فصلنامه مهندسی معدن
پیاپی 7 (تابستان 1388)

Optimization of stope boundaries has received less attention than that in open pit mines. However، few algorithms are available for optimization of stope boundaries، which are either tailored for a specific mining method or lack some significant geometrical and technical constraints. A greedy algorithm is described in this paper for optimization of stope boundaries in each level of an underground mine. The algorithm employs a graph of the 2D economic block model in which weight of edges indicate cumulative economic values of blocks. The proposed algorithm enjoys Dijikstra approach to find the maximum path length on the graph. Dijikstra method is one of the best methods for solving the greedy algorithms. Indeed، the path which is searched in model of mining area using this algorithm، defines limits of the optimized stopes which provide the highest economic value.

The grout injected into the joint with a primary velocity but solidifies gradually depending on the joint geometry and grout characteristics. Therefore the velocity changes completely، both in the perpendicular and in the injection direction. In the present study، the changes of two velocity components in the joints with various geometries are investigated using computational fluid dynamics (CFD) and finite volume numerical method. For this purpose joints are modeled as parallel smooth plates and the saw-tooth with different matednesses. The results show that velocity component in the injection direction of a joint with parallel smooth plates always reveal parabolic distribution towards the joint aperture. In the saw-tooth joint، velocity component in the injection direction increases in the narrowed locations and its profile changes from parabolic to undulated form. The velocity component perpendicular to injection direction in the joints with parallel smooth plates equals to zero from joint entry up to the point in which grout starts to solidify and after that point this component emerges and then changes. Vertical component of velocity is non-zero in the saw-tooth joint from joint entry and the changes both in quantity and direction depend on joint matedness، joint aperture ratio (k) and joint walls direction and dip.

The factors affecting copper extraction in heap extraction method is a very important issue in recent researches. Mathematical modeling of the extraction method provides different views to design of such processes. In this paper، a mathematical model is proposed for copper heap extraction from spherical and porous particles based on mass balance associated with chemical reaction in an unstable condition. The model specifies the factors that affect the output، for example: input grading، time of solvent flow، accumulation، dispersion rate and solvent concentration. For the model verification and calibration، column leaching test were used. The results indicate that the model prediction has good agreement with experimental findings. The solid bed includes particles of Sarcheshmeh copper ore (Kerman) and the solvent is thin Sulfuric Acid. This model could be used as a very powerful tool for the prediction of copper extraction at various conditions.

Clay minerals are largely available in nature and due to special characteristics of clay، have successfully been used for dam core as a water-tightening material. Taking into consideration the execution necessities and so as to reduce the associated costs، it is required to reassess fundamental of the conventional plastic concrete mix design used for constructing water tightening element of the large dams. In this study the effects of two different types of clay minerals with the intention of evaluating the possibility of changing portion of the clay materials on compressive strength of plastic concrete are investigated. The required samples have been prepared and tested according to a special laboratory program. The results indicate that the type of clay mineral has meaningful effects on the strength of the plastic concrete. The results also have shown that the slump of the new mixture of plastic concrete is dependent on the amount of clay in the mix design. Consequently an empirical equation is derived for estimation of compressive strength based on two parameters of clay content and sample age.

A large number of algorithms have already been developed to optimize open pit limits based on some assumptions and constraints. Therefore، it is normal to develop new algorithms to decrease existing limitations and increase their capabilities. The key group concept، mainly used for stability slope analysis is، in this paper، used to develop a new algorithm named “KG-PLO” to optimize open pit limits. The KG-PLO is implemented on an especial type of the economic block model of the mining area. The algorithm can present the true optimal limit because it is rigorous and have a mathematical proof. Since the KG-PLO enjoys a sequential procedure، the logic iterations are not too much. The KG-PLO algorithm has been developed based on the existing 2D key group approach. It is possible to improve the proposed algorithm concerning the further improvement of the key group concept، proportionally. A computer program in Mathematica media is prepared to implement the KG-PLO algorithm.

Subsidence is one of the inevitable phenomena of most underground mining and excavations، especially in long-wall mining methods (i. e. in filling، with out filling and mechanized long-wall methods). It may also occur in room and pillar mining methods (i. e. in both with and without pillar recovery methods). Subsidence phenomenon occurs due to some vertical and horizontal displacements of the ground surface located just above the excavated area. This may also in turn causes surface destructions and eventually result in irretrievable loss of life and property. In this study، a higher order displacement discontinuity method (HODDM) which is a subdivision of the boundary element method (BEM) was used to model the subsidence. To be able to evaluate the horizontal strains on the surface of the excavation the finite difference method (FDM) is also added to the proposed numerical method. The vertical displacement and the horizontal strain (relative displacement) of the ground surface of the excavating area can be evaluated by this modeling technique. It should be noted that، subsidence due to the mining of both horizontal and inclined (oblique) layers were considered in this study. Some of the numerical results are compared with their corresponding empirical ones given in the literature. This comparison shows a good agreement between the numerical and empirical results.

Beheshtabad 65 Km tunnel is the longest pressure tunnel in Iran. Near the inlet and outlet of the tunnel due to low level of ground water، leakage of water from the tunnel would be likely. In this article at first the tunnel route in zoned and Permeability، External water head and geotechnical parameters have been studied. Analytical Fernandez''s methods is introduced and briefly discussed and Leakage quantity and water head on the lining is determined using the method. The permeability of those Chainages that are supported by precast concrete segment، determined using Darcy low and considering segment Geometry. Then flow analysis by use of FLAC software is explained. In the last part analytical and numerical results are compared to each other and it is shown that the results are very similar. However numerical methods are preferable because they have ability to consider model details such as drainage pipes، arrangement and dip of layers as well as modeling transient seepage.