construction note no.6006
| subject: | railway sleeper retaining walls (used horizontally) |
| relating to design note nos: |
1073: vertical space; 2073: changes of level; 3073: terraced walls & steps; 3074: terracing with decks; |
As of June 2003, A new EC directive means it is illegal to use railway sleepers, or any creosote impregnated timbers under certain circumstances. Whilst this should not prevent most domestic use, please click here for more information.
Laying in of sleepers and fixing down
Retaining wall stepped up in increments
As we have seen in the above design notes, timber railway sleepers (railroad ties in usa) make an ideal material for constructing walls and terraces.
Cheaper to buy and quicker to construct than brick or block walls, they will form a solid and lasting solution to all terracing needs.
There are two main ways to use them, either vertically, (see construction note 6004) or horizontally. The former is ideal when creating curved walls but is more labour intensive and expensive due to 30% of the sleeper being buried. The latter metod, decribed here, is good for straight walling runs, which lie upon a simple strip footing.
Railways sleepers used horizontally can create solid, linear retaining walls, potentially to any height, although for very tall retaining walls I would recommend a proprietary inter-locking walling system.
construction method when used horizontally:
fig. four. Corner construction of raised bed
fig. five. Method of locking sleepers together using TimberLok fasteners
fig. six. Side elevation showing 25mm step-back of each layer
- Place a level concrete strip footing approximately 300mm wide by 200mm deep, depending on final bed height.
- Sleepers tend to vary slightly in thickness. therefore bed them on 25mm 4:1 mortar mix to even out the layers. this brings a 125mm thick sleeper to 150mm, an ideal height module to work with.
- Overlap sleepers as you would bricks; try to work in lengths and half-lengths to minimise wastage (see materials list below for further details on sleepers).
- Join sleepers using 200mm TimberLok fasteners (note a high-torque drill is needed).
- Use tie-backs on long straight sections of wall, or where height exceeds 1m.
- After 48 hours, place drainage medium as back fill.
- Pressure-wash exposed faces to remove tar residue (best done prior to construction to avoid contaminating beds).
- 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.
- On long straight stretches, or walls over 900mm height, horizontal tie-backs may be needed into the bank (see note 6007).
- Gaps between sleepers act as drainage outlets.
- Backfill rear of trench with drainage medium (gravel).
- Place topsoil to top 300mm (over drainage medium), tread down firmly.
- For planting beds, leave sleepers some 75mm above the soil level to allow for mulching.
summary:
- Plan terrace heights in sleeper lengths, or even divisions of, to minimise wastage
- Place sleepers to concrete footing on a 25mm bed sand/cement mortar
- Secure to sleepers below using 200mm TimberLok fasteners
- Place dowels to nail recesses on top row
- Avoid using short lengths of sleeper to top row
- Step back each row in 25mm increments
- Clean off sleepers with a pressure washer and detergent
- Place drainage medium behind sleepers
Other construction notes which relate to this subject:
