Raised bed - sleepers

[meddyg]

I knew I should have put the railway sleepers vertically
How can I fix one on top of  the other ? Metal plate with holes?
Perhaps some gardening sage ( ) has already done this?

[ferret]

if your lucky you can line the bolt holes up and hammer a metal bar down through them , or if you've overlapped them like brickwork get hold of some metal fence post's the sort that you use with chainlink fencing and just hammer them down as far as you can then just cut them off level,
one at each end and one in the middle usually does the job, or you could use half round fence post from the farm supplies.

[Stick]

I used Timberlok Screws for a raised bed made with logs.  Available up to 300mm on t'internet.  Not cheap but I found them very good.

[ferret]

I should have said the posts obviously go tight up against the sleepers on the out side. or if you want them really secure put the stakes/posts on each side of the sleepers and then use some 2.5mm plain wire to pull the top of the posts towards each other.

[a lower gear]

Big drill and lengths of rebar.