Rock Mechanics
Dariush Kaveh Ahangaran; Kaveh Ahangari; Mosleh Eftekhari
Abstract
Blast damage on the stability of the slopes plays an important role in the profitability and safety of mines. Determination of this damage is also revealed in the widely used Hoek-Brown failure criterion. Of course, this damage is used as a moderating factor in this failure criterion, and its accurate ...
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Blast damage on the stability of the slopes plays an important role in the profitability and safety of mines. Determination of this damage is also revealed in the widely used Hoek-Brown failure criterion. Of course, this damage is used as a moderating factor in this failure criterion, and its accurate determination is considered an important challenge in rock engineering. This study aims to investigate the effect of geological structures in blast damage factor using 3D discrete element modeling of two slopes with different directions of geological discontinuities. The dynamic pressure of the explosion is also simulated in three blastholes. To ensure the modeling results, other dynamic properties of the model have been selected based on the proven studies. An analytical analysis was conducted based on the failure zones (blast damage area), and quantitative and qualitative analyses were performed using the recorded PPV values during the blasting simulation. The results show that the geological discontinuities control, damp, and reduce blast damage. The expansion of blast damage is reduced by 75% along with the increase in rock mass strength, and the blast damage can expand up to 33 meters along with the decrease in strength. By reducing the distance of discontinuities, the role of discontinuities in damping becomes greater than other properties of the rock mass and the discontinuities further away from the blasting hole create more damping. The relation between the distance from the Hole and PPV values shows that for more realistic slope stability analysis results, the values of the damage factor in the Hoek-Brown failure criterion should be applied gradually and decreasingly in layers parallel to the slope surface.
Bijan Afrasiabian; Kaveh Ahangari; Ali Noorzad
Abstract
High-level vibrations caused by blasting operations in open-pit mining can exert adverse effects such as destruction of surrounding surface structures. Therefore, it is essential to identify the factors effective in mitigating the damaging effects of ground vibration in open-pit mines, and monitor them. ...
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High-level vibrations caused by blasting operations in open-pit mining can exert adverse effects such as destruction of surrounding surface structures. Therefore, it is essential to identify the factors effective in mitigating the damaging effects of ground vibration in open-pit mines, and monitor them. This study investigates the effects of some of the most important blast design parameters in a row of blast holes. According to the advantages of numerical methods, the 3D discrete element method is employed for this purpose. The Peak Particle Velocity (PPV) values are measured along the central hole at the distances of one meter. The results obtained demonstrate that an increase in the blast damage factor and inter-hole delay time results in higher PPV values. However, the increased delay time has no remarkable effect on reducing the development of the blast damage zone. On the other hand, as the decoupling increases, the PPV values diminish, leading to substantial reductions in the ground vibration and rock mass damage. It is also observed that the elimination of sub-drilling does not significantly reduce ground vibrations. The analysis of the results obtained from the numerical modeling show that the discontinuities of the rock mass act as a filter, which could decrease the wave energy by more than 90%. Moreover, it is found that the direction of the discontinuities also affects the emission of waves caused by the blast. The PPV values are reduced, and the damaged zone is less developed if the discontinuities are opposite of the slope surface.
Seyed Ahmad Mousavi; Kaveh Ahangari; Kamran Goshtasbi
Abstract
Blast and stress release create cracks, fractures, and excavation damage zone in the remaining rock mass. Bench health monitoring (BHM) is crucial regarding bench health and safety in blast dynamic loading. Several empirical criteria have been proposed for a quick estimation of different parameters of ...
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Blast and stress release create cracks, fractures, and excavation damage zone in the remaining rock mass. Bench health monitoring (BHM) is crucial regarding bench health and safety in blast dynamic loading. Several empirical criteria have been proposed for a quick estimation of different parameters of a rock mass in the zone damaged by the blast. This work estimates the rock mass properties behind the blast hole based on the generalized Hoek-Brown failure criterion and quantitative disturbance factor (D). Considering a constant D value, either zero or one, for the entire rock mass, remarkably alters its strength and stability, resulting in very optimistic or very conservative analyses. Therefore, D is considered based on the elastic damage theory, and numerical simulation is conducted based on the finite difference software FLAC to investigate the vibration and damage threshold by monitoring the peak particle velocity (PPV) in the bench domain with different geometries. According to the numerical simulation, as the depth behind the blast hole increases, the value of D decreases from one to zero almost non-linearly, resulting in a non-linear reduction in the Hoek-Brown behavioral model properties. It is found that using various parameters of rock mass in the blast-induced damage zone behind the hole leads to thoroughly different PPV values than the constant parameters. Accordingly, the approach to using the quantified values of parameter D is of great importance in the estimation of various properties of a rock mass in the blast-induced zone, as well as calculation of the vibration.
Seyed M. Pourhashemi; K. Ahangari; J. Hassanpour; Seyed M. Eftekhari
Abstract
Mechanized tunneling in rocks is based on fracture propagation and rock fragmentation under disc cutters. Rock chipping is an efficient kind of fragmentation process, while the grinding process may occur under special conditions. The cutter-head penetration is an appropriate parameter involved in order ...
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Mechanized tunneling in rocks is based on fracture propagation and rock fragmentation under disc cutters. Rock chipping is an efficient kind of fragmentation process, while the grinding process may occur under special conditions. The cutter-head penetration is an appropriate parameter involved in order to distinguish between the chipping and grinding processes in rock cutting. In this work, the grinding and chipping processes are investigated in the Uma-Oya water conveyance tunnel in Sri Lanka. The Uma-Oya project is a water transfer, hydropower, and irrigation system in the SE part of the central highland region of Sri-Lanka. From a geological viewpoint, most parts of the tunnel route in the studied section consist of very strong and abrasive metamorphic rocks that potentially are susceptible to grinding occurrence during the boring process under disc cutters. In this work, firstly, data processing is performed in order to identify the boundary between chipping and grinding. Then the chipping and grinding processes are modeled using the practical numerical and artificial intelligent methods. In the numerical modeling stage, we try to make the modeling as realistic as possible. The results obtained from these modeling methods show that for the penetrations less than 3 mm/rev, the grinding process is dominant, and for the penetrations more than 3 mm/rev, rock chipping occurs. Also, in the numerical modeling, no significant fracture expansion is observed in the rock when the penetration is less than 3 mm/rev. Moreover, it can be seen in the numerical modeling of the chipping process that the propagated fractures come together and the chips are created.
Gh.H. Ranjbar; K. Shahriar; K. Ahangari
Abstract
Although segmental tunnel linings are often used for seismic areas, the influence of segment joints on the segmental lining behavior under seismic loading has not been thoroughly considered in the literature. This paper presents the results of a numerical study investigating the effects of the rotational, ...
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Although segmental tunnel linings are often used for seismic areas, the influence of segment joints on the segmental lining behavior under seismic loading has not been thoroughly considered in the literature. This paper presents the results of a numerical study investigating the effects of the rotational, axial, and radial joint stiffness of the longitudinal joints on the structural forces in segmental tunnel lining under seismic loading. A 3D finite element method is adapted to establish elaborate numerical models of the segments. The validity of the numerical model was tested by comparing the results obtained with the well-known analytical methods presented by Wang and Penzien. The results demonstrate that by increasing the rotational stiffness of the segmental joint, the bending moment increases. When the rotational stiffness ratio is less than 0.5, the positive and negative bending moment variations are more. The numerical modeling results show the variations in the bending moment and the difference between the positive and negative bending moment values increased by increasing the acceleration of seismic loading. Moreover, it is significant for the values. By increasing the rotational stiffness ratio of the segmental joint, the axial force ratio decreases. By increasing the axial and shear stiffness ratio of segmental joint, the variations in the bending moment and axial force in segmental lining is not significant and is ignorable in designing segmental lining.
R. Satari; A. Akbari Dehkharghani; K. Ahangari
Abstract
Within the last few decades, copper has been identified as one of the most applicable metals by many researchers. These researchers have also been enthusiastic to predict the price of this valuable metal. These days, the available technical analysis methods have been highly applied in the financial markets. ...
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Within the last few decades, copper has been identified as one of the most applicable metals by many researchers. These researchers have also been enthusiastic to predict the price of this valuable metal. These days, the available technical analysis methods have been highly applied in the financial markets. Moreover, the researchers have used these methods to predict the suitable price trends. In the present work, some technical analysis tools including the Fibonacci series, Elliott waves, and Ichimuko clouds were practiced to scrutinize the price changes and predict the copper price. All copper prices from 2008 to 2016 were considered. Regarding the fractal property of these methods, the relations among prices were obtained within an eight-year time sequence. Since 2016, the copper price has been gradually deviated from its previous trend. Using the wave count and Elliott waves has specified that the wave number 1 and wave number 2 have been completed. Now, the time has come to develop the wave number 3. According to the relations introduced by the Elliott waves and the clouds made by Ichimiku, it was determined that the copper price would be almost $16000 per ton in 2022.
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
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.
