نشریه روش های تحلیلی و عددی مهندسی معدن
پیاپی 4 (پاییز و زمستان 1391)

Determination of chemical elements assay plays an important role in mineral processing operations. This factor is used to control process accuracy، recovery calculation and plant profitability. The new assaying methods including chemical methods، X-Ray fluorescence and atomic absorption spectrometry are advanced and accurate. However، in some applications، such as on-line assaying process، high accuracy is required. In this paper، an algorithm based on optimal estimator is presented to predict and correction on-line XRF errors. This research is based on the industrial real data collection for evaluating the performance of the presented algorithm. The quality of the obtained results was very satisfied; so that the RMS errors of Cu and Mo grades in rougher feed reduce to less than 0. 19 and 0. 006 and in final flotation concentration to less than 2. 48 and 0. 274، respectively. The results indicate that the mentioned method is quite accurate to reduce the on-line XRF errors measurement.

Determining the number and characteristics of joint sets is of great importance in any rock engineering operation. One of the most important characteristics of discontinuities is their orientation، relative both to each other and to any engineering structure or excavation face. In order to determine the number of joint sets، usually stereographic methods are used. This method mainly depends on the personal judgment therefore; separation of joint sets is very difficult when overlap occurs. In this paper، an algorithm is proposed according to Poisson process to determine the number and characteristics of joint sets. Discontinuities that are found in a region of defined dip and dip direction with a probability of more than a random event are put together in a group، so that dip، dip direction and clustering degree (i. e. the distribution of joints around a definite center) of that group can be determined. SETDISC program has been written in Fortran 90 language based on the proposed algorithm. To validate the proposed algorithm in SETDISC، 420 discontinuities of 11 scan line are analyzed and the computed results are compared by the results obtained by Dips. This comparison shows that the proposed algorithm has no personal judgment and can be used practically as a quantitative approach in joint clustering.

Convergence-confinement is one of the most popular methods which is used for analysis of stress and strain fields around a circular opening excavated in rock masses. It is assumed that the circular tunnel is excavated in a continuous، homogeneous، isotropic، initially elastic rock masses under hydrostatic loading. Selection of a suitable failure criterion is extremely important in the analysis since it affects the plastic zone and obtained displacement and stress field around the opening. Brown et al (1983) proposed a stepwise procedure based on Hoek-Brown criterion to obtain stress and displacement around a circular opening. A similar stepwise procedure is implemented in this study for Mohr-Coulomb criterion. Then the effect of Mohr-Coulomb and Hoek-Brown criteria on ground response curve is investigated for various models of rock mass behaviors. Finally a sensitive analysis is implemented for Mohr-Coulomb and Hoek-Brown criteria. By a comparison of Hoek-Brown and Mohr-Coulomb criteria، it can be concluded that the relative displacement in Mohr-Coulomb criterion is at least 5 times more sensitive than that in Hoek-Brown criterion to variation of strength parameters. It is obtained that varying rock mass strength parameters develops more relative deformation for medium-quality rock masses. Therefore، it should be carried out to preserve the inherent strength of rock masses by controlled blasting or mechanical excavation، especially for medium quality of rock masses (often with elastic-strain softening behavior).

Stability analysis & probable problems evaluation and solutions before construction of a structure، helps designer & constructor to make proper technical & economical evaluation، either a metro station designer or constructor. Qods Sq. Station is located in north development path of Tehran subway line 1 and located in Qods Sq. and Darband St. Effective parameters on stability of this station are geological conditions، underground water conditions، geotechnical properties of soil and temporary & permanent support system، traffic load، station displacement and surface settlement. Considering value and effect of these parameters and utilize them with finite element method، stability of this station analyzed in 10 possible ways to evaluate effects of traffic load، change in depth load and underground water level on station displacement and surface settlement، shear & axial force، stress and bending moment. Thereupon station was stable with 26mm displacement & 10mm surface settlement.

Due to the presence of outliers and existence of skewness in distribution of geochemical data، these types of data sets usually are compositional in type that closed form data system. Closed data system includes a data set that one or more constraints are applied on data. Summation of these data is always fixed and is equal to the one (100%). By calculating the correlation coefficients for open data set and comparing the result with the ones calculated for closed data set، it can be found that there is an increase for correlation values in the closed system that is unrealistic. Characteristics of closed data prevent from applying standard statistical techniques; thus، different methods are expressed to open the system. In this study،additive logratio transformation، centered logratio transformation and isometric logratio transformation method have been used to open geochemical data in Kuh-e Panj area. In order to compare the results of these three transformations to the closed condition، the correlation coefficient between the elements are calculated and cluster analysis is performed over the data. According to the results، data analysis after opening the system delivers outputs closer to the reality، and centered logratio transformation method can be considered as more preferable method than the other methods.

In most cities، the infrastructures need to be increased due to the population growth. Given that the large cities are overcrowded and there is less space for surface transportation، the creation of subsurface structures like tunnels is essential. The excavation of tunnels may cause diverse problems، such as settlements of surface buildings. So determining the amount of settlements caused by underground excavation and comparison with the amount of allowable buildings settlement is important. Methods of settlement prediction are divided into experimental، analytical and numerical methods. In this study، initially the ground surface settlement is evaluated by using the experimental and analytical methods in green field condition (without building existence) and then the effect of buildings existence on the changes in ground surface and tunneling impact on the deformation of the building caused by this movement are considered by numerical method. In this research، the part of shallow tunnel of the first line of Tabriz subway is studied. The numerical modeling has carried out by PLAXIS 3D TUNNEL. The results of numerical modeling show that the amount of the settlement caused by tunnel excavation reduces with the increase of the stiffness of foundation buildings. If building cross sectional area is extensive، the foundation settlement would be low and more uniform. Surface settlement curves show that settlement value reduces and settlement zone increases with the increase depth from first section to second section in the analytical method. However، this trend is reversed for the numerical method. It was also showed that passing the tunnel have negligible impacts on the buildings studied.

In rock mechanics، determination of stresses on the fracture plane is very important، because instability in a structure such as rock slopes caused by the combination of internal stresses. If limit equilibrium method is used to evaluate the stability، it is necessary to determine normal stresses in the fracture moment to estimate the shear strength parameters. One of the most important experimental criteria for determination of stresses on the fracture plane is Hoek-Brown criterion. In the present paper، efficiency of Hoek-Brown criterion is examined for prediction of stresses on the fracture plane based on the Mohr stress circle which estimates the stresses on the fracture plane according to the real fracture plane. Results show that there are some differences between stresses on the fracture plane obtained by the Hoek –Brown criterion and Mohr stress circle. Therefore، obtained shear strength parameters are depended on of Hoek-Brown envelope. Also، it is inferred that angle of fracture plane obtained using Hoek-Brown envelope differs from the real fracture plane، so the angle is in not a function of real fracture plane but it depends on Hoek-Brown envelope.

Crushing is the first stage of operations involving size reduction and separation of ores. Throughput، feed and product size، rock compressive strength، and abrasion index among main criteria of crusher selection. In this Paper، Selection of different primary crusher type based on above mention criteria using Elimination Choice Translating Reality (ELECTRE) is discussed. The crushers that are considered include Double toggle jaw، Single toggle jaw، High speed roll crusher، Low speed sizer، Impactor، Hammer mill and Feeder breaker crushers. Results have been offered the Double toggle Crusher as the suitable primary crusher.

At the grinding circuit of the Share-Babak copper concentration plant two 503 cm ×762 cm ball mills with motors of 2984 kW which are working with 10-cyclone (66. 8 cm diameter) clusters are used. In the initial design of the plant، it was assumed that this circuit could grind a feed rate of 721 t/h with size of 789 μm (80% passing size) to a product size of 90 µm (80% passing size). The study of the circuit during the last year indicated that due to variation of feed characteristics and non-optimized operating conditions P80 of the cyclone overflow (i. e.، flotation feed) was 128 µm with the standard deviation of 12 µm. In order to provide proper operating conditions، the ball mill percent solids was increased from 66 to 70%، and the ball load was also increased from 23 to 35%. On the account of increase in ball load، the mill power draw increased by 28%. To increase the performance of the cyclones، the cyclone feed solids concentration was decreased from 52 increased to 48 %. These changes decreased the P80 of the cyclone by 22. 7% and also lowered its variations by 40%.