It would be good to be able to specify foundation properties in layers for the sleeper retaining wall. Typically you will encounter variable layers of sand, fill or soft clay within the first 500mm to 1000mm of the pier excavation, after which we will typically be excavating into stiff clay.
Currently you can only allocate 1 set of properties for the foundation soil which will either result in an overconservative or under conservative result depending on what properties you apply. Given that the difference between soft clay to stiff clay can change the pier depth by around 1m (by means of changing Su) then I think it would be worth adding the feature if possible.