Timber Walls
 Most walls are constructed with this crib-type method using timbers that are 89 x 140 mm (3-1/2 x 5-1/2in), 140 x 140mm (5-1/2 x 5-1/2in), 140 x 191 mm (5-1/2 x 7-1/2in) or 191 x 191mm (7-1/2 x 7-1/2in). Used creosoted railway ties are often found in this type of construction but their rough, inconsistent texture and harmful effects on some plants make them less suited than CCAA-treated wood.
The timbers are installed in a pattern similar to a brick wall with the butt ends of timbers in one course offset from those in the courses above and below. The bottom course of timbers is placed below grade. In sandy soils special footing preparation is not required, but in less well drained soils a 150mm (6 in) deep gravel footing and 300 to 600mm (12 to 24in) of gravel backfill are recommended.
Each course of timbers is fastened to the course below using galvanized spikes or re-bars whose length is 1.5 times the thickness of the timbers. The timbers should be drilled first to prevent splitting.
In addition to the 15 degrees inward slope of the wall, vertical stability is achieved by installing tiebacks. These are single timbers inserted perpendicularly from the face of the wall into the soil backfill to a distance equal to their height above the base of the wall.
The end of the tieback is nailed to a 600 mm (24in) long deadman timber aligned parallel to the wall. Tiebacks should be placed in every second course on centres of 1.2 to 2.0m (4 to 6-1/2 ft) and offset from those in the course below. Begin on the second or third course from the bottom of the wall and end 240mm (9-1/2in) below grade at top. Do not install too many tiebacks as this will weaken their effect. Corners and jogs also provide resistance to overturning.
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