A possible continuum theory for densification and liquefaction of saturated sand     

Goodarz Ahmadi 《Mathematical Geology》1981,13(1):37-52

A previously developed continuum theory of granular media is applied to the problems of densification and liquefaction of saturated sand. An expression for the free energy of saturated sand is developed. The process of densification of sand subjected to cyclic shear stress is studied and several expressions for an increase of the solid volume fraction are obtained and discussed. The problem of the initial liquefaction of saturated sand samples under cyclic shear stress is then considered and several criteria relating the shear stress amplitude, over-burden pressure, time to liquefaction, and physical properties of the sand sample are established. Some semiempirical relations for field applications are also presented.  相似文献   

Mental health preparedness for natural disasters in Iran     

Naghmeh Sadeghi  Mohammad H. Ahmadi 《Natural Hazards》2008,44(2):243-252

Appropriate emergency preparedness and response rely on social, economical, cultural, and political infrastructures, which vary widely according to the level of the development of each country. Mental health damages are among the consequences of absence of such infrastructure, which have not been studied comprehensively till to date. In most countries, planning for natural disasters and earthquakes has been mainly focused on physical and economical impacts; however, lessons learnt from recent earthquakes in Iran and other countries show that psychological impacts need to be considered more seriously. The first responder to an emergency is really the affected community, which consequently should be mentally prepared by appropriate training programs. These should include simple psychosocial interventions developed for people with average level of education in a way to be easily understandable and practicable. After the Bam earthquake, local community volunteers have been selected and trained to provide post-disaster mental health services.  相似文献   

Experimental and analytical investigations on bearing capacity of strip footing in reinforced sand backfills and flexible retaining wall   总被引：2，自引：1，他引：1  

H. Ahmadi  M. Hajialilue-Bonab 《Acta Geotechnica》2012,7(4):357-373

This study focuses on the experimental and analytical investigations of small-scale physical model tests. For this purpose, a set of tests were conducted with and without reinforcement on the top of the backfill. The specimens were different in terms of parameters like the number of geotextile layers, the vertical distance between layers and the strip footing distance from the wall. Soil failure in the bearing capacity step and the backfill shear zones was analysed using particle image velocimetry methods. Bearing capacity of the strip footings was studied using analytical procedures. The results indicate that a reinforcing top zone of the flexible retaining structures may be more appropriate than unreinforced case. The ultimate bearing capacity and wall deflection can be significantly improved by increasing the number of reinforcement layers. When the three layers of reinforcement are used, there is an optimum vertical spacing of the layers at which the bearing capacity is the greatest (h/H?=?0.12, d/H?=?0.33 and u?=?B). The study shows that the analytical solution and the results from the experimental models are in good agreement.  相似文献   

Assessment of climate change impacts on rainfall using large scale climate variables and downscaling models – A case study     

Azadeh Ahmadi  Ali Moridi  Elham Kakaei Lafdani  Ghasem Kianpisheh 《Journal of Earth System Science》2014,123(7):1603-1618

Many of the applied techniques in water resources management can be directly or indirectly influenced by hydro-climatology predictions. In recent decades, utilizing the large scale climate variables as predictors of hydrological phenomena and downscaling numerical weather ensemble forecasts has revolutionized the long-lead predictions. In this study, two types of rainfall prediction models are developed to predict the rainfall of the Zayandehrood dam basin located in the central part of Iran. The first seasonal model is based on large scale climate signals data around the world. In order to determine the inputs of the seasonal rainfall prediction model, the correlation coefficient analysis and the new Gamma Test (GT) method are utilized. Comparison of modelling results shows that the Gamma test method improves the Nash–Sutcliffe efficiency coefficient of modelling performance as 8% and 10% for dry and wet seasons, respectively. In this study, Support Vector Machine (SVM) model for predicting rainfall in the region has been used and its results are compared with the benchmark models such as K-nearest neighbours (KNN) and Artificial Neural Network (ANN). The results show better performance of the SVM model at testing stage. In the second model, statistical downscaling model (SDSM) as a popular downscaling tool has been used. In this model, using the outputs from GCM, the rainfall of Zayandehrood dam is projected under two climate change scenarios. Most effective variables have been identified among 26 predictor variables. Comparison of the results of the two models shows that the developed SVM model has lesser errors in monthly rainfall estimation. The results show that the rainfall in the future wet periods are more than historical values and it is lower than historical values in the dry periods. The highest monthly uncertainty of future rainfall occurs in March and the lowest in July.  相似文献   

Source Rock Characterization and Petroleum Systems in North Ghadames Basin,Southern Tunisia     

Dhaou AKROUT  Hassène AFFOURI  Riadh AHMADI  Eric MERCIER  Mabrouk MONTACER 《Resource Geology》2011,61(3):270-280

This paper presents geochemical analysis of drilled cutting samples from the OMZ‐2 oil well located in southern Tunisia. A total of 35 drill‐cutting samples were analyzed for Rock‐Eval pyrolysis, total organic carbon (TOC), bitumens extraction and liquid chromatography. Most of the Ordovician, Silurian and Triassic samples contained high TOC contents, ranging from 1.00 to 4.75% with an average value of 2.07%. The amount of hydrocarbon yield (pyrolysable hydrocarbon: S2b) expelled during pyrolysis indicates a good generative potential of the source rocks. The plot of TOC versus S2b, indicates a good to very good generative potential for organic matter in the Ordovician, Silurian and Lower Triassic. However, the Upper Triassic and the Lower Jurassic samples indicate fair to good generative potential. From the Vankrevelen diagram, the organic matter in the Ordovician, Silurian and Lower Triassic samples is mainly of type II kerogen and the organic matter from the Upper Triassic and the Lower Jurassic is dominantly type III kerogen with minor contributions from Type I. The thermal maturity of the organic matter in the analyzed samples is also evaluated based on the T_max of the S2b peak. The Ordovician and Lower Silurian formations are thermally matured. The Upper Silurian and Triassic deposits are early matured to matured. However, Jurassic formations are low in thermal maturity. The total bitumen extracts increase with depth from the interval 1800–3000 m. This enrichment indicates that the trapping in situ in the source rocks and relatively short distance vertical migration can be envisaged in the overlying reservoirs. During the vertical migration from source rocks to the reservoirs, these hydrocarbons are probably affected by natural choromatography and in lower proportion by biodegradation.  相似文献   

Clinopyroxene chemistry in Tertiary alkaline volcanic rocks from Taleghan,central Alborz,Iran: Implications for two parental melts     

Mohammad Reza Ghorbani  Ahmad Reza Ahmadi  Massimo Tiepolo  Antonio Langone 《Chemie der Erde / Geochemistry》2013

In the Taleghan area of Alborz mountain range, two distinct units of alkaline rocks are identified. Whole rock major and trace element data does not provide a clue as to their common or different parental melts. However, major and trace element geochemistry of their included clinopyroxene phenocrysts, combined with the whole rock data, helped to infer that two parental magmas were involved in the evolution of volcanic succession in the Taleghan area.  相似文献   

Growth-strata geometry in fault-propagation folds: a case study from the Gafsa basin, southern Tunisian Atlas     

Riadh Ahmadi  Eric Mercier  Jamel Ouali 《Swiss Journal of Geoscience》2013,106(1):91-107

The structural and sedimentological study of fault-propagation folds in Southern Tunisia highlights a special geometry of the growth strata (strata deposited simultaneously with the formation or growth of a fold). This distinct geometry is visible in the uppermost growth-strata beds and consists of one flank with unconformity as opposed to the other flank with perfect conformity. This geometry can be explained by the mechanism of fault-propagation folding, with asymmetrical flank dips and hinge migration kinematics. This kinematics was originally predicted by the fault-propagation fold model, which facilitates the study of this special geometry in a narrow domain of sedimentation-to-shortening ratios. A plot projection provides a generalisation of the results of all types of fault-propagation folds by revealing the expected geometry of the growth strata. This study constitutes one of the most complete examples of kinematic model validation on a field scale.  相似文献   

MATLAB programs for the synthetic models     

Mahmoud Mehramuz  Hossein Zomorrodian  Khadijeh Ahmadi  Majid Mahood 《Arabian Journal of Geosciences》2013,6(10):3853-3864

The separation of residual gravity anomaly from regional gravity has considerably been studied for many years in gravity explorations. In addition, it is considered as a critical step in gravity data inversion. Some techniques have been developed for regional–residual anomaly separation both in space and frequency domains. One of these techniques for computing the regional anomaly is nonlinear filtering. In this paper, some techniques such as low-pass filtering, Butterworth, upward continuation, and nonlinear filtering are used to on synthetic gravity data in present of random noise and noise free for the purpose of residual–regional anomaly separation. The obtained results of techniques are compared with each other. The results have shown that separation methods are so efficient where synthetic models are located in shallow depth. Moreover, it is found that in comparison with other separation techniques, nonlinear filtering is more efficient in residual–regional anomaly separation and upward continuation technique is more efficient than Butterworth filter and low-pass filter. In addition, all of the obtained results have shown that Butterworth and low-pass filters are the same.  相似文献   

Reservoir Modeling by Data Integration via Intermediate Spaces and Artificial Intelligence Tools in MPS Simulation Frameworks     

Rouhollah Ahmadi  Ehsan Khamehchi 《Natural Resources Research》2013,22(4):321-336

Conditioning stochastic simulations are very important in many geostatistical applications that call for the introduction of nonlinear and multiple-point data in reservoir modeling. Here, a new methodology is proposed for the incorporation of different data types into multiple-point statistics (MPS) simulation frameworks. Unlike the previous techniques that call for an approximate forward model (filter) for integration of secondary data into geologically constructed models, the proposed approach develops an intermediate space where all the primary and secondary data are easily mapped onto. Definition of the intermediate space, as may be achieved via application of artificial intelligence tools like neural networks and fuzzy inference systems, eliminates the need for using filters as in previous techniques. The applicability of the proposed approach in conditioning MPS simulations to static and geologic data is verified by modeling a real example of discrete fracture networks using conventional well-log data. The training patterns are well reproduced in the realizations, while the model is also consistent with the map of secondary data.  相似文献   

Refining the OSL age of the last earthquake on the Dheshir fault,Central Iran     

M. Fattahi  H. Nazari  M.D. Bateman  B. Meyer  M. Sébrier  M. Talebian  K. Le Dortz  M. Foroutan  F. Ahmadi Givi  M. Ghorashi 《Quaternary Geochronology》2010,5(2-3):286-292

In Central Iran there are several cities along the Dehshir fault, which have similar geological conditions to that of the city of Bam prior to the 2003 earthquake (Mw 6.5), during which more than 30,000 lives were lost. Optical stimulated luminescence (OSL) samples were collected from the Dehshir fault in order to place constraints on its seismic history. The single aliquot regenerative (SAR) dose measurement protocol on coarse grained quartz extracts was used for this study. This SAR protocol had to be optimized for the low OSL sensitivity by varying both the preheat temperatures and test doses used. Dose recovery tests showed that given laboratory dose could be successfully recovered. However, replicate palaeodose (D_e) data were scattered and consequently ages based on mean D_e's had large uncertainties. As this is thought to largely reflect poor bleaching conditions prior to sediment burial at the site, various statistical procedures were employed in conjunction with the stratigraphic knowledge of the site to try and extract more refined burial ages from the samples. From this the timing of the last earthquake was estimated around 2.0 ± 0.2 kyr. This refined age suggests that the earthquake catalogue of Iran is incomplete and more paleoseismological investigation is required to recognize and date the previous events of Dheshir fault.  相似文献