Computational Mechanics Research and Support for Aerodynamics ...

Material MAT_005 (Soil and Crushable Foam) was used to model the soil. Volumetric compaction is
determined by a tabulated curve of pressure versus volumetric strain defined from a hydrostatic
compression test. A pressure-dependent flow rule governs the deviatoric behavior of the model:
( ) (3.14)
Where: , , are user-defined constants obtained from triaxial compression test. An example of
such failure surface definition is shown in Figure 3.28.
Figure 3.28 Strength envelope in terms of yield surface- second invariant of deviatoric stress and pressure
The shear failure of the soil is occurring when the s defined in Equation (3.14) becomes zero. It means
that the stress state defined by the second stress invariant is located on the yield surface. This material
definition has a simple implication stating that if the confining pressure of the material is very low,
accordingly low shear stress would cause the material to fail. In the case of scour slope stability lack of
confinement of the sand is causing fluid-like flow of material.
3.3.3. Procedure Flowchart
The procedure consists of the following steps:
1. Run the analysis in STAR-CCM+ up to the point where the slope angle exceeds significantly the
natural angle of repose of the sand. (This is the state where deviatoric shear stress in the soil
can cause the slope to slide.)
2. Extract the shape of the scour hole in the NASTRAN file format.
3. Import the NASTRAN file to LS-PrePost – a pre and post processor for LS-DYNA.
TRACC/TFHRC Y1Q3 Page 72