Gabion cage retaining walls: drainage and deadman needs?

Question

I'm having some difficulty finding information about gabion retaining wall construction.

We're building a 2' high gabion cage wall to hold back 2' of flat topsoil backfill.

There are two aspects I can't find definitive information on:

1) Drainage pipe/plane. Is that needed at all? I've built block retaining walls before where you want to backfill the wall with a french drain, drainable rock, and then filter fabric. But it seems to be a gabion wall, in itself, is a drainage plane. Is there any reason to just not line the back side of the cage with filter fabric before filling with rocks?

2) Deadmen. Are they generally needed for 2' walls? And, if so, any ideas how to do that with a gabion cage? I was thinking of hammering in some metal fence stacks 4' back, and then just wiring them to the cages. But not sure if that's even worth the effort.

Answer 1

There are two types of retaining walls: 1) cantilevered, and 2) gravity.

1) Cantilevered retaining walls rely on a wall that has a compression side and a tension side. The compression side relays on the compressive strength of the concrete, masonry, etc. The tension side relays on reinforcing steel.

2) Gravity retaining walls rely on the weight of materials pressing down more than side forces pressing from the side. There are a few issues with this system, including sliding, rotation, long term deterioration of the cage, etc. all of which are variables due to the type of soil. The reason there is very little information about these retaining walls is because any change in the soil can have significant affects on the wall.

So, these walls are generally oversized.

With regard to drainage from behind the gabion retaining wall, water is a great force that can destroy the wall. Therefore, more drainage (including filter fabric) the better.

With regard to the deadman, it’s not necessary for 2’ high retaining walls. In fact, it’s not even considered a retaining wall until 4’ high. At 2’ high, there isn’t enough pressure (force) on the wall for concern.