Meysam Bayat
Islamic Azad University, Najafabad Branch, Civil Engineering, Faculty Member
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Improvement of the mechanical properties of clayey soils by additional elements to enhance the strength under numerous freezing and thawing cycles has been considered as a serious concern for engineering applications in cold regions. The... more
Improvement of the mechanical properties of clayey soils by additional elements to enhance the strength under numerous freezing and thawing cycles has been considered as a serious concern for engineering applications in cold regions. The objective of the current study is to investigate the effect of nano-clay as a stabiliser on the mechanical properties of clay. To this end, the clay specimens were prepared by adding various percentages of nano-clay ranging from 0.5% to 3% by dry weight of soil and were experimentally tested under the uniaxial compression and tensile splitting tests under different curing times (0, 7 and 28 days) after experiencing various freeze–thaw cycles ranging from 0 to 11. It can be concluded from the results that nano-clay particles may be used as a stabiliser in geotechnical applications to improve soil property. The results indicate that the optimum moisture content (OMC) of specimens increases and the maximum dry density (MDD) decreases with the increasin...
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The use of wind turbines to generate electricity has increased in recent years. One of the most important parts of a wind turbine is the foundation, which should be designed accurately because it is influenced by difference forces. Soil... more
The use of wind turbines to generate electricity has increased in recent years. One of the most important parts of a wind turbine is the foundation, which should be designed accurately because it is influenced by difference forces. Soil cannot carry tension stress; thus, when a wind turbine foundation is applied eccentricity forces, a gap appears between the soil and foundation. The gap will have no positive effect on the ultimate bearing capacity of the foundation. This must be considered when designing the dimensions of an onshore wind turbine on a spread foundation using finite element software in order to avoid error during analysis. In the current study, a spread foundation of an onshore wind turbine was simulated using ABAQUS and PLAXIS-3D software. Based on the results, the effects of Soil-Structure Interaction (SSI), eccentricity of forces, soil strength parameters and the foundation buried depth on static response of the foundation are discussed. The results indicate that t...
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In this paper, the effects of Tuned Mass dampers (TMDs) on the reduction of the vertical vibrations of a real horizontally curved steel box-girder bridge due to different traffic loads are numerically investigated. The performance of TMDs... more
In this paper, the effects of Tuned Mass dampers (TMDs) on the reduction of the vertical vibrations of a real horizontally curved steel box-girder bridge due to different traffic loads are numerically investigated. The performance of TMDs to reduce the bridge vibrations can be affected by the parameters such as dynamic characteristics of TMDs, the location of TMDs, the speed and weight of vehicles. In the first part of this study, the effects of mass ratio, damping percentage, frequency ratio, and location of TMDs on the performance of TMDs to decrease vertical vibrations of different sections of bridge deck are evaluated. In the second part, the performance of TMD is investigated for different speeds and weights of traffic loads. Results show that the mass ratio of TMDs is the more effective parameter in reducing imposed vertical vibration in comparison with the damping ratio. Furthermore, it is found that TMD is very sensitive to its tuned frequency, i.e., with a little deviation ...
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In this paper, a series of unconfined compressive strength (UCS) tests were performed to study the effect of cement content, zeolite content, initial moisture content, number of freeze–thaw cycles, and curing time on the UCS of... more
In this paper, a series of unconfined compressive strength (UCS) tests were performed to study the effect of cement content, zeolite content, initial moisture content, number of freeze–thaw cycles, and curing time on the UCS of low-plasticity silty sand–clayey sand. The results indicate that zeolite can be used along with cement as a stabilizer to enhance mechanical behavior of the soils. The specimens containing cement and zeolite show better response with a higher UCS than the stabilized samples with cement or zeolite alone. The addition of zeolite has an important effect on the increase in both UCS value and failure strain of cement-stabilized specimen. However, the stress–strain curve of stabilized specimens is not influenced significantly by the increase of zeolite content from 3 to 9%. The UCS values of the stabilized specimens decreased as the number of freeze–thaw cycles increased. The cement-stabilized samples have freeze–thaw durability when zeolite content increases from 3 to 9%. The stabilized specimens with 6% cement and 9% zeolite have slightly higher freeze–thaw durability than other specimens. The UCS of the specimens compacted on the dry side is more than that of the compacted sample on the OMC or wet side of optimum for given additives contents. The specimens compacted on the dry side of optimum exhibited a lower failure strain. The implication of this work is significant in geotechnical practice; it provides a general knowledge of stabilization of soils using cement and zeolite and the quantities to use to achieve the desired geotechnical properties.
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Abstract Enhancement of the mechanical characteristics of ceramic fiber-reinforced soil samples by attaching nanosilica particles to the fiber surface has not yet been fully investigated. The present study took the novel approach of... more
Abstract Enhancement of the mechanical characteristics of ceramic fiber-reinforced soil samples by attaching nanosilica particles to the fiber surface has not yet been fully investigated. The present study took the novel approach of coating the ceramic fibers with nanosilica particles to improve the interfacial interaction of the fiber matrix. The results of direct shear and California bearing ratio (CBR) tests on treated soil specimens and the effects of ceramic fiber content, fiber length and nanosilica content on the mechanical behavior of silty sand are presented. The results showed that the addition of ceramic fibers to the silty sand significantly increased the shear strength and shear strain at the maximum shear stress. The dilative behavior of the soil specimens was found to decrease with the addition of ceramic fibers. The reinforced specimens with a ceramic fiber content of 1.5% and fiber length of 6 mm exhibited the highest peak shear strength. The effects of ceramic fiber content on the internal friction angle and cohesion of the reinforced specimens were dependent on the fiber length. The maximum CBR occurred at a fiber length of 18 mm. The addition of nanosilica noticeably increased the cohesion and slightly increased the internal friction angle. The improvements in the mechanical behavior of the soil after the addition of nanosilica could be attributed to its pozzolanic reaction. The addition of 1% nanosilica increased the influence of the ceramic fiber on the shear strength. In most cases, the addition of nanosilica had a negative effect on increasing the CBR of fiber-reinforced specimens.
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Abstract Semi-flexible pavement offers a high bearing capacity and resistance to rutting. It comprises a layer of cement mortar and one of porous asphalt and is subject to thermal cracking because of the difference in stiffness of these... more
Abstract Semi-flexible pavement offers a high bearing capacity and resistance to rutting. It comprises a layer of cement mortar and one of porous asphalt and is subject to thermal cracking because of the difference in stiffness of these materials. In this study, rubber powder (RP) was used to approximate the stiffness of the cement mortar relative to porous asphalt concrete in order to reduce thermal cracking. Nano silica (NS) was used to reduce the negative effect of RP on the compressive and flexural strength. The effects of these additives on the behavior of 20 mortar mixtures were investigated by mechanical testing and scanning electron microscopy. The results showed that 0.5% to 1% NS can prevent the fluidity loss and increase the drying shrinkage in the matrix. Three of the best-performing mortars were rated, and the optimum mixture was NS1-RP5 containing 1% NS and 5% RP. With an elastic modulus loss of about 20%, it exhibited the best performance and mechanical properties.
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Understanding the factors that influence the dynamic behavior of granular soils during cyclic loading is critical to infrastructure design. Previous research has lacked quantitative study of the effects of fouling index (FI), mean... more
Understanding the factors that influence the dynamic behavior of granular soils during cyclic loading is critical to infrastructure design. Previous research has lacked quantitative study of the effects of fouling index (FI), mean effective confining pressure, relative density, shear strain level and anisotropic consolidation, especially when the effective vertical stress is lower than the effective horizontal stress on the dynamic behavior of gravelly soils. The objective of the present study was to evaluate the dynamic behavior and volume change of both clean and fouled specimens for practical applications. To this end, cyclic triaxial tests with local strain measurements under both isotropic and anisotropic confining conditions were conducted. It is found that the fouled specimen with 50 % sand (i.e. the specimen which contains 50 % gravel and 50 % sand) has the highest shear modulus at low shear strain levels and the largest volume reduction and damping ratio at large shear stra...
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ABSTRACT Neural network analysis was used to construct models of unconfined compressive strength (UCS) as a function of mix composition using existing data from literature studies of pure compound additions to Portland cement paste. The... more
ABSTRACT Neural network analysis was used to construct models of unconfined compressive strength (UCS) as a function of mix composition using existing data from literature studies of pure compound additions to Portland cement paste. The models were able to represent the known nonlinear dependency of UCS on age and water content, and generalised from the literature data to find relationships between UCS and contaminant concentrations, resulting in the following ranking of the UCS values predicted for addition of the contaminants, on an equimolar basis: at 7 days, Cl≈Cr(III)>NO3−≈Cd>control>Zn≥Ni>Pb>Cu≫Ba; at 28 days, Cl>Cr(III)>NO3−≈control≥Zn≥Cd>Ni>Pb>Cu≫Ba. Application of the best neural network to other data suggested that Cs is a retarder and Cr(VI) has no effect. No trends could be discerned for Hg, K, Mn, Na and SO42−. The root-mean-square error for the best neural network seems to be an estimate of the interlaboratory error for UCS.
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Pile groups are commonly used in geotechnical engineering construction; thus, understanding the response of a pile group located near a soil slope is of practical value to structural design. The purpose of this study was to analyze the... more
Pile groups are commonly used in geotechnical engineering construction; thus, understanding the response of a pile group located near a soil slope is of practical value to structural design. The purpose of this study was to analyze the response of pile groups located in soil slopes with regard to axial load capacity, settlement, and horizontal displacement. For this purpose, a large-scale test setup (1.8 m × 0.90 m × 0.90 m) was developed. A series of physical modelling tests were performed to investigate the effects of the distance of the pile group from the slope crest, a square pile-group configuration, the pile-group direction (parallel or vertical direction relative to the slope direction), and the pile spacing on the axial loading response of the pile group. The results showed that the vertical bearing capacity and horizontal displacement of a pile group near sloping ground approached that of level ground and the zero, respectively, as the edge-to-slope crest distance increased. The reduction factor of the square pile groups increased with an increase in the pile spacing from 3 to 5 d p . The axial load capacity of the pile group increased with an increase in the number of piles in the group from 4 to 9. The horizontal displacement of the pile group towards the slope face increased as the distance from the slope crest and the pile spacing decreased. The response of the linear pile group located on the soil slope was dependent on the pile group direction relative to the slope direction. Responsible Editor: Zeynal Abiddin Erguler.
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The aim of this research was to explain the effects of relative density, mean effective stress, grading characteristics, consolidation stress ratio and initial fabric anisotropy produced during specimen preparation on shear wave velocity... more
The aim of this research was to explain the effects of relative density, mean effective stress, grading characteristics, consolidation stress ratio and initial fabric anisotropy produced during specimen preparation on shear wave velocity (Vs). It is shown that the Vs of the consolidated specimens under anisotropic compression stress is greater than that of the consolidated specimens under isotropic or anisotropic extension stress states at a given relative density and effective confining stress. It is also shown that the depositional technique that was used to create reconstituted specimens has important effect on the Vs. A parallel comparison of measured values from the resonant column and bender element tests is also presented. These results of the tests have been employed to develop a generalized relationship for predicting Vs of granular soils. The Vs model is validated using data collected from literatures. Based on the results, it can be conducted that the proposed model has a good performance and is capable of evaluating the Vs of granular soil.
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Abstract In the current study, Microbial-Induced Carbonate Precipitation (MICP) is used for the improvement of silty sand to mitigate wind erosion by spray-treating the soil surface layer with bacterial cell solutions. Wind tunnel, soil... more
Abstract In the current study, Microbial-Induced Carbonate Precipitation (MICP) is used for the improvement of silty sand to mitigate wind erosion by spray-treating the soil surface layer with bacterial cell solutions. Wind tunnel, soil pocket penetrometer, and Torvane shear tests were carried out on the biologically treated and untreated samples. The bacteria were sprayed at bacterial concentrations of 0.05, 0.1, and 0.5 g/m2 and the samples were exposed to wind speeds of 20.57, 26.18, and 31.79 m/s. The results showed that the effect of wind speed was more pronounced in the untreated samples than the treated samples. A marked decrease in wind erosion potential was observed in the treated samples which was dependent on the bacterial concentration. An increase in the bacterial concentration from 0.05 to 0.5 g/m2 and in the curing time from 2 to 28 days decreased the wind erosion of the treated samples. Pocket penetrometer values were primarily affected by curing time and were almost independent of the bacterial concentration. The pocket penetrometer values of the treated samples were generally less than 2 MPa, which indicates the possibility of root growth. The results of the Torvane shear tests indicate that bio-cementation through MICP also increased the shear strength development of loose sand deposits. Scanning electron microscopy images of the structure of the treated samples revealed that MICP bound the sand particles together through CaCO3 crystal formation in the voids between the particles.
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In order to accurately study the shear behavior of soil-structure interaction in civil engineering applications, it is necessary to have a correct understanding of the interface shear strength characteristics between soil and structure.... more
In order to accurately study the shear behavior of soil-structure interaction in civil engineering applications, it is necessary to have a correct understanding of the interface shear strength characteristics between soil and structure. The interface shear strength characteristics between soil and concrete play key roles in the response characteristics of structures under static loads. In the current study, a series of laboratory large-scale direct shear tests has been conducted on sand—concrete samples to investigate the shear strength characteristics between soil and concrete contact surface. The effects of various parameters such as relative density of sand, concrete surface roughness, normal stress level, and interface area ratio (Ar) along the shear zone were evaluated. The results showed that the sand-concrete interface shear strength characteristics influenced mainly by relative density of sand, normal stress level, concrete surface roughness, and Ar. An increase in concrete surface roughness resulted an increase in the mobilized friction between sand and concrete. The mobilized friction angles of sand-concrete interface with groove of 2 mm were about 55–67% higher than those of sand-concrete interface with a smooth concrete surface. The friction angle of sand-concrete interface decreased with increase in Ar value from 0.28 to 0.75. The mobilized friction angle decreased from 36 to 28° when Ar value increased from 0.28 to 0.78. A significant decrease of the friction angle value of sand-concrete interface was observed when Ar value increased from 0.78 to 1.
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In recent years, the use of waste materials as reinforcement elements such as glass, rubber and plastic waste increased significantly. Nowadays, the use of polyethylene terephthalate (PET) has grown substantially for drink bottles which... more
In recent years, the use of waste materials as reinforcement elements such as glass, rubber and plastic waste increased significantly. Nowadays, the use of polyethylene terephthalate (PET) has grown substantially for drink bottles which is one of the most important environmental hazards. In the current study, the effect of adding PET strips as reinforcement elements to a clayey soil has been studied by unconfined compressive strength and tensile strength tests. The compressive and tensile strengths of reinforced specimens with different PET contents (0%, 0.4%, 0.6%, 0.8% and 1% by the soil weight), lengths (12 mm to 21 mm) and widths (3 mm and 6 mm) have been investigated. It was found that addition of the PET strips to the clay resulted in an increase in both the compressive and tensile strengths. The optimum PET content was dependent on the both width and length of the PET strips. The maximum UCS was 321 kPa which observed in the specimen containing 0.8 % PET strips with 3 mm widt...
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In the current study, the effects of acid and alkaline rains on the physical properties of a particular type of clay with low plasticity is evaluated. In order to reproduce the process of interaction between artificial rain and soil, an... more
In the current study, the effects of acid and alkaline rains on the physical properties of a particular type of clay with low plasticity is evaluated. In order to reproduce the process of interaction between artificial rain and soil, an infiltration setup was fabricated. Solutions of diluted sulfuric acid (H2SO4) and dissolved sodium hydroxide (NaOH) were used to create acidic or alkaline rains, respectively. Distilled water was also used as a reference pH value. Subsequently, the reconstituted samples in a mold are infiltrated by acid or alkaline rains in different pH levels and different fluxes of rainfall. Atterberg limits, Coefficient of permeability, California bearing ratio (CBR) test, and unconfined compressive strength (UCS) of the soil samples were evaluated, to investigate the changes of the mechanical properties of the soil after being exposed to acid or alkaline rain. The obtained results indicated that acidic contamination had a strong influence on the strength characte...
Many studies have been done on the stabilization of weak soil using conventional chemical stabilizers such as lime, cement as well as modern materials such as nanoparticles; however, very few studies have examined the effect of coated... more
Many studies have been done on the stabilization of weak soil using conventional chemical stabilizers such as lime, cement as well as modern materials such as nanoparticles; however, very few studies have examined the effect of coated fibers on the strength of stabilized soil. This paper presents the results of a series of direct shear tests on soil specimens treated with ceramic fiber, nanosilica, and kaolin. The effects of ceramic fibers, fiber length, nanosilica, and kaolin on the mechanical characteristics and shear strength of silty sand was investigated. The results show that the addition of fiber to silty sand resulted in a significant increase in the strength of the soil specimens. The dilative behavior of the soil specimen decreased with the addition of ceramic fibers. The cohesion of the fiber-reinforced specimens increased when the fiber surface was coated with nanosilica or kaolin particles. The friction angle of the coated fiber-reinforced specimens decreased with the a...
This Letter presents a balanced-to-single-ended (BS) crossover for dual-band applications by using two rings included of composite right- and left-handed (CRLH) transmission lines (TLs) with controllable frequency ratio feature. Two... more
This Letter presents a balanced-to-single-ended (BS) crossover for dual-band applications by using two rings included of composite right- and left-handed (CRLH) transmission lines (TLs) with controllable frequency ratio feature. Two dumbbell defected ground structures (DGSs) are employed through balanced TLs to suppress out-of-band common-mode. Theoretical analysis expresses that the frequency ratio can be controlled by suitable selecting of the element values and the number of designing cells of the CRLH TLs. Furthermore, desired impedances and electrical lengths of DGSs are obtained at the frequency of common-mode rejection by using even- and odd-mode analyses. To validate the proposed structure, a dual-band BS crossover operating at 1.8 and 4.2 GHz is fabricated. Measurement results show that the fabricated proposed structure has good performance at the designed frequency bands.
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ABSTRACT This paper attempts to study the effects of acidic and alkaline waters on the geotechnical properties of a particular type of clay with low plasticity from the northeast areas of Isfahan that have been evaluated with pH values... more
ABSTRACT This paper attempts to study the effects of acidic and alkaline waters on the geotechnical properties of a particular type of clay with low plasticity from the northeast areas of Isfahan that have been evaluated with pH values adjusted from 3 to 8. The remoulded specimens were placed in moulds under the influence of acid and alkaline rains with different pH values and years of precipitation. Atterberg limits tests, soil permeability coefficient, California bearing ratio (CBR) test and unconfined compressive strength (UCS) of soil specimens with various pH values were used to evaluate soil mechanical changes relative to soil with neutral acidity. In order to identify internal structural mechanisms of soil before and after artificial raining on the specimens, scanning electron microscopy and pH drainage tests of specimens were performed. The results of the interaction of rain and soil with shifting from neutral values were evaluated over a period of precipitation fluxes from 1 to 20 years. In overall, the more is the acidity or alkalinity of the artificial rain, the more will increase the Atterberg limits and the soil permeability compared to the soil specimens under artificial rain with pH = 7; and the decreasing trend is observed in UCS values and CBR.
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AbstractThe shear modulus and damping ratio are important parameters for the design of structures subjected to dynamic loading and can be obtained by in situ and laboratory measurements. Previous r...
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AbstractMany studies have been carried out on the influence of freeze–thaw cycles on the mechanical behavior of cement- or lime-stabilized soils. However, very limited studies have considered the e...
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The aim of this research was to explain the effects of gravel content using the intergrain state concept, relative density and confining pressure on Gmax, G/Gmax–γ and D–γ curves and the reference strain (γr). A total of 45 G–γ and D–γ... more
The aim of this research was to explain the effects of gravel content using the intergrain state concept, relative density and confining pressure on Gmax, G/Gmax–γ and D–γ curves and the reference strain (γr). A total of 45 G–γ and D–γ curves derived from resonant column testing and cyclic triaxial testing along with S-wave velocity measurements obtained using the bender element technique were assessed. The test specimens were prepared with different gravel contents (0, 30, 50, 75 and 100%) under different relative densities (10, 30 and 60%) and mean effective confining pressures (100, 300 and 600 kPa). Comparison of the Gmax results of the resonant column and bender element tests was also carried out. The desired excitation frequencies and ratios λ/D50 and d/λ (where λ is wavelength, d is transmission path length and D50 is average particle size) were determined based on the bender element tests results. The test results were used to evaluate the empirical equation for prediction of Gmax and to develop a new prediction equation with which to estimate γr. The results of the tests were used to validate previous models and empirical curves.