"Railway sleepers" for a retaining wall

[rjm2k]

It's been suggested that I use railway sleepers to build a retaining wall, I've had a quote for this and the guy is talking about using tanilised posts which will be buried under the soil being retained. I queried the lifespan of the posts in such a position and was told they are guaranteed for 30 years, though they did suggest they could put gravel around them rather than soil. I'm not sure if I may end up doing the work myself but either way are tanilised posts suitable to be fully buried like this? I'm considering insisting on concrete posts instead.
TIA

 

[r896neo]

30 years is way off the mark. Getting half of that would be good. Whenever i do them i use off cuts of sleeper which are still treated but larger diameter timber so should last a little longer.

I advise people they will only have a lifespan of 15 years max but because they are a good bit cheaper than a masonary wall people still go for it instead.

Concrete posts make it more difficult because you can screw into concrete like you can a timber post.

Concrete would be much better but consequently much dearer too.