Rock Mechanics
M. Lak; M. Fatehi Marji; A.R. Yarahamdi Bafghi; A. Abdollahipour
Abstract
The explosion process of explosives in a borehole applies a very high pressure on its surrounding rock media. This process can initiate and propagate rock fractures, and finally, may result in the rock fragmentation. Rock fragmentation is mainly caused by the propagation of inherent pre-existing fractures ...
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The explosion process of explosives in a borehole applies a very high pressure on its surrounding rock media. This process can initiate and propagate rock fractures, and finally, may result in the rock fragmentation. Rock fragmentation is mainly caused by the propagation of inherent pre-existing fractures of the rock mass and also from the extension of the newly formed cracks within the intact rock due to the explosion. In this work, the process of extension of blast-induced fractures in rock masses is simulated using the discrete element method. It should be noted that, in this work, fracture propagation from both the rock mass inherent fractures and newly induced cracks are considered. The rock mass inherent fractures are generated using the discrete fracture network technique. In order to provide the possibility of fracture extension in the intact rock blocks, they are divided into secondary blocks using the Voronoi tessellation technique. When the modeling is completed, the fracture extension processes in the radial and longitudinal sections of a borehole are specified. Then a blast hole in an assumed rock slope is modeled and the effect of pre-splitting at the back of the blast hole (controlled blasting) on the fracture extension process in the blast area is investigated as an application of the proposed approach. The modeling results obtained show that the deployed procedure is capable of modeling the explosion process and different fracture propagations and fragmentation processes in the rock masses such as controlled blasting.
Rock Mechanics
R. Shafiei Ganjeh; H. Memarian; M. H. Khosravi; M. Mojarab
Abstract
Dynamic slope stability in open-pit mines still remains a challenging task in the computational mining design. Earthquake and blasting are two significant sources of dynamic loads that can cause many damages to open-pit mines in active seismic areas and during exploitation cycles. In this work, the effects ...
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Dynamic slope stability in open-pit mines still remains a challenging task in the computational mining design. Earthquake and blasting are two significant sources of dynamic loads that can cause many damages to open-pit mines in active seismic areas and during exploitation cycles. In this work, the effects of earthquake and blasting on the stability of the NW slope of Chadormalu mine are compared by a numerical modeling method. The dynamic results show that the maximum displacement under earthquake and blasting loads within the slope are 844 mm and 146 mm, respectively. According to the shear strain results, both the earthquake and blasting waveforms are destructive, while the earthquake waveforms cause more damages to the slope. Moreover, the deterministic and probabilistic seismic hazard analyses are carried out to assess the seismicity of the mine area. The experimental results indicate that the maximum values for the vertical and horizontal accelerations are 0.55 g and 0.75 g, respectively. The maximum calculated acceleration is then scaled to the selected earthquake accelerograms. In order to show the effective impact of the established scale, the model is executed using the original accelerograms. The results obtained show that the established scale prevents overestimation and underestimation of the displacement and strain. Therefore, applying scaled accelerograms in a dynamic slope stability analysis in mine slopes leads to more reliable and robust results. The overall results show that a strong earthquake causes plenty of damages to the slope, and consequently, interrupts the mining cycle. Hence, the seismic study and dynamic slope stability should be considered as a part of the computational mining design.
Rock Mechanics
M. Hosseini; A. R. Khodayari
Abstract
In an era of continued economic development around the globe, numerous rock-related projects including mining and gas/oil exploration are undertaken in regions with cold climates. Winters in the Iranian western and northwestern provinces are characterized by a high precipitation rate and a cold weather. ...
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In an era of continued economic development around the globe, numerous rock-related projects including mining and gas/oil exploration are undertaken in regions with cold climates. Winters in the Iranian western and northwestern provinces are characterized by a high precipitation rate and a cold weather. Under such conditions, rocks are exposed to long freezing periods and several freeze-thaw (F-T) cycles. It is thus necessary to examine the impact of these cycles on the physical and mechanical properties of rocks. Considering the abundant sandstone resources in Iran, in this work, we focused on the Lushan sandstone by investigating the effects of F-T cycles and freezing temperatures on the uniaxial and triaxial compressive strengths, cohesion, internal friction angle, and elastic modulus of the rocks. To study the impact of the number of F-T cycles on the strength of rocks, the specimens frozen at -16 °C were subjected to 1, 4, 8, 16, and 32 F-T cycles. Similar tests were also carried out on the specimens frozen at -24 °C. Furthermore, a number of tests were undertaken at the ambient temperature (25 °C) on specimens that did not undergo an F-T cycle. According to the results obtained, an increase in the number of F-T cycles and freezing temperatures reduced the uniaxial and triaxial compressive strengths, cohesion, internal friction angle, and elastic modulus due to the growth of the existing cracks and the nucleation of new cracks in the rock. Consequently, the effective porosity increased, whereas the dry specific gravity decreased with more F-T cycles and lower freezing temperatures.
Rock Mechanics
S. Moshrefi; K. Shahriar; A. Ramezanzadeh; K. Goshtasbi
Abstract
A new failure criterion was presented to predict the ultimate strength of shale under the triaxial and polyaxial state of stress. A database containing 93 datasets was obtained from the results of the uniaxial, triaxial, polyaxial compressive tests, an indirect tensile test was collected from reliable ...
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A new failure criterion was presented to predict the ultimate strength of shale under the triaxial and polyaxial state of stress. A database containing 93 datasets was obtained from the results of the uniaxial, triaxial, polyaxial compressive tests, an indirect tensile test was collected from reliable references, and this test was carried out on the shale samples taken from the southwestern oilfields in Iran. The database was used to evaluate the proposed criterion, and its accuracy was compared against the popular failure criteria in rock mechanics, particularly those used for stability analysis such as the Hoek-Brown, Mohr-Coulomb, Drucker-Prager, and Mogi-Coulomb failure criteria. In order to evaluate the model, seven important statistical indices were selected. Subsequently, curves from various failure criteria were fitted to the triaxial and polyaxial data, and the corresponding coefficients and statistical indices were determined. The results obtained indicated that, in all cases, compared to the other failure criteria, the proposed criterion succeeded to predict the ultimate strength at a higher accuracy. Also the proposed criterion was used calculate the uniaxial compressive and tensile strengths with a minimum error. For a further examination of the proposed criterion, a series of results from the triaxial test including the ductile failure data were utilized for evaluation of the applicability of the proposed criterion to the ductile zone. It showed that the criterion could predict the ultimate strength of shale over a wide range of stresses.
Rock Mechanics
E. Dadashi; A. Noorzad; K. Shahriar; K. Goshtasbi
Abstract
The utilization of the lining type in pressure tunnels is highly dependent on the geological and hydraulic conditions. There are two types of lining, namely concrete and steel lining but steel lining is one of the most expensive arrangements. To decrease the length of steel lining in these tunnels, the ...
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The utilization of the lining type in pressure tunnels is highly dependent on the geological and hydraulic conditions. There are two types of lining, namely concrete and steel lining but steel lining is one of the most expensive arrangements. To decrease the length of steel lining in these tunnels, the concrete lining, which prevents water seepage from the surrounding rock mass, is the appropriate alternative. In this work, a special attention is devoted to limit water losses in the concrete lining of pressure tunnel based on the critical reinforcing ratio in concrete lining. In order to evaluate the effect of internal water pressure on the permeability coefficient variation of the concrete lining and the surrounding rock mass, some simulations of reinforced concrete lining is implemented in the ABAQUS finite element software based on the coupled pore fluid-stress analysis. The results obtained indicate that although the critical reinforcing ratio has an important role in capturing the seepage flows and water losses, it is not sufficient to rely only on this parameter. However, among the various influential factors involved, a suitable arrangement of the reinforcement in the concrete lining should also be considered.
Rock Mechanics
H. Zebarjadi Dana; R. Khaloo Kakaie; R. Rafiee; A.R. Yarahmadi Bafghi
Abstract
Slope stability analysis is one of the most important problems in mining and geotechnical engineering. Ignoring the importance of these problems can lead to significant losses. Selecting an appropriate method to analyze the slope stability requires a proper understanding of how different factors influence ...
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Slope stability analysis is one of the most important problems in mining and geotechnical engineering. Ignoring the importance of these problems can lead to significant losses. Selecting an appropriate method to analyze the slope stability requires a proper understanding of how different factors influence the outputs of the analyses. This paper evaluates the effects of considering the real geometry, changes in the mesh size, and steepness of the slope, as the dimensional effects, and changes in the geomechanical parameters, as the media effects on the global slope stability of an open-pit mine using finite difference methods with a strength reduction technique. The case study is the Tectonic Block I in the old pit (steep slope) and the redesigned new pit (gentle slope) of the Choghart iron mine. In the first step, a series of 2D and 3D slope stability analyses are performed and compared in terms of safety and potential failure surface. The results obtained show that by considering the real geometry of the slope, the FOS3D/FOS2D ratio (3D-effect) is more than 1 in the all cases. The 3D-effect in the new pit is smaller than that in the old one. In the next step, sensitivity analysis of the cohesion and the friction angle is performed for the 2D and 3D analyses. The results obtained show that the sensitivity of the analyses in terms of the 3D-effect to the change in the friction angle, especially in a low-friction angle, is more significant than that to the change in the cohesion.
Rock Mechanics
H. Fattahi; N. Babanouri; Z. Varmaziyari
Abstract
The dynamic response of slopes against earthquake is commonly characterized by the earthquake-induced displacement of slope (EIDS). The EIDS value is a function of several variables such as the material properties, slope geometry, and earthquake acceleration. This work is aimed at the prediction of EIDS ...
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The dynamic response of slopes against earthquake is commonly characterized by the earthquake-induced displacement of slope (EIDS). The EIDS value is a function of several variables such as the material properties, slope geometry, and earthquake acceleration. This work is aimed at the prediction of EIDS using the Monte Carlo simulation method (MCSM). Hence, the parameters height, unit specific weight, cohesion, friction angle, vibration duration, and maximum horizontal acceleration are used to predict the EIDS values. To do this, a multiple non-linear regression relationship is first derived between EIDS and the independent variables. Then MCSM is performed based on the developed regression equation. The results obtained demonstrate that the stochastic approach used is able to successfully reproduce the EIDS values and calculate the confidence intervals. The average of the measured and simulated values for EIDS was 4.34 cm and 4.48 cm, respectively. Eventually, the results of a performed correlation sensitivity analysis revealed that the maximum horizontal acceleration had the greatest impact on EIDS.
Rock Mechanics
S. Ali Madadi; A. Majdi; M. H. Khosravi; A.R. Kargar
Abstract
Fracture mechanics is a vital component involved in studying the exact behavior of rock materials. Detection and assessment of the behavior of rock joints injected by grout plays an important role in numerical modelling in rock mechanic projects. The importance of mechanisms associated with initiation ...
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Fracture mechanics is a vital component involved in studying the exact behavior of rock materials. Detection and assessment of the behavior of rock joints injected by grout plays an important role in numerical modelling in rock mechanic projects. The importance of mechanisms associated with initiation and propagation of cracks due to hydraulic fracturing has led to a considerable interest in investigation and analysis of this phenomenon. In this work, the process of propagation of cracks on the wall of boreholes, drilled in single and bi-material structures, was simulated in ABAQUS software employing the extended finite element method. The energy method was implemented to obtain the stress intensity factor and energy release rate through applying J integral around the crack tip. The method was applied to two rock types, diorite and granite at the Chadormalu iron mine located in the central part of Iran. It was concluded that assuming the same geometry, the possibility of crack propagation at the boundary between two materials was more than the single material medium. Therefore, in dealing with a bi-material medium, if the purpose is to measure the in situ stresses, the measurement should not be performed on the boundary between the two materials.
Rock Mechanics
M. Zoorabadi
Abstract
Numerical modelling techniques are not new for mining industry and civil engineering projects anymore. These techniques have been widely used for rock engineering problems such as stability analysis and support design of roadways and tunnels, caving and subsidence prediction, and stability analysis of ...
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Numerical modelling techniques are not new for mining industry and civil engineering projects anymore. These techniques have been widely used for rock engineering problems such as stability analysis and support design of roadways and tunnels, caving and subsidence prediction, and stability analysis of rock slopes. Despite the significant advancement in the computational mechanics and availability of high speed computing hardware, the input data and constitutive models remain the main source of errors affecting the reliability of numerical simulations. The problem with the input data has been deepened more by introducing empirical-based methods such as GSI classification to downgrade the rock properties from laboratory scale to field scale. The deformability modulus and strength parameters are the main outputs of these downgrading techniques. Numerical modelling users simply apply these downgrading methods and run the model without considering the real mechanics behind the stress induced failure and deformation around the underground excavations. While to the contrary to the commonly used downgrading methods that produce a constant modulus for rock at all depths, the rock modulus is stress dependent and varies with depth. In addition to this, the mechanism of stress induced displacement is not similar to the deformation of a continuum model simulated with equivalent rock properties. Apart from the mechanical characteristics of rocks, the magnitude and orientation of in-situ stresses are two other important parameters that have significant impacts on stress induced rock fracturing. The impacts of these two parameters have also been neglected in many practical cases. This paper discuss this old fashioned topic in more details with presenting the known facts and mechanics which numerical modelling users ignore them due to the unquestioning acceptance of downgrading methods. It also covers the influence of the stress magnitude and orientation on stress induced rock fracturing.
Rock Mechanics
R. Rafiee; A. Azarfar
Abstract
One of the main concerns of an underground coal mining engineer is the safety and stability of the mine. One way that the safety and stability can be ensured is to know and understand the coal mine geology and how it reacts to the mining process. One technique that has shown a lot of success in the coal ...
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One of the main concerns of an underground coal mining engineer is the safety and stability of the mine. One way that the safety and stability can be ensured is to know and understand the coal mine geology and how it reacts to the mining process. One technique that has shown a lot of success in the coal mining industry for geologic technical evaluation purposes is the coal mine roof rating (CMRR). The CMRR classification is based on geotechnical data taken from the immediate roof layers within the mine. Since the uncertainty exists in geotechnical data, and CMRR process depends on the expert’s idea implicitly, the final value may be inaccurate. In this paper, the fuzzy type 2 is used to overcome this uncertainty. To design the fuzzy system for calculating the CMRR, only quantitative variables (UCS, spacing, and persistence) are considered as fuzzy inputs. Finally, the scores of CMRR and FCMRR for four units of Riccall mine are compared.
Rock Mechanics
N. Aziz; A. Mirzaghorbanali; G. Yang; S. Khaleghparast; H. Resekh
Abstract
There is an increasing need to determine accurately the strength properties of tendons for an effective ground control on mines and underground structures as well as on modelling simulations. The strength properties of cables, used as cable bolts, have been evaluated mainly by their ultimate tensile ...
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There is an increasing need to determine accurately the strength properties of tendons for an effective ground control on mines and underground structures as well as on modelling simulations. The strength properties of cables, used as cable bolts, have been evaluated mainly by their ultimate tensile strength, as this kind of test can be carried out in the field as well as in the laboratory. Only recently, there has been a growing interest in cable bolt failures in shear because of the documented field failure evidence. Accordingly, this paper reports various methods of shear testing of rock bolts and cables using different shear testing rigs, some have been developed by the rock bolting research team at the University of Wollongong. A programme of shear testing of a variety of cable bolts marketed in Australia was undertaken, the results of which were reported and conclusions were drawn. It was concluded that plain cable bolts were de-bonded during shearing when compared to spiral cables under the same testing conditions. In addition, both the single shear and double shear testing methodologies will result in the same outcome if there is no de-bonding, and a proper confinement is applied.
Rock Mechanics
H. Mohammadi; H. Darbani
Abstract
There are various criteria that need to be examined alongside each other when designing a longwall mining system. Challenges such as determination of the supported roof width, support system design, caving height determination, lateral or chain pillar size determination, and optimum support design for ...
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There are various criteria that need to be examined alongside each other when designing a longwall mining system. Challenges such as determination of the supported roof width, support system design, caving height determination, lateral or chain pillar size determination, and optimum support design for the main gate and tail gate roadways have to be tackled for this aim. Three-dimensional analysis would deliver the highest accuracy of induced stresses around the longwall working area. Thus, the main purpose of this paper is to develop a three dimensional geometrical computing model (3GCM) for calculating the induced stresses in both longitudinal and transverse loading orientations of the extraction panel. 3GCM is capable of studying the changes of induced stresses along the longitudinal orientation of working and the lateral pillar as well as the induced stresses ahead and behind of the face. The proposed computational model, for analyzing the vertical induced stresses, was used in one of the longwall workings in the Parvade-2 coal mine of Tabas, Iran. Validation of 3GCM has approved its high efficiency for the analysis of induced stresses within the working as well as surrounding areas.
Rock Mechanics
H.C. ZHAO; H.J. An; M.S. Gao
Abstract
Both the deformation characters and the failure mode of the large cross-sectional longwall installation roadway under compound roof are becoming an emergent issue than ever before due to the rapid development of modern mining equipment. Various engineering applications have revealed that the insufficient ...
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Both the deformation characters and the failure mode of the large cross-sectional longwall installation roadway under compound roof are becoming an emergent issue than ever before due to the rapid development of modern mining equipment. Various engineering applications have revealed that the insufficient design and inappropriate support technology are the main reasons for the fatal accidents associated with the sudden roof fall attributed to the separation of the overlying compound strata. The present research work, therefore, starts with a case study using the conventional support technology in order to demonstrate the importance of this issue followed by a summarization of the typical failure mode of the longwall installation roadway under compound strata with varied thicknesses. Then a simplified theoretical model is proposed and set up aiming at a better understanding of the distribution of the elastic-plastic zones as well as the effects of different caving procedures. The finite element analysis software program FLAC3D is adopted to evaluate the effect of the caving method and the reinforcement provided by an additional support. Then a case study conducted at a typical coal mine with compound roof condition is presented to verify the advantages of the proposed design. The results obtained show that the optimized design presented in this research work is effective to control the deformation of the surrounding rock, particularly in terms of separation of the overlying compound strata.
Rock Mechanics
M. Hosseini; A. R. Khodayari
Abstract
The fracture mechanics examines the development and expansion of cracks in solids and how they affect the deformation of materials. The stress intensity factors at the tip of the crack and the critical stress intensity factors or fracture toughness of materials are considered in the relevant criteria. ...
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The fracture mechanics examines the development and expansion of cracks in solids and how they affect the deformation of materials. The stress intensity factors at the tip of the crack and the critical stress intensity factors or fracture toughness of materials are considered in the relevant criteria. There are three main modes of applying forces to a crack including the tensile mode, shear mode, and mixed mode. Mode II fracture toughness, which is also called the shear mode, is an important parameter for investigating the rock behaviors. This parameter is used in many different areas such as mining and tunneling. Several methods have been proposed for determining the mode II fracture toughness. In this work, the Punch-True-Shear (PTS) test, standardized by the International Society for Rock Mechanics, was used to determine the fracture toughness while the confining pressure is present. The studied sample was the Lushan sandstone. In this work, notchd cylindrical specimens were prepared for PTS testing. In order to investigate the effect of confining pressure, some tests were conducted in the presence of the confining pressures of 0, 3, 5, 7, and 10 MPa, and to check the effect of temperature, some tests were conducted under 1, 5, and 10 heating and cooling cycles at 60, 100, and 150 ˚C as well as at the ambient temperature (25 °C). The confining pressure of 3 MPa was used in all the tests to examine the effect of temperature. The analyses results showed that with increase in the confining pressure, the mode II fracture toughness and the fracture energy would increase as well. By increasing the number of heating-cooling cycles, the mode II fracture toughness as well as the fracture energy would decrease leading to a reduced fracture toughness and energy for all the three modes of heating specimens up to 60, 100, and 150 ˚C. The effect of the number of heating-cooling cycles on reducing the fracture toughness and fracture energy was greater than the effect of temperature.
Rock Mechanics
M. B. Eslami Andargoli; K. Shahriar; A. Ramezanzadeh; K. Goshtasbi
Abstract
During the recent decades, the design and construction of underground spaces into rock salt have been particularly regarded for storing petroleum fluids, natural gas, and compressed air energy, and also for disposing nuclear and chemical wastes. The rock salt hosting such spaces will be subjected to ...
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During the recent decades, the design and construction of underground spaces into rock salt have been particularly regarded for storing petroleum fluids, natural gas, and compressed air energy, and also for disposing nuclear and chemical wastes. The rock salt hosting such spaces will be subjected to various types of monotonic/cyclic, short-term/long-term stresses during the construction and/or operation phases. On this basis, it is necessary to investigate the mechanical behavior of the rock salt under the effects of various monotonic short-term/long-term stresses. Out of the most important factors affecting the creep behavior of rock salt are the composition of minerals and size of the crystals comprising the rock salt, humidity, temperature, time, loading scheme, loading rate, strain rate, and loading period. In the present research work, a loading scheme and a loading period were considered. On this basis, in order to achieve a true understanding of the creep behavior of rock salt, it is necessary to determine the creeping coefficients via laboratory tests. Thus, twenty cylindrical (length to diameter ratio > 2) specimens of rock salt were prepared for conducting the creep tests. Two stepwise short-term creep tests (each at three stress levels, namely 4.4, 10.1, and 11.9 MPa, and 7.5, 12, and 17 MPa, respectively) and eighteen long-term creep tests (at six stress levels, namely 5.5, 7.5, 10, 12, 14, and 18 MPa) were conducted. Then, first, the creep coefficients were determined according to the Lubby 2 constitutive model. These coefficients were adjusted using the results of the creep tests. Afterwards, a creep experimental model was presented using linear and nonlinear regression of the creep test data. For validation of the results obtained, both the adjusted Lubby 2 constitutive model and the proposed experimental model were compared with the results obtained for the creep tests. Both models had fairly good agreements with the data for the creep tests at a determination factor of about 93%.
Rock Mechanics
E. Farrokh
Abstract
The study of downtime and subsequently machine utilization in a given project is one of the major requirements of an accurate estimation of TBM performance and daily advance rate. Interestingly, while it is very common to report the components of downtime when discussing a tunneling project in the literature; ...
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The study of downtime and subsequently machine utilization in a given project is one of the major requirements of an accurate estimation of TBM performance and daily advance rate. Interestingly, while it is very common to report the components of downtime when discussing a tunneling project in the literature; there has not been a great amount of in-depth studies on this topic in the recent years. This work presents an in-depth analysis of the different components of hard rock TBM tunneling downtime on the basis of the information about several TBM tunneling projects from around the world including some that are underway or completed in the recent years. This includes the comparison of the recorded downtimes with those predicted by the existing models for these tunnels. The results of this comparison show that with the existing models, there is a poor correlation between the predicted and the actual downtime component values. This indicates that the existing models might be outdated or, in some cases, incompatible with the newly developed technologies. In order to provide a more accurate downtime model, an in-depth statistical analysis of the information about the same tunnels, used for the comparative studies, is conducted to develop the new “hard rock TBM downtime model”. This model includes a set of formulas and tables as well as some charts to predict different activities’ downtimes for three major hard TBM types including open TBM, single-shield TBM, and double-shield TBM. The comparison between the new model predictions and the actual values show a good agreement. The results of this work can be very helpful for the evaluation of time and cost to complete a TBM tunneling project, especially when the downtime is expected to be high.
Rock Mechanics
M. Noroozi; R. Rafiee; M. Najafi
Abstract
Various structural discontinuities, which form a discrete fracture network, play a significant role in the failure conditions and stability of the rock masses around underground excavations. Several continuum numerical methods have been used to study the stability of underground excavations in jointed ...
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Various structural discontinuities, which form a discrete fracture network, play a significant role in the failure conditions and stability of the rock masses around underground excavations. Several continuum numerical methods have been used to study the stability of underground excavations in jointed rock masses but only few of them can take into account the influence of the pre-existing natural fractures. In this work, the pre-existing fractures are explicitly modeled as a Discrete Fracture Network (DFN) model, which is fully coupled with the FEM modeling for stability analysis of support systems in a diversion tunnel at the Rudbar Lorestan dam site. Hence, at first, using the surveyed data in the diversion tunnel and an estimation of the suitable probability distribution function on geometric characteristics of the existing joint sets in this region, the 3D DFN model was simulated using the stochastic discrete fracture networks generator program, DFN-FRAC3D. In the second step, a coupled 2D Finite Element Method and the prepared stochastic model were used for analysis of existent (based on technical reports) recommended support systems. The objective here is to grasp the role of the fracture networks on the results of the tunnel stability analysis using FEM modeling and also to compare the results with those obtained through stability analysis without considering the effect of fractures.
Rock Mechanics
A. Turanboy; E. Ülker; C. B. Küçüksütçü
Abstract
The intersection lines between discontinuity surfaces and their intersection points on the visible surfaces of any engineering structure may be the instability indicators. This paper describes a new approach to modelling the intersecting lines and points that would provide the first evaluation of any ...
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The intersection lines between discontinuity surfaces and their intersection points on the visible surfaces of any engineering structure may be the instability indicators. This paper describes a new approach to modelling the intersecting lines and points that would provide the first evaluation of any instability in an engineering structure characterized by the failure modes. In this work, the intersection lines were grouped according to their direction either in the reverse or in the same direction as the dip of the slope. Furthermore, the intersection lines are grouped according to various ranges of the interior friction angle, which can be selected by the users in a computer application developed for this work. The orientation of the intersecting lines and the location of the exposed intersection points are defined and assigned as the scatter points. These exposed points are clustered to determine the centroid locations. The K-means clustering is used in this step. Finally, all these analyses are integrated in a logical order, and the results obtained are used to assess the instabilities on the slope surface. Experiments are carried out on a rock cut along the Konya-Antalya (Turkey) highway, which is composed of limestone, to demonstrate the performance and results of the approach. The locations of the possible failure zones in the critical range of the interior friction angle are defined both visually and numerically along the slope. Experiments show that the proposed method is very useful and easy to implement and yields practical preliminary evaluation results pertaining to instabilities according to the basic failure modes.
Rock Mechanics
M. T. Hamzaban; H. Memarian; J. Rostami
Abstract
Rock abrasivity is an essential factor for selecting cutting tools, estimating tool wear and life, and ultimately, matching various mechanized excavation systems with a given geologic condition. It also assists engineers to determine economic limits of different cutting tools and machines used in civil ...
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Rock abrasivity is an essential factor for selecting cutting tools, estimating tool wear and life, and ultimately, matching various mechanized excavation systems with a given geologic condition. It also assists engineers to determine economic limits of different cutting tools and machines used in civil and mining projects. The Cerchar abrasion test is a simple and most widely used method for rock abrasivity assessments. However, it has some shortcomings to describe the steel-rock interaction during the cutting process. In this work, two new parameters are used to describe the pin-rock interaction in the Cerchar abrasion test and to evaluate the efficiency of the rock scratching process. A set of 41 different rock samples are tested by a newly developed testing device. The device provides a more precise control of the testing operational parameters, and measures the applied frictional force on the pin and its horizontal and vertical displacements on the sample surface. The results obtained are used to calculate the Modified Cerchar Abrasion Index (MCAI) and the Scratch Energy Index (SEi), as two newly developed parameters. The accuracy of the calculated parameters is discussed. Our investigations show that MCAI has closer correlations with rock mechanical parameters than CAI, and therefore, has a higher potential to estimate the rock cutting tool wear in tunneling applications. Also SEi shows sensible correlations with sample hardness and mechanical properties. The results obtained show that SEi can be used to compare the efficiency of various pin hardnesses to create scratches on various rock samples, and could be used as a determinative parameter in selecting the cutting tool hardness.
Rock Mechanics
S. Moshrefi; K. Shahriar; A. Ramezanzadeh; K. Goshtasbi
Abstract
A rock failure criterion is very important for prediction of the ultimate strength in rock mechanics and geotechnics; it is determined for rock mechanics studies in mining, civil, and oil wellborn drilling operations. Also shales are among the most difficult to treat formations. Therefore, in this research ...
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A rock failure criterion is very important for prediction of the ultimate strength in rock mechanics and geotechnics; it is determined for rock mechanics studies in mining, civil, and oil wellborn drilling operations. Also shales are among the most difficult to treat formations. Therefore, in this research work, using the artificial neural network (ANN), a model was built to predict the ultimate strength of shale, and comparison was made with support vector machine (SVM), multiple linear regression models, and the widely used conventional polyaxial failure criteria in the stability analysis of rock structures, Drucker-Prager, and Mogi-Coulomb. For building the model, the corresponding results of triaxial and polyaxial tests have been performed on shales by various researchers. They were collected from reliable published articles. The results obtained showed that a feed forward back propagation multi-layer perceptron (MLP) was used and trained using the Levenberg–Marquardt algorithm, and the 2-4-1 architecture with root-mean-square-error (RMSE) of 24.41 exhibits a better performance in predicting the ultimate strength of shale in comparison with the investigated models. Also for further validation, triaxial tests were performed on the deep shale specimens. They were prepared from the Ramshire oilfield in SW Iran. The results obtained were compared with ANN, SVM, multiple linear regression models, and the conventional failure criterion prediction. They showed that the ANN model predicted ultimate strength with a minimum error and RMSE being equal to 43.81. Then the model was used for prediction of the threshold broken pressure shale layer in the Gachsaran oilfield in Iran. For this, a vertical and horizontal stress was calculated based on a depth of shale layer. The threshold broken pressure was calculated for the beginning and ending of a shale layer to be 154.21 and 167.98 Mpa, respectively.
Rock Mechanics
A. Akrami; M. Hosseini; H. Sodeifi
Abstract
Hydraulic fracturing is used in the oil industry in order to increase the index of production and processing in the wells whose efficiencies have been dropped due to a long-term harvest or the rocks around the wells are of low permeability. Since the hydraulic fracturing operation is costly, it is of ...
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Hydraulic fracturing is used in the oil industry in order to increase the index of production and processing in the wells whose efficiencies have been dropped due to a long-term harvest or the rocks around the wells are of low permeability. Since the hydraulic fracturing operation is costly, it is of special importance to the project managers to determine the pressure required for hydraulic fracturing and the suitable pump for this operation. The numerical modelings used in this work are aimed to investigate the fracture pressure in the carbonate rocks of Bangestan reservoir in Ahvaz, Iran, and to determine a relationship between the pressure required for fracturing and the confining pressure. In this work, unlike the other ones in this field, the developed numerical models had no initial crack or fracture, and the path of the crack and how the crack grows were studied without any pre-determination and presumption. The results obtained show that, in most cases, the crack starts from the central part of the sample, and is extended to its two ends. The crack extension direction was along the borehole axis inside the sample and perpendicular to the lateral stress. The numerical modeling results were well-consistent with the experimental ones, indicating that the pump capacity constraints in the laboratory could be overcome through numerical modelings.
Rock Mechanics
M. Rezaei
Abstract
Estimation of the height of caved and fractured zones above a longwall panel along with the stability conditions of the goaf area are very crucial to determine the abutment stresses, ground subsidence, and face support as well as designing the surrounding gates and intervening pillars. In this work, ...
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Estimation of the height of caved and fractured zones above a longwall panel along with the stability conditions of the goaf area are very crucial to determine the abutment stresses, ground subsidence, and face support as well as designing the surrounding gates and intervening pillars. In this work, the height of caving-fracturing zone above the mined panel is considered as the height of destressed zone (HDZ). The long-term estimation of this height plays a key role in the accurate determination of maximum ground surface subsidence and the amount of transferred loads towards the neighbouring solid sections. This paper presents a new stability analysis model of caved material system in the goaf area. For this aim, a theoretical energy-based model of HDZ determination in long-term condition is developed. Then the stability condition of the caved material system is investigated using the principle of minimum potential energy. On the basis of the actual data gathered from the literature, the unstable time period of the caved material system is also calculated. Moreover, the effects of time- and temperature-related parameters and constant coefficients as well as their inherent relations with HDZ are evaluated. Furthermore, sensitivity analysis shows that the two temperature-related constants material constant and time are the most effective variables in HDZ, and the slope of material hardening is the least effective one. The estimated HDZ and the stability time of the caved materials can be successfully applied to determine the induced stress and the maximum surface subsidence, respectively, due to longwall mining.
Rock Mechanics
M. Hosseini
Abstract
Temperature has a significant role in many actions performed on rocks. An example would be the effect of temperature on rocks in the burial of nuclear waste, geothermal energy extraction, deep oil well drilling, and fires in tunnels. In addition, due to diurnal/nocturnal as well as seasonal temperature ...
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Temperature has a significant role in many actions performed on rocks. An example would be the effect of temperature on rocks in the burial of nuclear waste, geothermal energy extraction, deep oil well drilling, and fires in tunnels. In addition, due to diurnal/nocturnal as well as seasonal temperature variations, rocks undergo a process of heating and cooling. In the present work, the effect of temperature as well as heating and cooling cycles on the rock properties was studied. The utilized samples included tuff, andesite, and sandstone. In addition to natural samples, concrete was also studied in this research work. The aim of this work was to evaluate the effect of temperature on the tensile strength of rocks and the velocity of longitudinal waves in a single heating and cooling cycle of samples as well as evaluating the effect of the number of heating and cooling cycles on the tensile strength of rocks and the velocity of longitudinal waves. In order to investigate the effect of temperature on the tensile strength of rocks as well as the velocity of longitudinal waves in a single heating and cooling cycle, the samples were heated in a furnace. After cooling the samples, the Brazilian and the sound velocity tests were carried out on them. These tests were conducted at the three temperatures of 100, 200, and 300 °C. In order to examine the effect of the number of heating and cooling cycles on the tensile strength and the velocity of longitudinal waves, the samples were heated up to the temperature of 100 °C and then cooled down in order to reach the room temperature. In this case, the work was conducted in the three modes of 5, 10, and 15 cycles. The test results showed that the velocity of longitudinal waves and the tensile strength of samples decreased but their porosity increased. Reduction in the tensile strength varied in different rocks so that the greatest and lowest reduction in the tensile strength was observed in concrete and andesite, respectively.
Rock Mechanics
M. H. Khosravi; T. Pipatpongsa; J. Takemura; M. Amini
Abstract
A series of physical modeling tests were conducted by means of a beam type geotechnical centrifuge machine in order to investigate the drainage impact on the slope failure mechanism under centrifugal acceleration. Meanwhile, the phenomenon of stress redistribution in undercut slopes and the formation ...
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A series of physical modeling tests were conducted by means of a beam type geotechnical centrifuge machine in order to investigate the drainage impact on the slope failure mechanism under centrifugal acceleration. Meanwhile, the phenomenon of stress redistribution in undercut slopes and the formation of arching effect were studied. For this purpose, a poorly graded sandy soil (Silica sand No. 6) as well as a relatively well-graded sandy soil (Edosaki sand) were used as the modeling materials. The humid modeling material was compacted on a low friction oblique rigid plate simulating the potential slippage plane. The process of undercutting was conducted, while the earth pressure redistribution inside the model was recorded by means of a miniature set of pressure cells. The results obtained showed completely different failure mechanisms for the two different modeling soils. By undercutting the slope, the earth pressure redistributed and the arch action was formed in a slope model made from a well-graded soil leading to a clear arch-shaped failure. However, in using the poorly graded soil, the water was drained out during centrifuge g-up, the modeling material properties changed, and an avalanche failure was observed. Therefore, in selecting a humid compacted soil as the centrifugal modeling material, a well-graded soil is recommended.
Rock Mechanics
M. M. Samieinejad; N. Hosseini; K. Ahangari
Abstract
In order to analyze the slope stability in open-pit mines, the structural parameters of rock mass such as persistence and spatial orientation of discontinuities are characterized through field surveys, which involve spending high costs and times as well as posing high risks of rock toppling and rock ...
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In order to analyze the slope stability in open-pit mines, the structural parameters of rock mass such as persistence and spatial orientation of discontinuities are characterized through field surveys, which involve spending high costs and times as well as posing high risks of rock toppling and rock fall. In the present work, a new application of terrestrial digital photogrammetry is introduced for characterizing the rock mass structural parameters through preparing photogrammetry images from open-pit walls and building stereomodels. The data extracted from processing the stereo-model generations using photogrammetry images with different focal distances are highly consistent with the data collected through field surveys. However, it must be noted that the weather conditions, natural lighting angle, and applied observation scale may considerably affect the results obtained from stereomodel processing. Nevertheless, by taking into account the parameters such as time, cost, and full access to the required data, this new method can effectively be used in the estimation of rock mass structural parameters for analysis of steep slopes in open pits.
