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unsaturated-sand
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Characterizing the Effect of Fines Content on Small Strain Shear Modulus of Unsaturated Sandy Soils by Bender Element Test
, M.Sc. Thesis Sharif University of Technology ; Haeri, Mohsen (Supervisor) ; Khosravi, Ali (Supervisor)
Abstract
Small strain shear modulus, Gmax, is one of the most important parameters for characterization of the behavior of earth structures subjected to static or dynamic loading conditions. This research presents an experimental laboratory study on the effect of non-plastic fines content and hydraulic hysteresis on the maximum shear modulus of unsaturated sand-silt mixtures. In this regard, clean Firoozkuh No. 161 silica sand which is classified as poorly graded uniform sand was mixed with different percentages of silica non-plastic silt. A set of bender element tests were planned to carry out implementing two modified triaxial devices. The modifications on these two apparatus were to add HAV...
Use of Bio-Cementation for Reducing Land Subsidence
, M.Sc. Thesis Sharif University of Technology ; Khosravi, Ali (Supervisor) ; Pak, Ali (Supervisor) ; Ghobadi Nejad, Zahra ($item.subfieldsMap.e)
Abstract
Land subsidence is a gradual settling or sudden sinking of the land surface from changes that take place underground. There are different causes of land subsidence; most notably, groundwater overdraft and severe weather conditions. Subsidence of the land surface due to ground water overdraft is caused by an increase in the intergranular pressure in unconsolidated aquifers, which results in a loss of buoyancy of solid particles in the zone dewatered by the falling water table and accordingly compaction of the aquifer. In this study, an experimental approach was developed to examine applicability of Microbially induced carbonate precipitation (MICP) for land subsidence control under...
Coupled effects of suction and degree of saturation on large strain shear modulus of unsaturated sands
, Article Unsaturated Soils: Research and Applications - Proceedings of the 6th International Conference on Unsaturated Soils, UNSAT 2014 ; Vol. 2, issue , July , 2014 , p. 1559-1564 ; 978-1-138-00150-3 ; Ahmadinezhad, A ; Sadeghi, H ; Sharif University of Technology
Abstract
Predictions of soil behavior in response to dynamic loads require an understanding of dynamic properties of soil. Studies on dynamic properties of unsaturated soils at large-strains are quite limited, while some dynamic loadings, like earthquakes, are in the medium to large-strain ranges. A cyclic simple shear apparatus was developed to measure large-strain shear modulus and damping ratio under different matric suction or degree of saturation. Six cyclic tests, with referring to the soil-water retention curve, were conducted on clean medium sand. Results indicated that shear modulus slightly increases when suction varies from zero up to the air entry value. Approaching the residual value, a...
Studying the Dynamics Behavior of the Partially Saturated Sand under Different Hydro-mechanical Loading with Resonant Column- torsional Shear and Bender Elements Apparatuses
, M.Sc. Thesis Sharif University of Technology ; Khosravi, Ali (Supervisor)
Abstract
Considering the importance of studying dynamic characteristics of soils in the analysis of wave propagation and the design of earth constructions or soil-related structures, as well as the role of Resonant Column-Torsional Shear in determining the dynamic parameters, including shear modulus, damping ratio and wave velocity in soil, this device was designed and developed in this research. The apparatus developed is able to conduct both resonant column and torsional shear tests and also measure dynamic parameters in large ranges of strain. The unsaturated pressure panel built alongside this device and the especial design of the device components have made the above-mentioned experiments...
Evaluation of the Effects of Principal Stress Direction on Dynamic Properties of Unsaturated Sand by Hollow Cylinder Apparatus
, M.Sc. Thesis Sharif University of Technology ; Jafarzadeh, Fardin (Supervisor)
Abstract
Soils have an anisotropic response, and mechanical and dynamic properties of this material are greatly dependent on the direction and magnitude of principal stresses. A reliable assessment of the soil behavior and a good estimation of the soil parameters need to perform tests in similar condition with in-situ. From all the devices used for studying anisotropy of soils, hollow cylinder apparatus is the only apparatus that enables an independent control of both the direction and magnitude of the principal stresses. Moreover, one of the most controversial topics in the unsaturated soil dynamics is determining the shear modulus and damping ratio which are used for assessing many geotechnical...
Impact of Net Stress on Stress State of an Unsaturated Sand
, M.Sc. Thesis Sharif University of Technology ; Khosravi, Ali (Supervisor)
Abstract
Results of an advanced suction controlled triaxial test device in an attempt to define the constitutive relationship between suction stress and matric suction (Suction Stress Characteristic Curve, SSCC) for unsaturated sand was presented. The suction stress is a macroscopic stress that incorporates the effects of capillary van der Waals forces cementation, and electrical double-layer repulsion into the definition of effective stress for unsaturated soils. Results of previous studies on silt and clay indicated that variations in the suction stress, during drying path had a non-linear increasing trend with matric suction with greater values upon wetting. However, due to different material...
Impact of hydraulic hysteresis on the small strain shear modulus of unsaturated sand
, Article Soils and Foundations ; Volume 58, Issue 2 , 2018 , Pages 344-354 ; 00380806 (ISSN) ; Shahbazan, P ; Pak, A ; Sharif University of Technology
Japanese Geotechnical Society
2018
Abstract
The results of previous studies on silt and clay indicated that variations in the small strain shear modulus, Gmax, during hydraulic hysteresis had a non-linear increasing trend with matric suction, with greater values upon wetting. However, due to differences in material properties and inter-particle forces, a different behavior is expected for the Gmax of unsaturated sand. Although considerable research has been devoted in recent years to characterizing the behavior of the Gmax of sand during drying, less attention has been paid to the effect of hydraulic hysteresis on Gmax and its variations during wetting. In the study presented herein, an effective stress-based semi-empirical model was...
Evaluation of the effects of principal stress direction on shear modulus of unsaturated sand using hollow cylinder apparatus
, Article 7th International Conference on Earthquake Geotechnical Engineering, ICEGE 2019, 17 January 2019 through 20 January 2019 ; 2019 , Pages 3102-3108 ; 9780367143282 (ISBN) ; Ahmadi Givi, F ; Ahmadinezhad, A ; Silvestri F ; Moraci N ; Sharif University of Technology
CRC Press/Balkema
2019
Abstract
Determination of soil shear modulus is one of the most controversial topics in unsaturated soil dynamics. Due to the fact that soils have an anisotropic response, the shear strength and stiffness of geological materials are greatly dependent on the principal stress direction and the intermediate principal stress. In this study, the effects of principal stress direction on shear modulus of unsaturated medium-dense sand have been investigated using cyclic hollow cylinder apparatus. Three series of stress-controlled cyclic tests with different fixed principal stress directions were carried out on the sand sample under different values of suction. Results reveal that shear modulus of unsaturated...
Evaluation of the effects of principal stress direction on shear modulus of unsaturated sand using hollow cylinder apparatus
, Article 7th International Conference on Earthquake Geotechnical Engineering, ICEGE 2019, 17 January 2019 through 20 January 2019 ; Pages 3102-3108 , 2019 ; 9780367143282 (ISBN) ; Ahmadi Givi, F ; Ahmadinezhad, A ; Silvestri F ; Moraci N ; Sharif University of Technology
CRC Press/Balkema
2019
Abstract
Determination of soil shear modulus is one of the most controversial topics in unsaturated soil dynamics. Due to the fact that soils have an anisotropic response, the shear strength and stiffness of geological materials are greatly dependent on the principal stress direction and the intermediate principal stress. In this study, the effects of principal stress direction on shear modulus of unsaturated medium-dense sand have been investigated using cyclic hollow cylinder apparatus. Three series of stress-controlled cyclic tests with different fixed principal stress directions were carried out on the sand sample under different values of suction. Results reveal that shear modulus of unsaturated...
The Effect of Induced Anisotropy on the Dynamic Properties of Unsaturated Sand at Constant Suction by Hollow Cylinder Apparatus
, M.Sc. Thesis Sharif University of Technology ; Jafarzadeh, Fardin (Supervisor)
Abstract
Soils have an anisotropic response, and mechanical and dynamic properties of this material are greatly dependent on the direction and magnitude of principal stresses. A reliable assessment of the soil behavior and a good estimation of the soil parameters need to perform tests in similar condition with in-situ. From all the devices used for studying anisotropy of soils, hollow cylinder apparatus is the only apparatus that enables an independent control of both the direction and magnitude of the principal stresses. Moreover, one of the most controversial topics in the unsaturated soil dynamics is determining the shear modulus and damping ratio which are used for assessing many geotechnical...
Dynamic parameters of saturated and unsaturated sand at different ranges of shear strain levels in cyclic simple shear tests
, Article 14th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering ; 2011 ; Golshan, Z ; Sharif University of Technology
2011
Abstract
In order to evaluate dynamic properties of Babolsar and Toyoura sands at saturation levels of 25, 50, 75 & 100%, a series of cyclic simple shear tests were carried out. The SGI type cyclic simple shear device was used to study the shear modulus, G, and damping ratio, D, of the above mentioned sands at cyclic shear strain of 0.5, 5 & 10%. The effect of degree of saturation (S), vertical consolidation stress (σ vc) and number of loading cycles (N) were investigated. On the basis of the tests results, the shear modulus approximately remains constant by change of degree of saturation from 25 to 50% and decreases when reaches the degree of saturation 75%. Damping ratio approximately is constant...
Interpretation of CPT in unsaturated sands under drained conditions: A numerical study
, Article International Journal for Numerical and Analytical Methods in Geomechanics ; Volume 45, Issue 18 , 2021 , Pages 2732-2755 ; 03639061 (ISSN) ; Ahmadi, M. M ; Sharif University of Technology
John Wiley and Sons Ltd
2021
Abstract
A finite difference-based numerical model simulating the cone penetration process in unsaturated sands is presented. Mohr–Coulomb model (MCM) with simple modifications and Sun model (SM) were implemented to capture the unsaturated sand behaviour. It was shown that the cone tip resistance values resulting from the two models were fairly comparable. Predicted cone tip resistance values in dry, saturated and unsaturated sands using MCM were validated by the results of field and calibration chamber tests. Sensitivity analyses were performed, and the influence of parameters including relative density, mean effective stress and apparent cohesion due to suction on the tip resistance was...