The last version of the FEA slope analysis spreadsheet (presented here) allows the slope shape and element density to be easily varied.  This post looks at the effect of varying the density from very coarse to fine, with constant soil properties.

The element density was varied from a minimum of 24, up to a maximum of 5600, as shown in the screenshots below:

24 Elements:

5600 Elements:

Calculated maximum deflections with increasing reduction of the soil strength properties (friction angle and cohesion) are shown below:

It can be seen that:

• The coarsest mesh (24 element) shows almost none of the non-linear behaviour found in the other analyses.
• The 80 element mesh is significantly better, and the 350 element mesh (shown below) gives almost the same results as the two finer meshes.
• The 1400 and 5600 element meshes gave almost the same results
• The finest mesh gave the best visual representation of the circular arc of the slip failure surface.

Note that the analysis does not model non-linear geometric effects, and the deformations at the base of the slope are not realistic; nonetheless geometric effects (which are magnified by a factor of 100 in the diagrams) have only a small effect on the overall behaviour.

350 Element mesh: