DEM Triaxial Tests of a Seabed Sand

DEM triaxial tests were run in a 3D periodic boundary cell containing 5000 spherical particles employing the open source code YADE to replicate the behavior of some typical seabed sands (i.e. Leighton Buzzard and North Australian shelf). The contact law adopted was the Hertz-Mindlin no-slip solution together with a linear moment – relative rotation law meant to account for the non-sphericity of the real sand grains. The chosen contact law is based on 5 independent micromechanical (i.e. at the level of contacts) parameters: two elastic parameters for the Hertz-Mindlin law, intergranular friction and two parameters for the moment - relative rotation law. The values for the elastic constants and the intergranular friction adopted in the simulations were taken from the elastic and frictional properties of the minerals of the sand grains (mainly quartz). Simulations were run for different values of the two parameters of the moment - relative rotation law. Tests were carried out on samples generated at various initial relative densities (from loose to very dense). The obtained results were very encouraging since the stress-strain behavior exhibited by the numerical samples well matched the experimentally measured values of critical state friction angle and dilatancy angle. However, dense samples showed a less good agreement regarding the peak friction angle. The tests were carried out as part of a larger research program on the lateral soil-structure interaction for pipelines lying on sandy seabeds. An extensive program of 3D plain strain tests involving a plane strain section of the pipeline is currently underway.