| 1. |
- Zhang, Zhiqiang, et al.
(författare)
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Numerical Simulation of a Round Determinate Panel Test of Combined Concrete Panel and Welded Wire Mesh
- 2018
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Ingår i: Paper presented at the ISRM International Symposium - 10th Asian Rock Mechanics Symposium, Singapore, October 2018. - : International Society for Rock Mechanics and Rock Engineering / Society for Rock Mechanics and Engineering Geology.
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Konferensbidrag (refereegranskat)abstract
- The sprayed concrete layer, together with external welded wire mesh, has been widely used as an important surface support in underground excavation in civil and mining engineering. Recently, the load carrying capability of combined concrete layer and welded wire mesh was evaluated by a round determinate panel (RDP) test. However, performance assessment by using RDP specimens is hindered by the testing boundary condition and the failure pattern and mechanism of combined concrete layer and welded wire mesh remains unclear. In this paper, the numerical model of the RDP test was set up by means of a FEM code, ABAQUS, and a series of numerical tests were carried out to investigate the failure mechanism and the influence of boundary condition on the performance of the RDP tests. To ensure the constitutive model of concrete embedded in ABAQUS and the material parameters were correctly used, the numerical models were first calibrated by the laboratory results with different concrete panel thickness without using welded wire mesh. After that, the performance of the combined concrete layer and welded wire mesh was examined by using the calibrated concrete model and mesh model and the failure mechanism of the combined specimens was obtained. The results show that the failure pattern matches the laboratory observation rather well and the peak load carrying capacity of the combined concrete layer and welded wire mesh panel is a little higher than that of the concrete only panel but the residual load carrying capacity has been improved. The boundary condition has large effect on the load-displacement curve, which is discussed in detail in the paper. The objective was to develop a numerical methodology which could be used to evaluate the load carrying capacity of combined concrete layer and welded wire mesh and thereby improve the assessment of the performance of shotcrete and welded wire mesh on site.
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| 2. |
- Zhang, Zhi-qiang, et al.
(författare)
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Effect of fault on tunnel stability with different distribution
- 2013
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Ingår i: Global View of Engineering Geology and the Environment. - London : CRC Press, Taylor & Francis Group. - 9781138000780 ; , s. 279-285
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Konferensbidrag (refereegranskat)abstract
- For tunnel engineering, the fault that locates near tunnel always plays an important role on the stability of the surrounding rock mass and the safety of the supporting system. To investigate the influence of the fault on the tunnel stability, systematic numerical experiments are carried out via the FINAL code. Through these numerical experiment results, the displacement and the distribution of the stress in surrounding rock mass are analyzed for these cases of the different locations and dips of fault around tunnel periphery, and the stress in the sprayed concrete layer are analyzed as well. To simulate the characteristics of the fault located in the rock mass, the COJO element, embedded in the FINAL code, is used in all numerical experiments. The quantized results reflecting the rules of the change for the displacement, stress, plastic region in the surrounding rock mass are obtained also in this paper.
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| 3. |
- Alvarez, Manuel, 1980-
(författare)
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Distribution Network Planning Considering Capacity Mechanisms and Flexibility
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increasing penetration of distributed energy resources (DERs) has posed challenges to the distribution system operator (DSO) from the operation and regulatory point of view. High penetration of DERs could have negative impacts on the performance of the distribution grid, and depending on the regulatory framework, the DSO's remuneration as well. In liberalized electrical systems, the focus on promoting eciency has led to the implementation of an incentive-based regulation that exerts additional pressure on the DSOs to reduce costs. Additionally, the European Parliament Directive 2009/72/EC establishes a regulatory unbundling among the distribution, production, and retailing activities within the same vertically integrated electric utility.A way of helping the DSO to cope with the posed challenges is by providing it with exibility. This exibility can be acquired from the planning stage, and later be used during the system operation. This exibility can stem from the DSO's ability to exert control on the demand and the supply side to balance the system and correct its operational state.Based on the European DSOs' current situation at facing the increasing penetration of DERs, this thesis investigates in non-wired exible grid tools to solve the distribution network expansion problem. The investigation focuses on exibility providers, in particular on energy storage systems and hydropower, and also on capacity mechanisms to translate the capacity from DERs into the grid's capacity for planning purposes.Given that the share of renewable sources among the DERs is increasing, and considering the importance of energy storage systems in providing exibility to balance renewable energy production, the eort has been turned on to developing a hydropower model and a generic storage model that t both planning and operational studies.Given the need for gearing the DERs' behavior into the DSO's decision making process during the planning and operational timescales, the design and implementation of a distribution capacity mechanism have been developed. The design of the capacity mechanism has been conceived considering its integration within the distribution network expansion problem.The outcomes of this thesis can be synthesized as follows: 1) A generic hydraulic/storage model provided with an equivalent marginal cost that aids in considering the impact of present decisions in the future costs. 2) A market oriented distribution capacity mechanism that gears DERs and the DSOs to benefit mutually. 3) A distribution network expansion planning formulation that integrates the capacity resource from DERs through the distribution capacity mechanism.
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| 4. |
- Botelho, Anneliese H., et al.
(författare)
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Effects of parallel fractures near a free surface on velocity amplification of S-wave
- 2017
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Ingår i: Proceedings of the Ninth International Symposium on Rockbursts and Seismicity in Mines. - Santiago do Chile : University of Chile.
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Konferensbidrag (refereegranskat)abstract
- When rock support is designed in a seismically active underground mine, it is important tochoose the right ejection velocity and calculate corresponding kinetic energy. Field monitoringand back-analyses have shown that ejection velocity of the order of 10 m/s and higher can resultfrom seismic events of moderate magnitude. Such velocities are much higher than those predictedusing peak particle velocity (PPV) obtained from scaling laws. Many researches have reportedthe amplification of particle velocity near excavation surface. Velocity amplification of P-wavetravelling through fractured rock near a free surface was recently studied. The amplification ofseismic waves on the skin of excavation is of interest in case of large seismic events. Seismic eventswith large magnitude are often associated with slip along weaknesses or shear fracturing of intactrock, which according to observations radiate much stronger S-wave as compared to P-wave.In this paper, velocity amplification of S-wave was investigated by modelling the dynamicinteraction between fractured rock and a free surface using a 2D discontinuum-based numericalprogram, UDEC (Universal Distinct Element Code). A 1D model with a fractured zone wasused to represent the fractured rock in this investigation. It is found that the shear stress ratio,wave frequency, fracture stifness, fracture spacing and thickness of fractured zone afect thevelocity amplification, in which the shear stress ratio is the most crucial factor influencing wavetransmission. The results have proved that the interaction of the seismic wave and multiplefractures near the free surface strongly influences the ground motion.
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| 5. |
- Botelho, Anneliese H., et al.
(författare)
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Velocity amplification of obliquely incident s-wave through fractures near free-surface
- 2019
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Ingår i: Rock Mechanics for Natural Resources and Infrastructure Development - Full Papers. - : Taylor & Francis. ; , s. 1487-1494
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Konferensbidrag (refereegranskat)abstract
- The rockfall risk due to mining-induced seismicity reduces by installing appropriate rock support to absorb the kinetic energy from a seismic event, which is calculated by assuming the mass of ejected rock and its ejection velocity. Estimation of ejection velocity is normally based on scaling laws that do not consider the effect of the excavation free-surface and existing fractures near the excavation free-surface. Field monitoring studies have shown that the peak particle velocity on the free-surface can be much larger than the velocity in deep solid rock. The interaction between the fractures and the free-surface under incident S-wave is investigated by using a two-dimensional UDEC model with fractured zone characterized as one, two, three and four sets of parallel fractures with varied intersecting angles. The results show that wave amplification factor varies according to the incident wave angle, the number of fracture sets and fracture spacing.
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| 6. |
- Chen, Guanghui, et al.
(författare)
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Optimization of tunnel support parameters with consideration of seismic wave radiation pattern in the fault-slip burst
- 2017
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Ingår i: Journal of Mining and Safety Engineering. - : China University of Mining and Technology. - 1673-3363. ; 34:4, s. 715-722
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Tidskriftsartikel (refereegranskat)abstract
- As the underground mining extends gradually towards depth, more and more seismic events induced by fault slip occur and cause great damages, which have become a severe potential threat to mining safety. In view of the plane strain problems, through the three dimensional discrete model established, comparison and analysis was carried out between the equivalent calculation of plane strain in 3D model and a 2D discrete model. The results have shown that the research model developed to simulate the propagation of seismic wave in 3D is feasible and applicable. The study of the effect of radiation pattern on seismic propagation revealed and tested the direction of P-and S-wave propagation, which presents high consistency to double couple model of the fault slip. On this basis, the comparison with the design scaling law formulas proposed by Kaiser and associates finds that the existing design scaling law does not totally satisfy the demand of practical engineering. Numerical calculation and analysis with the three dimensional discrete model can further optimize the support parameters, provide better service for system design of mining support, and ensure the safety and high efficiency in mining.
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| 7. |
- Eitzenberger, Andreas, et al.
(författare)
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Numerical simulation of train-induced vibrations in rock masses
- 2012
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Ingår i: Harmonising rock engineering and the environment. - Leiden : CRC Press/Balkema. - 9780415804448 ; , s. 1189-1194
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Konferensbidrag (refereegranskat)abstract
- The vibrations generated by a moving train in a tunnel will radiate into the surrounding ground which, in densely populated areas, will reach nearby buildings and its residents. Analyses are commonly made where the aim is to estimate the ground-borne noise and vibrations levels that may occur in nearby buildings. A common assumption is to treat the rock mass as an isotropic, homogeneous, and linear elastic material. Thus, the influence of discontinuities on the propagation of waves is not considered in the analyses. Within this study, numerical simulations were performed to study the propagation of low-frequency waves through a rock mass near a tunnel. A single period sinusoidal wave was applied as dynamic source on the floor of the tunnel. Observation points were located on the ground surface and around the tunnel. The influence on wave propagation from overburden, position of a discontinuity in relation to the tunnel, and normal and shear stiffness of the discontinuity, was studied by using the Universal Distinct Element Code (UDEC). The results show that increasing overburden reduces the vibration levels on the ground surface. Furthermore, the influence of the normal and shear stiffness of discontinuities depends on where the horizontal discontinuity is positioned in relation to the tunnel. If the horizontal discontinuity is positioned above the dynamic source (e.g. above tunnel or in the tunnel wall) the vibration levels on the ground surface will be reduced but if the horizontal discontinuity is located below the dynamic source (e.g. below the tunnel) the vibration levels on the ground surface will be enhanced. In our analyses, discontinuities only have an impact on the wave propagation if the normal and shear stiffness of is ≤10 GPa/m.
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| 8. |
- Liu, Ye, et al.
(författare)
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First-principles investigation on the thermodynamic and mechanical properties of Y4Zr3O12 and Y2Ti2O7 oxides in ferritic alloy under helium environment
- 2024
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Ingår i: Journal of Materials Research and Technology. - : Elsevier. - 2238-7854. ; 29, s. 1872-1886
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the thermodynamic and mechanical properties of Y4Zr3O12 and Y2Ti2O7 oxides in ferritic alloys with and without Helium utilizing a systematic first-principles approach. Firstly, the atomic arrangement of Y and Zr atoms at cation 18f sites in δ-(Y–Zr–O) oxide is identified, while it is found that Y4Zr3O12 exhibits a more robust formation tendency than Y2Ti2O7. Furthermore, it is noted that both Y4Zr3O12 and Y2Ti2O7 oxides demonstrate a prior ability to trap Helium compared to the bcc-Fe matrix, which leads to a substantial enhancement on the stiffness of both oxides. The elastic moduli of both Y4Zr3O12 and Y2Ti2O7 oxide exhibit a gradual increase with the growing Helium concentration. As a result, the enhanced shear modulus of oxides and sustained shear modulus of the bcc-Fe matrix collectively contribute to the overall strength of ferritic alloys under Helium environments. The findings in this work propose valuable insights for guiding critical strategies in the design of high-performance oxide-dispersion-strengthened ferritic alloys, particularly for applications in Helium environments.
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| 9. |
- Ma, Xu, et al.
(författare)
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Investigation of Unstable Failure Potential of a Shear Slip Using DEM at an Underground Mine
- 2021
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 11:3, s. 59-83
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Tidskriftsartikel (refereegranskat)abstract
- During the winter season, ice causes major problems in many Swedish railway tunnels. Ice, rock and shotcrete in the roof and on the walls may come loose and fall down, installations and cables can break due to ice loads and the tracks can become covered with ice. To maintain safety and prevent traffic disturbances, many tunnels require frequent maintenance. The removal of ice, loose rock and shotcrete is expensive and potentially risky work for the maintenance workers. To reduce maintenance costs, it is important to improve our knowledge of frost penetration inside tunnels and investigate the effect of ice pressure and frost shattering on load-bearing constructions. The aim of this investigation was to gather information about the problems caused by water leakage and its effect on the degradation of a rock tunnel when subjected to freezing temperatures. There are many factors that determine whether frost or ice formations will appear in tunnels. To collect information on ice formation problems, field observations were undertaken in five of Sweden’s railway tunnels between autumn 2004 and summer 2005. For one of the tunnels, follow-up observations also took place in March during the years 2005, 2006 and 2007.
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| 10. |
- Ma, Xu, et al.
(författare)
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Unstable Shear Slip Failure and Seismic Potential Investigation Using DEM in Underground Mining
- 2023
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Ingår i: Mining, Metallurgy and Exploration. - : Springer Science and Business Media Deutschland GmbH. - 2524-3462 .- 2524-3470. ; 40:1, s. 405-420
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Tidskriftsartikel (refereegranskat)abstract
- Perturbations arising from mining operations significantly affect the stability of rock masses, and the influences aggerates with the rapid increase of mining-operation depths during recent years. The subsurface structures with major discontinuities subject to seismic hazards resulted from the shear-slip behaviors of rock masses. In order to identify the shear-slip regime of discontinuities and calculate seismic moment and seismic energy involved with shear-slip behaviors, we use discrete element modeling to study the shear slip failure along discontinuities in an underground mine. The recorded characteristic and properties of sub-contacts in DEM provide a basis for computing and visualizing the temporal and spatial distribution of seismic moment and seismic energy with mining operations. We computed the seismic energy and seismic moment using the numerical modeling method and the analytic method. We compared the result of summing seismic energy and seismic moment from the subcontacts of numerical models and the result of the analytic method. We confirmed that this tool can be used in comparative analyses. We also found that seismic moment and seismic energy, associated with shear stress drop and shear displacement increase, accumulate in the vicinity of major discontinuities. Mining operations at a greater depth cause greater changes of seismic moment and seismic energy, leading to a higher risk of inducing seismic hazards. Quantifying seismic potential using discrete element modeling can greatly facilitate the investigation of instability of geological discontinuities and thereby can help estimate the potential of seismic hazards.
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