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Thanks for the response Eric and Dave.
1. Im trying to raise it by approx. 400mm. Filling just a little lower than the second sleeper.
2. Just a budget soil which is non expansive.
3. I do know where the drain pipes are and i was intending to grade the top level towards the drain inlet.
4. The back end of that sleeper is just air. I have attached a photo to better explain. Basically our lot is higher that the property at the back. There is a post and panel wall and we have added two sleeper on top before the fence is installed.
do i still need the agi pipe given that the existing concrete retaining wall already have some sort of drainage?
I agree with @Dave-1's recommendation. It's better to be safe in this situation and have a drain on your side as well. This will keep the sleeper from getting waterlogged on your side. Which in turn will keep the soil stable and prevent the sleeper from moving.
If you need further assistance, please let us know.
Eric
I would paint the timber with bitumum paint so it lasts a lot longer than 20 years for normal logs in contact with soil and water for one. a good 3 coats. probably get 40 years.
I am going to say I dont think drainage is a problem where does the water output go any way except down and out into neibours yard ie the nateral water flow from your block.
But ideally you can add a AGi line back to storm water line on your house or down hill to your neibours storm water as your protecting them they would be smart to agree.
Ag pipe line against the fence line it wrapped with weed cloth making a stone column/ water path above it and add stones and lawn dirt at same time saves more work 
on a redig.
