Retaining wall options - gabion vs blocks

[andrew29]

Hi,

I need to replace old retaining walls. The solid concrete section is 25m long and 900mm sigh. The 2 side sections are made of concrete blocks. Max height of 900mm sloping down to 300mm.

Access is poor so it’ll be manual carry of the old and the new.

I’m thinking of gabions to reuse some of the old blocks and concrete at the back of the gabions. Saving cost and effort.

The existing foundation for the side walls is 30cm.

Some specific questions I have..

Will I get away with a 500mm deep gabion for 1000mm of height?

Are gabions really likely to stack up better from a cost and effort perspective? I’ll DIY.

Thanks for any suggestions and observations

[andrew29]

Photo attached

[Beardy]

I did a 80 metre long gabion wall 500 deep and 1 metre high. It is very a cost effective solution. I bought the cages from Permathene in Sydney

[andrew29]

Thanks, what did you fill it with? And is it holding up ok? Mine is perpendicular to the slope but I’m thinking that because it’s water permeable it should hold up.

[Camelot]

Any earth battering should not be more than 45 degrees regardless of the retaining wall system.

Gabion's are a good cost effective solution, if you need to go 2 high you would need to step the second row back from the face of the wall ideally by 50% of the depth of the Gabion.

Like you say you can take your time and put nice material to the front and rubble to the back, you can also plant inside the Gabion.

The downside is the Gabion will only last the life of the cage that supports the rubble/face material.

[andrew29]

sorry what do you mean by earth battering at 45 degrees?

I meant that my retaining wall is directly across the slope.

do you mean that the gabion itself should be angled back into the slope?

[Camelot]

sorry what do you mean by earth battering at 45 degrees?

I meant that my retaining wall is directly across the slope.

do you mean that the gabion itself should be angled back into the slope?

When backfilling above the height of the retaining wall (in your case a Gabion) the slope of the earth/backfill material from the back face of the wall should not be more than 45 degrees batter.

[andrew29]

Ok got it. Makes sense.

the slope above the wall will be nothing like 45 so I should be right.

i understand that only a minimal footing is needed with some geo fabric behind but no need for backfill with gravel and drainage pipe given that it’s water permeable? Does that sound right?

thabks heaps

[Camelot]

Ok got it. Makes sense.

the slope above the wall will be nothing like 45 so I should be right.

i understand that only a minimal footing is needed with some geo fabric behind but no need for backfill with gravel and drainage pipe given that it’s water permeable? Does that sound right?

thabks heaps

Like you say this retaining wall system is permeable, so shouldn't allow hydrostatic pressure to build, but you still need clean permeable fill don't use anything with clay in it

[Beardy]

Thanks, what did you fill it with? And is it holding up ok? Mine is perpendicular to the slope but I’m thinking that because it’s water permeable it should hold up.

I used basalt rock around the 100 to 150 diameter grade but you can use what is locally available to you and you like the look of

[Avondale]

Have you considered tanalised pine, hardwood sleepers?
I gather from photo the land slopes in the direction of the concrete block wall.
That wouldn't be holding up much dirt. So not load bearing

Is the concrete section cactus, or you don't like its appearance?
If latter is there another option and retain wall?

[andrew29]

The solid section is cactus and definitely needs replacing and is perpendicular to the slope so I’ll need something robust. The side section will do mich less ‘retaining’.

I reckon I’ll get a gabion 1 m high, .5 deep, 2m long, and trial one section.

reusing the old material to a degree and minimizing cost and effort puts gabions in front for me at this stage

[Fuzzie]

I've built a couple of DIY retaining walls. Around where I live the usual height not requiring engineering/council approval is 1m.

I've also been in the situation of having limited access and having to hand carry much of the materials for significant distances. I liked the idea of gabions but the amount of rock needed to be moved seemed disproportionate when going only 1m high.

I've ended up mostly using concrete retaining wall blocks such as these for price and convenience. They are easy to handle and position requiring only gravity placement, no mortar, no steel. At 1m high they generally only need a level packed gravel base. Easy to do with a mattock , a level and a tamper.

I had a landscaper do some work in my last house and he laid similar blocks on a concrete footing with the wall at 1.5m high. There was no obvious movement in that wall after 15 years.

Gabions can be seen used in a variety of road cutting sections and they clearly work, but I note these are usually several meters high and properly engineered. Getting the stacked level sizes correct is important. I was looking at doing something similar on my last house on a very steep slope, but the cost and effort seemed disproportionate to the desired result. For my proposed big project the engineer I spoke to wasn't enthusiastic and suggested just getting a crane truck to position large (cheaper) concrete blocks made out of "undelivered" concrete mix. Gabions otherwise now seem to be popular for 'designer' walls in outdoor room settings following "easy as" BHG projects....

[havabeer69]

the 1m height rule is usual in most coulncils, some are 900mm

also remember there are minimum distances from the fence line to the outer face of the wall that also need to be met to not attract council.



probably a bit more work to install vertical H posts, but there's quite a number of composite style retaining wall sleeprs available now, so super light weight and zero maintenance.

[andrew29]

Thanks, I’ll have a look at this…