IRANIAN JOURNAL OF MINING ENGINEERING (IRJME)
Year:2018 | Volume:13 | Issue:40 |Papers Count:13

Uncertainty in parameters required for analysis and design of structures is an important issue that is usually considered by rock engineers, which is caused by the developed equations and also the nature of rocks. Modulus of deformation is one of the geo-mechanical parameters widely utilized in design and analysis. But estimating this parameter using empirical models is associated with uncertainty and this causes mistakes in engineering decision making process. The purpose of this study is to develop a novel concept entitled uncertainty matrix for practical prediction of deformation modulus with high level of certainty. Therefore, modulus of deformation is obtained based on the uncertainty matrix and statistical methods. Later, using the uncertainty matrix and t distribution, the range for variation of deformation modulus is determined. As a case study and also for defining the elements of uncertainly matrix, models that are just functions of Rock Mass Rating (RMR) were used and data sets of sand-stone slopes in Kahar formation were applied. Results indicate that prediction of deformation modulus for rock mass using the developed method is more reliable in comparison with general methods. In addition, deformation modulus for the studied sand-slope is in the range of 23. 67

Sehezar area is located in southern Tonokabon in Mazandaran province, north of Iran, near Tarom– Hashdtjin belt. Occurrence of granitoid masses in the region can be important in terms of mineralization potential. Geological units exposed in the study area mainly consists of Palaeozoic to Cenozoic rocks. In this research, microscopic and petrographic studies were performed on a number of samples from the region, as well as granite samples for intrusions classification. In reflected light microscopy pyrite, chalcopyrite and magnetite were identified in some samples. Igneous rocks have granular, hyaloporphyritic and vitrophyric textures. Porphyry textures indicates the coincident of intrusions with volcanics and clastics probably originating from a same magmatism. The major minerals in igneous rocks include quartz, K-feldspar, plagioclase, and in some cases, hornblende, biotite, and pyroxene. The minor minerals are sphene, iron oxides, apatite and opaque minerals. Petrographic studies showed that the intrusive rocks are granite, granodiorite, syenite to quartz-syenite and quartz-monzonite. The magmatic rocks are alkaline to calc-alkaline, magnesian rich and fit in metaluminous to peraluminous field. The granites are peraluminous and I-type of active continental margin tectonic settin. Variography of stream sediments samples showed that the spherical model is the best fit for the data, and spatial correlation range for Au, Cu and Fe are approximately 350 m. Evaluation of geostatistics results by calculating the root mean square error (RMSE) and the mean absolute error (MAE) indicates the acceptable accuracy of variography model. According to the Meinert diagrams and spatial correlation of the elements, it is may be concluded that these intrusive masses are associated with iron-gold-copper mineralization.

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 resulting 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 important factors posing occupational hazards in the underground coal mines of Iran. The statistical study of the accidents occurred in Iran underground coal mines, especially recent events, confirmed the results of this research.

At Gol-E-Gohar iron ore concentration plant and Sarcheshmeh copper complex, SAG mills are used with the diameter of 9 and 10 meters and length of 2 and 4. 9 meters, respectively. Monitoring the operation in these two plants indicated that the tonnage of the mill at Gol-E-Gohar was lower than the nominal value with large variations and the Sarcheshmeh mill experienced liner breakages which in turn increased the non-scheduled shutdowns. In order to overcome these difficulties and to increase the performance, the charge trajectory, which is an important parameter, was studied in these two mills. To simulate the charge trajectory KMPCDEM software was used, which has been developed based on discrete element method (DEM). The results of simulations using two different liner designs were verified with a model mill of 1-m diameter and 22-cm length. The comparison indicated that inthe 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 considered significant given the experimental error of the test. Once the accuracy of the simulation was verified, it was used to simulate the charge trajectory in the two industrial SAG mills. The simulations showed that unlike the expectation, cataracting particles do not impact toe, they 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 impacts the toe region. To achieve such a goal, for Gol-E-Gohar SAG mill the release angle was increased from 7 to 30 degrees and for the mill at Sarcheshmeh, 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 where their performances were monitored during a period of twenty months. At Gole-E-Gohar, the feed rate increased by 17% and its variation reduced by 31% which indicats more stable operation. At Sarcheshmeh, the average number of broken liners decreased from 4. 2 to 1 and the variation of feed rate decreased by 30%. The promising results of liner change in the last few years resulted in replacement of old liners in the SAG mills of the two plants with the proposed liners.

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.

Esfordi phosphate concentrate with a total of 1. 2% rare earth elements, is one of the richest sources of REE in Iran. In order to investigate the effect of mechanical activation on dissolution of rare earth elements, planetary ball mill with 20 mm steel balls, with ball to powder ratio of 2: 1 and 15: 1 was used for 90 minutes in dry mode at standard pressure. Due to the high solubility of fluorapatite and low solubility ofREE-containing minerals in nitric acid, a two-stage leaching method was used. The first phase leaching residue, containing more than 99% of the rare earth elements in the initial concentrate, was mechnaicaly reactivated with a ball to powder ratio of 12: 1, then it was leached. Results showed that mechanical activation successfully improved the dissolution of rare earth elements from phosphate concentrate, from almost 1 percent (for initial concentrate) to 35. 79, 42, and 34. 33 percent for Ce, La, and Nd, respectively.

Determination of ore body domain is the main step at 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 without considering error and uncertainty, but geostatistics is a powerful tool, capable of determining 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 a Gaussian function and the rock type rule. Also, there are simple equations that can be applied for determination of ore domain, for example, distance function (DF) methods. DF defines the ore boundary by the Euclidian distance between two different points, then calibrating these distance values. In this study, statistical and geostatistical validations were applied to find the best simulation. The DF and TGS results were compared by assessing confusion matrices, overall error, and precision of the modeled domains. Moreover, different plans, and sections were qualitatively compared. Qualitative validations and comparisons, along with statistical and geostatistical validations indicated that TGS is a more efficient way to model the ore domain. Both methods were applied to study Gol-e-Gohar mine and results showed that in comparison with DF, TGS is capable of creating more precise domain simulations. In smaller scales, TGS algorithm is able to reproduce anisotropies better, while in larger scales DF can reproduce variability and anisotropies better than TGS algorithm.

: Design, selection and performance prediction of excavators are very delicate for project planning and cost estimation in mechanical mining and mechanized tunneling. Rock cuttability assessment in mechanized excavation includes investigation of rock mechanical behavior and rock-cutting tool interaction. Use of laboratory scale rock cutting tests is the most reliable method for accurate assessment of rock-tool interactive behavior in a situation close to its actual field condition. In this study, small scale linear cutting test was used for evaluating the rock cuttability and its relationship with rock mechanical parameters. To perform this action, rock samples of Upper-red sandstone were prepared for rock physical and mechanical characterization tests. The results obtained from cutting tests revealed that the cutting depth has a direct linear and a non-linear relationship with the cutting force, and the specific energy, respectively. Also, the cutting velocity showed no significant relationship with cutting force and specific energy. Moreover, the cutting forces obtained from the experiments showed a good agreement with those obtained from the theoretical model developed by Evans. However, these results are preliminary and need to be further verified with much larger cutting tests on various rock specimens.

In the executive process of a tunneling project, overbreak phenomenon is always one of the most important issues. Nowadays, according to the progress of industry and having new technologies introduced to tunneling industry and their gradual acceptance, traditional methods (drilling and blasting) are replaced by the new methods. Although, the overbreak issue has been largely controlled by project implementers, but it has never been completely eliminated from tunnelling projects. In this research, prediction and optimization of overbreak was discussed using intelligent networks. Best model was selected based on scoring, then it 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 blasing pattern. Due to the fact that over break is one of the main problems in tunneling, this reduction can have an important role in the quality and stability of the tunnel. After creating several optimization models and modifying its weights, the optimum amount for the overbreak was 1. 63 m2, which is 47% less than the lowest value achieved during execution process (3. 055 m2 ). The optimal pattern can be obtained with the least possible amount of overbreak.