- Shahid Beheshti University, Water and Environmental Engineering, Faculty Memberadd
- Geotechnical Engineering, Soil Mechanics, Earthquake Geotechnical Engineering, Foundation Engineering, Geomechanics, Pile Foundations, Geosynthetics, Finite Element Method, and 24 moreConstitutive Modeling, Computational geomechanics, Seismic soil-structure interaction (pile foundations), Computational Geomechanics and Modelling in Geotechnology, Sand Constitutive Modeling, Geomechanics and softcomputing, Multiscale Model of Geomechanics, Optimization Methods, Numerical Modeling, Soil Behavior, Soil Dynamics, Finite Element Simulations, Soil Foundations, Excavations, Genetic Algorithms, Water Resources and Environmental Engineering, Constitutional Law, Earthquake Engineering, Tunnel Engineering, Granular Media, MSW Mechanical Behavior, Laboratory Study, Critical State, and Compact Stateedit
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In this study, the influence of cyclic thermal loading on the mechanical response of an energy pile installed in saturated clay subjected to sustained combined axial/horizontal mechanical loading was investigated using physical modelling.... more
In this study, the influence of cyclic thermal loading on the mechanical response of an energy pile installed in saturated clay subjected to sustained combined axial/horizontal mechanical loading was investigated using physical modelling. After completion of the soil saturation process and prior to starting the thermo-mechanical loading, the pile fixation was released inducing pile head heave. When the rate of pile head heave became small, the model pile was subjected to compression axial loading of 100 N (i.e. 20% of the estimated ultimate axial load) followed by horizontal loading of 35, 71 and 109 N (corresponding to accumulative pile head horizontal displacements of 4, 7 and 12% of pile diameter) before subsequent 15 heating–cooling cycles. The results indicated that imposing heating–cooling cycles to the pile resulted in irreversible horizontal displacement, accumulating at a reducing rate as the number of thermal cycles increased. By the end of the 15th cycle, the accumulated irreversible horizontal displacement was estimated at 0·57, 1·15 and 1·84% of pile diameter under the horizontal loads of 35, 71 and 109 N, respectively. Reversely, thermally induced pile head axial displacement at the end of the 15th cycle is practically insignificant (smaller than 0·1% of pile diameter).
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Probabilistic seismic analysis provides a tool for considering uncertainty of the soil parameters and earthquake characteristics. In this paper, by considering soil uncertainties by using Monte Carlo simulation (MCs) along with Finite... more
Probabilistic seismic analysis provides a tool for considering uncertainty of the soil parameters and earthquake characteristics. In this paper, by considering soil uncertainties by using Monte Carlo simulation (MCs) along with Finite Element Method (FEM) dynamic time-series slope stability analysis of an earth dam has been investigated. For reliability assessment, the reliability index and probability of failure of slope stability safety factor in time domain are determined. Soil parameters uncertainties are modeled with normal distributions with and without consideration the cross correlation between cohesion and internal friction angle. To assess the effects of seismic loading, the slope stability reliability analysis is made with modified San-Fernando earthquake record. The results indicate that reliability assessment as dynamic time-series analysis is an efficient tool for safe design of dams. RÉSUMÉ: L'analyse sismique probabiliste est une méthode pour la prise en compte de l'in-certitude des paramètres du sol et des caractéristiques du séisme. Dans cet article, l'analyse dynamique série-chronologique de la stabilité de la pente des barrages en terre a été étudiée en considérant l'incertitude du sol par la méthode de simulation Monte Carlo et la méthode d'élé-ment fini. Afin d'évaluer la fiabilité, l'index de la fiabilité et le coefficient de la certitude de la stabilité pour la probabilité de la destruction de la pente dans le domaine temporel ont été déterminés. L'incertitude des paramètres du sol aux distributions normales avec/sans considér-ation de la corrélation croisée entre la cohésion et l'angle de friction interne ont été modélisés. De plus, la stabilité de la pente a été analysée par la méthode modifiée d'enregistrement des ondes sismiques de San Fernando afin d'évaluer les effets de la charge sismique. Les résultats montrent que l'évaluation de la fiabilité par l'analyse série-chronologique dynamique est une méthode efficace pour le design sûr des barrages.
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AbstractErosion is one of the key factors in environmental management and river restoration. Different mechanisms influence riverbank stability and mass failure, such as seepage erosion. The presen...
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Nowadays, more and more construction activities are carried out on highly compressible layers of soft soil. The engineering challenges for this kind of soil are that it commonly exhibits large amount of time-dependent strains. When soil... more
Nowadays, more and more construction activities are carried out on highly compressible layers of soft soil. The engineering challenges for this kind of soil are that it commonly exhibits large amount of time-dependent strains. When soil is subjected to a constant effective stress, it deforms over time that is called creep. Creep behavior influences the long-term settlement of grounds and movement of slopes and also piles that are used for slope stability due to lateral loading. Understanding the lateral response of pile placed in slope is an important issue of concern. In order to investigate slope stability of soft soils using pile foundation, in this paper the analyses have been performed for the pile located at the crest of the slope and at a distance from the crest considering soft soil creep.
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Improving the characteristics of local low-strength soils at the construction site is one of the appropriate approaches to employ the soils as a backfill of geogrid-reinforced soil (GRS) walls. In this study, the fiber-cement-treated... more
Improving the characteristics of local low-strength soils at the construction site is one of the appropriate approaches to employ the soils as a backfill of geogrid-reinforced soil (GRS) walls. In this study, the fiber-cement-treated sand–silt mixture was used as the backfill of walls. The post-earthquake performance of the walls was evaluated by applying the sinusoidal waves on 1 m high reduced-scale physical models and conducting a series of 1g shaking table tests. A comparison of the wall models constructed with treated and untreated backfill indicated the advantages of geogrid-reinforced fiber-cement-treated soil walls subjected to strong ground motion. The results revealed the better behavior of the wall models backfilled with treated soil mixtures under dynamic loading. Such improved performance was more evident in (i) deformation responses, including the lateral displacement of wall facing, deformation mode, failure surfaces, and settlement of backfill surface and (ii) acceleration response in different locations, including facing, reinforced, and retained zones of walls.
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As the use of geogrid reinforced soil (GRS) walls increases, appropriate solutions should be considered to improve their performance. In recent years, wall construction in the multi-tiered configuration has improved both static and... more
As the use of geogrid reinforced soil (GRS) walls increases, appropriate solutions should be considered to improve their performance. In recent years, wall construction in the multi-tiered configuration has improved both static and post-earthquake behavior, and become an appropriate approach to building high-reinforced soil walls. In addition to the above approach, treatment of the soil used as the wall backfill is also a suitable solution to enhance the wall performance. In this study, a combination of the two above concepts has been employed for better understanding the GRS wall behavior by developing a series of reduced-scale physical models. One-meter-high models in one- and multi-tiered fashion were tested backfilled with untreated and treated (by adding a combination of cement and polypropylene fibers) silty sand mixture. A comparison of the 1-g shaking table tests among wall models subjected to seismic waves indicated the influence of the treating solutions on the dynamic response of the walls. The findings suggest that use of the two proposed approaches in the GRS walls construction has a notable effect on the wall stability after construction and during an earthquake. It also improves the essential seismic parameters such as displacement and acceleration responses.
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Abstract Construction of mechanically stabilized earth (MSE) walls in multi-tiered configurations is a promising solution for increasing the height of such walls. The good performance of this type of walls after recent major earthquakes... more
Abstract Construction of mechanically stabilized earth (MSE) walls in multi-tiered configurations is a promising solution for increasing the height of such walls. The good performance of this type of walls after recent major earthquakes was reported in a number of technical studies. In the present study, an experimental approach was adopted to compare the seismic performance of single-tiered and multi-tiered MSE walls using physical modeling and through conducting a series of uniaxial shaking table tests. To do so, several geogrid-reinforced soil walls with wrap-around facing (i.e., three-, two-, and single-tiered) with a total height of 10 m were designed in the form of prototypes of 1-m-height wall models. The step-wise intensified sinusoidal waves were applied to the models in 14 typical forms. Comparing the shaking table test results confirmed the post-earthquake advantages of multi-tiered MSE walls. The results revealed that tiered walls exhibited better behaviors under earthquake loading in terms of the seismic stability of the wall, displacement of the wall crest, horizontal displacement of the wall facing, deformation mode and failure mechanism of the wall, settlement of backfill surface, and seismic acceleration responses.
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Dams are vital infrastructures that are expected to maintain their stability during seismic excitations. Accordingly, cemented material dams are an emerging type, which are being increasingly used around the world owing to benefiting from... more
Dams are vital infrastructures that are expected to maintain their stability during seismic excitations. Accordingly, cemented material dams are an emerging type, which are being increasingly used around the world owing to benefiting from advantages of both earth-fill and concrete gravity dams, which should be designed safely when subjected to strong ground motion. In the present paper, the seismic performance of a cemented sand and gravel (CSG) dam is assessed using incremental dynamic analysis (IDA) method by accounting for two failure modes of tension cracking and base joint sliding considering the dam-reservoir-foundation interactions. To take the seismic uncertainties into account, the dam is analyzed under a suite of ground motion records and then, the effect of friction angle for base sliding as well as deformability of the foundation are investigated on the response of dam. To carry out the analyses, the Cindere dam in Turkey is selected as a case study, and various limit st...
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Structural monitoring is the most important part of the construction and operation of the embankment dams. Appropriate instruments selection for dams is vital, as inappropriate selection causes irreparable loss in critical condition. Due... more
Structural monitoring is the most important part of the construction and operation of the embankment dams. Appropriate instruments selection for dams is vital, as inappropriate selection causes irreparable loss in critical condition. Due to the lack of a systematic approach to determine adequate instruments, a framework based on three comparable Multi-Attribute Decision Making (MADM) methods, which are VIKOR, technique of order preference by similarity to ideal solution (TOPSIS) and Preference ranking organization method for enrichment evaluation (PROMETHEE), has been developed. MADM techniques have been widely used for optimizing priorities and determination of the most suitable alternatives. However, the results of the different methods of MADM have indicated inconsistency in ranking alternatives due to closeness of judgements from decision makers. In this study, 9 criteria and 42 geotechnical instruments have been applied. A new method has been developed to determine the decision...
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Abstract In this paper, an experimental study for an eccentrically loaded circular footing, resting on a geogrid reinforced sand bed, is performed. To achieve this aim, the steel model footing of 120 mm in diameter and sand in relative... more
Abstract In this paper, an experimental study for an eccentrically loaded circular footing, resting on a geogrid reinforced sand bed, is performed. To achieve this aim, the steel model footing of 120 mm in diameter and sand in relative density of 60% are used. Also, the effects of depth of first and second geogrid layers and number of reinforcement layers (1–4) on the settlement-load response and tilt of footing under various load eccentricities (0 cm, 0.75 cm, 1.5 cm, 2.25 cm and 3 cm) are investigated. Test results indicate that ultimate bearing capacity increases in comparison with unreinforced condition. It is observed that when the reinforcements are placed in the optimum embedment depth ( u / D = 0.42 and h / D = 0.42), the bearing capacity ratio ( BCR ) increases with increasing load eccentricity to the core boundary of footing, and that with further increase of load eccentricity, the BCR decreases. Besides, the tilt of footing increases linearly with increasing settlement. Finally, by reinforcing the sand bed, the tilt of footing decreases at 2 layers of reinforcement and then increases by increasing the number of reinforcement layers.
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... Amir-kabir arch dam in Iran is chosen as a case study to investigate the nonlinear seismic behavior of the coupled system. ... Amung them, Tan and Chopra (1995a and b) used the boundary element method to compute the impedance matrix... more
... Amir-kabir arch dam in Iran is chosen as a case study to investigate the nonlinear seismic behavior of the coupled system. ... Amung them, Tan and Chopra (1995a and b) used the boundary element method to compute the impedance matrix and they analyzed the dam-reservoir ...
Transporting finer fractions inside the soil skeleton or the erosion of base soils within the filter are the two main challenges for earthen hydraulic structures, their foundations, and filter design. Soil particle morphology could... more
Transporting finer fractions inside the soil skeleton or the erosion of base soils within the filter are the two main challenges for earthen hydraulic structures, their foundations, and filter design. Soil particle morphology could influence pore size distribution and transport of fine grains; however, there is not sufficient knowledge on the effect of grain shape on internal erosion. Some experiments designed and conducted in the present study to evaluate the suffusion potential of aggregates with various shapes and different gradations. Particles with six types of grain morphologies and five gradations were collected, and 26 tests were performed. Furthermore, using 3D image processing and visual comparison, particle shape assessed in terms of three features, including sphericity, roundness, and roughness. Results indicated that particle shape influences flow rate, washed-out fine grains in permeameter wall, vertical strain, and mass loss. An increase in the sphericity and roundness causes an increase in the loss of fine grains, pipe in cell sidewall, and vertical strain. Concerning the particle regularity as an indicator of grain morphology, it was demonstrated that the grains with lower regularity are more resistant to suffusion, and thus the resistance to suffusion would decrease with particle regularity. Spherical glass bead and rounded/ medium sphericity specimens were more prone to suffusion at an equivalent or even lower hydraulic gradient than the soil samples with angular/low sphericity grains. Graphic abstract
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Due to the shortage of urban land, new buildings are constructed adjacent to old buildings. In this regard, there is limited information about the behaviour of the shallow foundations adjacent to the excavation. In this research, a series... more
Due to the shortage of urban land, new buildings are constructed adjacent to old buildings. In this regard, there is limited information about the behaviour of the shallow foundations adjacent to the excavation. In this research, a series of experimental and numerical studies are conducted on reinforced and unreinforced granular soils adjacent to excavation loaded with square footings. The experimental results are in good agreement with the numerical study. Numerical investigations were carried out on sandy excavation by varying the footing distance from the edge of the different granular excavations. It was found that by using three reinforcing layers, the ultimate bearing capacity would increase. Additionally, excavation has no significant effect in the vicinity of 4B, in which B is the footing width. Furthermore, the need to build new large buildings in the vicinity of each other has reduced the distances between square footings and, as a result, has created the phenomenon of interference in the footings and excavation. This occurs through the interference of wedges and rupture surfaces. Since this phenomenon bears a substantial result on the bearing capacity of shallow footings, this work investigates the effect of interference of ruptured wedges on the carriage capacity, settlement, and deformation of square footings. The optimum interference factor is defined at spacings of 2B and 3B for dense and loose reinforced sands, respectively. Furthermore, by including three continuous geogrid layers underneath two square footing interferences, their behaviour will be improved