Know about it but never used it - yet. Use of sand in the strip zone as the strips want the friction; should be, if I remember correctly at least 150mm each side. Clay can then be used in between.
Our contractor on my current project is proposing sand and flyash sandwiched layers. Specs, though, don't allow flyash alone.
If using Reinforced Earth (TM) Wall, they should confirm that the sandwich is agreeable to them. They are usually responsible for internal stability of the wall and this is part of the internal stability.
For me, cohesive soil will never be my consideration to be incorporated into reinforced soil wall system. Even though cohesive soil will give you the strength Cu, never forget that this kind of soil is also poor water draining. The retained water inside the RS system generates pore water pressure which reacts adversely to the overall strength of the wall.
Just my point of view
1. Reinforced Earth is a composite material. The basic idea is that the reinforcements supress the horizontal STRAIN in the soil causing a re-orientation of the velocity vectors into a more or less vertical and horizontal pattern.
2. In order to achieve this reorientation of the strain field, elastic properties for both the reinforcement and the soil are assumed.
3. Some fine grained soils exhibit elastic behaviour, some do not. This is why PI < 6 is specified in almost every MSE code around the world.
4. By embedding granular soil/reinforcing matrices in cohesive soils you will just shift the local faiure surface to the interface between the cohesive and granular materials. (acutally it will probably fail in sliding within the cohesive materials) Chances are you can design around this by treating the composite as a tie back.
5. The unresolved problem is what do you do about the plastic behaviour of the cohesive materials? These will continue to compress and creep so whatever facing system you consider needs to be able to accomodate those plastic strains. The cohesive materials will also settle and compress more quickly than they otherwise would do since you will have in effect, installed horizontal sand drains every reinforcement lift. If there is anything remotely sensitive to settlement on top of the wall forget it.
In my experience the problem is not that contractors want to use relatively good slightly cohesive materials (slightly clayey gravel for example). The problem is that as soon as someone suggests to use cohesive materials the contractor feels that the wall can become a tip for any old crap they want to throw in there. Inevitably you end up standing at the top of a wall - wellies deep in muck - with a wall beneath you that is leaning out a few feet.
