Loading...
Search for:
critical-state
0.005 seconds
Behavior of gravely sand using critical state concepts
, Article Scientia Iranica ; Volume 12, Issue 2 , 2005 , Pages 167-177 ; 10263098 (ISSN) ; Haeri, S. M ; Toll, D. G ; Sharif University of Technology
Sharif University of Technology
2005
Abstract
A series of consolidated undrained triaxial tests were performed in order to understand the behavior of a gravely sand. The material was selected from Tehran alluvium and is classified as gravely sand in the Unified Soil Classification System. Critical state concepts were used for interpretation of the behavior of the soil. The critical state line in q - p′ space was reasonably unique. However, it was not possible to define a unique critical state line in e -ln p′ space. The overall scatter, in the critical state line for the gravely sand studied, was ± 0.04, in terms of void ratio. Two reasons can be identified for this scatter. The first reason is the inevitable error in void ratio...
Evaluate of Undrained Behavior of Uncompacted Gravely Soil With Triaxial Apparatus Under Anisotropic Condition
, M.Sc. Thesis Sharif University of Technology ; Haeri, Mohsen (Supervisor)
Abstract
The study of the behavior of gravelly soil in undrained condition has been a major topic for researchers for decades. Liquefaction in gravelly soils in recent earthquake has exposed the importance and necessity of investigation on undrained the behavior of gravely soils in earthquakes. In this research, undrained behavior of gravely soils and the effects of initial static shear stress on their behavior have been investigated. In this experimental research a gravelly soil (GP) performed and a triaxial apparatus is used. All tests are performed under consolidated undraiend condition and the specimens are prepared by wet tamping method. The diameter of the specimen was 10 cm and the height was...
Critical state concepts for a cemented gravely sand
, Article Electronic Journal of Geotechnical Engineering ; Volume 10 E , 2005 ; 10893032 (ISSN) ; Haeri, S. M ; Sharif University of Technology
2005
Abstract
The shear behavior of a cemented gravely sand that can be considered as the representative of Tehran alluvium has been studied using triaxial equipment. Artificially cemented samples were prepared using gypsum plaster as the cementing agent. The plaster was mixed with the base soil at the weight percentages between 1.5 and 6. The critical state concepts were used to illustrate the mechanical behavior of tested soil. © 2005 ejge
Effect of soil structure and disturbance on hydromechanical behavior of collapsible loessial soils
, Article International Journal of Geomechanics ; Volume 17, Issue 1 , 2017 , Pages 1-15 ; 15323641 (ISSN) ; Khosravi, A ; Akbari Garakani, A ; Ghazizadeh, S ; Sharif University of Technology
American Society of Civil Engineers (ASCE)
2017
Abstract
To characterize the role of specimen disturbance and structure in the hydromechanical behavior of collapsible soils, two sets of wetting-induced collapse and suction-controlled triaxial tests were conducted on intact and reconstituted specimens of a loessial soil taken from a loess deposit in Gorgan, a city in the northeastern Golestan province of Iran. The testing approach used an advanced triaxial testing device that was specifically modified to control pressures applied to a soil specimen and to monitor and measure the amount of changes in volume and water content of the soil specimens during testing using highly sensitive digital sensors with an accuracy of 60.01 cm3. Results of the...
A modified two-surface plasticity model for saturated and unsaturated soils
, Article Indian Geotechnical Journal ; Volume 52, Issue 4 , 2022 , Pages 865-876 ; 09719555 (ISSN) ; Hajitaheriha, M. M ; Hasani Motlagh, A ; Sadeghi, H ; Sharif University of Technology
Springer
2022
Abstract
A modified two-surface critical state plasticity model for saturated and unsaturated soil is presented in this study. The key modification in new model is inclusion of an alternative yield surface used to simulate the behavior of unsaturated soils in addition to corresponding saturated conditions. Moreover, a numerical technique is used to obtain an incremental stress–strain response from loading curves. Modification is applied continuously in each incremental step to return the final stress states and hardening parameters to the yield surface. Results revealed that the adopted modeling approach can predict two independent sets of laboratory unsaturated experiments under various conditions...
The measurement of suction stress characteristic curve for a highly collapsible loessial soil
, Article Geotechnical Special Publication, 17 March 2015 through 21 March 2015 ; Volume GSP 256 , 2015 , Pages 2482-2491 ; 08950563 (ISSN) ; 9780784479087 (ISBN) ; Khosravi, A ; Ghazizadeh, S ; Anderson, J. B ; Iskander, M ; Suleiman, M. T ; Laefer, D. F ; Sharif University of Technology
American Society of Civil Engineers (ASCE)
2015
Abstract
This paper describes results of an advanced suction controlled triaxial test device on a loessial soil in an attempt to define the constitutive relationship between suction stress and matric suction (suction stress characteristic curve) for highly collapsible soils. Due to the presence of void spaces with different degrees of collapse potential within the soil matrix, the collapse phenomenon in loess is believed to be a continuous-stepwise reduction in volume rather than a sudden drop during wetting. Due to this unique volume change behavior, the definition of the suction stress characteristic curve for loess may require a soil-specific experimental testing approach capable of making precise...
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) ; Shahir, H ; Pak, A ; Sharif University of Technology
2007
Abstract
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...
An Investigation on the Effects of Liquefaction-Induced Lateral Spreading on Deep Foundations Using Finite Difference Method
, M.Sc. Thesis Sharif University of Technology ; Haeri, Mohsen (Supervisor)
Abstract
Liquefaction is an important phenomenon in geotechnical engineering which can cause severe damages to structures. Liquefaction-induced lateral spreading is defined as the lateral displacement in mild slopes or level grounds ending in free faces (such as quay walls) triggered by liquefaction in subsurface soil layers. During recent years, extensive studies have been conducted around the world documenting liquefaction induced lateral spreading and its effects on deep foundations. In the present study, a series of shaking table experiments which were previously conducted at Sharif University of Technology are numerically simulated using the three dimensional finite difference based program,...
Assessment of the Hydro-mechanical Behavior of Undisturbed Collapsible Soils by Conducting Unsaturated Triaxial Tests
, Ph.D. Dissertation Sharif University of Technology ; Haeri, Mohsen (Supervisor) ; Habib Agahi, Ghassem (Co-Advisor)
Abstract
Wide lands in IRAN are covered by the “Hydro – Collapsible” soils. These types of soils possess high apparent shear strength in their natural condition but are highly susceptible to volume collapse upon wetting. This behavior is generally attributed to their open, unstable soil fabric and their weak inter-particle bonding forces, which together yield a soil void structure that is susceptible to collapse.
Previous studies rarely investigated the roles of stress state level, matric suction and stress path on the hydro-mechanical nature of the collapse phenomenon. Also most studies dealt with conducting laboratory tests on remolded soil specimens through which the role of natural soil...
Previous studies rarely investigated the roles of stress state level, matric suction and stress path on the hydro-mechanical nature of the collapse phenomenon. Also most studies dealt with conducting laboratory tests on remolded soil specimens through which the role of natural soil...
Hydro-mechanical behavior of undisturbed collapsible loessial soils under different stress state conditions
, Article Engineering Geology ; Volume 195 , September , 2015 , Pages 28-41 ; 00137952 (ISSN) ; Haeri, S. M ; Khosravi, A ; Habibagahi, G ; Sharif University of Technology
Elsevier
2015
Abstract
A conventional triaxial test device was modified to characterize the hydro-mechanical behavior of a loessial soil during isotropic and shear loadings. This device is capable of precise and continuous measurements of water outflow during the application of loading. The tests were performed on "undisturbed" cylindrical specimens, which were taken from loessial deposits in Gorgan, a city in the northeast of Iran. Experimental measurements indicate that the hydro-mechanical behavior of loess is highly affected by the extent of applied mean net stress and the level of suction. During both isotropic and shearing stages of loading, the tested specimens may exhibit collapse, abrupt decrease in...
A critical state constitutive model for the isotropic thermal compression of structured sand–bentonite buffers
, Article Indian Geotechnical Journal ; Volume 49, Issue 4 , 2019 , Pages 398-408 ; 09719555 (ISSN) ; Karimi, A. H ; Hamidi, A ; Ahmadi, M. M ; Sharif University of Technology
Springer
2019
Abstract
The sand–bentonite mixture is used as the buffer layer in nuclear waste disposals. The buffer layer, as a non-permeable protective layer, is generally exposed to temperature gradients and the long-term subjection to temperature results in creep and more intact structure for the layer. In the present study, thermally induced structure and its effects on the isotropic compression behavior and volume change behavior of buffer layer are evaluated. Thermal consolidation tests were conducted using a modified triaxial cell capable of handling temperatures up to 90 °C. In order to investigate the effects of thermal gradients on the behavior of the mixture, saturated specimens were cured at constant...
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) ; Ghasemi Fare, O ; Pak, A ; Sharif University of Technology
2012
Abstract
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...
Thermo-mechanical analysis of Roller Compacted Concrete (RCC) dams (Jahgin Dam)
, Article Proceedings of the Symposium on the Application of Geophyics to Engineering and Environmental Problems, SAGEEP, 29 March 2009 through 2 April 2009, Fort Worth, TX ; Volume 1 , 2009 , Pages 417-427 ; 15548015 (ISSN) ; 9781615670512 (ISBN) ; Ghaemian, M ; Azimfar, S. M ; Sharif University of Technology
Abstract
In this paper a procedure for two-dimensional unsteady thermo-mechanical analysis of layered structures is presented, allowing the determination of the temperature and stress field at each step the construction period. The finite element method is employed in the methodology. Numerical simulation are focused on concrete structures, particularly roller compacted concrete (RCC) dams. A time varying elasticity modulus is introduced in the model. One case study is presented and analysis under different design approaches. Thermal effects must be considered in the process of designing of certain types of concrete structures in order to prevent the damage during either the construction phase (early...
Numerical investigation of the effects of soil densification on the reduction of liquefaction-induced settlement of shallow foundations
, Article Scientia Iranica ; Volume 16, Issue 4 A , 2009 , Pages 331-339 ; 10263098 (ISSN) ; Pak, A ; Sharif University of Technology
2009
Abstract
The liquefaction phenomenon is usually accompanied by a large amount of settlement. Based on the observations made in past earthquakes, ground improvement by densification is one of the most useful approaches to reduce the liquefaction-induced settlement. Currently, there is no analytical solution for evaluation of the amount of settlement and tilting of footings that are constructed on densified ground surrounded by liquefiable soil. A number of factors, such as underlying soil properties, dimensions of the footing and earthquake loading characteristics, cause the problem to become complicated. In this paper, the dynamic response of shallow foundations on both liquefiable and...
Evaluation of variation of permeability in liquefiable soil under earthquake loading
, Article Computers and Geotechnics ; Volume 40 , 2012 , Pages 74-88 ; 0266352X (ISSN) ; Pak, A ; Taiebat, M ; Jeremić, B ; Sharif University of Technology
2012
Abstract
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...
Dynamic behavior of pile foundations under cyclic loading in liquefiable soils
, Article Computers and Geotechnics ; Volume 40 , 2012 , Pages 114-126 ; 0266352X (ISSN) ; Pak, A ; Sharif University of Technology
Abstract
In this paper, a fully coupled three-dimensional dynamic analysis is carried out to investigate the dynamic behavior of pile foundations in liquefied ground. A critical state bounding surface plasticity model is used to model soil skeleton, while a fully coupled (u- P) formulation is employed to analyze soil displacements and pore water pressures. Furthermore, in this study, variation of permeability coefficient during liquefaction is taken into account; the permeability coefficient is related to excess pore water pressure ratio. Results of a centrifuge test on pile foundations are used to demonstrate the capability of the model for reliable analysis of piles under dynamic loading. Then, the...