Ahmad Asaadi | Razi University of Kermanshah, Iran (original) (raw)
Papers by Ahmad Asaadi
International. Journal of Mining & Geo-Engineering, 2015
The rock masses in a construction site of underground cavern are generally not continuous, due to... more The rock masses in a construction site of underground cavern are generally not continuous, due to the presence of discontinuities, such as bedding, joints, faults, and fractures. The performance of an underground cavern is principally ruled by the mechanical behaviors of the discontinuities in the vicinity of the cavern. During underground excavation, many surrounding rock failures have close relationship with joints. The stability study on tunnel in jointed rock mass is of importance to rock engineering, especially tunneling and underground space development. In this study, using the probability density distribution functions of negative exponential, log-normal and normal, we investigated the effect of joint trace length on the stability parameters such as stress and displacement of tunnel constructed in rock mass using UDEC (Universal Distinct Element Code). It was obtained that normal distribution function of joint trace length is more critical on the stability of tunnel, and exp...
Pile foundations are relatively vulnerable to lateral loads. During liquefaction-induced lateral ... more Pile foundations are relatively vulnerable to lateral loads. During liquefaction-induced lateral spreading, this vulnerability is particularly conspicuous due to a loss of strength and stiffness in the liquefied soil. A nonlinear effective stress analysis incorporating an elastoplastic constitutive model based on Finite Difference Method (FLAC 2D program) was used to numerically simulate shake table experiment on piles in laterally spreading soils. The soil-pile interaction has been properly considered by using interface elements. The main objective of this paper is to assess the accuracy of a 2D numerical simulation of physical models in predicting the dynamic response of pile foundations and to identify the capability of 2D numerical simulation for 3D effects such as shadow and neighboring effects in pile groups without a pile cap. Results are presented and discussed, in which the obtained response from the simulation is compared to that measured in the test. For the single pile, a fairly good agreement was observed between computed and measured results. It was also found that the shadow and neighboring effects reduced lateral load on the piles by few percent of difference compared with experimental results.
The prediction of liquefaction and resulting displacements is a major concern for earth structure... more The prediction of liquefaction and resulting displacements is a major concern for earth structures located in regions of moderate to high seismicity. This is particularly so for superstructures where large displacements and other types of geotechnical instability, could lead to life safety concerns. Previous studies show that soil liquefaction induced large lateral displacement has imposed damage to many structures supported on pile foundations during previous earthquakes. Pile foundations are originally designed to transfer the vertical loads. For this reason, piles are relatively vulnerable to lateral loads such as those imposed by ground shaking during strong earthquakes. In the case of soil liquefaction, the pile vulnerability is particularly conspicuous since the loss of strength and stiffness in the liquefied soil results in a nearly complete loss of lateral support for the embedded piles. The liquefied soil acts such a viscous fluid and experiences valuable displacements. This behavior can cause very large loads on pile foundations, both from inertial loads from the superstructure and kinematic loads from liquefied soil, hence inappropriate and unsafe design could leads to failure and severe damages to the pile foundations.
This dissertation describes the results of a numerical study on the dynamic response of pile foundations in liquefying soils during earthquake. A nonlinear effective stress analysis incorporating an advanced constitutive model is conducted using a 2D plain strain finite difference program FLAC, to modeling liquefying soil-pile-superstructure system.
In order to validate the accuracy of the numerical modeling, an experimental 1-g shaking table results of pile foundations in liquefiable soil is simulated to demonstrate the capability of the model for reliable analysis under dynamic loading. Thereafter effect of several variables on the dynamic response of single pile in liquefied soil is investigated by implementing a wide parametric study. In this regard, three different primary soil profiles are considered. The effects of soil relative density, pile length, boundary condition of pile head, thickness of liquefying soil layer, and intensity of the input ground motion are considered. The effects of superstructure loads are also considered to evaluate inertial soil-structure interaction. In addition, the influence of lateral distance of contiguous piles in two-dimensional pile group, called “shadowing effect” is studied especially.
The results of the parametric study accomplished in this dissertation provided a better insight into dynamic behavior of piles in liquefiable soil and some parameters have be known as key parameters.
The rock masses in a construction site of underground cavern are generally not continuous, due to... more The rock masses in a construction site of underground cavern are generally not continuous, due to the presence of discontinuities, such as bedding, joints, faults, and fractures. The performance of an underground cavern is principally ruled by the mechanical behaviors of the discontinuities in the vicinity of the cavern. During underground excavation, many surrounding rock failures have close relationship with joints. The stability study on tunnel in jointed rock mass is of importance to rock engineering, especially tunneling and underground space development. In this study, using the probability density distribution functions of negative exponential, log-normal and normal, we investigated the effect of joint trace length on the stability parameters such as stress and displacement of tunnel constructed in rock mass using UDEC (Universal Distinct Element Code). It was obtained that normal distribution function of joint trace length is more critical on the stability of tunnel, and exponential distribution function has less effect on the tunnel stability compared to the two other distribution functions.
Previous case histories have shown that soil liquefaction severely damaged many structures suppor... more Previous case histories have shown that soil liquefaction severely damaged many structures supported on pile foundations during earthquakes. As a result, evaluating the potential for instability is an important consideration for the safe and resistant design of deep foundation against earthquakes. In this study, the liquefaction susceptibility of saturated sand interacting by single concrete pile was simulated by means of finite difference method. A nonlinear effective stress analysis was used to evaluate soil liquefaction, and the soil-pile interaction was considered using interface elements. The parameter Ru was defined as the pore water pressure ratio to investigate liquefaction in the soil mass during time. A set of numerical models were carried out by three types of soil mass with various condensation (loose, semi-dense and dense) under three ground motion with different predominant frequencies and peak accelerations. The effect of these parameters was studied using excess pore pressure, lateral movement and settlement time histories. It was found that the pile can affect the liquefaction susceptibility of soil by comparing the near pile and free field responses. However, for various soil and earthquake characteristics, it was found that the depth of soil liquefaction and triggering, varies.
1st National Congress on Soil Mechanics and Foundation Engineering
Previous studies show that liquefaction induced large lateral displacement has imposed severe dam... more Previous studies show that liquefaction induced large lateral displacement has imposed severe damages to many structures supported on pile foundations during earthquakes. So, evaluating the potential for instability caused by the development of excess pore pressure is an important consideration to safe and resistant design of deep foundation against this event. In this study the liquefaction potential of saturated sand interacting by single concrete pile and the dynamic behavior of pile simulates by means of finite difference method. A nonlinear effective stress analysis is used to evaluating soil liquefaction and the soil-pile interaction is considered by using interface elements. The parameter Ru was defined as the pore water pressure ratio to investigate liquefaction in the soil mass during time. A set of numerical models carried out by three types of soil mass with various condensation (loose, semi-dense and dense) under three ground motion with different predominant frequencies and peak accelerations. Effect of these parameters is studied by the excess pore pressure, lateral movement and settlement time histories of liquefiable deposits at near pile and free-field. It is found that for various soil and various earthquake characteristics, the depth of soil liquefaction and it’s triggering, varies.
International. Journal of Mining & Geo-Engineering, 2015
The rock masses in a construction site of underground cavern are generally not continuous, due to... more The rock masses in a construction site of underground cavern are generally not continuous, due to the presence of discontinuities, such as bedding, joints, faults, and fractures. The performance of an underground cavern is principally ruled by the mechanical behaviors of the discontinuities in the vicinity of the cavern. During underground excavation, many surrounding rock failures have close relationship with joints. The stability study on tunnel in jointed rock mass is of importance to rock engineering, especially tunneling and underground space development. In this study, using the probability density distribution functions of negative exponential, log-normal and normal, we investigated the effect of joint trace length on the stability parameters such as stress and displacement of tunnel constructed in rock mass using UDEC (Universal Distinct Element Code). It was obtained that normal distribution function of joint trace length is more critical on the stability of tunnel, and exp...
Pile foundations are relatively vulnerable to lateral loads. During liquefaction-induced lateral ... more Pile foundations are relatively vulnerable to lateral loads. During liquefaction-induced lateral spreading, this vulnerability is particularly conspicuous due to a loss of strength and stiffness in the liquefied soil. A nonlinear effective stress analysis incorporating an elastoplastic constitutive model based on Finite Difference Method (FLAC 2D program) was used to numerically simulate shake table experiment on piles in laterally spreading soils. The soil-pile interaction has been properly considered by using interface elements. The main objective of this paper is to assess the accuracy of a 2D numerical simulation of physical models in predicting the dynamic response of pile foundations and to identify the capability of 2D numerical simulation for 3D effects such as shadow and neighboring effects in pile groups without a pile cap. Results are presented and discussed, in which the obtained response from the simulation is compared to that measured in the test. For the single pile, a fairly good agreement was observed between computed and measured results. It was also found that the shadow and neighboring effects reduced lateral load on the piles by few percent of difference compared with experimental results.
The prediction of liquefaction and resulting displacements is a major concern for earth structure... more The prediction of liquefaction and resulting displacements is a major concern for earth structures located in regions of moderate to high seismicity. This is particularly so for superstructures where large displacements and other types of geotechnical instability, could lead to life safety concerns. Previous studies show that soil liquefaction induced large lateral displacement has imposed damage to many structures supported on pile foundations during previous earthquakes. Pile foundations are originally designed to transfer the vertical loads. For this reason, piles are relatively vulnerable to lateral loads such as those imposed by ground shaking during strong earthquakes. In the case of soil liquefaction, the pile vulnerability is particularly conspicuous since the loss of strength and stiffness in the liquefied soil results in a nearly complete loss of lateral support for the embedded piles. The liquefied soil acts such a viscous fluid and experiences valuable displacements. This behavior can cause very large loads on pile foundations, both from inertial loads from the superstructure and kinematic loads from liquefied soil, hence inappropriate and unsafe design could leads to failure and severe damages to the pile foundations.
This dissertation describes the results of a numerical study on the dynamic response of pile foundations in liquefying soils during earthquake. A nonlinear effective stress analysis incorporating an advanced constitutive model is conducted using a 2D plain strain finite difference program FLAC, to modeling liquefying soil-pile-superstructure system.
In order to validate the accuracy of the numerical modeling, an experimental 1-g shaking table results of pile foundations in liquefiable soil is simulated to demonstrate the capability of the model for reliable analysis under dynamic loading. Thereafter effect of several variables on the dynamic response of single pile in liquefied soil is investigated by implementing a wide parametric study. In this regard, three different primary soil profiles are considered. The effects of soil relative density, pile length, boundary condition of pile head, thickness of liquefying soil layer, and intensity of the input ground motion are considered. The effects of superstructure loads are also considered to evaluate inertial soil-structure interaction. In addition, the influence of lateral distance of contiguous piles in two-dimensional pile group, called “shadowing effect” is studied especially.
The results of the parametric study accomplished in this dissertation provided a better insight into dynamic behavior of piles in liquefiable soil and some parameters have be known as key parameters.
The rock masses in a construction site of underground cavern are generally not continuous, due to... more The rock masses in a construction site of underground cavern are generally not continuous, due to the presence of discontinuities, such as bedding, joints, faults, and fractures. The performance of an underground cavern is principally ruled by the mechanical behaviors of the discontinuities in the vicinity of the cavern. During underground excavation, many surrounding rock failures have close relationship with joints. The stability study on tunnel in jointed rock mass is of importance to rock engineering, especially tunneling and underground space development. In this study, using the probability density distribution functions of negative exponential, log-normal and normal, we investigated the effect of joint trace length on the stability parameters such as stress and displacement of tunnel constructed in rock mass using UDEC (Universal Distinct Element Code). It was obtained that normal distribution function of joint trace length is more critical on the stability of tunnel, and exponential distribution function has less effect on the tunnel stability compared to the two other distribution functions.
Previous case histories have shown that soil liquefaction severely damaged many structures suppor... more Previous case histories have shown that soil liquefaction severely damaged many structures supported on pile foundations during earthquakes. As a result, evaluating the potential for instability is an important consideration for the safe and resistant design of deep foundation against earthquakes. In this study, the liquefaction susceptibility of saturated sand interacting by single concrete pile was simulated by means of finite difference method. A nonlinear effective stress analysis was used to evaluate soil liquefaction, and the soil-pile interaction was considered using interface elements. The parameter Ru was defined as the pore water pressure ratio to investigate liquefaction in the soil mass during time. A set of numerical models were carried out by three types of soil mass with various condensation (loose, semi-dense and dense) under three ground motion with different predominant frequencies and peak accelerations. The effect of these parameters was studied using excess pore pressure, lateral movement and settlement time histories. It was found that the pile can affect the liquefaction susceptibility of soil by comparing the near pile and free field responses. However, for various soil and earthquake characteristics, it was found that the depth of soil liquefaction and triggering, varies.
1st National Congress on Soil Mechanics and Foundation Engineering
Previous studies show that liquefaction induced large lateral displacement has imposed severe dam... more Previous studies show that liquefaction induced large lateral displacement has imposed severe damages to many structures supported on pile foundations during earthquakes. So, evaluating the potential for instability caused by the development of excess pore pressure is an important consideration to safe and resistant design of deep foundation against this event. In this study the liquefaction potential of saturated sand interacting by single concrete pile and the dynamic behavior of pile simulates by means of finite difference method. A nonlinear effective stress analysis is used to evaluating soil liquefaction and the soil-pile interaction is considered by using interface elements. The parameter Ru was defined as the pore water pressure ratio to investigate liquefaction in the soil mass during time. A set of numerical models carried out by three types of soil mass with various condensation (loose, semi-dense and dense) under three ground motion with different predominant frequencies and peak accelerations. Effect of these parameters is studied by the excess pore pressure, lateral movement and settlement time histories of liquefiable deposits at near pile and free-field. It is found that for various soil and various earthquake characteristics, the depth of soil liquefaction and it’s triggering, varies.