Constructing a tropical hardwood wall & steps around a parking area with used Azobe railway sleepers

These pictures show the different stages we went through in building the railway sleeper walls around a parking area. 
For those following in our footsteps, these are some of our lessons!
1) Ensure that the holes for the upright 'retaining post' railway sleepers are as deep as you can make them. At least 600mm in our case. We used bags of postcrete to cement them in place - about 3-4 bags per hole.
2) Used Azobe railway sleepers, like all reclaimed railway sleepers, vary in length, depth and width by sometimes 10mm or more. However much you juggle them around like a jigsaw puzzle, you need to accept that there will be gaps and different levels. When you are in the middle of the job you become obsessed about these variations, however at the end of the job you stand back, and realise that the overall finished look is great, and that the previously irritating differences have somehow disappeared! If you start with a solid level base, the rest should flow successfully. 
3) The Timberlok screws are brilliant, BUT you must first pre-drill the Azobe railway sleepers with a 6mm pilot hole, otherwise the screws may get stuck or snap. In order to make this pilot hole, you must only drill in about a cm at a time, and then withdraw the wood drill, so as to clear the wood shavings from the hole, and then drill a bit further etc... If you don't do this, the drill will overheat, smoke, and eventually bend, snap or go blunt. 
4) Cutting Azobe railway sleepers is like cutting concrete. You will need either a chainsaw or a circular saw with the sharpest of blades. Expect to re-sharpen your chainsaw every 2 or 3 cuts. Let the weight of the chainsaw cut the timber, rather than exerting massive pressure on it out of frustration or impatience.
5) Azobe railway sleepers are really heavy to lift - getting on for 100kg each. Take massive care to protect your back, hands and feet, and use whatever mechanical help you've got.   
All in all, a project that we are really happy with. It has a satisfying weathered and rustic appearance that will last for years. 
Ben and Jerry

African Azobe tropical hardwood railway sleepers (Walls and posts)
2.6m x 240mm x 140mm (approx)
Jarrah tropical hardwood railway sleepers (Steps)
1.2m x 300mm x 125mm Says.. supplies new and used hardwood & softwood railway sleepers throughout the UK.
Many thanks for the brilliant step by step photos of your excellent project, and the really useful advice you have shared. Many projects involve learning as you go along, and so any knowledge or discoveries from other people who have already trodden the same path is warmly welcome!