Rock Mechanics
Kapoor Chand; Radhakanta Koner
Abstract
In open-pit mine, safety of internal dumps is a significant pointer on the economic perspective of the overall project. It has been found in several studies that unplanned and random deposition of the overburdened material is the main reason for mishaps and failure. The study utilized unmanned aerial ...
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In open-pit mine, safety of internal dumps is a significant pointer on the economic perspective of the overall project. It has been found in several studies that unplanned and random deposition of the overburdened material is the main reason for mishaps and failure. The study utilized unmanned aerial vehicles (UAVs) to map the mine dumps, and the precise 3D geometry of the same was reconstructed to evaluate the safety using numerical methods. A framework is proposed to assess and identify the potential zone of instability in the mine dumps. The study was conducted at the open-pit mine at the Raniganj coalfield of Paschim Bardhaman in West Bengal, India. The study assessed the internal dump safety using a 3D limit equilibrium method and numerical methods. Finally, optimum parameters are suggested for the mine dumps geometry under the prevailing geo-mining conditions of the mine site. The framework proposed here for assessing critical zones in mine dumps is cost-effective, easy to use, quick, and efficient.
Rock Mechanics
Tanveer Wagay; Manju Suthar
Abstract
An experiment was conducted to evaluate the load-bearing capacity of a soil nailing system that consisted of four 10mm nails and four 12mm nails, reinforced in a slope with three different flexible facing materials: geo-composite facing, aluminium facing, and galvanized iron facing. The nails were spaced ...
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An experiment was conducted to evaluate the load-bearing capacity of a soil nailing system that consisted of four 10mm nails and four 12mm nails, reinforced in a slope with three different flexible facing materials: geo-composite facing, aluminium facing, and galvanized iron facing. The nails were spaced 200mm apart horizontally and vertically from centre to centre. The results of the stress-strain test showed that the geo-composite and galvanized iron facings with 12mm diameter nails exhibited high strength of 0.25N/mm2 with less displacement. The relationship between stress, displacement, and the type of nails used with identical facing was examined. The stability of the slope was also analysed to investigate the impact of nail parameters and type of facing on displacement under varying loading conditions.
Rock Mechanics
Erfan Amini; Masoud Mojarab; Hossein Memarian
Abstract
Landslides are defined as the downward movement of a portion of land materials under the direct influence of gravity. Landslides would get triggered by a wide spectrum of initiative factors such as earthquakes as a site effect of that event. In the vicinity of Tehran, significant historical earthquakes ...
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Landslides are defined as the downward movement of a portion of land materials under the direct influence of gravity. Landslides would get triggered by a wide spectrum of initiative factors such as earthquakes as a site effect of that event. In the vicinity of Tehran, significant historical earthquakes have occurred; therefore, tracing them could enhance the Tehran’s historical earthquake catalogue, due to the reason Tehran is a metropolitan and capital of Iran. However, paleoseismology could not determine the magnitude and seismic characteristics of historical earthquakes. Mobarak Abad landslide is a large and historical landslide located on Haraz road, a vital artery connecting Tehran to the Mazandaran Province, and there are significant faults like Mosha, North Alborz, and Khazar in its neighborhood. Hence, it is probable that this landslide occurred due to the generation of dynamic force resulting from an earthquake. Therefore, in this study, the geometrical characteristics of the landslide were measured by field surveying. Then with the empirical equations proposed by various researchers, we estimated the landslide volume and the magnitude of the corresponding earthquake, respectively. In the following, the epicenter and hypocenter of all the historical earthquakes within 200 kilometers of the landslide were identified. Then we utilized some conditions such as Keefer's graphs, error value in epicenter location, and peak ground acceleration to omit earthquakes and identify the corresponding earthquake event. The results demonstrate that two earthquakes of 1830 AD and 855 AD with a maximum acceleration of 0.16g are more probable than the 743 AD earthquake.
Rock Mechanics
vahab sarfarazi; Hadi Haeri; Mohammad Fatehi Marji; Gholamreza Saeedi; Amir Namdarmanesh
Abstract
In this paper, the effect of variations in the number and area of the rock bridges on the non-persistent discontinuities is investigated. In this regard, blocks containing rock bridges and joints with dimensions of 15 cm * 15 cm * 15 cm are prepared from plaster. The available rock bridges that have ...
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In this paper, the effect of variations in the number and area of the rock bridges on the non-persistent discontinuities is investigated. In this regard, blocks containing rock bridges and joints with dimensions of 15 cm * 15 cm * 15 cm are prepared from plaster. The available rock bridges that have occupied 0.2, 0.4, and 0.6 of the shear surface show latitudinal extension along the shear surface. There are variations in the number and extension of the rock bridges in the fixed area. For each of the samples, tests are performed on three blocks of the same material, by putting it under various direct normal stresses. Normal stresses were 3.33, 5.55, 7.77 kg/cm2. Also the obtained shear strength by laboratory tests was compared with the outputs of Jenning's criterion and Guo and Qi's criterion to determine the accuracy of these criteria for predicting the shear strength of non-persistent joints. The results show that the tensile crack started in the rock bridge under normal stress of 3.33 kg/cm2. Mixed-mode tensile shear cracks were propagated in the rock bridge under a normal stress of 5.55 kg/cm2, while a pure shear crack developed in the rock bridge under a normal stress of 7.77 kg/cm2. With the increase of normal stress, the number of microfractures increased. The variance in the number of rock bridges in the fixed area of the rock bridge does not affect the friction angle along the shear surface. Furthermore, the cohesion along the shear surface shows a small decrease with the increasing number of rock bridges. Also by the increase in the area of rock bridges, the friction angle along the shear surface remains constant, while at the same time, there is an almost linear increase in cohesion. Guo and Qi's criterion predicts the shear strength of the non-persistent joint exactly close to the shear strength of the physical samples.
Rock Mechanics
sajjad rezaei; ramin rafiee; Mohammad Ataei; Morteza Javadi
Abstract
The stability of waste dumps is a significant and at times critical issue in the development of surface mines. Due to insufficient space for waste disposal, environmental concerns, and various other factors, Mine No. 4 at Golgohar Sirjan is not capable of establishing a new waste dump. Given the existing ...
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The stability of waste dumps is a significant and at times critical issue in the development of surface mines. Due to insufficient space for waste disposal, environmental concerns, and various other factors, Mine No. 4 at Golgohar Sirjan is not capable of establishing a new waste dump. Given the existing limitations of the mine, the investigation has focused on increasing the dump capacity through the implementation of benches. In this research work, the stability of the waste dump has been investigated using the limit equilibrium method with the Slide3D software, along with a Monte Carlo simulation approach for probabilistic analysis. The results obtained from these methods have been compared with each other. The acceptable safety factor considered for this assessment ranges from 1.15 to 1.2. By adding benches to the eastern waste dump of the mine, a displaced volume equivalent to 36,715.565 cubic meters has been added to the capacity. The constructed model is based on the topography of the area, with dimensions of 1850 meters in length, 1750 meters in width, and 160 meters in height. The results indicate that the safety factor of the waste dump has been calculated as follows using the Spencer, Janbu, and Bishop methods respectively: 1.26, 1.199, and 1.226. Mine No. 4 needs to extract 983.58 million tons of waste to produce 73 million tons of iron ore. In total, by discharging 428 million tons of waste in the northeastern and eastern dumps and adding a bench, a volume of 555.571 million tons of waste is available for disposing of the remaining waste. Considering the remaining waste volume, space must be allocated for waste disposal to Mine No. 4.
Rock Mechanics
M. Hazrati Aghchai; P. Moarefvand; H. Salari Rad
Abstract
Displacements around a tunnel, occurring as a result of excavation, consist of the elastic and plastic parts. In this paper, we discuss the elastic part of displacements as a result of excavation, called net displacement. In general, the previous analytical solutions presented for determining the displacements ...
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Displacements around a tunnel, occurring as a result of excavation, consist of the elastic and plastic parts. In this paper, we discuss the elastic part of displacements as a result of excavation, called net displacement. In general, the previous analytical solutions presented for determining the displacements around a circular tunnel in an elastic medium do not give the net displacements directly. The well-known Kirsch solution is the most widely used method for determining the induced stresses and net displacements around a circular opening in a biaxially-loaded plate of homogeneous, isotropic, continuous, linearly elastic material. However, the complete solution for obtaining the net displacements has not been presented or highlighted in the available literature. Using the linear elasticity, this paper reviews and presents three different analytical methods for determining the net displacements directly as well as induced stresses around a circular tunnel. The three solution methods are the Lame' method, airy stress function method, and complex variable method. The tunnel is assumed to be situated in an elastic, continuum, and isotropic medium in the plane strain condition. The solutions are presented for both the hydrostatic and non-hydrostatic in situ stresses in the 2D biaxial loading condition along with an internal pressure. Loading and unloading in tunneling occurring as a result of excavation and stress differences between the induced and initial ones are considered to evaluate the net displacements directly. Finally, some examples are given to demonstrate the complete solution and show the difference between the net elastic displacements as a result of excavation and total elastic displacements that are not real.
Rock Mechanics
A. Dadi-givshad; M. Ahmadi; H. R. Nejati
Abstract
One of the methods used to investigate the damaged zone in rock structure is the acoustic emission method. This method is based on receiving the elastic waves that are produced by deformation and cracking of the rock mass around the underground excavation. In this research, a study is conducted on the ...
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One of the methods used to investigate the damaged zone in rock structure is the acoustic emission method. This method is based on receiving the elastic waves that are produced by deformation and cracking of the rock mass around the underground excavation. In this research, a study is conducted on the rock samples by a numerical method to investigate the damaged zone caused by the excavation of circular space on it. For this purpose, 33 cube samples of three different material types including sandstone, concrete, and cement-plaster mortar are prepared. A circular hole is drilled in the center of each sample. The hole diameter is 20 or 25 mm. The samples are loaded uniaxially or biaxially with different stress rates. It is tried to study the acoustic events occurring in the samples during the test, and their locations are investigated. Then the experiments are evaluated by a numerical method using the FLAC3D software and some developed codes. The relation between the sample damaged zone where the acoustic events have occurred during the loading period and the numerical elements that reach a degree of tensile and shear yield is studied. The results obtained show that the amount of cumulative acoustic parameters in cement-plaster mortar specimens is more than the others. In fact, the finer grains, the more amounts of energy and counts will be produced. Also, the results show that with increase in the lateral pressure and loading rate, the amount of cumulative energy and counts decreases.
Rock Mechanics
A. Turanboy; E. Ülker; C. Burak Küçüksütçü
Abstract
Estimation of the possible instability that may be encountered in the excavation slope(s) during the planning and application steps of the rock excavation processes is an important issue in geoengineering. In this paper, a modelling method is presented for assessing the probability of wedge failure involving ...
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Estimation of the possible instability that may be encountered in the excavation slope(s) during the planning and application steps of the rock excavation processes is an important issue in geoengineering. In this paper, a modelling method is presented for assessing the probability of wedge failure involving new permanent or temporary slope(s) along the planned excavation direction. The geostructural rock slopes including wedge blocks are determined geometrically in the first step. Here, a structural data analysis system that includes a series of filterings, sortings, and linear equations used to reveal the necessary geometric conditions for the wedge form is developed and used. The second step involves the 3D visualization and Factor of Safety (FS) using the limit equilibrium analysis of wedges on both the actual and planned new excavation surfaces. The last step is the Monte Carlo simulation, which is used in assessing the instabilities on the actual and planned new excavation surfaces. These new slope surfaces that have not yet been excavated are called the virtual structures. As a result of this work, the mean and probabilistic FS variations in the planned excavation direction are obtained as profiles. We suggest the preliminary guidelines for the mean and probability of the wedge failure in the excavation direction. The model is tested on a motorway cut slope. The FS results obtained from the Monte Carlo simulation calculations are compared with the mean results and the changes are revealed with the reasons.
Rock Mechanics
Sh. Bacha; Z. Mu Long; A. Javed; Sh. Al Faisal
Abstract
Rock burst is the most attractive and hot research area in geomechanics, mining, and civil engineering due to the increasing depth of mines and construction of deep underground structures. It has also been a severe problem in ground control measures in the last few decades. Many studies have been done ...
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Rock burst is the most attractive and hot research area in geomechanics, mining, and civil engineering due to the increasing depth of mines and construction of deep underground structures. It has also been a severe problem in ground control measures in the last few decades. Many studies have been done by different researchers in order to minimize the hazards of rock burst and to provide a safe mining/working environment. It is important to review the current advancement of rock burst prediction and its preventive measures. This paper reviews the experimental progress of rock burst warning, prediction, control measures, and potential damage measures. Different effective methods of rock burst prediction and control are also described.
Rock Mechanics
A. Asgari; A. Ramezanzadeh; Seyed M. E. Jalali; B. Brouard
Abstract
Ensuring the stability and integrity of underground gas storage salt caverns is a very complicated subject due to the non-linear and time-dependent behavior of rock salts under complicated thermal and mechanical loading conditions. For this reason, pressure and temperature fluctuations in the caverns ...
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Ensuring the stability and integrity of underground gas storage salt caverns is a very complicated subject due to the non-linear and time-dependent behavior of rock salts under complicated thermal and mechanical loading conditions. For this reason, pressure and temperature fluctuations in the caverns and their surrounding strata must be integrated into the analysis and the numerical tools that are used for this purpose. LOCAS, a 2D axisymmetric finite-element code, dedicated to the stability analysis of underground salt spaces, was applied to assess the effects of various operating and geometrical parameters on the cavern behavior. In this paper, we aimed to give an overall assessment of the behavior of the salt caverns used for natural gas storage. In this work, some specific loading scenarios were considered first, followed by thorough parametric and sensitivity analyses to reveal the impacts of the geometrical parameters and operational parameters involved on the behavior of salt caverns using the modern stability criteria. The findings showed that the onset of dilation was more likely to happen within the first cavern life cycle when pressure dropped to the minimum level. As for the potential of tension occurrence in the surrounding rock, this is more likely to happen by increasing the number of operation cycles, especially in the upper one-third of the cavern wall. Finally, it was seen that the cavern depth and minimum cavern internal pressure had even more important influences than the others on the salt cavern behavior.
Rock Mechanics
A. Alikhani; M. Taheri Moghadder; H. Mohammadi
Abstract
One of the most effective parameters in economics of open-pit mines is the pit slope angle, so that the slope angle more than the optimum value increases the probability of a large failure in the pit wall and the slope angle less than the optimum value leads to increasing stripping ratio and reducing ...
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One of the most effective parameters in economics of open-pit mines is the pit slope angle, so that the slope angle more than the optimum value increases the probability of a large failure in the pit wall and the slope angle less than the optimum value leads to increasing stripping ratio and reducing net present value of mine. Therefore, in this paper, considering the limit equilibrium methods of modified Bishop and modified Janbu and numerical models of the slope stability analysis, the effect of overall slope angle on the Economics of open pit mines was investigated. In addition, it was shown that selecting the overall slope angle less than the optimum value leads to reducing the depth of open-pit mining (the ultimate pit depth) and consequently, reducing the net present value of mine. Finally, in homogenous and Isotropic media, the results of Bishop and Janbu and numerical modeling are close together.
Rock Mechanics
M. Rezaei; M. Asadizadeh
Abstract
Bedrock unconfined compressive strength (UCS) is a key parameter in designing thegeosciences and building related projects comprising both the underground and surface rock structures. Determination of rock UCS using standard laboratory tests is a complicated, expensive, and time-consuming process, which ...
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Bedrock unconfined compressive strength (UCS) is a key parameter in designing thegeosciences and building related projects comprising both the underground and surface rock structures. Determination of rock UCS using standard laboratory tests is a complicated, expensive, and time-consuming process, which requires fresh core specimens. However, preparing fresh cores is not always possible, especially during the drilling operation in cracked, fractured, and weak rocks. Therefore, some attempts have recently been made to develop the indirect methods, i.e. intelligent predictive models for rock UCS estimation, which require no core preparation and laboratory equipment. This work focuses on the application of new combinations of intelligent techniques including adoptive neuro-fuzzy inference system (ANFIS), genetic algorithm (GA), and particle swarm optimization (PSO) in order to predict rock UCS. These models were constructed based on the collected laboratory datasets upon 93 core specimens ranging from weak to very strong rock types. The proposed hybrid model results were compared with each other, and the real data and multiple regression (MR) results. These comparisons were made using coefficient of correlation, mean of square error, mean of absolute error, and variance account for indices. The comparison results proved that the ANFIS-GA combination had a relatively higher accuracy than the ANFIS-PSO combination, and both had a higher capability than the MR model. Furthermore, the ANFIS-GA and ANFIS-PSO model results were completely in accordance with the UCS laboratory test, and they were more accurate than the previous single/hybrid intelligent models. Lastly, a parametric study of the suggested models showed that the density and Schmidt hammer rebound had the highest influence, and porosity had the lowest influence on the output (UCS).
Rock Mechanics
H. Sarfaraz; M. Amini
Abstract
One of the most important instabilities of rock slopes is toppling failure. Among the types of toppling failure, block-flexural failures are more common instability which occurs in nature. In this failure, some rock blocks break because of tensile stresses, and some overturn under their weights, and ...
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One of the most important instabilities of rock slopes is toppling failure. Among the types of toppling failure, block-flexural failures are more common instability which occurs in nature. In this failure, some rock blocks break because of tensile stresses, and some overturn under their weights, and next to all of them topple together. Physical and theoretical modeling of this failure is studied by Amini et al. in 2015. Due to the complexity of this failure mechanism, no appropriate numerical model has been proposed so far. In this research, first, a literature review of toppling failure is summarized. Then, using UDEC software as distinct element method (DEM), the experimental models were analyzed numerically, and Voronoi joint model was applied to simulate the failure. The results of numerical simulations are compared with the outcomes of physical models and analytical solution. The comparison illustrates that numerical modeling has good agreement with corresponding experimental tests and theoretical approach. Also, the results show that although the mechanism of block-flexural toppling failure is complicated, the numerical code is well capable to analyze of this failure.
Rock Mechanics
L. Nikakhtar; Sh. Zare; H. Mirzaei Nasir Abad
Abstract
One of the main issues involved during tunnel construction with tunnel boring machines is the tail gap grouting. This gap is between the external diameter of tunnel lining and the excavation boundary that is filled with high-pressure grouting materials. In this work, three different approaches of gap ...
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One of the main issues involved during tunnel construction with tunnel boring machines is the tail gap grouting. This gap is between the external diameter of tunnel lining and the excavation boundary that is filled with high-pressure grouting materials. In this work, three different approaches of gap grouting modeling in the FLAC3D software are investigated with a special attention to the influence of the grout material hardening process. In the first approach, the grout is modeled as a liquid during injection, and considering the TBM advancement and its hardening time, the grout characteristics are changed to the properties of the solid grouting. In the second approach, the grouting material from the beginning of injection is considered with the properties of solid grouting in the model, and the liquid phase is ignored. In the third approach, without considering the back-filled grouting area in the model geometry, only the injection pressure is applied to the end of the shield and behind the installed segments. The validity of the approaches is evaluated with respect to the maximum ground surface settlement. All the three approaches estimate different surface settlement but the result of the first approach is closer to the monitoring data. Also as a sensitivity analysis, in this work, we investigate the effect of the elastic modulus of liquid and solid grouting materials on the amount of surface settlement that can help to gain a more accurate insight into the effect of grout mixture.
Rock Mechanics
M. H. Kadkhodaei; E. Ghasemi
Abstract
The CERCHAR abrasivity test is very popular for determination of rock abrasivity. An accurate estimation of the CERCHAR abrasivity index (CAI) is useful for excavation operation costs. This paper presents a model to calculate CAI based on the gene expression programming (GEP) approach. This model is ...
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The CERCHAR abrasivity test is very popular for determination of rock abrasivity. An accurate estimation of the CERCHAR abrasivity index (CAI) is useful for excavation operation costs. This paper presents a model to calculate CAI based on the gene expression programming (GEP) approach. This model is trained and tested based on a database collected from the experimental results available in the literature. The proposed GEP model predicts CAI based on two basic geomechanical properties of rocks, i.e. rock abrasivity index (RAI) and Brazilian tensile strength (BTS). Root mean square error (RMSE), mean absolute error (MAE), Nash-Sutcliffe efficiency (NSE), and coefficient of determination (R2) are used to measure the model performance. Furthermore, the developed GEP model is compared with linear and non-linear multiple regression and other existing models in the literature. The results obtained show that GEP is a strong technique for the prediction of CAI.
Rock Mechanics
K. Abdolghanizadeh; M. Hosseini; M. Saghafiyazdi
Abstract
Natural and artificial materials including rocks and cement-based materials such as concrete and cement mortar are affected both physically and chemically by various natural factors known as weathering factors. The freeze-thaw process, as a weathering factor, considerably affects the properties of rocks ...
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Natural and artificial materials including rocks and cement-based materials such as concrete and cement mortar are affected both physically and chemically by various natural factors known as weathering factors. The freeze-thaw process, as a weathering factor, considerably affects the properties of rocks and concrete. Therefore, the effect of the freeze-thaw process on the physical and mechanical properties of materials should be taken into account in areas with the risk of this process. Given that few studies have been conducted on the effect of the freeze-thaw process on the fracture toughness, in this work, we aimed at investigating the effects of the freeze-thaw cycles and freezing temperature on the mode I and mode II fracture toughness of cement mortar. To this end, specimens were exposed to 0, 5, 10, 20, and 30 freeze-thaw cycles, and the mode I and mode II fracture toughness was determined in different cycles. The effect of freezing temperature in a freeze-thaw cycle on the mode I and mode II fracture toughness was also investigated. The damage factor was also defined based on the effective porosity of cement mortar, and its changes with the number of freeze-thaw cycles and mode I and mode II fracture toughness were studied. Finally, the decay function model provided by Mutluturk was investigated. According to the results obtained, the mode I and mode II fracture toughness of cement mortar decreased linearly with increase in the number of freeze-thaw cycles. The mode I and mode II fracture toughness decreased linearly with increase in the freezing temperature in a freeze-thaw cycle. The damage factor increased with increase in the number of freeze-thaw cycles, and, additionally, its relationship with mode I and mode II fracture toughness exhibited a linear behavior.
Rock Mechanics
I. Kheyrandish; M. Ahmadi; H. Jahankhah
Abstract
During an earthquake, the better performance of segmental tunnel lining, compared to the continuous in-cast concrete lining, is generally related to the joints between segments. In order to better understand the influence of the segment joints, their effect on the internal forces induced in tunnel lining ...
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During an earthquake, the better performance of segmental tunnel lining, compared to the continuous in-cast concrete lining, is generally related to the joints between segments. In order to better understand the influence of the segment joints, their effect on the internal forces induced in tunnel lining simultaneously with the effects of the other influential parameters should be considered. In this work, the segmental joints were simulated by the representative stiffnesses and effects of these characteristics in relation to the other parameters such as the soil-liner interface behavior, number of segments in each ring and thickness of segments on the internal forces induced in structure were investigated. For this purpose, 2D numerical analyses were performed and the results obtained were discussed. Results showed that under the seismic condition, the components that had the most significant role on the internal axial forces induced in the segmental lining were rotational stiffness and axial stiffness of joints. Also the bending moments were more affected by the rotational stiffness. Generally, the radial joint stiffness had a less effect on the induced internal forces. With increase in the number of segments and their thickness, the effect of joint stiffness on the internal forces increases and the design of joints should be given more attention; however, the effects of joint stiffness and frictional behavior at the soil-liner interface on the maximum induced forces are almost independent from each other. Also in a specified joint behavior, by variation in each one of the other parameters including the soil-liner interface condition, number of segments and their thickness, the absolute magnitude of the maximum induced internal forces sometimes change significantly.
Rock Mechanics
H. Sarfaraz; M. H. Khosravi; M. Amini
Abstract
In layered and blocky rock slopes, toppling failure is a common mode of instability that may occur in mining engineering. If this type of slope failure occurs as a consequence of another type of failure, it is referred to as the secondary toppling failure. “Slide-head-toppling” is a type ...
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In layered and blocky rock slopes, toppling failure is a common mode of instability that may occur in mining engineering. If this type of slope failure occurs as a consequence of another type of failure, it is referred to as the secondary toppling failure. “Slide-head-toppling” is a type of secondary toppling failures, where the upper part of the slope is toppled as a consequence of a semi-circular sliding failure at the toe of the slope. In this research work, the slide-head-toppling failure is examined through a series of numerical modeling. Phase 2, as a software written based on the finite element method, is used in this work. Different types of slide-head-toppling failures including blocky, block-flexural, and flexural are simulated. A good agreement can be observed when the results of the numerical modeling are compared with those for the pre-existing physical modeling and analytical method.
Rock Mechanics
Gh. H Ranjbar; K. Shahriar; K. Ahangari
Abstract
According to the wide application of segmental lining in mechanized tunneling, recognizing the behavior of segmental lining joints is important in tunnels designing. In the structural analysis of the tunnel segmental lining, segmental joints can be considered as elastic joints, and their stiffness characteristics ...
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According to the wide application of segmental lining in mechanized tunneling, recognizing the behavior of segmental lining joints is important in tunnels designing. In the structural analysis of the tunnel segmental lining, segmental joints can be considered as elastic joints, and their stiffness characteristics are affected by the rotational, shear, and axial stiffness. The purpose of this work is to investigate the effect of the rotational, shear, and axial stiffness of segmental lining joints on the internal forces (bending moment and axial force)under the static conditions. For this purpose, a 3D numerical analysis was carried out using the ABAQUS software. The results obtained show that by increasing the rotational stiffness of the segmental joint, the bending moment increases, and for lower values of rotational stiffness, the bending moment variations are higher, while the axial force variations are very slight in comparison with the bending moment. By increasing the axial and shear stiffness of the segmental joint, changes of the bending moment and axial force in segmental lining are negligible.
Rock Mechanics
J. Mohammadi; M. Ataei; R. Kakaie; R. Mikaeil; S. Shaffiee Haghshenas
Abstract
Prediction of the production rate of the cutting dimensional stone process is crucial, especially when chain saw machines are used. The cutting dimensional rock process is generally a complex issue with numerous effective factors including variable and unreliable conditions of the rocks and cutting machines. ...
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Prediction of the production rate of the cutting dimensional stone process is crucial, especially when chain saw machines are used. The cutting dimensional rock process is generally a complex issue with numerous effective factors including variable and unreliable conditions of the rocks and cutting machines. The Group Method of Data Handling (GMDH) type of neural network and Radial Basis Function (RBF) neural network, as two kinds of the soft computing method, are powerful tools for identifying and assessing the unpredicted and uncertain conditions. Hence, this work aims to develop prediction models for estimating the production rate of chain saw machines using the RBF neural network and GMDH type of neural network, and then to compare the results obtained from the developed models based on the performance indices including value account for, root mean square error, and coefficient of determination. For this purpose, the parameters of 98 laboratory tests on 7 carbonate rocks are accurately investigated, and the production rate of each test is measured. Some operational characteristics of the machines, i.e. arm angle, chain speed, and machine speed, and also the three important physical and mechanical characteristics including uniaxial compressive strength, Los Angeles abrasion test, and Schmidt hammer (Sch) are considered as the input data, and another operational characteristic of the machines, i.e. production rate, is considered as the output dataset. The results obtained prove that the developed GMDH model is able to provide highly promising results in order to predict the production rate of chain saw machines based on the performance indices.
Rock Mechanics
M. Lotfi; B. Tokhmechi
Abstract
Nowadays, Barton’s Joint Roughness Coefficients (JRC) are widely used as the index for roughness and as a challenging fracture property. When JRC ranking is the goal, deriving JRC from different fractal/wavelet procedures can be conflicting. Complexity increases when various rankings outcome from ...
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Nowadays, Barton’s Joint Roughness Coefficients (JRC) are widely used as the index for roughness and as a challenging fracture property. When JRC ranking is the goal, deriving JRC from different fractal/wavelet procedures can be conflicting. Complexity increases when various rankings outcome from different calculation methods. Therefore, using Barton’s JRC, we cannot make a decision based on the proven mathematical theories because each method has a different rank. Ideally, these rankings must be equal but, in practice, they are different for each method. To solve this problem and to achieve a robust and valid ranking for JRC, Condorcetand Borda count methods have been used. These methods have been proposed as fusion approaches. Re-ranking of JRC using different methods integrated with Condorcet showed confusion in ranking of the JRC4, JRC5, and JRC6 profiles. This ambiguity is equal to equalizing decision conditions about all the three at the examination of the winners, losers, and draws in pairwise matrices. Therefore, Borda Count was applied and resulted in robust rankings. In fact, a new approach for a roughness measurement is presented. A new JRC ranking called JRCN is introduced. This new ranking shows a lower sum of squared errors (0.00390) in comparison with the original JRC ranking method (0.00410) and ranked JRCN1 to JRCN10. Thus it is proposed to consider JRCN as a new and improved version of JRC rankings.
Rock Mechanics
M. Akhyani; R. Mikaeil; F. Sereshki; M. Taji
Abstract
Predicting the wear performance of circular diamond saw in the process of sawing hard dimensional stone is an important step in reducing production costs in the stone sawing industry. In the present research work, the effective parameters on circular diamond saw wear are defined, and then the weight ...
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Predicting the wear performance of circular diamond saw in the process of sawing hard dimensional stone is an important step in reducing production costs in the stone sawing industry. In the present research work, the effective parameters on circular diamond saw wear are defined, and then the weight of each parameter is determined through adopting a fuzzy rock engineering system (Fuzzy RES) based on defining an accurate Gaussian pattern in fuzzy logic with analogous weighting. After this step, genetic algorithm (GA) is used to determine the levels of the four major variables and the amounts of the saw wear (output parameter) in the classification operation based on the fixed, dissimilar, and logarithmic spanning methods. Finally, a mathematical relationship is suggested for evaluation of the accuracy of the proposed models. The main contribution of our method is the novelty of combination of these methods in fuzzy RES. Before this work, all Fuzzy RESs only use simple membership functions and uniform spanning. Using GA for spanning and normal distribution as membership function based upon our latest work is the first work in fuzzy RES. To verify the selected proposed model, rock mechanics tests are conducted on nine hard stone samples, and the diamond saw wear is measured and compared with the proposed model. According to the results obtained, the proposed model exhibits acceptable capabilities in predicting the circular diamond saw wear.
Rock Mechanics
M. Nikkhah; M. A. Ghasvareh; N. Farzaneh Bahalgardi
Abstract
In general, underground spaces are associated with high risks because of their high uncertainty in geotechnical environments. Since most accidents and incidents in these structures are often associated with uncertainty, the development of risk analysis and management methods and prevention of accidents ...
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In general, underground spaces are associated with high risks because of their high uncertainty in geotechnical environments. Since most accidents and incidents in these structures are often associated with uncertainty, the development of risk analysis and management methods and prevention of accidents are essential. A deeper recognition of the factors affecting the implementation process can pave the way for this purpose. Risk rating of projects is a key part of the risk assessment stage in the risk management process of each project. Various multi-criteria decision-making methods, as quantitative approaches, are used to allow them to be used in the risk rating issue of each project. In this work, a new model is provided for risk management of Mashhad Urban Railway Line 3 using the game theory and multi-criteria decision-making methods. Based on the answers of the specialists and experts to the prepared questionnaires, various risk groups identified using the TOPSIS and AHP multi-criteria decision-making methods are ranked. Accordingly, the group of economic risks, as the most important risk and social risk group, is ranked as the least significant in both methods. In the following, the appropriate response to the main risks of the ratings is proposed based on the modeling of the game theory, and ranked in terms of importance. Also the worst risk scenario in the project is identified, and the appropriate responses for this state are also expressed in order of importance. The results obtained indicate that the risk of financing problems is the most significant risk, and other risks are ranked in terms of importance in the next ranks. Additionally, the use of new financing methods at times of credit scarcity and project financial problems is also considered as the most important response to the risk in this project.
Rock Mechanics
M. H. Askarbioki; F. Kargaran Bafghi; M. Mokhtari; M. Khaleghi
Abstract
Oil leakage causes soil contamination and induces changes in the physical and mechanical properties of soils. In areas contaminated with oil products such as gasoline, the implementation of civilian operations requires determination and prediction of soil behavior in the existing conditions. In this ...
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Oil leakage causes soil contamination and induces changes in the physical and mechanical properties of soils. In areas contaminated with oil products such as gasoline, the implementation of civilian operations requires determination and prediction of soil behavior in the existing conditions. In this research work, the effect of oil contamination by gasoline obtained from the National Oil Company in the Yazd Province is considered to investigate the effect of contaminants on the geotechnical properties of fine-grained sand. In order to examine the geotechnical characteristics of contaminated soil, compaction, undrained triaxial (CU), and consolidation tests are conducted. The tests are carried out on the samples of clean soil and contaminated soil with 1, 3, and 5% gasoline. The results obtained show that added gasoline reduces the optimum moisture content and increases the maximum dry density. In addition, based on the results of the triaxial test, the amount of friction angle and the cohesion of clay sand decrease by 21% and 14% with increasing contamination up to 5%, respectively, compared to the clean soil sample. Furthermore, adding gasoline significantly increases the compressibility and compression index.
Rock Mechanics
E. Bakhshi; V. Rasouli; A. Ghorbani; M. Fatehi Marji
Abstract
In this work, we used a grain-based numerical model based on the concept of lattice. The modelling was done to simulate the lab experiments carried out on the mortar samples. Also the analytical solutions corresponding to the viscosity-dominated regime were used to estimate the fracture length and width, ...
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In this work, we used a grain-based numerical model based on the concept of lattice. The modelling was done to simulate the lab experiments carried out on the mortar samples. Also the analytical solutions corresponding to the viscosity-dominated regime were used to estimate the fracture length and width, and the results obtained were compared with the numerical simulations. As the analytical solutions are proposed for a penny-shaped fracture with no presence of any obstacle such as natural interfaces, in this work, we presented the results of lattice simulations for hydraulic fracturing in the cement sample, similar to the lab, but with no natural fractures, and compared the results obtained with analytical solutions. The results indicated that in the case of a continuous medium, the analytical solutions may present a reasonable estimation of the fracture geometry. Also the viscosity-dominated leak-off model showed a better match between the analytical solutions and the numerical simulation results, confirmed by observing fluid loss into the sample in the lab post-experiment. In the case of assuming leak-off, the results indicated that the fracture width and length would reduce. However, it should be noted that in real cases, rock formations exhibit fractures and inhomogeneity at different scales so that the applications of the analytical solutions are limited.
