نشریه روش های تحلیلی و عددی مهندسی معدن
پیاپی 20 (پاییز 1398)

The longwall method is the most commonly method used in extraction of coal layers. The mining review records shows that the majority of the dangers of coal underground mines related to the sudden and uncontrolled roof fall-out of the stopes. Predicting the behavior and the ability to destroy the roof rock is very important for the successful execution of longwall method and reducing its risks. In this study, we will present a new fuzzy classification system by using the theory of fuzzy sets and fuzzy multi-criteria approach to evaluate the roof quality of the coal mines. 

In the first step, 8 parameters were selected as effective factors in the classification system. This selection was performed after reviewing the parameters affecting the roof quality of coal mines. The parameters include: Uniaxial Compressive Strength (UCS), Brazilian Tensile Strength (BTS), moisture sensitivity, spacing and continuity of discontinuities, thickness of layers, joints slope and difference of stopes’ and critical joints’ orientation.
 

Fuzzy classification system was presented after determining the parameters weight. The fuzzy classification system can evaluate and categorize the roof quality of coal mines. The classification qualitatively classified the quality of roofs in 3 classes (good, fair and poor). 

In order to evaluate the performance of the fuzzy classification system data of to 15 stopes in Eastern Alborz coal mines were evaluated. The results of this study showed that we can evaluate the quality of the roof rock with fuzzy classification system with high reliability in for coal mines roofs.

In this paper, a new algorithm was offered for collision detection and packing random volumes. Among the features of this algorithm is its packing feature which is capable of packing particles with any shape. Then, using PSO algorithm, the optimal state of this packing algorithm was obtained. Finally, in order to validate the optimized algorithm, the results were compared with the results of digital packing algorithm. This comparison showed that the new packing method proposed in this paper (the optimized packing method of using control points) provides good results compared with digital packing method. 

Unlike dynamic packing methods, geometric packing methods allow the rapid packing of a large number of particles; these packing structures can be used as the initial state (initial input) in numerical analysis of discontinuous materials. Geometric packing methods, in fact, improve the efficiency of the particles preparation phase for numerical analysis and dynamic simulation. For example, sorting and preparation of hundreds of particles through using dynamic methods may take several hours, while using geometric methods, it may take less than few minutes. The disadvantage of geometric methods is that as the particles do not reach dynamic balance in these methods, no information is obtained about the contact forces. However, geometric methods is close enough to the particles mechanical balance. As a result, the packing structure obtained by these methods can be used as a good starting point for dynamic simulations.
 

The new packing algorithm offered in this paper is based on control and placement of each shape by using boundary points (the outer surface points of the shape) or all points of the shape. Hence, this algorithm is capable of packing the particles with any shape. This new algorithm was originally designed for collision detection and packing of two random shapes and, then, was generalized to N particles. Finally, using Particle Swarm Optimization (PSO), it was optimized. 

The new packing algorithm was generalized to N particles and, using the algorithm of PSO, it was optimized. After the optimization of this packing algorithm, it was validated through comparing its results with the results of digital packing method; and it was observed that, in comparison with the digital packing method, the new packing method proposed in this paper (the optimized packing method of using control points) can offer good results. In the optimized packing method of using control points, the following factors have a significant impact on the packing quality and density of particles:
The order of adding particles into the container.
The number of the times the answers are repeated (M), the increase of which leads to the higher density and quality of packing.
Prioritizations of the criteria for the calculation of fitness function (through determining the values of K1 and K2 coefficients).

The complex mechanical behavior of masonry structures depends strongly on the interface between brick and mortar. The purpose of the present study is to investigate and compare the shear behavior of brick–mortar interface using experimental and numerical methods in order to model unreinforced masonry walls subjected to in–plane compressive and shear loadings. Numerical modeling of masonry walls is performed using an algorithm based on the distinct element method (DEM). Obtaining shear and normal stiffness, adhesion and friction angle of brick–mortar interface, as well as the maximum permissible load on the unreinforced walls at different compressive stresses are among the important achievement of present study. 

The fracturing mechanism in masonry is a complex phenomenon due to existing two brittle materials with distinct material properties. The mechanical behavior of masonry is strongly affected by the behavior of mortar joints. In this paper, after obtaining resistance and behavioral properties of brick-mortar interface, the behavior of unreinforced masonry walls has been investigated. 

As previously mentioned, modeling has been performed by DEM approach using 3DEC. Due to the capability of distinct element method to explicitly represent the motion of multiple, intersecting discontinuities, these methods are particularly suitable for the analysis of masonry structures in which a significant part of the deformation is due to relative motion between the blocks. In the DEM modeling, the Mohr-Coulomb failure surface with a tension cut–off is chosen for blocks and Coulomb–slip model is chosen for joints with zero thickness representing mortar bands. 

The average normal and shear stiffness of the brick–mortar interface was equal to 42.82 and 122.46 (MPa/mm). The adhesion and friction angle of the brick– mortar interface was equal to 0.7 MPa and 37.7 degrees, respectively. The relationship between shear stress and shear displacement of the brick–mortar interface is presented and the maximum permissible load of unreinforced masonry walls subjected to in–plane compressive and shear loadings was calculated using distinct element method (DEM).

Uncertainties of economic parameters have an indispensable role in mining evaluation projects. Therefore, evaluation of a mining project without considering the available uncertainties is incorrect and unreliable. Metal price uncertainty is the most important parameter in a mine economic uncertainty. Many researchers have studied the role of economic uncertainties in the production planning. But majority of these studies are conducted in one-element deposits and the two-element deposits are rarely investigated. In this research the binomial tree technique valuation is used to compute the production planning evaluation in two element deposits for price uncertainty. It is concluded that the mine evaluation suggests greater net present value when price uncertainty is considered for both element. 

The main sources of uncertainty arising at the beginning of a mine project can be categorized into three groups: geology uncertainties, engineering uncertainties and economic uncertainties. Many researchers studied these types of uncertainties. In majority of the aforementioned researches, price uncertainty effect was investigated only for one- element deposits, which can result in an inaccurate valuation. Therefore, in this paper, the binomial tree method was used for determining the effect of price uncertainty in valuation of two-element deposits. 

In this research the binomial tree technique valuation is used to compute the production planning evaluation in two element deposits for price uncertainty in four scenarios: Assuming price certainty for both elements; assuming price uncertainty for first element and price certainty for second element; assuming price certainty for first element and price uncertainty for second element; assuming price uncertainty for both elements. 

It is concluded that the mine evaluation suggests least NPV of 245.05 thousand dollars when price certainty is considered for both elements and greater NPV of 349.6 thousand dollars when price uncertainty is considered for both elements. The sensitivity analysis showed that even by changing input economic parameters, the NPV, which was computed in price uncertain for both elements, was the greatest.

Summary
One of the most important results of the linear rock cutting process is the accurate estimation of the cutting forces applied to the disc cutter which can be a prelude to the development of models for predicting the performance of all tunnel boring machines (TBM). In this study, numerical modeling of rock cutting process by a disc cutter using finite element code ABAQUS has been implemented. For model validation, the results of the linear cutting machine tests (LCM) by Previous researchers have been applied. After solving the proposed model, the forces on the disc were calculated in three directions of the rock cutting model and the mean of each force was calculated by a code that was developed in MATLAB software. Comparison of laboratory results and numerical modeling shows 11.1% error for the mean normal force, 5.6% error for the average rolling force, and 10% error for the average lateral force. By comparing the results of numerical modeling and linear cutting experiments, we can conclude that there is a good agreement between them.
 
In this study, a numerical model of linear rock cutting process based on finite element method (commercial code  ABAQUS) was used. To validate the proposed model, Rostami's (1997) linear rock cutting test on the Indiana limestone sample was used. Due to the unavailability of this rock sample, data from other texts were used to obtain input parameters to the model. A model assembly with a single disc cutter similar to laboratory test was simulated. By solving the proposed model, the forces applied to the cutter were calculated.
 
Methodology and Approaches
In order to model linear rock cutting procedures, Commercial finite element code ABAQUS/CAE was employed and for validating that, laboratory linear rock cutting test by Rostami (1997) was considered. Rock and disc cutter models was built in ABAQUS GUI module and to simulate rock behavior of rock model, a linear strength criterion was implemented in the model. Boundary Condition for disc cutter was similar to TBM’s working status with linear velocity of 2 meter per seconds and angular velocity of 9.3 radians per seconds.
 
Results and Modeling shear forces showed a similar trend to the experimental results. On the other hand, the comparison of the cutting forces of the experimental test with the numerical model results showed 11.1, 5.6 and 10% differences for the normal, rolling and lateral forces, respectively. This discrepancy seems to be due to the complexity and nonlinearity of the rock-cutting problem and the impossibility of considering all the parameters governing to rock-cutting process with a natural disc cutter. However, further analysis is being done by modeling on other rock samples to confirm the results.

In this study, satellite images, and aeromagnetic data were analyzed to investigate the geothermal potential in the Ardebil-Sabalan area in Ardebil province. Thermal activity monitoring in and around active volcanic areas using remote sensing is an essential part of volcanology nowadays.In this study, a geothermal survey is conducted in sabalan area of Ardebil province in NW IRAN using TIR data from Landsat-7 Enhanced Thematic Mapper Plus (ETM+) and ASTER (AST L1B) sensor. Magmatism contributes abundant thermal source to study area and the faults provide thermal channels for heat transfer from interior earth to land surface and facilitate the present of geothermal anomalies. The magnetic investigations showed that a deep magnetic anomaly exists in the southern part of the area. These magnetic anomalies were correlated with thermal anomalies. 

Development of advanced tools in remote sensing and geophysical exploration geothermal during recent decades indicates the necessity and importance of these tools in industry. They defined thermal anomalies as areas with temperatures higher than the spatial background. Thermal infrared (TIR) remote sensing is one of the essential methods to prospect the geothermal resources. Remote sensing is an important technique for activity monitoring in and around active volcanic areas in this study, a geothermal survey is conducted in the Sabalan area of Ardebil province in NW IRAN using TIR data from Landsat-7 Enhanced Thematic Mapper Plus (ETM+) and ASTER sensor and Geophysical Aeromagnetic data analyzing. Thermal infrared remote (TIR) sensing is an efficient technique to obtain the land surface temperature (LST). With ever increasing attempts on looking for alternative energy sources, TIR remote sensing has become a popular technique in the exploration of geothermal resources. The first application of TIR remote sensing in geothermal exploration can be dated back to the middle of 20th century. The aim of this study is to analyze remote sensing and Aeromagnetic data for evaluating the geothermal potential zones in an area located in the eastern of Ardebil Province. 

The data studied in this research includes ASTER – ASTL1 B (day and night) reflectance and LST products, for the year 2009, Landsat ETM+ day-time image on 2015, aeromagnetic data collected by Houston Texas Co., America, in 1974-1977. A comparison of the day-time and night-time images can reveal the surface thermal differences for detecting geothermal anomalies. In order to identify geothermal zones, image processing land surface temperature (LST) methods using ENVI software were applied on the using TIR data from Landsat-7 Enhanced Thematic Mapper Plus (ETM+) and ASTER sensor and Geophysical Aeromagnetic data analyzing from the study area. 

The results of this work also suggest that TIR remote sensing is an important technique for geothermal exploration with its high efficiency, simplicity and accuracy in temperature retrieval. Three thermal anomalies were detected on the maps and charts obtained for the average temperature difference and apparent thermal inertia. One anomaly is located in the Sabalan area and the other one is situated in the Northern part of the Ardebil side. the results of magnetic interpretations confirmed thermal anomalies showing a deep magnetic anomaly in the southern region and another magnetic anomaly in the hot spring.

Reverse time migration (RTM) as a new seismic imaging method solves the two-way wave equation and has been implemented through three main steps including forward and backward wave-field extrapolation from the source and receiver and employing a proper imaging condition. RTM models all types of wave without any dip limitation. This is very important regarding the drawbacks of ray-based and one-way wave equation imaging methods in properly imaging the complex geological media. Despite the above superiorities, low frequency artifacts especially in large reflection angles (60 to 90 degree) are the main drawback of RTM which cover and reduce the migrated image quality. Therefore, the aim of this paper is to improve the imaging condition as the heart of RTM to suppress the low frequency artifacts and use the useful information of the large reflection angle domain (60 to 90 degree) and produce a high quality image. This was achieved by presenting a new imaging condition including a weighted function based on the reflection angles. Finally, the RTM results using the new proposed imaging condition was presented and compared with the results of some conventional and modern similar methods. 

Seismic imaging is based on numerical solutions to wave equations, which can be classified into ray-based (integral) solutions and wave field-based (differential) solutions. In complex geological structures such as subsalt media, the velocity variation leading to complex multi-pathing reflections. Hence ray-tracing may fail to image the subsurface properly and cannot image steeply dipping reflectors corresponding to the velocity model. On the other hand, one-way wave propagation extrapolates wave-fields vertically and cannot accurately model waves that propagate nearly horizontally. they fail to handle waves propagating at wider angles, especially those near or beyond 90°. RTM directly solves the full (two-way) acoustic wave equation and incorporates all type of waves propagating in different directions. Hence, it has proved to be the preferred imaging algorithm in many geologically complex basins. RTM can image the complex geological media properly which is beyond the limits of one-way wave equation-based migration algorithms. Nevertheless, RTM has its limitations. The major drawback is the low frequency artifacts produced by the image condition (zero cross-correlation at lag) or by strong velocity contrast which is the main topic of this paper to be developed to suppress the RTM artifacts. 

To suppress the RTM artifacts, the imaging condition as the heart of RTM was developed. A new presented imaging condition includes the separated down-going and up-going wave-fields and a new weighted function based on the reflection angles. It  is implemented to suppress the low frequency artifacts for large reflection angles and maintain the useful information for the same reflection angle domain through an advance procedure.
 

RTM results using the presented imaging condition indicates that the low frequency artifacts was suppressed properly and the subsurface geological structures was imaged as well as possible in final migrated image I comparison the other seismic imaging methods.

Hydraulic fracturing is one of the most important methods for the propagation of oil and gas reservoirs, which is used to increase the inflow to well bore in low permeability formations. Various parameters such as in-situ stress field, joints and natural fractures of the formation, the fluid rheology, the mechanical properties of the formation, injection fluid flow and perforation affect the hydraulic fracturing pressure. In this research, a triaxial machine was designed and built for experimental investigation of the hydraulic fracturing in conditions close to the field conditions, so that all three of the main stresses in field conditions are applied in laboratory tests. Then, the influence of different perforation parameters such as perforation geometry (including length, diameter and shape), phase of perforation (in both vertical and horizontal wells) and minimum horizontal stress in the presence of perforation, using 38 artificial specimens (plaster + sand) with dimensions of 10×10×10 cm, was considered on the geometry and breakdown pressure, pressure-time diagram, and the development of micro-cracks. The results showed that increasing the perforation diameter, changing the perforation angle to the maximum horizontal stress and increasing the minimum horizontal stress in the case of reverse fault, rises the breakdown pressure. 

Hydraulic fracturing is a stimulation technique used in oil and gas wells to increase the inflow to well bore in low permeability formations. Various parameters such as in-situ stress field, joints and natural fractures of the formation, the fluid rheology, the mechanical properties of the formation, injection fluid flow and perforation affect the hydraulic fracturing pressure. Currently, more than half of the USA oil and gas wells are not able to produce without the use of hydraulic fracturing technology. Many researchers have studied hydraulic fracturing behavior of rocks since decades ago. The researches have showed that hydraulic fracturing operations increase the production of oil wells by up to 30 percent and increase gas wells by 90 percent. 

In this research, a triaxial machine was designed and built for the experimental study of hydraulic fracturing and to apply in-situ stresses with different values. This machine has the ability to apply anisotropic stresses in laboratory scale. Abaqus software was utilized to design the machine in terms of stability against the applied stresses. Then, using physical modeling, 38 samples with dimensions of 10×10×10 cm including plaster and sand were constructed and the influence of different perforation parameters such as perforation geometry (including length, diameter and shape), phase of perforation (in both vertical and horizontal wells) and minimum horizontal stress in the presence of perforation on hydraulic fracturing operations were investigated. Finally, the breakdown pressure, hydraulic fracturing geometry, pressure-time diagram and the development of micro-cracks were studied. 

The results of this study showed that increasing the perforation diameter, changing the perforation angle to the maximum horizontal stress and increasing the minimum horizontal stress in the case of reverse fault, rises the breakdown pressure. Also, the increase of the perforation length and its geometry have not significant effect on the breakdown pressure. Additionally, the change in the perforation angle and the minimum horizontal stress relative to the change in the perforation geometry, including length, diameter, and shape, have more effect on the breakdown pressure and changing the perforation angle relative to changing the in-situ stress in the horizontal well bore is more effective on the breakdown pressure.

In this paper, by focusing on the deposit which is located in the in eastern of Isfahan as a case study, in the first step, by using fuzzy Nicolas method the appropriate extraction method is selected. The results showed that according to the characteristics of ore deposit, the block caving method is the most suitable method. Then, based on the effective cross-section analysis, the desired range of block caving mine was selected. In the following, the undercut plan, major apex and the draw-bell were designed. Determination of induced stresses and displacement and stability analysis of a suitable support system design is vital, since in the block caving method the major apexes and haulage roads must be stable for a long time. In this paper, the finite difference method is used to determine the induced stresses on the major apex and haulage road when undercutting and draw-bell extraction. The results of the numerical analysis showed that the combination of IP steel and shotcrete support system should be used for the stability of the apexes and the haulage loads. Finally, the IP 120 steel frame and 20 cm thick shotcrete is selected as the proper support system. 

Block caving is a method that is completely based on the principles of caving. This method is based on the assumption that ore fractures and breaks by itself, due to the presence of internal stresses and forces caused by the weight of the ore body and also the downward movement of the broken rocks. The deposit is divided into large blocks, usually square in shape. Each block is undercut completely by a horizontal slot. Gravity forces due to the presence of millions of tons of ore and waste, being in the block and above and around the block, act on the rock masses, and successive fracturing occurs in this way, affecting the entire block in a gradual manner. In the block caving method, the major apexes and haulage roads remain stable for a long time. Therefore, determination of induced stresses and study of their stability and displacement for suitable support system design is vital. 

In this paper, firstly, the appropriate extraction method is selected by using fuzzy Nicolas method. Then, based on the effective cross section analysis, the desired range of block caving mine is selected. Finally, by using numerical molding method the appropriate support system is selected for major apexes and haulage road. 

The results of numerical analysis showed that the combination of steel IP and shotcrete should be used for the stability of the apexes and the haulage loads. Finally, the IP 120 steel frame and 20 cm thick shotcrete is selected as the proper support system.