Question
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Hi we want to lay a raised lawn on a concrete base we have taken down a garage and have the base we have thought of using railway sleepers for the  surround and we would like to know the best way to do it ie how much soil to lay the turf on thanks, Linda

Answer
Yep, you will have to break up that concrete, or have it removed.
If you leave the concrete down,without breaking it up, there will be no drainage, except out at the sides, and that will keep the soil soggy.
You might look into some of the other ideas on what to do with such an area.
For instance,how about a side patio(if it is at the side of the house) with a sitting area, some attractive pots of various sizes to hold plants. Maybe one of those patio fire places.. they come in many styles.
At Home Depot, Lowe's and such places, you can but lovely fired tiles,in 12"squares, and some in larger sizes, and many colors. they look like marble, slate, and granite. They could be layed directly on the pavement.There are also clever ways to paint them etc. Look at the how-to books at home Depot,Lowe's etc, and look at the patio and decks. You will find all sorts of ideas.
Even if you put in 12 to 14 inches of soil, you would still have that drainage problem.
If you are going to have the pavement broken up, and lay in the soil, you could go as shallow as 8 inches of soil. I would suggest 1 part planters or landscaper's mix, and 1 part sandy loam. the planter's or landscaper's has peat, humus and all the good stuff you need in there.
I am not sure what you mean by railroad sleepers, is that what I call railroad ties?
Be sure they are not coated with creosote. That will leach into whatever you plant, and probably kill it.
They would be attractive, but you would have to put some sort of liner between the soil and the ties, so the soil wouldn't absorb the creosote, or make sure you get untreated ones.
Hope this helps you.
Charlotte