The construction of your railway sleeper retaining wall will be determined by difference in ground levels.
Most people only need to retain up to 600mm of soil so this is an easy task, which often creates an interesting and attractive feature in the garden.
The method you choose for construction will be influenced by the height.
Sleepers laid horizontally
Sleepers can be either stood on edge, which needs fewer sleepers but will need some additional supports or laid flat which is great for raised beds and lower height walls needing less additional support often just landscaping screws to join the railway sleepers.
Sleepers placed vertically
Great for medium height walls of about 1 metre high using hardwood sleepers.
Landscaping screws are great for joining sleepers together they are screwed in without needing pre-drilling and hold sleepers very firmly.
It is advisable to place shingle behind the railway sleepers, particularly for taller structures. This can aid the life span of the sleeper and assist drainage, ensuring any water drains to the bottom and doesn't run out between sleepers. Use a membrane on the back of the sleepers if the shingle is likely to spill through any gaps left between the sleepers.
Health & Safety
Sleepers are heavy and care should be taken when handling. Second-hand sleepers are treated with creosote so skin contact should be avoided. Taller structures may collapse if not constructed properly so if in any doubt consult a qualified engineer.