Undrained behavior of silty sand: effect of the overconsolidation ratio     

Ahmed Djafar Henni  Ahmed Arab  Mostefa Belkhatir  A. Saaed Hamoudi  Hamid Khelafi 《Arabian Journal of Geosciences》2013,6(2):297-307

This experimental study deals with the effect of the overconsolidation ratio on the monotonic undrained shear behavior of silty sand. The study is based on the undrained monotonic triaxial tests for the overconsolidation ratios (OCR?=?1, 2, 4, and 8), with different silt contents ranging from 0% to 40%. The laboratory tests were carried out at an initial relative density of Dr?=?50%. The paper is composed of two parts. The first one presents the tested soils; the second one gives an analysis of the test results and discusses the influence of the overconsolidation ratio on the shear strength of the soil. The test results indicate that the shear strength of the soil increases with the increase of the overconsolidation ratio resulting in an increase of soil dilatancy. The increase in the amount of fines from 0% to 40% increases the phase of the contractancy and consequently reducing the phase of dilatancy of the tested material  相似文献   

Electron acoustic double layers in a plasma with a <Emphasis Type="Italic">q</Emphasis>-nonextensive electron velocity distribution     

Hamid Reza Pakzad  Mouloud Tribeche 《Astrophysics and Space Science》2011,334(1):45-53

Electron-acoustic double-layers (EA-DLs) are addressed in a plasma with a q-nonextensive electron velocity distribution. The domain of their allowable Mach numbers depends drastically on the plasma parameters and, in particular, on the electron nonextensivity. As the electrons evolve far away from their thermodynamic equilibrium, the negative EA-DLs shrinks and may develop into compressive EA-DLs. Our results may be relevant to the double-layers observed both in the auroral region and the plasma sheet of Earth’s magnetosphere (during enhanced magnetic activity). These DLs associated parallel electric fields are thought to be responsible for particle (electrons and ions) acceleration. Furthermore, our theoretical analysis brings a possibility to develop more refined theories of nonlinear cosmic DLs that may occur in astrophysical plasmas.  相似文献   

Effect of <Emphasis Type="Italic">q</Emphasis>-nonextensive distribution of electrons on ion acoustic shock waves in dissipative plasma     

Hamid Reza Pakzad 《Astrophysics and Space Science》2011,334(1):55-60

Ion acoustic shock waves (IASWs) are studied in a plasma consisting of nonextensive electrons and ions. The dissipation is taken into account the kinematic viscosity among the plasma constituents. The Korteweg-de Vries-Burgers (KdV-Burgers) equation is derived by reductive perturbation method. Shock waves are solutions of KdV-Burgers equation. It is shown that acceptable values of q-parameter (where q stands for the electron nonextensive parameter) are more than 3 in a weakly nonlinear analysis. We have found that the amplitude of shock waves decreases by an increasing q-parameter.  相似文献   

Ion-acoustic shock waves in a plasma with weakly relativistic warm ions, thermal positrons and a background electron nonextensivity     

Mouloud Tribeche  Hamid Reza Pakzad 《Astrophysics and Space Science》2012,339(2):237-241

A weakly nonlinear analysis is carried out to derive a Korteweg–de Vries-Burgers-like equation for small, but finite amplitude, ion-acoustic waves in a dissipative plasma consisting of weakly relativistic ions, thermal positrons and nonextensive electrons. The travelling wave solution has been acquired by employing the tangent hyperbolic method. Our results show that in a such plasma, ion-acoustic shock waves, the strength and steepness of which are significantly modified by relativistic, nonextensive and dissipative effects, may exist. Interestingly, we found that because of ion kinematic viscosity, an initial solitonic profile develops into a shock wave. This later evolves towards a monotonic profile (dissipation-dominant case) as the electrons deviate from their Maxwellian equilibrium. Our investigation may help to understand the dissipative structures that may occur in high-energy astrophysical plasmas.  相似文献   

Assessment of floodplain landuse and channel morphology within meandering reach of the Talar River in Iran using GIS and aerial photographs     

Saleh Yousefi  Hamid Reza Moradi  Hamid Reza Pourghasemi  Reza Khatami 《国际地球制图》2013,28(12):1367-1380

Abstract

The main objective of this study is to investigate and monitor the landuse and morphological changes in the floodplain part of the Talar River, northern parts of Iran. In the present study, the aerial photographs have been used to produce landuse maps of the floodplain for three periods including 1968, 1994, and 2013. The quantitative analysis of the produced landuse maps showed that the floodplain has undergone substantial landuse changes. Moreover, the sediment bar and the beach area have been decreased about 97 and 90%, respectively, during the 45-year period. Substantial increases of 192 and 622% have been observed for orchards and residential areas, respectively. On the other hand, not only the forest and riparian vegetation were decreased but also the average width of river was decreased about 25.5 m. In addition, flow length of the study reach increased about 8 m. The RNCI was about ?0.7 m per year indicating sedimentation process. During the period of 1968–2013, Caspian Sea has retreated about 150 m and the delta of Talar River was changed. This study showed that morphological actions during first 26 years (1968–1994) were the stable and last 19 years had the change period, especially sedimentation (bar).  相似文献   

A context-aware personalized travel recommendation system based on geotagged social media data mining   总被引：1，自引：0，他引：1  

Abdul Majid  Gencai Chen  Hamid Turab Mirza  Ibrar Hussain  John Woodward 《International journal of geographical information science》2013,27(4):662-684

The proliferation of digital cameras and the growing practice of online photo sharing using social media sites such as Flickr have resulted in huge volumes of geotagged photos available on the Web. Based on users' traveling preferences elicited from their travel experiences exposed on social media sites by sharing geotagged photos, we propose a new method for recommending tourist locations that are relevant to users (i.e., personalization) in the given context (i.e., context awareness). We obtain user-specific travel preferences from his/her travel history in one city and use these to recommend tourist locations in another city. Our technique is illustrated on a sample of publicly available Flickr dataset containing photos taken in various cities of China. Results show that our context-aware personalized method is able to predict tourists' preferences in a new or unknown city more precisely and generate better recommendations compared to other state-of-the-art landmark recommendation methods.  相似文献   

Identifying geological hazards related to tunneling in carbonate karstic rocks - Zagros, Iran   总被引：1，自引：0，他引：1  

Hamid Reza Zarei  Ali Uromeihy  Mostafa Sharifzadeh 《Arabian Journal of Geosciences》2012,5(3):457-464

The construction of tunnels in carbonate karstic rocks has always been the most hazardous and problematic task in civil and mining engineering, as it can threaten tunneling project from safety, time and economic aspects. Therefore, it is essential to identify hazards resulting from construction in early stages of a project. The present paper is aimed to identify main geological hazards related to tunneling in carbonate karstic rocks in the Zagros Mountains. The process of identification relies upon a review of construction experiences obtained from several projects with a focus on the Kuhrang Tunnels. Obviously, groundwater inrush and tunnel flooding, ground inflow and fill-back of the tunnel, instability of weak fill materials, and TBM jamming are the main potential hazards of tunneling in the Zagros Mountains, imposing huge problems during construction. Inadequate understanding of hazards and not being prepared enough to take appropriate countermeasures are the main sources of the problems. In addition, the investigation of the present study provides guidelines to reduce the risks of tunneling in the carbonate karstic rocks with similar geological condition.  相似文献   

Seismic response of pile foundations in liquefiable soil: parametric study   总被引：2，自引：1，他引：1  

Asskar Janalizade Choobbasti  Meysam Saadati  Hamid Reza Tavakoli 《Arabian Journal of Geosciences》2012,5(6):1307-1315

The performance of pile foundations in liquefiable soil subjected to earthquake loading is a very complex process. The strength and stiffness of the soil decrease due to the increase in pore pressure. The pile can be seriously destroyed by the soil liquefaction during strong earthquakes. This paper presents the response of vertical piles in liquefiable soil under seismic loads. A finite difference model, known as fast Lagrangian analysis of continua, is used to study the pile behavior considering a nonlinear constitutive model for soil liquefaction and pile?Csoil interaction. The maximum lateral displacement and maximum pile bending moment are obtained for different pile diameters, earthquake predominant frequencies, Arias intensities, and peak accelerations. It is found that the maximum lateral displacement and the maximum pile bending moment increase when the predominant earthquake frequency value decreases for a given peak acceleration value.  相似文献   

Mechanical and Physical Characterization of Tabriz Marls, Iran     

Ali Hooshmand  Mohammad H. Aminfar  Ebrahim Asghari  Hamid Ahmadi 《Geotechnical and Geological Engineering》2012,30(1):219-232

Three types of marls can be found in the Tabriz area (Iran): yellow, green, and gray/black marls. In the present paper, strength and deformation characteristics of Tabriz marls and their stress–strain behavior are investigated by various in situ and laboratory tests. In order to study the deformation behavior of these marls, various experiments such as the pressuremeter test, plate loading test (PLT), seismic wave velocity test, uniaxial compression test, standard penetration test (SPT), and direct shear test were carried out. Ranges of strain at the elastic and failure points were determined. Young’s and shear modulus were obtained. Test results showed that the strength characteristics increase with depth. The value of deformation modulus determined by the pressuremeter test was in good agreement with those obtained from the PLT. This implies that pressuremeter is a suitable in situ test for characterizing the deformation modulus of marl. Deformation modulus obtained from pressuremeter and plate loading tests were approximately 4–5 times the results of uniaxial compressive test and the deformation modulus obtained from seismic data was about 30–50 times the static deformation modulus. Stress–strain curves showed that the maximum value of strain at the elastic and failure points and the minimum value of strength and deformation modulus are corresponding to the yellow marls while the minimum value of strain and the maximum value of strength and deformation modulus are corresponding to the gray/black marls. Some empirical relationships between different characteristics of Tabriz marls were also derived.  相似文献   

An investigation on the ground motion parameters and seismic response of underground structures          下载免费PDF全文

Hamid Reza Nejati  Morteza Ahmadi  Hamid Hashemolhosseini 《地震科学（英文版）》2012,25(3):253-261

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