Search for: pore-pressure
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    Effect of direction of principal stress on cyclic behavior of dense sands

    , Article Geotechnical Special Publication ; 2014 , pp. 1317-1326 ; ISSN: 08950563 ; ISBN: 9780784413272 Jafarzadeh, F ; Zamanian, M ; Sharif University of Technology
    Soils have an anisotropic response, and changing the inclination and magnitude of the major principal stress will affect the collapse potential and brittleness and the shear strength and shear stiffness. A series of undrained cyclic tests on dense Babolsar and Toyoura sands with induced anisotropy were conducted using automatic hollow cylinder apparatus. Special attention was paid to the significant role of the principal stress direction (α). Results show that changes in α has significant effect on the type and the quantity of strains that directly affect the excess pore water pressure generation. Changes in α would change the deformation mode and soil stiffness. Stiffness reduction has led... 

    An experimental study on mechanical behavior of a calcite cemented gravelly sand

    , Article Geotechnical Testing Journal ; Volume 41, Issue 3 , May , 2018 , Pages 494-507 ; 01496115 (ISSN) Shakeri, M. R ; Haeri, S. M ; Shahrabi, M. M ; Khosravi, A ; Sajadi, A. A ; Sharif University of Technology
    ASTM International  2018
    In the study presented herein, a simple method for laboratory calcite cementation of a reconstituted gravelly sand was presented. This method was used to prepare cemented gravelly sand specimens, which have similar natural characteristics to alluvial deposit of the city of Tehran. The formation and distribution of calcite bonds, as well as the effectiveness of the presented calcite cementation method in increasing interparticle cohesion, as observed in weakly to moderately cemented soil in Tehran, were evaluated by means of chemical analysis, X-ray diffraction technique, and unconfined compressive strength tests. The cementation technique was used to prepare triaxial specimens with calcite... 

    Investigation the Effect of Content and Plastisity of Plastic Fines on Liquefaction Resistance of Sand Using Cyclic Simple Shear Tests

    , M.Sc. Thesis Sharif University of Technology Hassani, Mehrdad (Author) ; Ahmadi, Mohammad Mehdi (Supervisor)
    Regarding the existing contrary in the literature in relation to the effect of plastic fine on sand liquefaction behaviour, we decided to study this effect. Amounts of 5, 15, and 25 percent of two types of plastic fine, Kaolinite with PI=19 and Bentonite with PI=116 added to Firoozkooh Sand and 68 stress controlled tests were conducted using cyclic simple shear apparatus. In all teste the frequency of shear loading and consolidating vertical effective stress were constant and 0.1 Ht and 100 kPa respectively. Reaching excess pore water pressure ratio to the maximum value (r_u=Max) and reaching double amplitude shear strain to the value of 5% have been considered as liquefaction critera. In... 

    Study of Hole Pressure Effect on the Oil Recovery from Dead Ends in Polymer Flooding in Petroleum Reservoirs

    , M.Sc. Thesis Sharif University of Technology Zirrahi, Mohsen (Author) ; Ramezani Saadat Aabadi, Ahmad (Supervisor)
    Most of residual oil is difficult to displace and recover during water flooding process. One of the most important chemical flooding processes is polymer flooding that can improve microscopic and macroscopic sweep efficiency. Since, a large percent of reservoirs rocks is consisted of the dead ends in which oil remains immobile during water flooding, study of sweep efficiency from dead ends is important to improve oil recovery efficiency. In this study, effects of polymer flooding on oil recovery from dead end in glass micromodel have been studied experimentally and obtained results are compared with those of simulation of polymeric fluids in this micromodel. A correlation has been presented... 

    Evaluation of variation of permeability in liquefiable soil under earthquake loading

    , Article Computers and Geotechnics ; Volume 40 , 2012 , Pages 74-88 ; 0266352X (ISSN) Shahir, H ; Pak, A ; Taiebat, M ; Jeremić, B ; Sharif University of Technology
    Liquefaction phenomenon is usually accompanied by large amounts of settlement owing to disruption of soil structure. In addition to that, large settlement also occurs by a significant increase in soil permeability during seismic excitation. To properly simulate the post-liquefaction settlement, it is important to take the compressibility properties of the liquefied sand as well as the permeability increase into account. Using initial permeability coefficient in the course of simulation of liquefaction leads to underestimation of settlement. In addition to that, using unrealistic values for permeability may cause erroneous predictions of other aspects of soil behavior. Therefore, an accurate... 

    Evaluation of behaviors of earth and rockfill dams during construction and initial impounding using instrumentation data and numerical modeling

    , Article Journal of Rock Mechanics and Geotechnical Engineering ; Volume 9, Issue 4 , 2017 , Pages 709-725 ; 16747755 (ISSN) Rashidi, M ; Haeri, S. M ; Sharif University of Technology
    In this study, the behavior of gavoshan dam was evaluated during construction and the first impounding. A two-dimensional (2D) numerical analysis was conducted based on a finite difference method on the largest cross-section of the dam using the results of instrument measurements and back analysis. These evaluations will be completed in the case that back analysis is carried out in order to control the degree of the accuracy and the level of confidence of the measured behavior since each of the measurements could be controlled by comparing it to the result obtained from the numerical model. Following that, by comparing the results of the numerical analysis with the measured values, it is... 

    Constitutive modelling of cemented gravelly sands

    , Article Geomechanics and Geoengineering ; Volume 4, Issue 2 , 2009 , Pages 123-139 ; 17486025 (ISSN) Haeri, S. M ; Hamidi, A ; Sharif University of Technology
    A constitutive model is developed for a cemented gravelly sand. The model is based on the separation of the cemented soil to the uncemented part and cemented bonds and combining the mechanical behaviour of each part using consistency and energy equilibrium equations. The uncemented part was modelled using the Pastor et al. (1985) model for sands. A new model was developed and proposed for the cemented bonds. Combination of these parts resulted in the modelling of cemented soil behaviour with a very good consistency both in drained and undrained conditions. The pore pressure in undrained conditions and the volumetric strains in the drained state were also modelled successfully using this... 

    Energy dissipation in saturated loose sand models in one and two-dimensional shaking table tests

    , Article 6th International Conference on Physical Modelling in Geotechnics, ICPMG'06, Hong Kong, 4 August 2006 through 6 August 2006 ; Volume 1-2 , 2006 , Pages 463-467 ; 041541587X (ISBN); 9780415415873 (ISBN) Jafarzadeh, F ; Hamidi, A ; Lotfiazad, F ; Sharif University of Technology
    In this paper the relation between dissipated energy and pore pressure is studied using 1 g shaking table test results. Toyoura sand is used for the physical models. Both one and two dimensional variable phase loadings are applied to the models. Shear work was calculated using accelerations and displacements and normalized to the mean effective stress. Pore water pressure was also normalized to the vertical effective stress. The results show that the pore pressure has a unique relationship to the shear work no matter whether the shaking is one or two dimensional. The results also show that the generated normalized pore pressure is independent of loading type and confinement. © 2006 Taylor &... 

    The behaviour of an artificially cemented sandy gravel

    , Article Geotechnical and Geological Engineering ; Volume 23, Issue 5 , 2005 , Pages 537-560 ; 09603182 (ISSN) Haeri, S. M ; Hosseini, S. M ; Toll, D. G ; Yasrebi, S. S ; Sharif University of Technology
    The major section of the city of Tehran, Iran has been developed on cemented coarse-grained alluvium. This deposit consists of gravely sand to sandy gravel with some cobbles and is dominantly cemented by carbonaceous materials. In order to understand the mechanical behaviour of this soil, a series of undrained triaxial compression tests and unconfined compression tests were performed on uncemented and artificially cemented samples. Portland cement type I was used as the cementation agent for preparing artificially cemented samples. Uncemented samples and lightly cemented samples (1.5% cement) tested at high confining pressure showed contractive behaviour accompanied with positive excess pore... 

    Application of fuzzy set theory to evaluate the effect of pore pressure build-up on the seismic stability of Karkheh Dam, Iran

    , Article Journal of Earthquake Engineering ; Volume 12, Issue 8 , 2008 , Pages 1296-1313 ; 13632469 (ISSN) Shafiee, A ; Bahador, M ; Bahrami, R ; Sharif University of Technology
    It is a current practice to employ composite claya mixture of clay and aggregates that float within the clayey matrixas the core of embankment dams that have classically been constructed from pure clays. Experience has shown that significant pore pressures could build up during cyclic undrained loading in composite clays. This may threaten dam stability during earthquake loading. However, it is difficult to attribute a single value to excess pore pressure in conventional seismic stability analysis because of the random nature of earthquake loading, leading to uncertainty in the evaluation of factor of safety against sliding. This article evaluates the importance of pore pressure build-up in... 

    Simulation of Rainfall-triggered Landslides with Considering the Rheology Changes in Sandy Soils

    , Ph.D. Dissertation Sharif University of Technology Ghorbani, Ramin (Author) ; Taghizadeh Manzari, Mehrdad (Supervisor) ; Hajilouy-Benisi, Ali (Co-Supervisor)
    This study presents an integrated two-dimensional numerical framework for simulating rainfall-induced landslides from instability initiation to post-failure flow. The discrete element method (DEM) is used to establish a rheological model that relates the apparent viscosity of a granular sand to shear rate, normal stress, and water saturation. A theoretical model is developed to determine water distribution and water-induced forces between particles for different saturations. The resulting forces are embedded in a 3D shear cell as a numerical rheometer and a wet sand is sheared between two walls. A power law rheological model is obtained as a function of inertia number and saturation. It was... 

    Study of pore pressure variation during liquefaction using two constitutive models for sand

    , Article Soil Dynamics and Earthquake Engineering ; Volume 27, Issue 1 , 2007 , Pages 60-72 ; 02677261 (ISSN) Taiebat, M ; Shahir, H ; Pak, A ; Sharif University of Technology
    Numerical analyses of liquefiable sand are presented in this paper. Liquefaction phenomenon is an undrained response of saturated sandy soils when they are subjected to static or dynamic loads. A fully coupled dynamic computer code is developed to predict the liquefaction potential of a saturated sandy layer. Coupled dynamic field equations of extended Biot's theory with u-P formulation are used to determine the responses of pore fluid and soil skeleton. Generalized Newmark method is employed for integration in time. The soil behavior is modelled by two constitutive models; a critical state two-surface plasticity model, and a densification model. A class 'B' analysis of a centrifuge... 

    Effect of cement type on the mechanical behavior of a gravely sand

    , Article Geotechnical and Geological Engineering ; Volume 24, Issue 2 , 2006 , Pages 335-360 ; 09603182 (ISSN) Haeri, S. M ; Hamidi, A ; Hosseini, S. M ; Asghari, E ; Toll, D. G ; Sharif University of Technology
    The behavior of a cemented gravely sand was studied using triaxial compression tests. Gypsum, Portland cement and lime were used as the cementing agents in sample preparation. The samples with different cement types were compared in equal cement contents. Three cement contents of 1.5%, 3.0% and 4.5% were selected for sample preparation. Drained and undrained triaxial compression tests were conducted in a range of confining pressures from 25 kPa to 500 kPa. Failure modes, shear strength, stress-strain behavior, volume and pore pressure changes were considered. The gypsum cement induced the highest brittleness in soil among three cement types while the Portland cement was found to be the most... 

    Coupled hydro-mechanical analysis of underground gas storage at Sarajeh field, Qom formation, Iran

    , Article Journal of Natural Gas Science and Engineering ; Volume 92 , 2021 ; 18755100 (ISSN) Bakhtiari, M ; Shad, S ; Zivar, D ; Razaghi, N ; Sharif University of Technology
    Elsevier B.V  2021
    Production or injection of fluids from/in an underground storage site causes variations of pore pressure and stress states. These fluctuations significantly affect implications for hydraulic fracturing, wellbore integrity, top surface subsidence and heave, fault-reactivation, and stability of reservoir and caprock. Therefore, in order to keep optimal conditions during the process of gas injection and production, it is of paramount importance to have accurate estimates of the pore pressure. In this investigation, coupled fluid flow and geomechanical simulations, as well as rock mechanical tests, are performed on the Sarajeh field, Iran to investigate the geomechanical behavior of the Sarajeh... 

    A vacuum-refilled tensiometer for deep monitoring of in-situ pore water pressure

    , Article Scientia Iranica ; Volume 27, Issue 2A , 2021 , Pages 596-606 ; 10263098 (ISSN) Sadeghi, H ; Chiu, A. C. F ; Ng, C. W. W ; Jafarzadeh, F ; Sharif University of Technology
    Sharif University of Technology  2021
    Real-time measurement of soil water pressure has been recognized as an essential part of investigating water ow in unsaturated soils. Tensiometry, amongst different measuring techniques, is a common method for direct evaluation of water pressure. However, the lower limit of measurable water pressure by a conventional tensiometer becomes even more limited by increasing its length in the vertical installation. This paper describes the development of a Vacuum-Refilled Tensiometer (VRT) for monitoring soil water pressure independent of installation depth. This is achieved by fixing the distance between pressure sensor and ceramic cup together with incorporating an ancillary vacuumre filling... 

    The effect of gypsum cementation on the mechanical behavior of gravely sands

    , Article Geotechnical Testing Journal ; Volume 28, Issue 4 , 2005 , Pages 380-390 ; 01496115 (ISSN) Haeri, S. M ; Hamidi, A ; Tabatabaee, N ; Sharif University of Technology
    The behavior of a cemented gravely sand is studied using triaxial tests. Drained and undrained tests were performed on dry and saturated specimens, and stress-strain characteristics of the soil, along with volumetric and pore pressure changes, were identified. The gypsum plaster was used as the cement agent and was mixed with the soil in different percentages. The tests were done in the usual range of confining pressures, from 25 to 500 kPa. Test results show that dilation occurs even at the highest confining stress and the least cement content. The behavior of the cemented soil is found to be more brittle in drained condition than the undrained one. However, the brittleness of soil... 

    Investigation of the influence of permeability coefficient on the numerical modeling of the liquefaction phenomenon

    , Article Scientia Iranica ; Volume 19, Issue 2 , 2012 , Pages 179-187 ; 10263098 (ISSN) Rahmani, A ; Ghasemi Fare, O ; Pak, A ; Sharif University of Technology
    The soil permeability coefficient plays a key role in the process of numerical simulation of the liquefaction phenomenon. Liquefaction causes a considerable increase in soil permeability, due to the creation of easier paths for water flow. The work presented in this paper tries to investigate the effects of permeability coefficient on the results of numerical modeling of the liquefaction phenomenon. To do this, a fully coupled (u-P) formulation is employed to analyze soil displacements and pore water pressures. Two different versions of a well-calibrated critical state bounding surface plasticity model, which possesses the capability to utilize a single set of material parameters for a wide... 

    Finite volume coupling strategies for the solution of a Biot consolidation model

    , Article Computers and Geotechnics ; Vol. 55, issue , January , 2014 , p. 494-505 ; ISSN: 0266352X Asadi, R ; Ataie-Ashtiani, B ; Simmons, C. T ; Sharif University of Technology
    In this paper a finite volume (FV) numerical method is implemented to solve a Biot consolidation model with discontinuous coefficients. Our studies show that the FV scheme leads to a locally mass conservative approach which removes pressure oscillations especially along the interface between materials with different properties and yields higher accuracy for the flow and mechanics parameters. Then this numerical discretization is utilized to investigate different sequential strategies with various degrees of coupling including: iteratively, explicitly and loosely coupled methods. A comprehensive study is performed on the stability, accuracy and rate of convergence of all of these sequential... 

    Electrodeposition of long gold nanotubes in polycarbonate templates as highly sensitive 3D nanoelectrode ensembles

    , Article Electrochimica Acta ; Volume 75 , 2012 , Pages 157-163 ; 00134686 (ISSN) Bahari Mollamahalle, Y ; Ghorbani, M ; Dolati, A ; Sharif University of Technology
    Elsevier  2012
    Electrodeposition of long and well-defined gold nanotubes in polycarbonate (PC) templates is still a major concern due to pore blockage problems. In the present study, we introduce a novel method for electrodeposition of long gold nanotubes within the pores of PC templates for the first time. In order to deposit gold atoms onto the pore walls preferentially, pore walls were functionalized with a coupling agent. Short and thin Ni nanotubes were then electrodeposited at the bottom of the pores. Gold nanotubes were subsequently electrodeposited at constant potentials and low solution concentrations. The morphology of nanotubes was characterized by electron microscopy and their formation... 

    Response of a group of piles to liquefaction-induced lateral spreading by large scale shake table testing

    , Article Soil Dynamics and Earthquake Engineering ; Volume 38 , 2012 , Pages 25-45 ; 02677261 (ISSN) Haeri, S. M ; Kavand, A ; Rahmani, I ; Torabi, H ; Sharif University of Technology
    Liquefaction-induced lateral spreading has imposed severe damages to many important structures supported on pile foundations during past earthquakes. As a result, evaluation of pile response to lateral spreading is an important step towards safe and resistant design of pile foundations against this destructive phenomenon. Current paper aims to study the response of a group of piles subjected to liquefaction-induced lateral spreading using a large scale 1-g shake table test. General test results including time-histories of accelerations, pore water pressures, displacements and bending moments are presented and discussed in this paper. In addition, distribution of lateral soil pressure on...