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Collaborating Authors
Isfahan University of Technology
Digitisation of Hard Rock Tunnel for Remote Fracture Mapping and Virtual Training Environment
Janiszewski, M. (School of Engineering, Aalto University) | Uotinen, L. (School of Engineering, Aalto University) | Rinne, M. (School of Engineering, Aalto University) | Baghbanan, A. (Isfahan University of Technology)
Abstract The knowledge of geometrical properties of discontinuities is of crucial importance in the rock mass characterisation process. Recent advances in photogrammetry allow for an easy digitisation procedure of rock surfaces so that digital 3D models can be used for remote site characterisation. This paper presents a methodology to digitise tunnel rock surfaces using Structure from Motion digital photogrammetry for remote measurements of discontinuities. The proposed method is applied on a 12 m long and 4 m high tunnel section of an underground research tunnel at Aalto University in Finland, which is scanned using Canon 5Ds R DSLR camera and Canon 14 mm f/2.8 and 35 mm f/1.4 lenses. The photos are then processed in commercially available photogrammetric software โ RealityCapture. As a result, a high-resolution 3D point cloud of the tunnel wall is produced. The point cloud is used for semi-automatic measurements of fracture orientations. In addition, a digital twin of the tunnel section with photorealistic surface texture is created and implemented into virtual reality (VR) system โ Virtual Underground Training Environment (VUTE) developed for training of rock mass characterisation. The VUTE system enables remote visual inspection of the rock surface and virtual measurements of the orientation of discontinuities with designated virtual tools. The semi-automatic measurements extracted from the 3D point cloud using a discontinuity extractor software are compared with measurements performed in VR as well as with manual measurements performed in the tunnel. The results demonstrate that all three mapping methods identify three major joint sets with analogous orientations. The automatic fracture mapping method achieves the highest density of the measurements, allows repeatability, and enables other parameters to be extracted automatically, such as persistence and spacing of the discontinuities. This confirms the advantage of automatic analysis of discontinuities on 3D point clouds of tunnel rock surface digitised using photogrammetry. 1 Introduction The discontinuities in the rock mass are one of the most critical factor that governs its geomechanical behaviour. Because of that, the knowledge of the geometrical and mechanical properties of discontinuities is a crucial component in the design of stable underground structures (Hudson & Harrison, 2000). The orientation of discontinuities is typically mapped manually using a geological compass at rock outcrops. However, manual mapping of discontinuities has several limitations. First, the timeframe for the measurements is constrained, especially in underground tunnels due to time pressure of excavation cycles. Second, it is also limited to only the accessible tunnel faces. Most importantly, manual fracture mapping is biased due to human factors, such as previous experience or motivation of the person doing the measurements (Gaich et al. 2003).
- Europe > United Kingdom > England (0.28)
- Europe > Finland (0.25)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type (0.87)
ABSTRACT One of the best techniques employed in ground reinforcement is grouting which concerns complex characteristics and factors. There are few reported researches about physical modeling of grout spreading in fractured media. However, they have not addressed the effect of multiple operational and structural parameters on grout spreading in different discrete fracture network patterns around an injection wellbore. Since there are many different parameters, which control grout spreading in fractured media, laboratory experiments can help to identify the most effective ones. In this research, Taguchi experimental design was used to study grouting on laboratory scale. The experiments consider various discrete fracture network features. Fracture network, grout viscosities, injection pressure, and time were considered to calculate grout spreading in a pipeline system. According to the statistical analysis and the confident level of the statistical tests, the effect of operation parameters on grouting is more significant compared to that of the geometrical properties of fractured rock mass. In other words, geometrical parameters of fracture network affect grouting process to some extent but the impact of operational parameters is more dominant.
- Asia > Middle East > Iran (0.29)
- Europe > Finland (0.19)
Abstract In this paper, the forces acting on tunnel lining due to dry condition and groundwater pressures were studied. Firstly, the effect of the forces acting on tunnel lining under dry condition was studied numerically for the Sabzkouh tunnel as an actual case study. This tunnel is a deep tunnel that is bored through Zagros Mountains in Iran by a hard rock Tunnel Boring Machine (TBM). Secondly, the effect of hydrostatic pressures on tunnel lining was evaluated. The lining of a bored tunnel usually consists of precast concrete segments that are reinforced by steel bars. These segments must be capable to withstand all loads caused by earth (e.g. rock and water pressures), construction conditions (e.g. thrust forces) and utilization (e.g. traffic loads) without unallowable deformations. A Finite difference code was used to analyze Sabzkouh tunnel lining. The final results show that the values of bending moments, axial forces and shear forces in the precast concrete lining can be reduced under fully-drained conditions, although, the drainage is more effective in weak rocks rather than strong rocks. 1. Introduction In recent years, mechanized tunneling has developed increasingly, and the benefits of full-face tunnel boring machines have been recognized. Design methods for segmental tunnel linings used in mechanized tunnel constructions typically employ numerical bedded beam models and/or classical analytical solutions for the determination of structural forces (i.e. moments and shear and axial forces) and simple load spreading assumptions for the design of the reinforcement in joint areas (Gall et al., 2018). Basically, the forces acting on the tunnel lining depend on construction procedures and in many cases, these forces enhances during construction rather than after construction. The measurement of the induced bending moments and normal forces are difficult, but the numerical analyses give more reliable results than analytical and closed form solutions. The behavior of lining segments is affected by the complex construction features, for example the sequential excavation process and backfill grouting. Therefore, developing a framework to accurately predict the lining forces and deformations is essential for the purpose of structural safety and optimum design (Zhao et al., 2017).
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Materials > Construction Materials (0.89)
- Energy > Oil & Gas > Upstream (0.69)
- Water & Waste Management > Water Management > Water Supplies & Services (0.46)
Stress-Dependent Perforation in Carbonate Rocks: An Experimental Study
Norouzi, Peyman (Isfahan University of Technology) | Hashemolhosseini, Hamid (Isfahan University of Technology) | Baghbanan, Alireza (Isfahan University of Technology)
Summary Perforation with shaped charges as a conventional well-completion technique is widely used in the oil industry. Different phenomena influence perforation performance and depth of penetration (DOP). The authors examined the effect of in-situ stresses and shot density on DOP and created fracture patterns in concrete and limestone samples with surface and polyaxial/triaxial-stress-loading conditions. To achieve this aim, we designed and developed a polyaxial-perforation test machine. We optimized the number of experimental tests using the Taguchi-design test method. The Taguchi orthogonal scheme is well-known and is a highly recommended method to optimize the number of required experiments (Taguchi 1990; Ross 1996; Jeyapaul et al. 2005; Gupta et al. 2014). Our experimental setup resembles vertical wells in the strike/slip-faulting regions and horizontal wells in the reverse-faulting regions. The results show that DOP is more controlled by stresses normal to the shooting direction in polyaxial tests than by the stress in the direction of penetration. DOP and the maximum hole diameter from the second charge had a direct relation with shot density. The DOP observed in polyaxial-loading conditions was a little lower than in the triaxial-loading mode, where the mean value of stresses normal to the shooting direction in the polyaxial tests was the same as the horizontal stresses in the triaxial tests. In both surface and triaxial-loading conditions, the patterns of perforation fractures were radial and regular, whereas the cracks created were oriented along the direction of maximum horizontal stress in the polyaxial tests.
- North America > United States (1.00)
- Europe (1.00)
- Asia > Middle East > Iran (0.47)
- Research Report > Experimental Study (1.00)
- Research Report > New Finding (0.84)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (0.31)
In this work, a new method is proposed for production of double-curvature domeshaped part. Also, the effects of process parameters on radius of curvature of the obtained dome-shaped part are investigated experimentally. The Taguchi experimental design method is employed to study various parameters, which significantly affect the amount of radius of curvature in the laser forming of a doubly curved dome-shaped part. The length of irradiating line, number of irradiating lines, laser beam diameter, laser output power, and scanning speed are considered in the evaluations. AL27(3) Taguchi standard orthogonal array is chosen for the design of experiments. The level of importance of the process parameters on the radius of curvature is determined by using analysis of variance. The optimum process parameters combination is obtained by using the analysis of signal-to-noise (S:N) ratios. The variation of radius of curvature of the obtained dome-shaped part with process parameters is mathematically modeled by using the regression analysis method and a closed form equation is derived. The results show the length of irradiating line, number of irradiating lines, laser output power, laser beam diameter, and scanning speed have the most importance effects on the radius of curvature of the obtained dome-shaped part, respectively. Also, it is concluded from results that there is an optimum length for irradiating line that leads to minimum radius of curvature of obtained dome-shaped part. 1. Introduction Laser forming is a flexible forming process that needs no hard tooling or external forces. Laser forming is used in many sheet metal processes such as bending and spatial forming of plates and alignment of metallic and nonmetallic components. in laser forming, a sheet is irradiated with a defocused laser beam, thereby inducing rapid localized heating followed by cooling as the laser beam moves on to an adjacent area. in the heating stage, if the thermal strains in the irradiated zone exceed the elastic strains, then these strains are converted into plastic compressive strains. in the cooling stage, the sheet will undergo shrinkage and therefore a complex shape of the workpiece can be formed. Many of researches in the field of laser forming have been focused on two-dimensional (2D) laser forming. However, in order to advance the process further to industrial applications, it is necessary to study and digest three-dimensional (3D) laser forming. 3D laser forming is very complicated in comparison with 2D studies, and therefore few researches have been reported in this field. Ueda et al. (1994) proposed a strain-based method for line heating of a plate. Using finite element method, they computed strains and decomposed the strains into the in-plane and bending strains. Then the regions with large in-plane strains were selected as heating zones and heating direction was selected normal to the minimum principal strain. Jang and Moon (1998) developed an algorithm to determine heating lines for plate forming by line heating method. They first calculated the lines of curvature of a prescribed surface and evaluated the points of extreme principal curvatures along the lines. They then classified and grouped those points based on their principal directions and their distances. They obtained heating lines by linear regressions on the grouped points. Yu et al. (2000) presented algorithms for optimal development of a smooth continuous curved surface into a planar shape. The development process is modeled by in-plane strain from the curved surface to its planar development. Ishiyama and Tango (2000) proposed a method to determine heating paths where the heating lines for bending strain and in-plane strain are independently calculated by using two procedures:contour heating method and conversion algorithm to the orthogonal compressive inherent strain. Hennige (2000) investigated the differences in the forming behavior of sheet metal parts using straight and curved irradiations. Also, using radial and circular laser scan paths, he produced a dome-shaped plate from a circular blank. Shin and Lee (2002) proposed a nondimensional relationship between input parameters and final deformation during line heating process by using the flame heat. Kim (2009) developed a method which is reliable and easy to apply, to solve the inverse problem in the laser forming process. They proposed a distance-based method and an angle-based method to generate an irradiation path strategy and to obtain desired angles at each irradiation path. Liu et al. (2004) suggested an optimal process planning strategy to determine scanning paths and heating condition for laser forming of general doubly curved shapes. They also studied two distinctive types of doubly curved surfaces, pillow, and saddle shape, and validated their proposed methodology by experiments. Zhang et al. (2007) simulated laser forming of a plate with a B-spline curve path. They also investigated various temperature fields, displacement fields, and stress and strain fields. Their results showed that peak temperatures of the upper surface and the warped curvature increase when the path curvature increases. Kim and Na (2003) proposed a new method for 3D laser forming of sheet metals. Their method used geometrical information rather than a complicated stress-strain analysis. Using this method, they showed that total calculation time is reduced considerably while provided enhanced accuracy. Chakraborty et al. (2012) used a combination of radial and circular laser scan paths and produced a bowl-shaped surface. Also, they investigated the effects of various process parameters, such as laser spot diameter, laser power, and scan speed, on the in-plane and out-of-plane forming of stainless steel circular blanks for various circular and radial scan schemes. In the all of previous researches that were mentioned earlier, there was not suggested a comprehensive and easy method for production of doubly curved dome-shaped part. Some of them have limited capabilities in the production of doubly curved shapes and the other have very much complexities in the prediction of heating lines for proposing an irradiating scheme. Also, heating lines that are suggested with those methods are very complex curves and some of them are difficult to use in a CNC controller.
- Asia > Middle East > Iran (0.46)
- North America > United States (0.28)
- Research Report > New Finding (1.00)
- Research Report > Experimental Study (1.00)
A new reference model for 3D inversion of airborne magnetic data in hilly terrain โ A case study from northern Sweden
Abtahi, Sayyed Mohammad (Isfahan University of Technology) | Pedersen, Laust Bรถrsting (Uppsala University) | Kamm, Jochen (University of Mรผnster) | Kalscheuer, Thomas (Uppsala University)
ABSTRACT The inherent nonuniqueness in modeling magnetic data can be partly reduced by adding prior information, either as mathematical constructs or simply as bounds on magnetization obtained from laboratory measurements. If a good prior model can be used as a reference model, then the quality of estimated models through an inverse approach can be greatly improved. But even though data on magnetic properties of rocks might exist, their distribution may often be quite irregular on local and regional scales, so that it is difficult to define representative classes of rock types suitable for constraining geophysical models of magnetization. We have developed a new way of constructing a reference model that varies only laterally and is confined to the part of the terrain that lies above the lowest topography in the area. To obtain this model, several estimated 2D magnetization distributions were constructed by data inversion as a function of the iteration number. Then, a suitable 2D model of the magnetization in the topography was chosen as a starting point for constructing a 3D reference model by modifying it with a vertical decay such that its average source depth was the same for all horizontal positions. The average source depth of the reference model was chosen to satisfy the average source depth obtained from analyzing the radial power spectrum of the area studied. Finally, the measured magnetic data were inverted in three dimensions using the given reference model. For a selected reference model, shallow structures indicated a better overall correlation with large remanent magnetizations measured on rock samples from the area. Throughout the entire model, the direction of magnetization was allowed to vary freely. We found that the Euclidean norm of the estimated model was reduced compared with the case where the magnetization direction was fixed.
- Europe > Sweden (0.65)
- Asia > Middle East > Iran (0.46)
- Geology > Rock Type > Igneous Rock (0.46)
- Geology > Mineral > Native Element Mineral (0.46)
- Geology > Structural Geology > Tectonics (0.46)
- North America > United States > New Mexico > San Juan Basin (0.99)
- North America > United States > Colorado > San Juan Basin (0.99)
- North America > United States > Arizona > San Juan Basin (0.99)
- (2 more...)
Effects of Matrix Permeability and Fracture Density on Flow Pattern in Dual Porous Rock Masses
Namdari, S. (Isfahan University of Technology) | Baghbanan, A. (Isfahan University of Technology) | Habibi, M. J. (Isfahan University of Technology)
ABSTRACT: In this paper, effect of matrix permeability and fracture density on flow pattern and overall permeability is presented. According to the literature, dual fracture method (DFM) is an efficient numerical method for investigating the flow in dual porous mediums. In this method, matrix permeability is presented with polygons called voronoi elements (VE) and discrete fracture network (DFN) is used to show fracture system. It is expected that a permeable matrix has to lead to higher overall permeability. Effects of fracture density and aperture patterns on overall permeability and representative elementary volume (REV) have been studied as well. Using a computer code based upon Monte Carlo simulation technique, DFNs with different aperture patterns and densities were generated with regard to real field data. All these models were numerically analyzed via computer code using Distinct Element Method (DEM). The results show that permeability increases with fracture density and with adding permeable matrix to the model, huge increases in overall permeability occur in most cases. Also it was revealed that there is a relationship between overall permeability and DFN aperture pattern. With increasing the density of fractures, REV decreased as well. 1 INTRODUCTION Understanding flow process in naturally fractured dual porous media is of interest in environmental engineering applications, in geohydrology or in oil reservoirs engineering, when porous material is made of rocks, which is crossed by networks of fractures. Recently, fractured rocks attracted the attention in connection with the problem of geological isolation of radioactive waste. Dual porous media often exhibit a variety of heterogeneities, such as fractures, fissures, cracks, and macro-pores or inter-aggregate pores. The granular rock mass consists of solid rock, cut by a network of fractures. Water flows unevenly through an intricate network of paths formed by fracture intersections and micro-channels between matrix blocks or grains (Jourde et al. 2002). Recently, permeability of the matrix is becoming progressively more important. Previously, due to computing limitations, it was accepted that permeability of the matrix is so low and it can be neglected. But with advances in earth sciences for the past few years, precision and reliability in predicting the overall permeability became more important in earth projects and matrix permeability is an important factor for a precise calculating and predicting of the overall permeability. There are some methods to study a Dual Permeability Medium. In 1993, Zimmerman (Zimmermann et al. 1993) created a numerical model for dual porosity mediums. In the same year a simple but useful numerical method was developed to estimate the overall permeability in a Dual Porosity-Dual Permeability medium by Priest. Bai expanded an analytical solution for flow in oil reservoirs in 1994. Different types of fracture geometry such as connected and unconnected fracture systems in a Dual Permeability Medium were investigated by Odling (Odling 1997).
Abstract Fluid flow in fractured rock is controlled by flow paths in a network of discrete pre-existing fractures. The same can be said for fracture networks induced by loading or unloading. In both cases, or in the combined case, the determination or evolving modification of an equivalent permeability tensor is necessary for up-scaling the equivalent continuum hydro-mechanical properties of a fractured rock. The evolution of fracture aperture during shearing and the associated dilation process control the permeability of single fractures and fracture networks. In order to understand this process, a number of rotated Discrete Fracture Networks is generated with different mean fracture orientations. Permeability tensors are calculated, from distinct element hydro-mechanically coupled models, when initial fracture apertures are correlated with fracture trace length in 2D models at different stress ratios. A non-linear behavior between normal stress-normal displacements of fractures is adopted so that both scale and stress-dependent normal stiffness of the fractures can be considered. The results show that overall permeability continued to decrease, with the increase of stress ratio, when zero dilation is assigned to the fractures. However, when the dilation mechanism of the fractures is modeled, equivalent permeability decreases with increasing stress magnitudes when stress ratio is not large enough to initiate shear dilation processes in a fracture. In this case, normal closure of the fractures is the dominating mechanism for decreasing the overall permeability of models. When stress ratios increased up to k=3 or higher, most of the fractures will experience shear dilation with increasing overall flow rates of models. Flow rate distribution at different stress ratios show that a small number of large fractures with large initial aperture values remains conductive in all stress conditions and control the permeability and flow pattern of the models significantly. With increasing stress ratios, it becomes more and more difficult to establish an equivalent permeability tensor, compared with the non-stressed model. For models with non-zero values of fracture dilation angle, the existence of permeability tensor is not affected by changing in the magnitude of dilation angle when small stress ratio is applied. However, when stress ratio increases up to k=3 or higher, the values of dilation angles lead to additional contributions from shear dilations of fractures which become the main reason for increasing of permeability, compared to the models with lower dilation angle.
- Asia > Middle East > Iran (0.28)
- North America > United States > California (0.28)
- Research Report > New Finding (0.88)
- Research Report > Experimental Study (0.66)
Estimation of Rock Mass Deformation Modulus in Bakhtiary Dam Project in Iran
Sanei, M. (Isfahan University of Technology) | Rahmati, A. (Isfahan University of Technology) | Faramarzi, L. (Isfahan University of Technology) | Goli, S. (Isfahan University of Technology) | Mehinrad, A. (Bakhtiary Joint Venture Consultants (BJVC))
Abstract The deformation modulus of rock mass is an important parameter for the design of underground structures and foundations. In this study, 3 new equations with statistical analyses were developed for estimation of rock mass deformation modulus using a database of 47 plate loads, 86 dilatometers and 9 flat jack tests in Bakhtiary Dam Project in Iran. Finally, by data processing and the statistical analyses, the best new equation was suggested for the estimation of deformation modulus in Bakhtiary Dam. Introduction Deformation modulus is one of the most important parameters in rock engineering projects. The deformation modulus of a rock mass is measured by in situ tests, such as dilatometer and plate load or flat jack tests. Also, in situ tests are expensive and time-consuming. Therefore, the deformation modulus of a rock mass is often estimated indirectly from classification systems. Many authors have developed several empirical models for estimation the deformation modulus by classification systems such as RMR, Q, GSI, RQD and RMI like Bieniawski, 1978; Serafim and Pereira, 1983; Nicholson&Bieniawski, 1990; Mehrotra, 1992; Grimstad & Barton, 1993; Mitri et al., 1994; Hoek & Brown, 1997; Read et al., 1999; Palmstrom & Singh, 2001; Barton, 2002; J. Carvalho, personal communication, 2004; Galera et al., 2005; Hoek & Diederichs, 2006. Also, Mohammadi & Rahmannejad, 2009 and Khabbazi et al., 2012, estimated rock mass deformation modulus by using regression and artificial neural networks analysis and a rock mass classification system, respectively.
- Asia > Middle East > Iran (1.00)
- South America > Colombia > Risaralda Department > Pereira (0.25)
- Geology > Geological Subdiscipline > Geomechanics (0.74)
- Geology > Rock Type (0.48)
ABSTRACT After a period of 12 years of operation of the cathodic protection system in a gas compressor stations, the CP potential distribution had changed for various reasons, such as pipelines coating degradation, isolating flanges failures, alterations in pipeline systems, and reinforced concrete foundation (RCF) systems. Isolating flanges failures creates galvanic corrosion between the pipelines and the Cu grids of the earthing system, and the steel rods in the RCF, which consumes part of the CP currents, thus non-uniform potential distribution. The extent of CP current required had become so high that was beyond the capacity of the rectifiers. Some areas had become seriously underprotected and some others seriously overprotected. Meanwhile the interference with other neighboring foreign buried pipeline, also had increased. In this paper the results of correcting measures for these problems is reported.
- North America > United States > Texas (0.20)
- Asia > Middle East > Iran (0.15)