Richards-Buckingham equation

Hi,

I'm trying to solve the Richards-Buckingham equation for single-phase water flow in unsaturated porous media. Constitutive relationships and the variational formulation are developed here:

https://www.authorea.com/users/23640/articles/61529

I created a problem description file inspired from the examples in the diffusion section of the web site. However, the solution doesn't converge. Maybe the variational form wrong, maybe the equations part of the PDF is wrong, maybe its the options. I don't know. The PDF is hosted on GitHub.

https://github.com/sergeetiparent/EnvGeotech/blob/master/Richards-Buckingham...

Anyone interested in giving a hand on this case? My ultimate goal is to model solute transport in unsaturated soils.

Thanks!

Essi