has never been eliminated. In this research, using intelligent network of prediction and optimization, over break was discussed. After selecting the best model based on scoring, the selected model was used for optimization. The R2 and RMSE values of the selected model were 0.921, 0.4820, 0.923 and 0.4277 for training and testing, respectively. The Artificial bee colony (ABC) algorithm, which is one of the new optimization algorithms, was used to optimize these parameters of the explosion pattern. Due to the fact that over break is one of the main problems in tunneling, this reduction can contribute to a good tunnel and stability. After creation several models of optimization and variations in its weights, the optimum amount for the over break was 1.63 m2, which is 47% less than the lowest value (3.055 m2). The optimal pattern can be obtained with the least amount of the over break.