railway sleeper bridges

construction note no.6008

subject:	railway sleeper bridges
relating to design note nos:	3032: bridges;

As we have seen in the above design note, timber railway sleepers (railroad ties in usa) make an ideal material for constructing small and medium sized bridges.

Across a small ditch or stream, two or three sleepers laid side by side may be enough to span across from side to side. Sleepers are so thick that they only need supporting each end - but adequately!

Larger spans of more than one sleeper length (generally 2.5m) will need a central support or a post and cross-beam support method. Supports should not be sleepers as they contain large residues of creosote. I have seen old telegraph poles immersed in ponds with no apparent detriment, but I wouldn't advise it.

Due to their rugged nature, I believe that sleepers are best used for simple structures without handrails. More elaborate or complex bridges should perhaps be made from sawn timbers. A separate construction note will be written on this subject.

construction method for a supported sleeper bridge:

1. Legs for supports should be of sawn oak, preferably 150x150mm, or of round chestnut poles of 200mm - 250mm diameter. These should be peeled (ie. no bark)
2. Where support posts are in a pond, they should be placed on a concrete pad, within a lined pond, or concreted into old car tyres dug into the pond base mud. Pour concrete once crossbeams attached, to allow for positioning.
3. Crossbeams should be sited at the correct level and made of 50x150 sawn oak. These are bolted through onto the posts. Where poles have been used, a notch will have to be cut in to present a flat face for the beam.
4. Fix sleepers to cross-beams using 200mm TimberLok fastenings.
5. Use tie-backs on long straight sections of wall, or where height exceeds 1m.
6. After 48 hours, place drainage medium as back fill.
7. Pressure-wash exposed faces to remove tar residue (best done prior to construction to avoid contaminating beds).
8. Once concrete has set, (minimum 48 hours) wire backs of sleepers together using 3mm galvanised wire and 30mm fencing staples. Do this just below the soil line.
9. On long straight stretches, or walls over 900mm height, horizontal tie-backs may be needed into the bank (see note 6007).
10. Gaps between sleepers act as drainage outlets.
11. Backfill rear of trench with drainage medium (gravel).
12. Place topsoil to top 300mm (over drainage medium), tread down firmly.
13. For planting beds, leave sleepers some 75mm above the soil level to allow for mulching.

Other construction notes which relate to this subject:

choose a subject: 6002: timber raised beds 6004: vertical sleeper ret. walls 6006: horizontal sleeper ret. walls