نشریه روش های تحلیلی و عددی مهندسی معدن
پیاپی 16 (پاییز و زمستان 1397)

Summary
Prediction of deformation modulus for rock mass in analysis and design of rock structures is very important. Because deformation modulus represents behavior of rock mass subjected to stresses. Up to now, various empirical models for prediction of deformation modulus were developed. In this research, efficiency of different models for prediction of deformation modulus is evaluated. Latter, according to the fuzzy model a sufficient model is developed and results are compared with the empirical models. Results indicate the efficiency of new proposed model in comparison with the available models. Determining geo-mechanical parameters for analysis and design of rock structure is inevitable. Deformation modulus of rock mass is one of the most important geo-mechanical parameters. Estimation of deformation modulus for rock mass utilizing empirical models is widely used in civil and mining engineering projects. This is because of by spending less time and cost an acceptable estimation is achieved. But there are differences between results of empirical model and real values of modulus which leads to uncertain decisions for designers in choosing appropriate model. Thus, it is important to investigate and evaluate the experimental models. Fussy model is one of the best models that is proposed for determining the deformation modulus in the present study. Methodology and Approaches For efficiency evaluation of 19 available models and also the proposed model, 33 data sets of different dam’s constructions in Iran is collected. Root Mean Squared Error , Mean Absolute Percentage Error and index of higher squared correlation coefficient are applied for evaluation of models’ performance. According to the performance indices two models are selected between different empirical that indicates the best prediction. Also results show the efficiency of proposed fuzzy model for prediction of deformation modulus.

In this paper, DFN-DEM simulation using PFC3D software to evaluate the effect of joint intensity variation on tunnel support systems performance has been performed. Three dimensional distinct element software of PFC3D is considered for numerical modeling in this paper. This software has many advantages such as ability to create three-dimensional distinct joints with limited size and with different statistical characteristics, flexibility in different conditions and ability to monitoring a momentaril caving and falling during tunnel stability analysis. In this paper, at the first stage, by using of discrete fracture network (DFN) modeling and based on the surveyed data from access tunnel to the gallery of Rudbar Lorestan dam, fractures in this region have been simulated in the software and then is linked to the intact rock model. Finally, the performance of tunnel support systems of shotcrete and steel frame relative to change of the rock mass fracture intensity is investigated. The obtained results indicate more resistance of steel frame against fracture intensity variation compare with the shotcrete support system. Serious damage to shotcrete support system occurs by doubling the number of joints, while about the steel frame, serious damage occurs with four times the number of joints. Therefore, by increasing joint intensity which is caused by various factors such as explosions, earthquakes and etc, the steel frame support system has higher reliability.

In parts of constructing east-west t lot of line 7 Tehran subway, the excavating machine (EPB-TBM) passes from the top of the Abouzar’s wastewater conveyance tunnel with clear distance of 2.25 m. The FLAC 3D has been used to model this problem and find the deformations and forces of ground and linings. The modeling results show that after excavating subway tunnel, lining of Abouzar tunnel will be moving upward due to the increasing plastic zones and stress relaxation. This rate of displacement induced the internal force more than allowable designed amount in concrete lining of Abouzar tunnel. Generally, excavation a tunnel near another tunnel may lead to significant interaction effects, which mainly dependent on tunnels position relative to each other (parallel or cross), the distance between two tunnels, tunnel dimensions, lining rigidity, stress and boring environment condition as well as the method of tunnel boring. The interaction between adjacent tunnels have been investigated by different researchers using methods such as analytical and empirical, field observation, physical modeling and numerical modeling. In the current project, the tunnel of Tehran metro line 7 passes with a distance of 2.25 meters from the top of the Abuzar tunnel. Because of the nature of three-dimensional problem of interaction between underground spaces, numerical modeling is an appropriate tool for the analysis of these complicated problems. Therefore, FLAC3D software have been used in order to investigate into the interaction analysis. The purpose of modeling is study on stability of support system of Abuzar tunnel during tunnel excavation of Tehran metro line 7. Methodology and Approaches: In this paper, the finite difference method (FDM) is used for modeling and solving the problem. FLAC 3D program which uses FDM was selected in order to study the interaction between the two tunnels, in construction stage. For this purpose, at first Abouzar tunnel modeled and excavated, then impact of stepwise excavating of line 7 Tehran subway on lining system of Abouzar tunnel is investigated numerically. History of Internal forces, bending moments and structural displacement of Abouzar’s tunnel lining have been provided and studied. Engineering recommendations have been proposed in different-leveled intersecting tunnels. Results and Conclusions: The results of modeling show that after excavation of metro tunnel, the support system of Abuzar tunnel will be uplifted because of increasing the plastic zone and stress relaxation. This displacement causes internal forces in Abuzar tunnel lining which are more than allowed values.

Summary: Based on statistics, flyrock is the main reason of 20 to 40% of blasting induced accidents in mines. Therefore, the accurate prediction of flyrock has a remarkable role on reducing its detrimental effects. In this paper, a model tree was developed for flyrock prediction using M5P technique. This model was trained and tested by the blasting database of Sungun copper mine. The results showed that the proposed model can estimate the flyrock with an acceptable error. Flyrock is one of the most challenging safety issues of blasting operation in open pit mines, which always threatens the safety of personnel and equipment. Thus, the accurate prediction of flyrock seems necessary for determination of safe blasting zone. During past years, many empirical models have been developed using artificial intelligence techniques for flyrock prediction. Most of these models do not indicate the relationship between input and output parameters, so they are opaque and vague. The main purpose of this paper is to construct a transparent and understandable model for flyrock prediction. Methodology and Approache: In this paper, a model is developed for flyrock prediction using M5P technique. This technique presents a tree structure which contains linear equations in its leaves and using these equations the flyrock can be predicted easily. In this model, the flyrock distance is estimated using the most important controllable blasting parameters (i.e. burden, spacing, stemming, blasthole length, blasthole diameter, powder factor and mean charge per blasthole). Results and Conclusions: The accuracy and efficiency of proposed model was evaluated using various statistical indices such as coefficient and determination (R2), variance account for (VAF) and root mean square error (RMSE). These indices were obtained 92.1%, 92%, and 3.9, respectively. Therefore, it can be concluded that M5P technique is a suitable and efficient means that provides an acceptable prediction for flyrock. Furthermore, the results indicated that the burden and blasthole diameter are the most and the least effective parameters on flyrock prediction, respectively. The output of this model can be considered as a preliminary estimation of flyrock, based on which the risk of hazards and potential accidents can be reduced to a desirable extent.

Summary: In rock engineering, the effect of scale on the strength and deformation properties of the rock mass is one of the most important issues. Prediction of uniaxial compressive strength in different diameters using the specimen size-effect models is valuable. To specify the application scope of the specimen size-effect models in the rock and concrete specimens, few significant study have so far been carried out. This paper proposed a model of appropriate size-effect in sedimentary rocks and concrete specimens. Another object of this paper was discussion on the effect of specimen size and grain size on uniaxial compressive strength of rock and concrete specimens using statistical and experimental methods. The results of this study can be used for engineering designs in or on rocks and are more useful for determining of the elastic constants and compressive strength of rock. Dependence of compressive strength on the specimen size has a fundamental role in the designing of rock structures. In the rock mechanics, to determine the specimen size-effect on the mechanical behavior of intact rock, have been used many experimental and analytical methods. In the area of rock mechanics and solid mechanics, the most notable proposed analytical models to predict the specimen size-effect on the uniaxial compressive strength are including the Weibull statistical theory (1951), the Hoek and Brown empirical theory (1980), the specimen size-effect model using fracture energy theory (Bazant, 1983 and 1984), the multi-fractal scaling model (Carpinteri et al., 1995), the fractal fracture size-effect model (Bazant, 1997) and the unified size-effect model for intact rock (Masoumi et al., 2015). To specify the application scope of these models in the rock and concrete specimens, few significant study have so far been carried out. Methodology and Approaches: Statistical analysis of this study, were conducted in each size-effect model by means of a non-linear least-squares fitting algorithm and Levenberg-Marquardt method using SPSS software. In experimental study, three concrete blocks of approximately 500mm×500mm×500mm in size with three different grain sizes (0-12, 0-20 and 0-25) were manufactured. After the curing time, using a laboratory drilling machine, cylindrical specimens were obtained from blocks with diameters of 56, 68, 72 and 94 mm and with a length-to-diameter ratio of 2.0 (L/D=2.0) according to the recommendation of International Society of Rock Mechanics (ISRM, 2007). ACI-211 standard and ASTM C33 standard were utilized for mixture design of samples and required grain sizes respectively. Results and Conclusions: In the sedimentary rocks and concrete specimens, respectively, there was a good agreement between outputs of laboratory tests with the specimen size-effect model using fracture energy and the multifractal scaling model. In experimental study, results of uniaxial compressive strength tests for grain sizes 0-20 and 0-25 mm indicated as the specimen diameter increased, uniaxial compressive strength initially increased and then decreased. The results of this study confirmed grain size effect on the predictions of specimen size-effect models which by increasing the grain size, correlation coefficient values of different models reduce. These results can be used for engineering designs in rocks and concrete mixtures.

The variation of feed characteristics of the Choghart Iron Processing Plant has resulted in the reduction of AG mill efficiency. In this research, the possibility of converting the Choghart AG mill to SAG mill to stabilize the mill power draw and improve the grinding process was investigated. The JKSimMet software was used to simulate the circuit and predict the effect of charging steel balls to the AG mill. The results of grinding tests on the ore samples were used to simulate the circuit. The product size distribution predicted by the software was very close to the actual product size of the AG mill. The simulation of the circuit, using different tonnage of 100 mm steel balls showed that the mill throughput could increase by around 6 percent with a slight increase in the mill product size. The actual results of adding the steel ball to the plant were in agreement with the simulation results. Summary: simulation of Choghart AG mill circuit was performed and the effect of charging steel ball on the mill performance was evaluated. The possibility of grinding the Choghart oxidized and high ratio ore in this circuit, at a reasonable throughput, was investigated. Based on the simulation results a plant-scale experiment on a batch of oxidized ore was also performed. It was shown that charging 100 mm steel balls, at around 5% volume of the AG mill, facilitated the grinding of oxidized ore. The throughput of Choghart AG mill circuit was lower than the expected level for grinding the oxidized (or high Fe/FeO ratio) ores. Converting the AG mill to SAG mill to increase the grinding of this type of ore was an option which was investigated. The circuit was simulated by JKSimMet software and then adding of steel ball to the system was evaluated. The results were validated using the plant-scale studies. Methodology and Approaches: Sampled from the feed and product streams were collected, the relevant grinding tests were conducted and the selection and breakage functions of the ore were determined. The ore breakage test results and the specification of the feed material and AG mill and vibrating screen were used as input data to the JKSimMet software. Then charging different tonnage of the steel balls to the AG mill was evaluated. Plant-scale experiments were also conducted. Results and Conclusions: Based on the impact and abrasion tests of the feed samples this ore was considered as a medium hard type ore. The simulation result for the mill product size distribution was very close to the actual data of the plant. Therefore this software could be used to predict other changes in the circuit. The simulation results showed that by adding 5 and 10 percent (volume) of 100 mm steel balls to the Choghart AG mill its throughput could be increased by around 3 and 7 percent, respectively. The plant scale experiments with the same type of steel ball were in agreement with the simulation results. As it was expected the mill product size slightly increased.

One of the most important part in geochemical exploration studies is separating anomalies from background for different elements. There are many methods for this purpose. One of these methods is based on fractal geometry. In this paper concentration-number and concentration- area fractal models were used for separating anomaly from background for Cu, Mo, Fe2O3 and Sb in Siahrood 1:100,000 sheet, NW Iran. First 1238 stream sediment samples were taken and analyzed. Then with drawing the log- log elemental plot the threshold values obtained for anomaly separation. Log –log plots can be divided into three segments or phases that correlate with lithological formation, faults and alteration in the study area. By using the results of fractal modelling the anomaly maps were drawn and anomaly regions were identified. Elemental anomaly maps resulted from concentration-area and concentration- number fractal models were compared with the locations of mine indexes in the study area. Results showed that there was a good correlation between the locations of mine indexes and anomaly region for both fractal models. But the concentration-are fractal model could hit more mine indexes. This is more obvious for Cu. Results also showed that most of the Cu, Fe and Mo anomalies located in igneous rocks, altered igneous rocks and faults. Because of activity of hydrothermal solutions in intrusive rocks in the northern part of the study area and volcanic rocks in central parts, intrusive and volcanic rocks altered and quartzite veins and mineralization zones occurs. Delineation of anomalies from background is an essential task in geochemical exploration. Geochemical data are usually characterized by their spatial positions, meaning that elemental concentration varies spatially. The concentration–area model (C–A model) has been developed and applied by many geoscientists. Another useful model for separating anomaly from background is the number–size model (N–S model), which has been widely used by many geoscientists. Methodology and Approaches: Concentration-number and concentration- area fractal models were used for separating anomaly from background. Then with drawing the log- log elemental plot the threshold values obtained for anomaly separation. By using the results of fractal modelling the anomaly maps were drawn and anomaly regions were identified. Elemental anomaly maps resulted from concentration-area and concentration- number fractal models were compared with the locations of mine indexes in the study area. Results and Conclusions: Results showed that there was a good correlation between the locations of mine indexes and anomaly region for both fractal models. In other words most of anomalies derived from C-A and N-S models hits mine indexes in the region. But the concentration-are fractal model hit more mine indexes. This is more obvious for Cu. Results also showed that most of the Cu, Fe and Mo anomalies located in igneous rocks, altered igneous rocks and faults.

Rock mass deformation modulus (Erm) has been considered as the most typical parameter illustrating the pre-failure mechanical behavior of rock mass. Erm is a basic input parameter for most rock engineering projects including tunneling, support designing, foundation designing, etc. For these purposes, it is necessary to obtain this parameter before starting numerical modeling. Intact rock elastic modulus is measured by uniaxial compression strength test in laboratories. But, the existence of discontinuities, makes a great difference between the mechanical properties of rock mass and intact rock. Erm can be estimited by emprical equations or determined by in-situ tests such as plate loading, dilatometer, flat jacking, and radial jacking tests. The plate loading test is a common test to determaining rock mass deformation modulus of rock mass that has been used in several project around the world. Erm of rock masses in Bakhtiari dam site is determined by Plate loading tests using different loading plate sizes and different stress values. Bakhtiari dam site is located in southwest part of Iran, almost 70 km northeast of Andimeshk city (Khuzestan province), and 65 km southwest of Dorud city (Lorestan province). In recent paper, it has been compared the obtained Erm from plate loading tests with different stress values and different plate sizes Plate loading tests at Bakhtiari Dam site are carried out using rigid loading plates with diameters of 650 and 915 mm and under maximum stresses equal to 20 and 40 MPa. In this test, two opposite areas in test galleries are loaded using rigid loading plates by means of hydraulic pump system. During tests, the rock displacements are measured using borehole extensometers that fixed in several positions inside the boreholes drilled in the center of each loading area. The deeper extensometer in each borehole (used as a fixed point) is positioned at the end of borehole at depths more than 6 m. Erm is calculated according to ASTM D 4394 – 08.
In case of two maximum stress values of 20 and 40 MPa, no significant difference is evaluated. Conversely, using two different diameter plates in same position result in significant differences between results. For high quality rock masses, the larger the plate diameter is, the greater the evaluated Erm is. This difference is recognized related to the ratio of gallery dimension proportional to loading plate size.