نشریه روش های تحلیلی و عددی مهندسی معدن
پیاپی 8 (پاییز و زمستان 1393)

Because of the stability، atomic and biological accessibility problems of the heavy metals، they are considered as serious pollutants of the environment. The sediments of Sarcheshmeh copper mine in Iran contain high concentrations of these pollutants. and thus environmental evaluation and ranking them based on emission levels is important for timely environmental measures with the lowest operating costs. The first aim of this study is the environmental risk evaluation of these sediments by determining the contamination factor، pollution load index، enrichment factor and Geoaccumulation index. The second aim is ranking these metals based on the level of critical risk using the Multi Attribute Decision Making (MADM) methods. In this study، first، by determining risk evaluation indices، we set out to assess heavy metals contamination (Co، Cu، Mo، Zn، Cr، Mn، Ni، Pb، Ti and Fe) in the sediments of Sarcheshmeh copper mine which conduce to the tailings dam. Then، by collecting expert opinions on the relative importance of each of the mentioned indicators، through final weighting of the indices using Antropy Shanoon method، heavy metals in the sediments of the study area were ranked and clustered using ELECTRE III method. Based on measured results of the risk evalution indices، the intensity of contamination to these metals were as Fe> Cu> Co> Ti> Mn > Pb > Cr، and all the metals except for copper، zinc and iron cited almost in the unpollutant limit. Also based on ranking results، the ten risks were clustered in seven categories with iron and copper having the highest pollution and critical risk amongst the heavy metals in the sediments under study، respectively.

Evaluating the effects of sulfuric acid solution used in leaching of copper metal on hydro- mechanical behavior of rock mass، and also understanding of chemo- hydro- mechanical coupling processes related to this phenomenon are the main objectives of this research work. Biotechnology is regarded as one of the most promising and certainly the most revolutionary solution to the defects of pyrometallurgy. It holds the promise of dramatically reducing the capital cost of the projects. It also offers the opportunity to reduce the environmental pollution. A set of laboratory experiments were implemented for evaluating the influences of sulfuric acid with different pH values; 1، 3 and 5 on the properties of three types of Andesite rock joints in heap leaching site of DAREZAR copper mine. Joint roughness coefficient، joint shear stiffness، joint aperture، and shear strength of degraded rock joints in different sulfuric acid concentrations were measured. Using a Discrete Fracture Network-Distinct Element Method (DFN-DEM) approach، the effect of chemical solution on permeability of the fractured rock mass is evaluated. The numerical modeling results show that with decreasing pH value of copper metal leaching solution، the coefficients of equivalent permeability tensor increases. The effect of ratio of horizontal to vertical stresses (k0) on hydraulic properties of Andesite rock mess is also negligible.

The accurate estimation of ore grade plays an important role for the mine evaluation، planning and designing. According to some existing problems when using conventional methods such as Kriging for grade­ estimation of deposit. In this research، the performance of intelligent estimators such as multilayer perceptron neural network، adaptive neuro-fuzzy inference system and support vector regression were investigated for grade estimation in Masjeddaghy porphyry copper (gold) deposit located in East-Azerbaijan province. For this purpose since divided assay data achieved from 31 exploratory boreholes into training and test subsets، optimum structure and designing parameters value of the mentioned methods were determinated by using the genetic algorithm and based on the training dataset. Finally the validation indicators calculated for estimation grades of testing dataset for used estimators. According to the results، support vector regression method showed higher generalization capability and computational efficiency in copper grade estimation. Also close and better results of this method than ordinary Kriging indicate that support vector regression method can be used as rapid، accurate approaches and better than other intelligent estimator for grade in same problems.

Evaluation of interaction between new and existing underground spaces is one of the important problems in tunneling in urban areas. In some cases it is necessary to excavate tunnels close to each other’s. This، in turn، will lead to important interaction between these tunnels. In this paper، using 3D numerical modeling of line 1 twin tunnels of Tabriz urban railway، excavation stability of these tunnels، using critical strain of Sakurai، have been studied. Also displacement pattern of lining in both twin tunnels (Sahand & Sabalan) have been investigated. In next step، effect of excavation of these tunnels on the subsidence of surface and adjacent buildings، using Cramer criteria and finite difference method (FLAC 3D)، have been studied. For the purpose of study of the interaction effects between these tunnels، forces and moments that act on the segmental lining of each tunnel and their safety factor have been verified. Eventually، stability of pillar that lies between two tunnels، have also been evaluated. The results show that: 1-twin tunnels of Tabriz metro will be stable during excavation. 2-Surface subsidence due to excavation of these tunnels will have no important effect on existing structures. 3-Safety factors varies between 5-10 on the different positions of segmental lining. 4- Pillar that lies between twin tunnels will be stable

Subsurface rocks (by their nature) are filled with cracks and pores which are saturated with one or more fluid phases (water، air، oil، etc.). These fluids have a significant influence on the mechanical behavior of a rock mass. Closing the state of the stress to failure surface and pore pressure effect on the rock deformation are among these influences of pore fluids. To account for these effects، one should investigate the rock mass response in an elastic medium with porosity. Therefore، poroelastic theory should be used. In poroelastic medium the governing equations، stress-strain and strain-displacement relations are affected by pore pressure and reciprocal effects of displacements and pore pressure. In this paper، firstly the constitutive equations and other required relations for describing a poroelastic medium are presented. Then the coupled effect of pore pressure and displacements is removed by using a potential method. Differential equations of time-dependent and time-independent are solved for a point force and point source which gives Green’s functions. Resulted Green’s functions can be used in any suitable numerical method such as boundary element method to investigate the response of rock mass to poroelastic effects.

Today، with the increasing need for simulation of granular materials and simulation of materials grading، creating random volumes and surfaces have become significantly important. Since discontinuous materials have particles with random shapes، thus، creating random volumes and using them as separate blocks in the analysis of discrete element can significantly help to adjust the numerical analysis results of discontinuous materials to the experimental results. In this paper، an appropriate process is offered to create and prepare particles with complex shapes in order to use them in the analysis of discontinuous materials by discrete element method. To this end، using two new proposed algorithms، random surfaces and volumes are created. Then، in order to use the produced random surfaces and volumes in the analytical software that uses discrete element method، an algorithm is offered to reproduce them through assembling the spheres on each other. Finally، since the initial input in the analysis of discontinuous materials is a packing set of discrete blocks by offering a new packaging algorithms، these discrete blocks are got packed. All algorithms were successfully implemented and the random volumes are generated and displayed in geometric modeling environment.

Hydraulic Fracturing method was developed to increase the productivity of low permeability reservoirs. In this method، it is very important to predict the hydraulic fracturing geometry to ensure a safe and optimum design. Hydraulic fracture propagation is affected from natural discontinuities (fault، joint…) in fractured reservoirs. In this study، the interaction of hydraulic fracture with natural fractures and consequently the fracture propagation and variation of fluid pressure inside the hydraulic fracture is studied numerically. The numerical program (2DFPM) was developed based on combination of boundary element method (displacement discontinuity method (DDM)) and finite difference method (FDM). The validity of the numerical program was verified by KGD model. Different conditions of hydraulic and natural fracture interaction are modeled and the effect of natural fracture on distribution of fluid pressure profile along the hydraulic fracture length is studied. The results show that the interaction condition and injection parameters of fluid have more influence on the hydraulic fracturing method.

Today، large underground spaces for multiple strategic projects including hydroelectric power plants، storage of oil and gas، nuclear waste disposal، etc. are important. Stability analysis is of great importance due to the large dimensions of these spaces. In this paper، at first according to the discontinuities orientation and stress conditions of the region، appropriate direction for excavations is selected. The rock mass strength properties including the shear strength of discontinuous rock mass and the modulus of deformation using in situ tests was determined. The numerical modeling results have been summarized. Stress conditions in the study area were determined using a hydraulic fracture tests. In the next step، Using analytical relations and numerical method (Discrete Element Method، 3DEC); as well as، with regard to occurring rock burst phenomenon between the two caverns، and changing of distance between these caverns، the proper optimum distance is determined. Finlay using the result of numerical modeling and based on the plastic zone، a suitable support system (consists of length of tendons and rock bolts at different parts of caverns and axial stress applied to those) has been suggested.