Timber Tie Back Specifications.
> This wall will always be built with a batter of a minimum of 25%. This helps with the strength of the wall in counter balancing, therefor putting less pressure on the ties and anchors.
> There is NO plastic placed in behind the wall, the gravel is allowed to fall slightly into the space of the rails.
> It is best to use the 200x100mm (8”x4”) sleepers for the long rails and for the spacers and ties use 150x75mm (6”x3”). This will create a 75mm (3”) gap over a 200mm (8”) rail so there is less chance that the gravel will fall out of the face.
> The ties will return back into the retained material a minimum of 0.9m (3ft) although the further the better. The piece fixed on the end (usually a cut piece of sleeper) cut to a minimum of 0.9m (3ft) to be effective and fixed at 90% creating a T effect. It is best to bolt this to the tie with a gal bolt as well as two gal spike nails.
> Try and cut the retained material to this same shape catering for the tie, the less you disturb the ground behind the wall the better. However If you are back filling this area then it doesn’t matter, just make your Tie and T pieces longer, the more surface area and fill placed in front of the T the better.
> Spacers and ties are fixed 1.2m (4ft) apart. So you will end up with one at the end and one in the middle of each rail. The spacers are just sleeper pieces cut shorter (the same dimension as the ties) but they are not used as ties.
> I have also used a Gal chain to use as a reinforcing where this tie is fixed to the wall, especially if it’s fixed at the end of the rails and is shared between the two. See diagram 07
> Spacers are generally cut about 300 – 400mm (1’ to 1’4”) long. They are also fixed onto the rails at 90 deg. so from the face of the wall you see the end of the spacer, just like the ties.
> A minimum of 20mm (3/4”) gravel is used as a filter and is filled right to the top of the wall generally a minimum of 100mm (4”) thick, more is better, this allows any moister to escape out the face of the wall. You can use a filtering material like Landscape Fabric between the gravel and the dirt.An Agg pipe can be used if you wish, this will get rid of Storm water and the seepage moisture quicker of course, but it’s not necessary for the walls sake.
Anchor and Tie Ideas.
> These ties should be placed at the base of the wall being above the first rail and then at every second rail above that. You only need one tie per two rails but try to stagger the ties as the wall is being built, from the end of the rails to the middle as well as the layers as the wall gets higher, the more variation the better.
> How far you set the ties back into the retained material can also vary but you want a minimum of 0.9m (3ft)
> An alternative to using sleepers as ties due to rock for lack of room for example, then you can use a gal chain fixed either to the rails or I tend to fix it to the top side of a spacer, with the other end fixed to a gall pipe or eyelet set in a solid concrete anchor, this has a depth in the ground of a minimum of 900mm (3ft) the bigger the better.
> Another method to fix the chain or sleeper ties to, is to a series of posts set in concrete in the ground behind the wall, I would use 125mm (5”) logs as they are multi directional. You don’t obviously need as many of these posts (one per 2.4 – 3m) (8 – 10’) as the closed face walls as there is not as much pressure against the wall due to the open face. The gal chains or sleeper ties can then be fixed or wrapped around these logs for an anchor.