IRANIAN JOURNAL OF MINING ENGINEERING (IRJME)
Year:2011 | Volume:5 | Issue:10|Papers Count:11

Selection of proper number and location of boreholes are major tasks in design of exploration network. Boreholes normally drilled for insitue testing and sampling. A challenging issue in sampling is determination of number and location of samples. The logic of optimum sampling is sequential. This work presents a comparison between single and multiple stages sampling in Semilan dam site. First, the single-stage sampling was tested; using geotechnical data (Lugeon and RQD) of 23 boreholes and indicator function. Based on indicator functions, Lugeon parameter divided to four and RQD to three indexes. The other application of indicator functions, is converting qualitative to quantitative data in order to define indicators of various structures and lithology of the studied dam site. Then, indicator variograms of each parameter, in various directions, were calculated and their variogram parameters were extracted. Based on the average kriging error, Lugeon, RQD and lithology index were also divided into four indexes. Consequently, the function for locations of additional drillings, based on their relation with risk and uncertainty is defined. Function for location of additional drillings is found to be equal to Lugeon multiply to estimation error multiply to index of dam structures; divided by RQD multiply by lithology index.Next, two stages sampling was studied starting with 12 boreholes, according to sample density.All the process was repeated once again and according to function of additional drilling locations, 8 boreholes were selected for the second level or phase of drilling. Based on kriging and neural network estimator, and using normalized data, desired parameters were estimated.In the present study, kriging variance and estimation error in two stages sampling decreased more, compare to one stage sampling, although the numbers of boreholes decreased from 23 to 20. Reduction of estimation error is related to the layout of the first stage boreholes between the second stage ones.

Reservoir permeability is a critical parameter for the evaluation of hydrocarbon reservoirs. There are a lot of well log data related with this parameter. In this study, permeability is predicted using them and a supervised committee machine neural network (SCMNN) which is combined of 30 estimators. All of data were divided in two low and high permeability populations using statistical study. Each estimator of SCMNN was combined of two simple networks to predict permeability in both low and high classes and one gating network, considered as a classifier, classified data to these two classes. Thus, each low and/or high input data would predict in related network. This SCMNN was used to predict permeability on the data of one of petroleum reservoirs of south-west of Iran. 210 samples of this reservoir were available. Because of the fewness of data 80% of them were used as training data and 20% of them were used as validation and testing data. The overall fitting between predicted permeability versus measured ones was qualified through R2 (R=correlation coefficient) to be 97.72% which is considered appropriate. Whereas, R2 in the simple network in the best stat was 84.14%. The high power and efficiency of SCMNN are indicated by lower bias and better R2 in results.

Forming the air-core, is the one of flow properties in hydrocyclone. The swirling flow causes a cylindrical low pressure area at the axis of hydrocyclone which is constant throughout the entire length of the hydrocyclone. Air-core affects the separation efficiency. In this study, low pressure areas were used to predict air-core diameter. Computational Fluid Dynamics (CFD) method was used to determine the pressure distribution inside of hydrocyclone. Three models including: the renormalization group k-e model, the Reynolds stress model, and the large-eddy simulation model, were compared for the prediction of aircore dimension. Air-core diameter was evaluated by using three planes, one on cylindrical part and two on conical section. Results show that, the RSM turbulence model is more accurate than two other models.

In order to control settlement induced by tunneling in urban area, effective parameters in the excavation procedures should be determined with respect to the geotechnical properties and construction methods. In NATM, round length and sequence of excavation phases are the significant parameters that affect on tunneling economically and technically. These two factors have a great relationship with time and cost of tunneling projects. Therefore, determination the optimum amount of those parameters is the main challenge in such projects. In this paper, the effects of round length and excavation phases on surface settlement in line four of Tehran metro, still in construction, were evaluated. To do the analyses, a three-dimensional finite element package was used to simulate the tunnel operations for different number of round length. The results showed that, regarding to the geotechnical properties and tunnel dimensions in line four areas, the round length was determined conservatively. Therefore, it can be suggested that in order to improve efficiency, the round length is determined 2 and 3 meter in upper and lower parts of tunnel cross-section, respectively.

Mining activities often produce long-term environmental pollution and create many problems comprising acid drainage generation and discharging heavy metals to the surface and groundwater resources. The principal environmental concerns associated with waste rock dumps result from the oxidation of sulfide minerals, mainly pyrite within the from dwaste materials, when such minerals are exposed to atmospheric oxygen and/or water, they undergo rapid oxidation that produces acid waters. There are many mechanisms to make available oxygen within the waste dumps. Diffusion in the gaseous and aqueous phase through pores in the waste materials is the dominant mechanism for transporting the atmospheric oxygen from surface to the depth where the oxidation takes place. In this paper, oxygen diffusion and pyrite oxidation processes within the dump materials has been modeled using a finite volume code called PHEONICS in Sarcheshmeh copper mine. The analytical solution has been used to calibrate the numerical model. Both analytical and numerical methods show that the diffusion coefficient has an important role in pyrite oxidation and pollution generation. The results obtained from the numerical modeling further show that the pyrite reached to 13.8 % in surface samples of waste dumps after 4 years of the beginning of the oxidation process. It increased gradually with depth and reached to its initial percent (18.5 %) at a depth of 2.5 m within the dump where no oxygen is available to oxidize pyrite. The results obtained from such studies can be used in designing appropriate methods in order to minimize environmental pollution and their impacts to water resources.

Zinc sulfide concentrate which is produced from Irankoh mine ore, contains indium. In this study, recovery conditions of indium from leaching residue of roasted zinc sulfide concentrate were investigated. Indium concentration in leaching residue of zinc sulfide concentrate was 145ppm. Optimum values of effective parameters were as follows: initial concentration of sulfuric acid solution of 100 g/L, temperature of 90°C, leaching time of 3 hours and the amount of required sodium sulfide for iron reduction 1.5 iron stoichiometric ratios. Then, indium was selectively precipitated from the leach solution. For selective indium precipitation, the pH of leaching solution was adjusted to six using ammonia in 90°C, and indium precipitation time was considered to be 10 minutes. Concentration of indium in resulting precipitation was 2650ppm. Finally, the resulting precipitation was dissolved using hot sulfuric acid solution, and the solution was subject to solvent extraction and cementation using zinc powder to recover indium. Total recovery of indium from zinc leaching residue was obtained more than 92% and product purity was more than 94.5%.

Determination of bid prices for hard rock TBM drives needs to estimation of tunneling machine advance rate. On the other hand determination of machine advance rate requires to estimation of machine utilization. This paper propose an equation for estimation of open TBM utilization based on rock mass classification system (Q & RMR) and disc thrust of TBM machine. For this purpose Pearson test is used for evaluation of correlation between utilization, RMR, Q, Disc thrust, MQ (Modified Q), NRMR (None modified RMR). Whereas stability status of tunnel affect on the utilization factor, rock mass classification indexes have a significant relationship with the machine utilization. Statistical analyses show that there is significant relationship between MQ (Modified Q), NRMR (None modified RMR) and utilization factor. Ultimately the best equation is offered for estimation of utilization factor.

In underground coal mines, due to occurrence of probable events and the consequent risks, normally a reliable safe environment is not provided for the work forces and operational equipments. Through the risks, two main considerable damages may happen. First, the human injuries namely fatality, disability or maim and organ fractures and second the economical damages such as amortization and loss of mining equipments, and closure of working faces and galleries. Considering these types of crucial events this study aims on reducing the likely risks particularly in East Alborz Coal Mines Company. For this purpose, based on probability of event occurrences, their severities and outcomes the relevant risks have been assessed and analyzed. To achieve this goal by taking into account the occurrence probability and intensity a number of measures or standards were developed by the authors. Risk Priority Number (RPN) was introduced. By employing RPN the most impressive uncertainty factor in East Alborz Coal Mines Company was recognized. Finally, with the regard to the degree of damages caused by the events, a practical procedure for risk reduction in the mines has been presented.

Short term production scheduling determines the sequence of ore and waste blocks extraction on shifty, daily, weekly or monthly bases. The objective of this production scheduling was to determine the block extraction period according to the production constraints including; grade blending, mine and mill capacity, and slope constraints. Several mathematical models have been proposed for short term production scheduling, but the equipment access constraints have not been incorporated effectively in that models. In this paper the mathematical model of short term production scheduling was developed in order to insure that a block can only be removed if all nine overlaying blocks and two or three surrounding blocks have been removed, in the previous or current periods. This goal was achieved by defining equipment access constraints. Mathematical inequalities were presented for equipment access constraints based on integer programming, according to the type of block access modes. These models were then applied to a case study, using Excel 2007 and solved via Premium Solver Version 9.0 software.

This study has been carried out on the stability analysis and the support systems design of the water conveyance tunnel and surge tank of Gotvand dam. The stability analysis of underground openings is one of the most important subjects in rock mechanics principles. There are four different methods for the analysis of underground openings. These are: closed form solutions, numerical methods, empirical methods and physical modeling. Nowadays the numerical and empirical methods are more widely used all over the world. In This research, analyses have been carried out by finite difference method (component of numerical methods) and Q and RMR (component of empirical methods) rock mass classifications. The numerical software used for analyzing the tunnel stability was Flac3D. This software is capable of determining the values of induced stresses and displacements around the underground openings. The results obtained from stability analyses show that the underground excavation is unstable; therefore, installation of a support system is necessary. After installation of support systems, the value of maximum displacement is less than Sakurai’s critical displacement, therefore, the underground excavation will be stable. The recommended support systems are:1) Installation of systematic grouted bolt by 7m long and spacing 1.5×1.5m with shotcrete by 150mm thick in surge tank2) ) Installation of systematic grouted bolt by 5m long and spacing 2×2 m and with shotcrete by 70mm in conveyance tunnel and box.