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Natural Resources Research - The northwest of Iran is considered as a promising geothermal zone owing to its geographical properties, tectonic features, and thermal activities, particularly in... 相似文献
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Brittleness Effect on Rock Fatigue Damage Evolution 总被引：1，自引：0，他引：1
The damage evolution mechanism of rocks is one of the most important aspects in studying of rock fatigue behavior. Fatigue damage evolution of three rock types (onyx marble, sandstone and soft limestone) with different brittleness were considered in the present study. Intensive experimental tests were conducted on the chosen rock samples and acoustic emission (AE) sensors were used in some of them to monitor the fracturing process. Experimental tests indicated that brittleness strongly influences damage evolution of rocks in the course of static and dynamic loading. AE monitoring revealed that micro-crack density induced by the applied loads during different stages of the failure processes increases as rock brittleness increases. Also, results of fatigue tests on the three rock types indicated that the rock with the most induced micro-cracks during loading cycles has the least fatigue life. Furthermore, the condition of failure surfaces of the studied rocks samples, subjected to dynamic and static loading, were evaluated and it was concluded that the roughness of failure surfaces is influenced by loading types and rock brittleness. Dynamic failure surfaces were rougher than static ones and low brittle rock demonstrate a smoother failure surface compared to high brittle rock. 相似文献
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Hamid Reza Nejati Morteza Ahmadi Hamid Hashemolhosseini Mohammad Hayati 《Geotechnical and Geological Engineering》2012,30(5):1137-1146
Ground surface vibration produced by moving train is one of the most important aspects in urban areas. The purpose of this study is the probabilistic analysis of ground surface vibration, which is generated by metro transportations. For this reason, Tehran metro line 4 is considered as a case study. In this paper, at first, a new procedure is used to simulate train dynamic load. In the second step, based on the variation of geomechanical properties and train characteristics in Tehran metro line 4, more than 60 numerical models are simulated. The results of numerical simulations are analyzed by multivariate statistical technique and an equation for prediction of peak particle velocity (PPV) in the ground surface is presented. In the next step, probabilistic analysis is done using Monte Carlo Simulation (MCS). Finally, sensitivity of input data on ground surface vibration is discussed and the impact of geomechanical properties and train characteristics on the surface vibration is considered. Based on the probabilistic analysis, PPV in the surface region of Tehran metro line 4 is <2.76?mm/s with 95?% probability. 相似文献
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Active geological and young faulted zones have made Iran’s territory one of the most seismological active areas in the world according to recent historical earthquakes. Some of the deadliest earthquakes such as Gilan 1990 and Kermanshah 2018 caused tens of thousands fatalities. If such violent earthquakes affect strategical structures of a country, indirect losses would be more concerning than direct losses. Nowadays there is no doubt about the vital role of tunnels and underground structures in urban areas. These facilities serve as nonstop functional structures for human transportation, water and sewage systems and underground pedestrian ways. Any external hazard subjected to underground spaces, such as earthquake could directly affect passenger’s lives and significantly decrease whole system reliability of public transportation. Commonly two earthquake levels of intensities, Maximum Design Earthquake (MDE) and Operating Design Earthquake (ODE) were used in seismic design of underground structures. However, uncertain nature of earthquakes in terms of frequency content, duration of strong ground motion, and level of intensity indicate that only the two levels of earthquake (ODE and MDE) cannot cover the all range of possible seismic responses of structures during a probable earthquake. It is important to evaluate the behavior of tunnel under a wide range of earthquake intensities. For this purpose, a practical risk-based approach which is obtained using the total probability rule was used. This study illustrates a framework for evaluation seismic stability of tunnels. Urban railway tunnels of Tehran, Shiraz, Ahwaz, Mashhad, Isfahan and Tabriz were considered as study cases. Nominal value of seismic risk for three main damage states, including minor, moderate and major were calculated. 相似文献
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An investigation on the ground motion parameters and seismic response of underground structures 
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下载免费PDF全文 Peak ground acceleration (PGA), frequency content and time duration are three fundamental parameters of seismic loading. This study focuses on the seismic load frequency and its effect on the underground structures. Eight accelerograms regarding different occurred earthquakes that are scaled to an identical PGA and variation of ground motion parameters with ratio of peak ground velocity (PGV) to PGA, as a parameter related to the load frequency, are considered. Then, concrete lining response of a circular tunnel under various seismic conditions is evaluated analytically. In the next, seismic response of underground structure is assessed numerically using two different time histories. Finally, effects of incident load frequency and frequency ratio on the dynamic damping of geotechnical materials are discussed. Result of analyses show that specific energy of seismic loading with identical PGA is related to the seismic load frequency. Furthermore, incident load frequency and natural frequency of a system have influence on the wave attenuation and dynamic damping of the system. 相似文献
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Mixed mode crack propagation in low brittle rock-like materials 总被引：3，自引：0，他引：3
Abdolhadi Ghazvinian Hamid Reza Nejati Vahab Sarfarazi Mir Raouf Hadei 《Arabian Journal of Geosciences》2013,6(11):4435-4444
Mixed mode fracture is quite common in rock structures. Numerous investigators have used the Brazilian disk specimens with a central crack for investigating modes I, II, and mixed fracture toughness in brittle materials. In this study, analytical, experimental, and numerical investigations were planned and performed on Central Straight Through Crack Brazilian Disk (CSCBD) specimens. Ranking of geometrical parameters effective on the value of stress intensity factors (SIFs) of CSCBD specimens were obtained using stochastic analysis. Furthermore, experimental tests were undertaken in order to evaluate the crack propagation in rock-like material of low brittleness. Finally, numerical modeling was performed to assess the effect of crack length on the failure mode of CSCBD specimens. Analytical analyses revealed that the inclination angle of the crack with respect to the diametrical load has the most important impact on the SIFs among the geometrical parameters of CSCBD specimen. Performed experimental and numerical analyses also confirmed the effect of inclination angle and crack length and their impact on the mode of failure of the tested specimen. 相似文献
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Mahmoodzadeh Arsalan Mohammadi Mokhtar Farid Hama Ali Hunar Hashim Ibrahim Hawkar Nariman Abdulhamid Sazan Nejati Hamid Reza 《Natural Hazards》2022,111(2):1771-1799
Natural Hazards - Because of the disasters associated with slope failure, the analysis and forecasting of slope stability for geotechnical engineers are crucial. In this work, in order to forecast... 相似文献
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V. Sarfarazi A. Ghazvinian W. Schubert M. Blumel H. R. Nejati 《Rock Mechanics and Rock Engineering》2014,47(4):1355-1371
The effect of joint overlap on the full failure behavior of a rock bridge in the shear-box test was numerically investigated by means of the particle flow code in two dimensions (PFC2D). Initially, the PFC2D was calibrated by use of data obtained from experimental laboratory tests to ensure the conformity of the simulated numerical model’s response. Furthermore, validation of the simulated models was cross-checked with the results from direct shear tests performed on non-persistent jointed physical models. By use of numerical direct shear tests, the failure process was visually observed and the failure patterns were seen to be in reasonable accordance with experimental results. Discrete element simulations demonstrated that macro shear fractures in rock bridges are because of microscopic tensile breakage of a large number of bonded discs. The failure pattern is mostly affected by joint overlap whereas the shear strength is closely related to the failure pattern. The results show that non-overlapping joints lost their loading capacity when nearly 50 % of total cracks developed within the rock bridge whereas the overlapping joints lost their loading capacity as soon as cracks initiated from the joint walls. Furthermore, progressive failure or stable crack growth was seen to develop for non-overlapped joints whereas brittle failure or unstable crack growth was seen to develop in overlapped joints. 相似文献
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