Reza Asadi is an experienced geotechnical engineer at ATC Williams. He recently delivered his PhD completion seminar at the Department of Infrastructure Engineering, University of Melbourne, under the supervision of Associate Professor Mahdi M Disfani and Dr Behrooz Ghahreman-Nejad. Reza’s research focuses on the mechanical behaviour of rockfill materials.
Advanced Numerical Modelling in the Mechanical Behaviour of Rockfill Using Discrete Element Method
Reza’s project combines advanced numerical modelling and analytical work to contribute to developing new knowledge and design tools for understanding the mechanical behaviour of rockfill materials. The research project is a collaboration between ATC William (ATCW) and the University of Melbourne, effectively leveraging the expertise of industry and academia.
A cost-effective alternative based on a decade of dedicated research
ATCW has been responsible for the design and construction supervision of many large rockfill dams (100 m to 250 m in height) over the past four decades and has initiated this project to allow accurate characterisation of rockfill for design purposes. Preliminary research studies began almost a decade ago, in 2014, under the direction of Behrooz Ghahreman-Nejad, ATCW’s Chief Technical Officer and an honorary senior fellow at the University of Melbourne. These comprised standard laboratory triaxial and direct shear testing on scaled-down rockfill samples to investigate the effects of particle shapes and grading on rockfill strength, determination of particle size grading using digital imagery, and numerical modelling using the Discrete Element Method (DEM).
Studying rockfill materials poses significant challenges due to the time-consuming, labour-intensive, and costly nature of conducting laboratory tests on large particles (generally from less than 1 cm to over 1 m). However, Reza’s research offers a cost-effective alternative by utilising Discrete Element simulations of large-scale testing in a virtual laboratory. This approach provides a clear understanding of the effective parameters and fundamental phenomena that govern the behaviour of rockfill materials.
Rockfill behaviour is influenced by various parameters at different scales. In the microscale, the primary factors affecting rockfill behaviour are rock mineralogy, crack distribution, and grain breakage. These parameters dictate the behaviour of individual rock particles and their interactions within the rockfill. At the meso-scale, the shape of the particles, surface roughness, intact rock strength, and the state of stress, especially the confining stress, is considered the dominant factors.
New framework utilises large-scale triaxial testing
Reza has developed a comprehensive framework for predicting the mechanical behaviour of rockfill, considering the effective parameters. The DEM is employed to model the behaviour of granular materials at the particle scale. This method utilises the basic equation of motion (i.e. Newton’s Second Law) to describe the movement of individual grains.
This research has examined various influential parameters, such as particle shapes, stress paths, confining stress, particle characteristic strength, and boundary conditions. The characteristic strength of individual particles in the model was calibrated using regular Point Load or Unconfined Compression tests. Subsequently, these calibrated values were applied in large-scale triaxial testing models.
The modelling outcomes and findings strongly correlate with the results of large-scale triaxial tests conducted at the IDIEM laboratory at the University of Chile. This alignment highlights the reliability and accuracy of the modelling approach in capturing the mechanical behaviour of rockfill materials under different conditions.
– Bulging failure mode in triaxial modelling using combined TBFM-MPRM
– Shear plane failure mode in triaxial modelling using combined TBFM-MPRM
A significant contribution to geotechnical engineering
Finally, through advanced numerical modelling and the collaborative efforts of industry and academia, Reza’s PhD research has the potential to make ground breaking contributions to the field of geotechnical engineering. It aims to facilitate the development of improved design tools and practices related to rockfill materials, ultimately enhancing the safety and efficiency of projects involving rockfill embankment dams and other geotechnical structures.
You can follow Reza on Linkedin here
