Fa
  • Ph.D. (1993)

    Civil Engineering, Geotechnical Engineering

    Civil and Mineral Engineering, University of Minnesota, Minneapolis, United States

  • M.Sc. (1987)

    Civil Engineering, Geotechnical Engineering

    Civil Engineering, Shiraz, Shiraz, Iran

  • B.Sc. (1984)

    Civil Engineering

    Civil Engineering, Iran University of Science and Technology, Tehran, Iran

  • Finite element and discrete element modeling of geomaterials
  • Fracture mechanics
  • Plasticity analysis and its application in rock and soil mechanics
  • Development of computer codes for numerical modeling of geomaterials
  • In situ testing of geomaterials

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    Curriculum Vitae (CV)

    Physical and numerical evaluation of effect of specimen size on dynamic tensile strength of rock

    P Asadi, MJ Ashrafi, A Fakhimi
    Journal Paper , , {Pages }

    Abstract

    Insights on crack initiation and propagation in reinforced concrete beams, a bonded-particle approach

    M Shirzehhagh, A Fakhimi
    Journal Paper , , {Pages }

    Abstract

    Combined SPH-DEM modeling of solid-fluid interactions

    M Rajab Doost Khoshdel, E Taheri, A Fakhimi
    Journal Paper , , {Pages }

    Abstract

    Numerical Modeling of Effect of Specimen Size on Dynamic Tensile Strength of Rock

    P Asadi, A Fakhimi
    Journal Paper , , {Pages }

    Abstract

    A Micromechanical Model for Simulation of Rock Failure Under High Strain Rate Loading

    Mohammad Reza Majedi, Mohammad Afrazi, Ali Fakhimi
    Journal PaperInternational Journal of Civil Engineering , 2020 July 24, {Pages 15-Jan }

    Abstract

    Quasi-brittle materials such as rock are rate sensitive materials and their behaviour under dynamic loading is not identical with that under static loading. In this study, numerical Brazilian tensile tests are conducted using a Split Hopkinson Pressure Bar system in an attempt to reproduce the dynamic increase factors (DIF) of the experimental tests. The rock is modelled by a bonded particle system made of spherical particles which interact at the contact points. The numerical results indicate that while the bonded particle system with a simple contact bond model can closely mimic the static behaviour of the sandstone specimens, it lacks what is needed for a rate dependent material. Therefore, a micromechanical model in which the contact bo

    Strength and deformation behaviour of sand-rubber mixture

    Salman Rouhanifar, Mohammad Afrazi, Ali Fakhimi, Mahmoud Yazdani
    Journal PaperInternational Journal of Geotechnical Engineering , 2020 August 29, {Pages 15-Jan }

    Abstract

    Loose specimens with a void ratio of 0.86, corresponding to a relative density of 30% for the pure sand, and normal stresses of 50, 100 and 150 kPa were used in this work to study strength and deformation behaviour of sand rubber mixtures. Three types of rubber particles with D-rubber/D-sand?=?0.25, 1, and 4, and different rubber to sand ratio of 5, 10, 15, 20, 25, 30, 40 and 50% were investigated by performing more than 300 direct shear tests. The shear strength and deformation characteristics of sand-rubber mixtures were dependent on rubber proportions of the mixtures and size ratio. Angle of friction and cohesion intercept increased and reduced when up to 20% rubber fraction was used, but reduced and increased afterwards. Di

    FEM-BPM simulation of SHPB testing for measurement of rock tensile strength

    MR Majedi, M Afrazi, A Fakhimi
    Conference Paper54th US Rock Mechanics/Geomechanics Symposium , 2020 September 18, {Pages }

    Abstract

    Rock is a rate dependent material and this rate dependency needs to be considered when dynamic loading such as rock blasting is of interest. In this study, CA3 computer program which is a hybrid bonded particle-finite element program is used to numerically simulate the Brazilian tensile test in the Split Hopkinson Pressure Bar (SHPB) testing. The rock is idealized using the Bonded Particle Model (BPM) while the incident and transmission bars are simulated by a finite element system. It is shown that the induced damage and brittle failure in the Brazilian specimen is consistent with the physical observation. On the other hand, the dynamic tensile strength of the simulated rock is much smaller than the physical result suggesting that inertia

    Effect of Loading Direction on Interaction of Two Pre-Existing Open and Closed Flaws in a Rock-Like Brittle Material

    M Alitalesh, M Yazdani, A Fakhimi, M Naeimabadi
    Journal PaperUnderground Space , 2019 May 28, {Pages }

    Abstract

    Investigations of the growth, interaction, and coalescence of cracks are important because they help to provide tools for the more realistic modeling of rock masses containing low persistence discontinuities and better estimations of the strength and stiffness of a rock material. Understanding the coalescence mechanism is useful for justifying the mechanism of continental crustal deformation, evaluating the structural failure of slopes with rock bridges, and analyzing the stability of tunnels when a mode I or mix mode failure mechanism is involved. The evaluation of crack growth can provide valuable information about the mechanism for the formation of new geological structures, and the formation, evolution, and growth of faults. This paper

    Visual detection of a cohesionless crack in rock under three-point bending

    Qing Lin, Bin Wan, Siqi Wang, Shiyuan Li, Ali Fakhimi
    Journal PaperEngineering Fracture Mechanics , Volume 211 , 2019 April 15, {Pages 17-31 }

    Abstract

    Crack initiation and propagation in rock involve the development of a nonlinear zone around the crack tip called fracture process zone. The existence of fracture process zone influences the fracture behavior and therefore it must be carefully investigated. This zone is normally idealized as a cohesive zone whose mechanical properties are difficult to measure. In this study, a relatively simple approach is proposed to identify the properties of the cohesive zone and the length of the cohesionless crack in a sandstone specimen under three-point bending. Two types of specimens were tested: beams with center notch and with smooth boundary. The digital image correlation (DIC) was utilized to obtain the opening displacement around the position wh

    Dilation angle in bonded particle simulation of rock

    A Fakhimi, S Norouzi
    Journal PaperComputational Particle Mechanics , Volume 6 , Issue 2, 2019 April 15, {Pages 195-211 }

    Abstract

    A model that allows micromechanical parameters to soften as a measure of plastic deformation is discussed. In particular, a microdilation angle is involved to help for calibration of macroscopic volumetric deformation. Through biaxial and shear tests numerical simulations, it is shown that macrodilation angle of bonded particle system can be controlled only when small particles are used. The genesis pressure that causes small overlap of particles has an impact on dilation angle as well and can be utilized as a controlling factor to calibrate a bonded particle material for dilation angle and post-peak behavior.

    Simulation of Multi-Phase Medium Using BPM-SPH Hybrid Method

    Mahmud Yazdani, Ali Fakhimi, Mohsen Mazhary
    Journal PaperModares Civil Engineering journal , Volume 19 , Issue 4, 2019 November 10, {Pages 0-0 }

    Abstract

    The precision and speed of numerical simulations of physical phenomena has led to their increasing use in designing and research applications. These precision and speed are owed to the improvements in numerical methods and significant advancements in computing power of CPUs and GPUs.Particle-based methods are some of the most recently developed numerical simulation methods. Development of these methods has been long delayed due to the need for a relatively high computational effort.

    Physical and numerical evaluation of rock strength in Split Hopkinson Pressure Bar testing

    A Fakhimi, P Azhdari, J Kimberley
    Journal PaperComputers and Geotechnics , Volume 102 , 2018 October 1, {Pages 11-Jan }

    Abstract

    Split Hopkinson Pressure Bar (SHPB) testing was used to evaluate the strength characteristics of sandstone under uniaxial compressive loading. The physical results suggest that rock strength increases under dynamic loading. A hybrid bonded particle-finite element model was used for numerical simulation of SHPB tests. A parameter called rock strength enhancement coefficient was introduced which is multiplied by the relative velocity of particles at the contact points to increase the bond strength between the particles. It is shown that a much better match between the physical and numerical results is realized if this enhancement coefficient is applied in the numerical simulation.

    Numerical and experimental study of the optimal location of concrete piles in a saturated sandy slope

    Mohammad Hajiazizi, Moslem Bavali, Ali Fakhimi
    Journal PaperInternational Journal of Civil Engineering , Volume 16 , Issue 10, 2018 October 1, {Pages 1293-1301 }

    Abstract

    The stability of a soil slope, reinforced by a concrete pile, is studied both experimentally and numerically in this work. Our study suggests that when the concrete pile is located in the middle of the slope (at x/r = 0.5), the soil structure collapses under a pressure of 10.9?kPa that is the highest overburden pressure to cause instability of the tested reinforced sandy slope. However, when the pile is located in the upslope (at x/r = 0.75) or downslope (at x/r = 0.25), the slope failure occurs under a pressure of 7.8 or 3.12?kPa, respectively. Therefore, our experimental work suggests that a pile located at the middle of the slope can provide the optimum reinforcement of the soil structure studied in this work.

    Bonded Particle-Finite Element Simulation of Rock in Split Hopkinson Pressure Bar Test

    P Azhdari, J Kimberley, A Fakhimi
    Conference Paper52nd US Rock Mechanics/Geomechanics Symposium , 2018 August 21, {Pages }

    Abstract

    Dynamic uniaxial compressive strength of Pennsylvania blue sandstone was investigated using split Hopkinson pressure bar both physically and numerically. A hybrid finite-discrete element code called CA3 was employed to simulate the physical tests. The incident and transmitted bars were modeled using finite elements while the rock specimen was represented by a bonded particle discrete system. The incident stress pulse measured in the physical test was utilized as the input for the numerical simulation and was applied to the free end of the incident bar. Analysis of the numerical results suggests an underestimation of the dynamic rock strength; the effect of axial and circumferential inertia of the specimen didn’t manifest the strength valu

    Insights on rock fracture from digital imaging and numerical modeling

    Ali Fakhimi, Qing Lin, Joseph F Labuz
    Journal PaperInternational Journal of Rock Mechanics and Mining Sciences , Volume 107 , 2018 July 1, {Pages 201-207 }

    Abstract

    Rock fracture and the induced displacement field are investigated through physical and numerical experiments. A Berea sandstone specimen with a central notch was tested in three-point bending. Digital image correlation (DIC) was used to obtain the displacement patterns as the fracture initiated and propagated. The DIC results clearly show the development of a damage zone and displacement discontinuity along the center line of the beam at peak load. It is suggested that a traction-free or cohesionless crack may exist before the unstable growth, a condition normally ruled out in the literature based on numerical modeling within the frame work of a cohesive zone finite element analysis. In this note, the displacement profiles determined from D

    Numerical analysis of effective parameters in direct shear test by hybrid discrete–finite element method

    M YAZDANI, AA FAKHIMI, M Alitalesh
    Journal Paper , Volume 18 , Issue 300830, 2018 January 1, {Pages 13-24 }

    Abstract

    Determination of soil engineering properties such as shear strength is essential to analysis many geotechnical problems. Therefore, determination of the reliable values for this parameter is very important. For this purpose, direct shear test as one of the oldest test to examine the shear strength of soils, is conducted on soil samples. There are too many factors which could affect results of direct shear test. Laboratory tests are expensive, difficult and time consuming, hence using numerical method to simulate experimental test and study effective factors can be useful. In this paper direct shear test was numerically modeled using CA2 hybrid finite element-discrete element method code. CA2 solves explicitly equations of motion together wi

    A micromechanical model for studying the effect of ductility and micro-crack intensity on rock strength characteristics

    S Norouzi, A Fakhimi
    Conference Paper51st US Rock Mechanics/Geomechanics Symposium , 2017 August 28, {Pages }

    Abstract

    The bonded particle model is a powerful tool in studying the mechanical behavior of rock. The common practice in simulation of rock failure using this model is to allow brittle fracture of the contacts between particles or at most tensile softening at the contact points ignoring the shear softening of the material. To overcome this shortcoming, a plasticity model that allows both tensile and shear softening of the filling material at the contact points of the particles was implemented in the CA2 computer program. The model was calibrated to mimic the elastic behavior of the Pennsylvania blue sandstone. It is shown that for a more ductile material, there is less scatter of micro-cracking at the peak load. Furthermore, the ductility parameter

    Cohesionless crack at peak load in a quasi-brittle material

    Ali Fakhimi, Ali Tarokh, Joseph F Labuz
    Journal PaperEngineering Fracture Mechanics , Volume 179 , 2017 June 15, {Pages 272-277 }

    Abstract

    A three point bending fracture test was performed on a typical quasi-brittle material (Berea sandstone). The loading was continued into the post-peak region where crack growth was visible along the center line of the beam. Subsequent inspection of a portion of the specimen showed that part of the fracture offered no resistance to loading – a cohesionless crack existed. Digital image correlation was used to study the nature of the displacement discontinuity associated with the cohesionless (traction free) crack. The pattern identified in the post-peak region was used as a guide to study the displacement discontinuity at peak load. Two possibilities are offered: (1) The critical opening was developed at peak load. (2) A cohesionless crack,

    Scaling of the fracture process zone in rock

    Ali Tarokh, Roman Y Makhnenko, Ali Fakhimi, Joseph F Labuz
    Journal PaperInternational Journal of Fracture , Volume 204 , Issue 2, 2017 April 1, {Pages 191-204 }

    Abstract

    The zone of microcracks surrounding a notch tip—the process zone—is a phenomenon observed in fracture of quasi-brittle materials, and the characterization of the process zone is the topic of the paper. Specimens of different sizes with a center notch fabricated from a granite of large grain (Rockville granite, average grain size of 10 mm), were tested in three-point bending. Acoustic emissions were recorded and locations of microcracks were determined up to peak load. The results show that both the length and width of the process zone increase with the increase of the specimen size. Furthermore, the suitability of a proposed theoretical relationship between the length and width of the process zone and specimen size was st

    Bonded Particle Simulation of Cavity Expansion Test in Rock

    Fatemeh Molaei, Ali Fakhimi
    Journal Paper , 2017 January , {Pages }

    Abstract

    Cavity expansion theory is a useful theory that has found some utilizations in geotechnical engineering. Specifically, it has been used widely to analyze problems related to deep foundations (V?sic, 1972), stability analysis of underground excavation (Ladanyi, 1967), insitu testing (Mayne, 2001), and penetration tests (Salgado and Prezzi, 2007). Due to the usefulness and applications of this theory, there are several reports in the literature about the numerical analyses of the cavity expansion tests (eg Vu et al. 2005; Vrakas 2016; Tarokh et al. 2016; Molaei et al. 2016; Menendez et al. 2017).Borehole breakout is a direct consequence of the in-situ stresses and stress concentration in rock resulting in preferential rock failure and has bee

    Current Teaching

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    Teaching History

    • MS.c.

      Finite Element Methods

    • 2020
      Sadeghian Axiri, MohammadHossein
      Laboratory study of particle breakage of masjed soleyman dam rockfill materials under static loading
    • 2021
      Rezazadeh, Hamed
    • 2021
      Sadeghi, Mohammad
    • 2018
      Shirzehhagh, Mojtaba
      Numerical and Experimental Modeling of Interaction of Reinforcing Element and Rock
    • 2019
      Rajab Doost Khoshdel, Mohsen

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