Browsing by Author "Ghalehjough, Babak Karimi"

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Application of Grey Wolf Optimizer to Develop New Global GMPE for Estimating Peak Ground Acceleration
(Springer Int Publ Ag, 2023) Ghalehjough, Babak Karimi; Agahian, Saeid
Ground motion prediction equations (GMPEs) are open challenge problems that have been developed since 1964. Parametric and nonparametric methods predict ground motion characteristics such as peak ground acceleration (PGA), velocity, displacements, and spectral accelerations. In the present study, the grey wolf optimization (GWO) algorithm was used to obtain a new and developed GMPE for predicting PGA. Data from recorded earthquakes from all over the world were collected, and after filtering of M-w and distance parameters, close to 2000 data were used for modelling. Three parameters of M-w (4-7.9), epicentral distance (0.25-115 km) and geological conditions (soft soil, stiff soil, rock) were used as input parameters for estimating PGA. Many previous studies classified geological conditions based on shear wave velocity at the top 30 m (Vs30), without taking into account the effect of Vs30 at each group. In this study, the effects of Vs30 were considered separately for each geological group too. Results showed that PGA decreased by increasing Vs30 and moving from soft soil toward rock. Finally, the relationship was compared with the other two relations suggested for the local region and global earthquakes, and despite the simplicity of the suggested relation gained by the GWO method, it estimated PGA in terms of accuracy to a good and acceptable level.
Experimental and Numerical Investigation for Estimating Optimal Depth-Bearing Capacity of Randomly Fiber-Reinforced Sandy Soils
(Natl Inst Science Communication-NISCAIR, 2022) Kucukcongar, Dogan Seyda; Celik, Semet; Ghalehjough, Babak Karimi
Reinforcing will lead to improved mechanical properties of soil. Using different additives can help to increase bearing capacity, strength, or other important properties. In this study, poorly graded sandy soil was improved by adding synthetic fiber, and a strip footing was placed and loaded on unreinforced and reinforced soil. Samples were prepared in two relative densities of 50% and 65% and the soil was reinforced in 1B, 2B, 2.5B, and 3B depths (B is width of model footing). Bearing capacity and shear failure surfaces of soil that were analyzed by the Particle Image Velocimetry (PIV) method at different settlement to footing width ratios were obtained and compared. At the same time, experimental conditions were modeled with finite element method, and the results of shear failure surfaces were compared with experimental modeling. Results showed that reinforcing the soil under the strip footing forwarded shear failure surfaces toward downer surfaces from 1B up to 3B. In soils with a relative density of 50%, the main reinforcing depth was 2B and after 2B reinforcing did not have a considerable effect on improving the soil. By increasing the relative density from 50% to 65%, the effective reinforcing depth increased from 2B to 2.5B. Experimental and numerical modeling of soil under strip footing showed that the optimum reinforcing depth was between 2B and 2.5B that by increasing the reinforcing depth, the general shear failure behavior went toward local shear failure surfaces. The results of the study can be used as a reinforcing method and applied to real soil improvement applications in industry depending on the purpose of soil reinforcing for economic and efficient improvement design.
Freezing-Thawing Resistance Evaluation of Sandy Soil, Improved by Polyvinyl Acetate and Ethylene Glycol Monobutyl Ether Mixture
(Techno-Press, 2020) Fard, Ata Rezaei; Moradi, Gholam; Ghalehjough, Babak Karimi; Abbasnejad, Alireza
Freezing-thawing cycles have significant effect on soils engineering behavior in frozen areas. This effect is more considerable in fine-graded than coarse-grained soils. The objective of this study is improving soil durability and strength in continues freezing-thawing cycles. For getting this purpose mixture of Polyvinyl Acetate (PVAc) and Ethylene Glycol Monobutyl Ether (EGBE) has been added to fine-grained soil and final prepared samples were tested at different freezing-thawing cycles. PVAc was mixed with 1%, 2% and 3% of soil weight. Half of PVAc weight was used as weight of EGBE. Freezing-Thawing cycles were exposed to samples and they were tested at different cycles. Results showed that adding mixture of PVAc+EGBE improved strength and durability of samples up to 10 freezing-thawing cycles. Unconfined compress strength tests were applied to samples and stress and strain of samples were tested on failure time. Behavior of samples was different at different percentages of mixture. Results showed that increasing amount of PVAc from 1% to 2% had more considerable effect on final stress than 2% to 3%. Using higher percentages of PVAc + EGBE mixture leaded to that samples carried more strain before collapsing. Another result gained from tests was that, freezing-thawing effect was more considerable after fourth cycles. It means differences between first and fourth cycles were more considerable than differences between fourth and tenth.