This research was undertaken by Dr. Jiansheng Xiang at Imperial College under the direction of Dr. J-P Latham
For granular geomaterials with very large particles such as quarried rock-fill or armourstone rock blocks and concrete units used for breakwater protection, both the complex angular shapes and transient stress levels (sometimes approaching material strengths, especially tensile strengths) have an important impact on the granular material behaviour. DEM simulation struggles to capture the shape details and the deformations associated with stress wave transients during multi-body collisions. The 3D FEMDEM code, (Xiang, Munjiza and Latham 2009) introduced and uploaded to VGW in 2008, has precisely these necessary modelling attributes.
The potential ability to capture an entire system of boulders during dumping/placement is illustrated below. An irregular-shaped rock block is obtained from a library of quarried aggregate shapes captured by laser scanner. The shape chosen here is not dissimilar to a possible armourstone shape and is represented at a suitable resolution in order to produce a simulation with ~300 blocks relatively quickly.
These figures show the FEMDEM capability to model such a system of monosized angular rock-like boulders (bodies of about 40 kg) during dumping in a 5.26m×5.3m×3.87m bin (front face not shown). Part of the motion history is captured and stress development in time and space has been contoured with a default colour scale indicating Von Mises stress. The simulation is set up for convenience as a space filling array of identical rocks. The random disorder soon takes over, and a highly energetic compressive phase is followed by a net dilation phase of bouncing back. The movie shows a simulation where a realistic coefficient of friction acts on the contacting boulders resulting in rapid energy dissipation as the particles quickly come to rest. The simulation results point towards a future where FEMDEM analyses can look at the accurate and detailed dynamic stress transients within flowing granular systems as well as pseudo-static responses to loaded systems.
Xiang, J., Munjiza, A. and Latham, J.-P., 2009. Finite strain, finite rotation quadratic tetrahedral element for the combined finite-discrete element method. International Journal for Numerical Methods in Engineering. 79(8), 946-978. doi: 10.1002/nme.2599