نشریه روش های تحلیلی و عددی مهندسی معدن
پیاپی 29 (زمستان 1400)

Most hydrothermal ore deposits are controlled by geological structures. They are often a product of multistage hydrothermal activities, as a result, primary alteration haloes usually overlap in the vertical direction. By distinguishing the hydrothermal stages associated with ore-forming processes, one can determine the timings of hydrothermal activities and use the results as a method to identify blind mineralization. In order to explore probable blind mineralized zones of the Aliabad deposit, it is necessary to evaluate the element concentrations towards the depth or margins of the deposit. Modeling primary geochemical haloes could be useful in this stage. The Aliabad porphyry Cu-Mo deposit, located in the southern segment of Central Iran and adjacent to the northern border of the Urmia-Dokhtar volcanic belt and east of the Dehshir fault. Ore bodies at the Aliabad deposit are primarily controlled by structural features, which provide an opportunity to investigate the zonality in primary halos in this copper-molybdenum porphyry deposit. The primary geochemical characteristics of the mineral deposit were studied based on geochemical analysis of 1559 core samples from 24 drill holes. The formation of the primary geochemical haloes, which joins the ore body up to the surface, can be associated with hydrothermal fluid diffusion through fracture (fissures) zone developed in the rocks of the folding axis in the mining area. Along the vertical direction, the concentrations of Cu, Ag, and Fe shows an increasing trend from the surface to the ore body, at all boreholes; while the concentration of Pb, Mn, and Bi are decreased with depth at the same environment. A detailed zonality sequence of indicator elements is obtained using the variability index of these elements: Pb → (Bi, Mn, Mo) → Cr → Ni → (Sb, V, Zn) → (Ag, Co, Cu, Fe, S) → P. According to this zonality, indexes such as Vz4=Pb×Mn/Cu×Ag and Vz5=Pb×Mn/Cu×Ag×Co can be constructed and considered as a significant criterion for predicting the Cu potential at a particular depth. Studying the distribution of the zoning indexes at different levels revealed high values of proposed indexes in the northwest and south of the area.  It can be concluded that copper mineralization will continue to deeper and unexplored parts of the deposit northwest of the study area. Consequently, it is suggested that further investigations concentrate on geophysical operations and it is highly recommended to drill additional boreholes at these areas. It is noteworthy that new drillings of the northwestern part must continue deeper than current boreholes (>150 m); because geochemical zonality indexes are extended to deeper parts. This extension is not observed for the southern part, so, additional drillings at the southern part can be shallower than 150 m.

Inhomogeneity and discontinuities play a key role in the resistance and behavior of rock masses. Today engineers have a wide range of methods to analyze the stability of rock slopes. Due to its simplicity and speed of evaluation, static analysis methods continue to play a special role in the stability assessment of jointed rock slopes. One of the most well-known static methods used in the stability analysis of rock slopes is the Key Block method (KBM), which is based on key block finding and analysis. In this method, if none of the key blocks are unstable, it implies that rock mass is stable. Occasionally, the combination of several stable blocks has led to the formation of a group of blocks that sometimes leads to instability. Therefore, the stability analysis of the jointed rock masses leads to study groups of blocks that are potentially dangerous for the stability of a rock slope. The Key Group method (KGM), with its progressive approach, finds these critical groups and focuses the stability calculations on these groups. Until now, methods SKGM, PKGM, OKGM have been proposed to remove the limitations of this method and its development. In order to increase the efficiency, accuracy, and speed of this method and to develop it in three dimensions, it is decided to combine it with one of the numerical methods. The standard Discontinuous Deformation Analysis method (DDA) is an implicit method based on the finite element method. This is a sophisticated numerical method for modeling the quasi-static and dynamic behavior of rock block systems in discontinuous rock masses. The goal of this paper is to use the potency of the numerical method of DDA to analyze the candidate key group. For this purpose, the DDA computer program was developed with Mathematica programming language and combined with the KGM software. The resulting package, after selecting the key group by the KGM method, proceeds to analyze it with the DDA method. Two examples are solved illustrating the reasonable results and the efficiency of this developed method compared to that of the original KGM and SKGM. The results validated the proper accuracy and good performance of the procedure developed in this research.

Nowadays, due to the increasing urban environments, increasing the density of surface structures and the lack of space for intra-urban transportation, the need to implement underground structures such as tunnels and subway stations in urban environments has been felt more than ever. One of the important factors in the implementation of deep underground stations in urban environments is the choice of suitable excavation methods that have a significant impact on the stability of the tunnel space during excavation, surface sinking caused by drilling, and also the long-term stability of the excavated space. In this research, considering the geotechnical characteristics of the land and the geometry of the station under study, three common methods for excavation of subway station, including NATM, STM, and cut & cover methods with support systems such as shotcrete, piles and ribs, fore polling and nailing numerically modeled and have been evaluated and reviewed for the stability of the space and tunnel wall displacement. Numerical modeling of various methods for implementing this space has been done using the finite difference method with FLAC3D software. Sensitivity analysis for changing geometric parameters of support systems was done. According to the results, the maximum displacement in the environment around the station is related to the cut & cover method and the minimum is related to the STM method with the nailing support system.

To assess the safety of the foundation, the ultimate bearing capacity, as well as the settlement of the footing, should be studied. The bearing capacity of a footing built near the slope has been widely investigated. However, the published research work which focused on the settlement of the footing close to the slope is very limited. In many cases, the foundations should be built adjacent to a slope. Since geomaterial behavior is usually time-dependent, and due to the limited published research work on the time-dependent settlement of the foundation on a slope, in this study, a semi-analytical method has been used to obtain the elastic and viscoelastic settlement of a foundation rested on a slope. The proposed method has been developed based on the theory of elasticity by combining a transformed Airy stress function and finite difference method. To facilitate the use of the proposed solution, as well as investigating the effect of slope characteristics and footing geometry on the settlement, a set of elastic and time-dependent settlement charts have been proposed. The results indicate that the slope angle, the normalized footing distance from the crest, and the slope height play a prominent role in the settlement behavior of footing. By increasing the normalized footing distance or decreasing the slope angle, the settlement of the edges of the foundation tends to be equal and the behavior like a footing rested on a horizontal ground surface can be observed. Also, by decreasing the height of the slope, this behavior, i.e. behave like a footing on half-space, will happen in the smaller normalized footing distance.

 One of the most challenging safety problems in open pit mines is backbreak during blasting operation, and its prediction is very important for a technically and economically successful mining operation. To avoid backbreak, different parameters such as physicomechanical properties of rock mass, explosives properties and geometrical features of the blasting pattern should be considered. This paper presents a new solution of multiple linear regression (MLR), particle swarm optimization algorithm (PSO) and artificial neural networks (ANNs) to estimate the backbreak induced by bench blasting, based on major controllable blasting parameters. To this aim, Angouran mine in Iran was considered and blasting pattern parameters for 73 operations were collected. In addition, back-break was measured in each operation. Considering the previous investigations and also collected data from the mine, burden, spacing, hole length, stemming, charge per delay, RQD, number of row and powder factor were selected as input parameters. In order to find the better solutions, the constructed models were implemented in PSO algorithms. Also, the prediction of backbreak was investigated using ANNs. According to the obtained results, the PSO algorithm is a suitable tool for optimizing models and obtaining more accurate prediction of backbreak. Among the presented empirical models, the optimized exponential model with PSO algorithm with a RMSE (0.31) and R2 (0.87) shows the better results in prediction of backbreak and it is suitable for practical use in Angouran mine. Considering the sensitivity analysis, among the input parameters, length of stemming and charge per delay have shown the most and the least effect on the backbreak, respectively. The results of ANNs show that multilayer networks are more powerful and efficient than single-layer in prediction of backbreak.

Wellbore stability analysis, selecting the optimum drilling direction, and determining the safe and stable mud weight windows are among the major geo-mechanical challenges in the oil and gas industries. In this study, the wellbore stability analysis and the optimal drilling direction have been numerically modelled by finite element method (FEM) considering the importance of wellbore stability and recognizing instabilities using the data of Sivand oil field. The numerical modeling of wells behaviors has been performed in two modes of elastic and elastoplastic deformations using ABAQUS software. The numerical results have been done using the two failure criteria, namely Mohr-Coulomb and Drucker-Prager and compared together, considering the effect of intermediate principal stress, Drucker-Prager failure criterion has been selected as a suitable failure criterion for this study. In addition, the numerical results have shown that the vertical well is the optimal drilling direction. Then, by applying the NYZA method, the safe mud weight window has been determined. The validity of the proposed mud window for a vertical well has been approved by applying the Mohr-Coulomb analytical method. Finally, the safe and stable mud window for the vertical wellbore has been proposed.