Hassan Rahimi; H. Ahmadi
Abstract
Introduction: Cracking of earth dams is a one of the main threat causes of stability of embankment dams. In this research by modeling of the behavior of an embankment dam and employing conditions of the earthquake, the reasons of cracking were inspected using by modeling of earth dam behavior. Based ...
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Introduction: Cracking of earth dams is a one of the main threat causes of stability of embankment dams. In this research by modeling of the behavior of an embankment dam and employing conditions of the earthquake, the reasons of cracking were inspected using by modeling of earth dam behavior. Based on the literature, one of the main causes of dam failures is sliding and cracking of the dam structure during earthquake. Localized liquefaction of foundation soils was one of the causes of the observed post-earthquake distress within these dams.
Material and Methods: In order to study the causes and the results of crack on earth dams, Mahmoodabad earthen dam with a height of 19 m, is located in Zanjan province, northwest of Iran, which suffered a longitudinal crack on the crest and slight sliding of the upstream slope due to 2001 Avaj earthquake was studied. This dam has faced earthquake two times with an interval of two years. During the first earthquake with the magnitude about 6.6 in Richter scale small longitudinal cracks had created on the crest. The developed cracks had been repaired by injecting the cement and then has been hidden by passing the time. After the second earthquake with the magnitude about 6.5 in Richter scale the hidden cracks had been appeared again and the slight movement of the upper slopes of dam reported. Based on the site investigation and documented information about dam, including maps and parameter data, the behavior of the dam has modeled by using Plaxis as a finite element model. In order to check the accuracy of the design of dam, the stability analysis has been conducted using by Xslope as a limit equilibrium model. The foundation conditions and the Geotechnical properties of the layer beneath the dam has been inspected by open excavation.
Results and Discussion: Underground investigation about Geotechnical properties of dam foundation has showed that there is a thin sandy layer confined in alluvium material of the river base beneath the dam structure. In fact , this layer has not been considered in the analysis as well in design. Because of fully saturated condition of this layer in an operation period of dam it might subjected to liquefaction during the happening of the earthquake. Evaluation of liquefaction potential of this layer based on Seed and Idriss (1971) diagram showed probability of this phenomenon. To prove this hypothesis, the stability analysis had been conducted in two different conditions by including the thin sandy layer and without considering the mentioned layer. The analysis showed in the case of absence of sandy layer the required safety factor was satisfied, but including the sandy layer leads cause the safety factor dropped to 0.84 that means accruing of liquefaction in the thin layer would lead to structural instability of the studied dam. The simulation of the behavior of dam by employing the accrued earthquake acceleration confirmed the liquefaction has been accrued in the thin sandy layer. The results of finite element simulation showed the depth of the cracks on the crest is about 2 meters and also the upstream slope has slipped about 81 mm to the reservoir of the dam. These results was consistent with the observed values. To overcome the next risks, also to repair the damaged parts of the dam, 3 different methods had been proposed. The curing technics was deploying of the reservoir and removing of the damage part of the dam and as well the thin sandy layer and reconstructed that part of dam, Deploying of reservoir of the dam and adjusting the slope of the upper shoulder to stable condition and at least repairing the developed cracks by injecting cement slurry and tolerate the current condition without imposition any additional costs to the project. The third method has been selected, but for any probable risky condition monitoring of the dam has been advised.
Conclusion: Based on the overall results of the investigations, it was concluded that cracking and sliding of upstream shell is mainly due to the presence of a loose, fine sandy layer under the base of the dam which was liquefied during the earthquakes. In order to overcome the problem, one of the three offered solutions, including modification of cracks by injecting cement slurry, was applied and after roughly 9 years, the provided reports confirmed the adequacy of the applied solution.
Y. Khoshkhoo; parviz irannejad; ali khalili; Hassan Rahimi; A. Liaghat; P. Erik Jansson
Abstract
In this research calibration and uncertainty analysis of COUP model with focus on soil temperature simulation for 3-hours time scale have been performed for Hamedan synoptic station. The Generalized Likelihood Uncertainty Estimation (GLUE) was used for this object. In order to simulate the soil temperature, ...
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In this research calibration and uncertainty analysis of COUP model with focus on soil temperature simulation for 3-hours time scale have been performed for Hamedan synoptic station. The Generalized Likelihood Uncertainty Estimation (GLUE) was used for this object. In order to simulate the soil temperature, 22 parameters were chosen and by using the Monte Carlo stochastic sampling method from the uncertainty space of the parameters, 25000 scenarios were produced and model simulations were implemented. For separate behavioral and non-behavioral simulations, 3 criteria including Nash-Sutcliff, Mean Bias Error, and Root Mean Square Error were considered and acceptable thresholds for each criterion were defined. With applying the acceptable thresholds, 253 behavioral simulations were detected and used for calibration and uncertainty analysis of the model. Based on posterior parameter distributions some parameters were recognized as sensitive parameters. The median of behavioral simulations was considered for model calibration and the uncertainty analysis of the model was performed based on 90% confidence levels of behavioral simulation errors. The results showed that calibration of the model has considerably improved the performance of the model in comparison to default parameter values. In addition, the uncertainty analysis showed that the uncertainty of parameters has been considerably decreased in most cases with application of the GLUE method. Other differences between simulated and observed values were attributed to other sources of model uncertainty.
H. Ahmadi; H. Rahimi; A. Soroush
Abstract
Abstract
At present study constant rate of strain (CRS) consolidation under Non-Darcy condition was investigated. In this study a governing conditions of drainage pore water were investigated using proposed equation. The CRS experiments under different rates of strain were conducted on different soil ...
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Abstract
At present study constant rate of strain (CRS) consolidation under Non-Darcy condition was investigated. In this study a governing conditions of drainage pore water were investigated using proposed equation. The CRS experiments under different rates of strain were conducted on different soil samples. Results these experiments and there comparison with proposed equation showed that flow of pore water drainage in the most part or each test was Non-Darcy and changed to Darcy condition in the final one forth of test. According to the results the threshold that Non-Darcy flow changes to Darcy is dependent on variations of relative pore water pressure versus total strain and it can be determined based on variations in inclination of relative pore water pressure-total stress curve.
Keywords: Consolidation, Constant strain, Non-Darcy flow, Pore pressure
M. Ghobadi Nia; H. Rahimi; E. Flavia; T. Sohrabi; A.A. Pourbabaee; U. Vasconcelos
Abstract
Abstract
A previous study on agricultural drains in Khuzestan province of Iran has indicated that carbonate calcium is the main component of the deposited salts in drainage envelops. To investigate the process of precipitation of carbonate calcium under different conditions including chemical, bio-chemical, ...
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Abstract
A previous study on agricultural drains in Khuzestan province of Iran has indicated that carbonate calcium is the main component of the deposited salts in drainage envelops. To investigate the process of precipitation of carbonate calcium under different conditions including chemical, bio-chemical, aerobic and an-aerobic, a through laboratory investigation on geotextile drain envelop was conducted. The results of the studies showed that activity of the micro-organisms in aerobic conditions causes an increase in the bicarbonate content and consequently, increase in the pH of the medium. Any increase in pH would intensify the precipitation of carbonate calcium. The results also indicated that due to the activity of micro-organisms, more than 90% of existing calcium would be precipitated. While in a chemical environment, only 30% of existing calcium would precipitate. Thus, in a biochemical environment, micro-organisms would cause more calcium to be deposited. The results also indicated that the activity of the bacteria would cause formation of bio-films which in turn would provide a more suitable environment for precipitation of salts. By intensifying deposition of salts, there is higher potential for clogging of the drainage envelops including geotextile filters.
Keywords: Agricultural Drain, Calcium Carbonate, Drainage Envelope, Geotextile, Aerobic and An-aerobic, biofilm
S.M. Soleimanpour; M. Soufi; H. Rahimi
Abstract
Abstract
Gully erosion is a kind of water erosion that has high priority in Fars Province due to sediment production and enormous damages to land, roads and infrastructures. In this study, 15 gullies were selected and their morphometric characteristics, such as catchment area, soil, cover vegetation ...
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Abstract
Gully erosion is a kind of water erosion that has high priority in Fars Province due to sediment production and enormous damages to land, roads and infrastructures. In this study, 15 gullies were selected and their morphometric characteristics, such as catchment area, soil, cover vegetation and climate were measured. In order to determine influential factors on the sediment production and gully development, relationship between gully volume as dependent variable and gully characteristics such as, length, width, depth and watershed characteristics such as area, slope, form factor, particle size, vegetation cover and maximum raining during 24 hour as independent variables were analyzed by using step wise method in SPSS (recipe 13) software. The results revealed that sediment production due to gully development was related to five variables of clay, sand, silt, slope and cover vegetation of the watershed above the gully heads. This result implied on the impact of the characteristics of soil, geology and watershed on the sediment production of gullies. Impact of soil and geologic factors indicated were more important than watershed characteristics. Investigation on the topographic threshold indicated that positive environmental than exponent implied that sub surface runoff is dominant on gully development. These results also indicate the impact of field observations proved the dominance of subsurface acting due to tunneling the geological formation on the gullies sediment yield.
Keywords: Gully Erosion, Sediment Yield, Topographic Threshold, Konartakhte, Fars Province
