Study and Analysis of the Failure Mechanism of Tuff Rock based on Laboratory Tests and Three-Dimensional Numerical Modeling
Hossein
Niknafs
Dept. of Mining, Shahid Bahonar University of Kerman, Iran
author
Hossein
Jalalifar
Dept. of Petroleum, Shahid Bahonar University of Kerman, Iran
author
text
article
2017
per
Summary
Failure mechanism is different due to stress conditions and rock types, and it is very important to stability of structures. One of the investigations of failure mechanism’s techniques is using triaxial compression test. The aim of the research is determination of failure plane and failure mechanism of Rhyolite Tuff experimentally in different confining pressures and then investigating failure mechanism numerically using three-dimensional finite difference method in details. From the experimental results it was found that with increasing confining pressure, failure angle changes from vertical to oblique. Then numerical model was calibrated with laboratory data and analyzed the details of failure process, which could not be investigated experimentally. Investigations showed that failure process, started with plastic strains at the center of the sample and continued to achieve shear failure plane. Moreover, the results showed that the numerical model is in good agreement with the laboratory tests.
Introduction
Given the increasing production of minerals, the need to expand and deepen mines is inevitable. With deeper mining, sustainability issues have become more important. All of underground structures have been constructed in rock and the recognition of the rock mechanics issues in relation to the stability of these structures is very important. One of the main topics of rock mechanics, which plays a significant role in the stability of structures, is the rock failure mechanism. Since these structures are located deep in the ground and the behavior of rock failure in different conditions of stress is different, recognizing the rock deformation process under stress conditions can provide a better picture of rock behavior in real conditions .When the distribution and turbulence of the stress creates an imbalance in the rock mass, rock failure occurs by the distribution and interconnection of the micro cracks. Still, there are ambiguities about how rocks are really broken and how the cracks begin to spread. Therefore, prediction of models for fracturing of rocks is very complicated, and it is impossible to predict the failure of rocks with simple models. Therefore, fundamental studies are needed to evaluate the failure process and damage of rocks in different stages of stress.
Methodology and Approaches
By using uniaxial and triaxial tests, a stress-strain graph was drawn for a rhyolite rock sample. Analyzing the experimental results, it was observed that, with increasing lateral stress, rock resistance increased, and the direction of the fracture plane was maximally illuminated and more angular than the direction of the main stress. It was also found that the behavior of rock with the Mohr Columb's failure criterion is good. For numerical modeling of laboratory experiments, cohesion parameters, internal friction angle, shear modulus, volume modulus and specific gravity were used. To calibrate the model, the meshes and the rate of application applied to the top of the specimen were changed to see the fracture and ultimate strength similar to the laboratory sample in the numerical model. After calibrating the model, the details of the failure stages were carefully examined.
Results and Conclusions
In numerical models with increasing lateral stress, the angle of deflection compared to the original stress was increased. Tensile plastic strains were formed at the beginning of the loading at the center of the sample. As the loading steps progressed, shear plastic strains started from the corners of the sample and proceeded to the center of the sample. This condition continued until the complete failure of the model and the creation of the plane shear failure. Also, with increasing lateral stress, the initiation of plastic strain occurred in higher stresses and later formed in the sample. Plastic tensile strains appeared at the center of the sample at the beginning of the loading. In the following, the strain began from the two corners of the sample and extended towards the center of the sample. It then extended its path until a plane was formed. Shear and tensile strains were formed in the form of shear-n and (tensile-n) in the sample. These strains may create a shear failure sheet. In fact, joining these strains continuously created a failure plane in the model. The final shear plane was the result of shear-n joining of the shear strains.
Journal of Analytical and Numerical Methods in Mining Engineering
Yazd University
2251-6565
7
v.
13
no.
2017
1
13
http://anm.yazd.ac.ir/article_972_65a1c973cecea49d8f8eff09cc129ff0.pdf
The Probabilistic Analysis of Block Economic Value (BEV) in Open-Pit Mines Considering the Effect of Uncertainties in Metal Price and Operational Costs
Masoud
Zare Naghadehi
Dept. of Mining, Hamedan University of Technology (HUT), Iran
author
Hesam
Dehghani
Dept. of Mining, Hamedan University of Technology (HUT), Iran
author
Roya
Naderipour
Dept. of Mining, Hamedan University of Technology (HUT), Iran
author
text
article
2017
per
Summary
In this research, the Block Economic Value (BEV) and project NPV in an open-pit mine has been analyzed probabilistically by using the Monte Carlo Simulation (MCS) method to deal with the uncertainties in the nature of the most important economic parameters including metal price and operational costs. The results showed that the outcomes are closer to the reality by this method compared to the results of the classic methods.
Introduction
The basic input in the process of open-pit limit optimization is a set of block values representing the net economic worth of each block. Based on the estimated block economic values (BEV’s), the optimizer selects the optimum destination of each block in order to maximize the overall pit value under some given technical constraints. A dollar value is usually assigned to each block by estimating the revenue of recoverable metal at a given fixed metal price and subtracting applicable mining, processing and other costs. The variation trend of metals price and mining costs over the years shows that deterministic assumptions for values of such parameters will result in errors in the process of BEV calculation. The effective parameters such as metal price, operating costs, grade etc. are always assumed deterministic in the conventional methods of BEV calculation. While, these parameters have, obviously, uncertain nature.
Methodology and Approaches
In this paper, the BEV and project NPV were initially determined using Whittle’s formula based on deterministic economic parameters. Then the Monte Carlo Simulation (MCS) method was employed and the economic uncertainties such as the metal price and cost uncertainties were taken into account. The economic data of Grassberg Copper Mine were utilized to achieve this goal.
Results and Conclusions
The results showed that the Monte Carlo simulation method is highly capable of estimation of economic uncertainties. The estimated block economic values using this method are closer to the actual values compared to other methods and the error percentage is lower. As well, it was observed that the net present values obtained by the Monte Carlo simulation are closer to the reality compared to the other calculations.
Journal of Analytical and Numerical Methods in Mining Engineering
Yazd University
2251-6565
7
v.
13
no.
2017
15
26
http://anm.yazd.ac.ir/article_973_305ee828b527d88b7fed916f0147b931.pdf
The Joint Shape Determination in Rock Mass by the Statistical Simulation
Mehdi
Zamani Lenjani
Yasouj University, Engineering and Technical Faculty, Civil Engineering Department
author
text
article
2017
per
Summary
Geometry of joints or joint shapes is one of the geological characteristics, which is important for determining the strength and stability of rock mass. Here joint shapes mean the geometric forms of joints when looking from the direction normal to the joint planes. There is not enough literature and references about the shape of the joints. Some of them consider approximately the joint shapes as square, rectangular, circular or even elliptical forms. We usually observe the traces of joints as segments in rock outcrops but it is difficult to see their shapes in the outcrops of underground openings. In this research the parallel joints which form a joint set, are created by the statistical simulation for different joint shapes. Then by comparing the simulated joint distribution with the real joint set distribution from outcrop measurements, it is possible to predict the shape of joints in rock masses. The simulation results showed that the joint set distributions will not follow the classic statistical distributions such as logarithmic, power, exponential or Poisson. They are complex in nature and have a skewness to the left.
Introduction
One of the important parameters of discontinuities in rock mass is the shape and geometry of joints. The effects of joint shape and its geometry in rock mass resistance properties are defined by many rock mechanics and engineering geologist specialists. They assumed the shape of joints as square, rectangle, circular and elliptical features.
Methodology and Approaches
For determination the shape of joints in rock masses in this research the statistical engineering is applied. The joints and discontinuities are considered two-dimensional planes. Then by intersection of a random plane normal to the joint set planes the simulation of joints in outcrop were obtained. At the end by the distribution of the joints obtained from the simulation, one can determine the shape of the joints.
Results and Conclusions
The results showed that the joints with circular, uniform shapes and with the relative movements have the exponential distribution of trace length. But for nonuniform cases the distribution approaches the normal distribution. A uniform distribution was observed for the square or the diamond shape of the joints.
Journal of Analytical and Numerical Methods in Mining Engineering
Yazd University
2251-6565
7
v.
13
no.
2017
27
33
http://anm.yazd.ac.ir/article_975_b9ae1a13eee2cbf78ddc233ef0083d52.pdf
Numerical Modeling of Hydro-Mechanical Behavior of Rock Joints under Direct Shear Loading
Behnam
Ghobadi
Dept. of Mining and Metallurgy, Tarbiat Modares University, Iran
author
Hamidreza
Nejati
Dept. of Mining and Metallurgy, Tarbiat Modares University, Iran
author
Kamran
Goshtasbi
Dept. of Mining and Metallurgy, Tarbiat Modares University, Iran
author
text
article
2017
per
Summary
This papers focuses on the permeability of rock joint under direct shear tests and a comprehensive study was made to numerically evaluate the hydro-mechanical behavior of rock joints.
Introduction
Rock mass permeability is a key parameter in rock engineering projects such as repositories for radioactive waste, dam foundations, excavation of tunnels and caverns, geothermal energy plants, oil and gas production, etc. Due to the stiffer rock matrix, most parts of rock mass permeability are related to the joints and discontinuities. Further, shear and normal stress, shear and normal deformation, joint roughness and etc. affect rock joint permeability. Therefore interaction between stress and permeability is a crucial factor during different stages of reservoir’s life such as: assessment, productivity and management.
Methodology and Approaches
In the present paper, it is intended to consider the permeability of rock discontinuity in direct shear test. For this purpose, a distinct element code is used to develop numerical modeling of the direct shear test. UDEC has the capability to perform the analysis of fluid flow through the fractures and voids of a system of impermeable blocks. Steady-state pore pressures can be assigned to zones within deformable blocks and boundary conditions may be applied in terms of fluid pressures or by defining an impervious boundary. The fluid-flow calculation can also be run either coupled or uncoupled with the mechanical stress calculation. A fully coupled mechanical-hydraulic analysis is performed in which fracture conductivity is dependent on deformation, and conversely, joint fluid pressures affect the mechanical computations. Two main experimental stress conditions under which the shear force of rock joints can be determined, are the Constant Normal Load condition, CNL, and the Constant Normal Stiffness condition, CNS. The numerical model was calibrated with experimental tests and it was tried to confirm the validity of the developed model. Finally, a sensitivity analysis was made to investigate the effect of mechanical rock joint parameters and properties of fluid on the flow rate of discontinuities.
Results and Conclusions
Variation of shear stress and rock joint transmissivity with shear displacement compared in the both numerical model and experimental test and it is shown that the results of numerical modeling have a good agreement with results of experimental models from literature. Numerical analyses revealed that with increasing the shear displacement, increases hydraulic aperture and flow rate of discontinuities. Also it is revealed that joint roughness coefficient has a direct relation with flow rate of discontinuity.
Journal of Analytical and Numerical Methods in Mining Engineering
Yazd University
2251-6565
7
v.
13
no.
2017
35
44
http://anm.yazd.ac.ir/article_976_da2cf0c18de3b5ea1daf03fe2b60bbd0.pdf
Estimation of Anomalous Values by Using an Appropriate Combination between Mahalanobis Distances and Three Widely Used Data Mining Methods; Case Study: Parkam
Seyyed Saeed
Ghannadpour
Dept. of Mining and Metallurgy, Amirkabir University of Technology, Iran
author
Ardeshir
Hezarkhani
Dept. of Mining and Metallurgy, Amirkabir University of Technology, Iran
author
Taraneh
Roodpeyma
Dept. of Mining and Metallurgy, Amirkabir University of Technology, Iran
author
text
article
2017
per
Summary
Importance of detecting anomalous values from background is undeniable; so many different methods have been developed. On the other hand, prediction is a powerful tool in the process of each task’s planning. Using data mining methods for finding patterns between data can answer this requirement. Due to the necessity of high processing accuracy, the performance of a separation method has been evaluated. This performance is combined with three data mining methods. Finally we introduced the best combination (Mahalanobis Distance and Decision Tree) with the most accurate predictions. In order to reduce error and risk to save costs, time, energy and access to the more valuable predictions, in following paper we have studied Mahalanobis Distances to separate anomalous values and combined the results with three methods: K–Nearest Neighbor (KNN), Naïve Bayes Classifier and Decision Tree (DT) then achieved to the best combination with the least error rate.
Introduction
Mahalanobis distances method was used to assess prospective areas of Parkam district based on the two variables (Cu and Mo grade) and anomalous values have been defined based on the grades of copper and molybdenum. Then the three mentioned algorithms were trained by 4 parameter data grades of copper and molybdenum, coordinates of each samples (X and Y) and the results of our separation method as well, finally predictive equations were achieved in order to inform about other random samples. The best combination could be useful to predict with high accuracy in each plan.
Methodology and Approaches
Mahalanobis distances method is an effective multivariate method on separation of anomalous values from background. Various data mining methods have been developed to classify data. Three most important and common methods are K–Nearest Neighbor, Naïve Bayes Classifier and Decision Tree; They can be used to find features that can distinguish different classes from each other.
Results and Conclusions
After separation of anomalous values by applying Mahalanobis distances, combined models have been produced. Then actual data have been seen as the test ones to evaluate the accuracy of predictions. At last, based on the resubstitution rate, that is 0.0053, for designed system via Decision Tree technique and anticipating only 2 out of 377 numbers of samples as the background samples instead of anomalous ones, this method was recognized as the more pragmatic approach than KNN and Naïve Bayes approaches producing 0.0239 and 0.061 error rate and predicting 9 and 23 numbers of anomalous values as the background samples respectively. According to the much more acceptable error rate for designed network by combination of Mahalanobis Distances and Decision Tree methods, we can introduce that as a much more reliable and useful method in order to achieve the most accurate predictions to the decision makers in the industry.
Journal of Analytical and Numerical Methods in Mining Engineering
Yazd University
2251-6565
7
v.
13
no.
2017
45
57
http://anm.yazd.ac.ir/article_974_3a4628eaf032d142d0cadab4f6b21cbe.pdf
Prediction of Rotational Torque to Operate Drilling Using Hybrid ANN with Biogeography-Based Optimization Algorithm
Hadi
Fattahi
Dept. of Mining, Arak University of Technology, Iran
author
Zohre
Bayatzade
Dept. of Mining, Arak University of Technology, Iran
author
text
article
2017
per
Summary
Horizontal directional drilling (HDD) is a popular method for installation of both steel and plastic underground pipelines. Besides selecting the appropriate type and size of reamers the rotational torque is another important parameters that must be predicted for performing the reaming operation. In this study, hybrid artificial neural networks (ANN) with biogeography-based optimization (ANN-BBO) model were applied for predicting rotational torque. In fact BBO was used to better regulate the weights and biases of the ANN model. In this study, axial force on the cutter/bit, rotational speed of the bit, the length of drill string in the borehole, the total angular change of the borehole, the radius for the ith reaming operation, the mud flow rate and the mud viscosity are applied as input variables to predict the rotational torque. To assess the ability of the model to predict the rotational torque, West–East Natural Gas Transmission project in China was used. Results indicate that this model has high potentials for estimating the rotational torque using a set of listed input parameters.
Introduction
A major concern of many HDD projects is prediction of required rotation torque. It has been established that the required rotational torque at the drill rig depends on various factors, including geological conditions, drilling method, reamer cutter/bit size and type, rotary speed, axial force on bit, drilling mud properties, borehole diameter, length of drill string in the borehole, and borehole trajectory. In this area in recent years, studies have been done using traditional statistical methods, but this study focuses on the application of artificial intelligence in this field.
Methodology and Approaches
In this study, ANN method and BBO algorithm is used. We used BBO to better regulate the weights and biases of the ANN model. BBO is an evolutionary algorithm that is inspired by biogeography. In BBO, a biogeography habitat indicates a candidate optimization problem solution, and it is comprised of a set of features, which are also called decision variables, or independent variables. BBO consists of two main steps: migration and mutation.
Results and Conclusions
In this paper, 75% of the data sets were assigned for training purposes while 25% was used for testing of the network performance. Network with 7-8-1 structure is optimized and the results indicate that this model has high potentials for estimating the rotational torque.
Journal of Analytical and Numerical Methods in Mining Engineering
Yazd University
2251-6565
7
v.
13
no.
2017
59
70
http://anm.yazd.ac.ir/article_845_b6c5f0b727e67f868efef2ee6b3387c4.pdf
Geochemical Data Analysis of Irankouh (Isfahan) Pb- Zn Mine, Using Exploratory Data Analysis (EDA) and Fractal Methods
Seyed Hossein
Mojtahedzadeh
Dept. of Mining and Metallurgy, Yazd University, Iran
author
Mahdi
Bemani
Dept. of Mining and Metallurgy, Yazd University
author
Saeede
Malekzade
Dept. of Mining and Metallurgy, Yazd University, Iran
author
text
article
2017
per
Summary
Anomaly and lead-zinc index recognition of an area between Tappeh-Sorkh and Gushfil, in Irankouh Pb- Zn mine, near Isfahan, was investigated. Interpretation for 12 elements, using 804 soil samples, was conducted. After early activities for censored data correction and transforming data for preparing normal distribution, anomalies recognition and separation were done using classical statistics, fractal and EDA (Exploratory Data Analysis) methods. Plotted anomalies maps prepared by three methods, show good conformity. Therefore, further studies in the regions showed overlapping resulted anomalies by three methods. Also detailed exploration by using geophysical IP methods was proposed.
Introduction
Irankouh mine is located in Irankouh Mountains, 25 km southwest of the Isfahan city. Four mining area, including Tappeh-Sorkh, Gushfil, Khane – Gorgi are distinguished and their ore reserve has been determined separately. The aim of this research was anomaly and lead-zinc index recognition in the area between Tappeh-Sorkh and Gushfil. In this research 804 soil samples were taken and analyzed for 35 elements, but for interpretation only 12 elements were used. Anomalies recognition and separation were conducted using classical statistics, fractal and EDA (Exploratory Data Analysis) methods.
Methodology and Approaches
In the first step censored values were corrected, then the normality test on corrected datasets accomplished and showed that Ca, Mg and S have normal distribution. Other elements, which did not show normal distribution, were normalized by Log – normal and 3-parameters log distribution methods. Based on the parameters obtained from classical statistics and standard formula the anomaly and the background values were separated, using area- concentration model of fractal method. Also separation of anomaly from background in EDA method, was done with boxplot. Then the anomaly maps of elements for 3 methods were plotted.
Results and Conclusions
Comparison of the maps prepared by three methods, showed a good conformity. Since fractal is a structural method, it is more reliable. Further studies in the regions showed overlapping resulted anomalies by three methods. Pb, Zn and Cd were expanded in North-west, center and South-east. For more confirmation, detailed exploration by using geophysical IP methods is suggested in this area.
Journal of Analytical and Numerical Methods in Mining Engineering
Yazd University
2251-6565
7
v.
13
no.
2017
71
90
http://anm.yazd.ac.ir/article_977_e5d7c160823c7714a083f8d89ba4cd33.pdf
Evaluating Fatigue of Intact Crystalline Rocks under Completely Reversed Loading
Saeed
Jamali Zavareh
Department of Mining Engineering, Isfahan University of Technology, Iran
author
Hamid
Hashemolhosseini
Department of Civil Engineering, Isfahan University of Technology, Iran
author
Alireza
Baghbanan
Department of Mining Engineering, Isfahan University of Technology, Iran
author
Mohsen
Khoshkam
Department of Mining Engineering, Isfahan University of Technology, Iran
author
Hadi
Haghgouei
Department of Mining Engineering, Isfahan University of Technology, Iran
author
text
article
2017
per
Summary
The fatigue behavior under completely reversed loading for two crystalline quarry stones in Iran; Natanz gabbro and Green onyx, which have different mineral compositions and formation conditions, were evaluated using a new developed apparatus. The obtained S-N curves followed common “Wöhler relationship” in the variation of applied amplitude stress versus loading cycle number. In addition, the endurance limit is perceived for both tested rocks as well as observed in ferrous metals. The endurance limit for Natanz gabbro and Green onyx were evaluated 14.7MPa (0.53 of its tensile strength) and 10.8Mpa (0.6 of its tensile strength), respectively.
Introduction
During fatigue phenomenon cyclic loading causes a material to fail prematurely and suddenly like a brittle failure at a stress level less than determined strength under monotonic condition. Rock formations and structures such as faults, joints, bedding planes, underground reservoirs, tunnels walls, bridge abutments, roads and dams’ foundations, etc. can be subjected to dynamic loadings resulting from vibrations of the earth’s crust, through major earthquakes, rock bursts, rock blasting and drilling and also, traffic. Reaction of rocks to cyclic and repetitive stresses resulting from dynamic loads has been generally neglected with the exception of a few rather limited studies. In this research work, the fatigue behavior of two crystalline quarry stones in Iran; Natanz gabbro and Green onyx which have different mineral compositions and formation conditions were studied under completely reversed loading.
Methodology and Approaches
The stress-life method was applied and fatigue behavior and the existence of the endurance limit for two crystalline quarry stones in Iran; Natanz gabbro and Green onyx which have different mineral compositions and formation conditions were evaluated using a new developed apparatus. The developed fatigue testing machine was inspired by rotating beam fatigue testing machine (R. R. Moore) which is commonly used for laboratory fatigue test in metals.
Results and Conclusions
The obtained results (S-N diagram) followed common “Wöhler relationship” in the variation of applied amplitude stress versus loading cycle number. In addition, results showed that both rocks have endurance limit. The results also illustrated that the endurance limits for both tested rocks are ranged between 0.4 and 0.6 of their tensile strengths. The endurance limit for Natanz gabbro and Green onyx were evaluated 14.7MPa (0.53 of its tensile strength) and 10.8Mpa (0.6 of its tensile strength), respectively. The agreement between the obtained results and presented results in fatigue of other materials showed that the offered method can be applied for studying the fatigue of rocks.
Journal of Analytical and Numerical Methods in Mining Engineering
Yazd University
2251-6565
7
v.
13
no.
2017
91
100
http://anm.yazd.ac.ir/article_855_be1eaf5379a6d23e5ad13010853784d7.pdf
Multivariate statistical analysis of geochemical data in Kervian region
Sima
Garousinejad
Department of Mining Engineering, Isfahan University of Technology, Iran
author
Ahmad Reza
Mokhtari
Department of Mining Engineering, Isfahan University of Technology, Iran
author
Farimah
Ayati
Department of Geology, Payame Noor University, Iran
author
text
article
2017
per
Summary
In the present study the sample catchment basin approach has been used in addition to multivariate statistical analysis over geochemical dataset collected in Kervian area in Iran. Sample catchment basin has reasonably detected the favorable zones in the present study and the proven Au mineralization has validated the results.
Introduction
Stream sediment data application method has been widely used and accepted in exploration of different deposit types in mineral exploration industry and has shown its efficiency in this context. The sample catchment basin approach is a technique for processing of stream sediment data that is employed for removal of lithological impact from existing variation in chemical content of the samples.
Methodology and Approaches
The target area covers 617 km2 in which 299 stream sediment samples were collected for chemical analysis. In addition, digitized 1:100000 geological and 1:50000 topographical maps were used for creation of sample catchment basins considering the sampling point positions. In order to remove the impact of background contribution to geochemistry of stream sediment by this technique the following procedure has been taken into account: 1- estimation of uni-element background concentration of element of interest for every lithology and then estimation of uni-element background value for every sample catchment basin 2- removal of the background concentration from measured concentration of element for each sample 3- dilution correction of residual values by taking the catchment area size into account 4- analysis of dilution correction values and delineating the anomalous basins.
Results and Conclusions
The sample catchment basin method was employed and data processing was completed as mentioned above which resulted in delineation of anomalous Au values extended south-westerly. The results are compatible with known gold occurrences located in this part of the map. There are weak to moderate anomalous basins positioned south east and east of the known mineralization covered with the same sedimentary units as mineralization area that could be assumed promising. However, sample catchment basin has successfully highlighted the anomalous basins which were not detected through analysis of raw dataset. Employing this method has led to introduction of more areas for further prospecting, decreasing the chance of false negative anomaly. Comparison between processed dataset with the sample catchment basin approach and raw data set has demonstrated the superiority of the sample catchment basin approach.
Journal of Analytical and Numerical Methods in Mining Engineering
Yazd University
2251-6565
7
v.
13
no.
2017
101
112
http://anm.yazd.ac.ir/article_978_76916276ca4d0e511632b77b07d7c4bb.pdf
Stability Analysis and Support System Design of Penstock Tunnels Bifurcation with Headrace Tunnel of Rudbare-Lorestan Dam Project
Hossein
Behzadinejad
Department of Mining Engineering, Isfahan University of Technology, Iran
author
Lohrasb
Faramarzi
Department of Mining Engineering, Isfahan University of Technology, Iran
author
Mohammad
Darbor
Department of Mining Engineering, Isfahan University of Technology, Iran
author
text
article
2017
per
Summary In this research, stability of penstock tunnels bifurcation with headrace tunnel of Rudbare-Lorestan dam powerhouse was studied. Due to the weak rock masses at the bifurcation area, the numerical modeling using FLAC3D was performed. According to the results of numerical modeling and determination of plastic zone and the empirical methods, the temporary support system consists of shotcrete and rock bolt with adequate length are suggested. Based on laboratory and in situ tests, the geomechanical parameters are determined. Introduction Today, large underground structures are constructed in order to transfer the water, oil and gas storage, underground power plants, radioactive waste repositories and etc. With the development and upgrade of infrastructures, tunnel construction is increasing all over the world and tunnel engineers are more aware of the importance of the safety and economics of tunnel construction. Stability of underground structures depend on size and geometry of construction, excavation technique, in situ stress conditions and support system and its installation time. Methodology and Approaches In order to estimate the deformation modulus of the rack mass in the headrace tunnel, in situ tests including of plate loading and dilatometer tests were performed. Then elasto-plastic behavior was defined for the rock mass by mohr-columb criterion and model was executed numerically to reach static stability. The Bifurcation cavern have been excavated by heading and benching method that is executed through drill and blasting technique. Results and Conclusions The empirical method suggest shotcrete with rock bolts to support weak rock masses. Also the numerical analysis demonstrate the installation of rock bolts with shotcrete as a temporary support system. Due to the large plastic zone caused by excavation processes, the value of the advancing step 0.8 m was determined. Also, the analysis of rock mass plastic zone in bifurcation area determined a suitable length of 6 meters for rock bolts. During the excavating of rock pillars, the value of change in the axial force acting on the rock bolt in the right wall of the tunnel No. 1, was increased. Also, the excavation of tunnel No. 2 at a distance of 11 meters from the tunnels No. 1, No. 4 and No. 5, was shown the less influence on the value of axial forces applied to the rock bolts. After the 16 stages of excavation advancement steps and installation of support systems, the maximum values of displacement in the roof, floor and walls of the bifurcation, were respectively 2.8, 3.67 and 1.5 cm
Journal of Analytical and Numerical Methods in Mining Engineering
Yazd University
2251-6565
7
v.
13
no.
2017
113
123
http://anm.yazd.ac.ir/article_979_cf41ab68aedaf51ccda19032d6b8bf0d.pdf