Concrete filled brick retaining - wall max height
Concrete filled brick retaining - wall max height
(OP)
Hi,
I've been told there is a maximum height of 1100mm (3ft something) on brick retaining walls (2 brick skins with a 100mm concrete filled cavity).
I think it has to do with deflection, however I'm not sure.
Does anyone else know why this is and if it's true?
I guess there is an issue with the wet concrete applying too much pressure over a certain height, although I imagine you could solve that with a slow pour rate or multiple pours.
I assume also with this type of wall that because you don't have the 'clean-out blocks' of concrete block walls, so you may get dodgy corefill at the bottom... Maybe that is why the height is limited..
Any thoughts..?
Thanks
I've been told there is a maximum height of 1100mm (3ft something) on brick retaining walls (2 brick skins with a 100mm concrete filled cavity).
I think it has to do with deflection, however I'm not sure.
Does anyone else know why this is and if it's true?
I guess there is an issue with the wet concrete applying too much pressure over a certain height, although I imagine you could solve that with a slow pour rate or multiple pours.
I assume also with this type of wall that because you don't have the 'clean-out blocks' of concrete block walls, so you may get dodgy corefill at the bottom... Maybe that is why the height is limited..
Any thoughts..?
Thanks






RE: Concrete filled brick retaining - wall max height
RE: Concrete filled brick retaining - wall max height
the concept of filled grout space does little to improve the lateral strength that is required for a retaining wall. For that total wall thickness, a partially reinforced CMU wall or poured in place concrete with steel closer to the surface would be more efficient.
The sloppy unclean cores can affect the vertical capacity, but not the lateral strength to a great extent.
Original poster - where are you located?
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Concrete filled brick retaining - wall max height
I assume he has reinforcement in the grout filled cavity.
RE: Concrete filled brick retaining - wall max height
I'm in Australia.
Doing a number on the liquid pressure for a 1.8m high wall seems like it is very high for brick ties to resist..
RE: Concrete filled brick retaining - wall max height
RE: Concrete filled brick retaining - wall max height
Also worthwhile keeping an eye on your minimum concrete core thickness. At low wall heights, for design purposes you can get away with very thin cores. You may need to adopt a minimum thickness of say 150mm to accomodate your vertical reinforcement, laps with the starter bars, and still allow compaction.
VB
RE: Concrete filled brick retaining - wall max height
Since it is so low, the suggested limit of 1.2 m per lift could be applied (if you have a micrometer on the job).
The wall may be a true retaining wall if there was no load applied later, but reinforcement in the center would not add much and a 6"(150 mm)CMU would carry more load laterally and vertically. Clean-outs would be inane, silly and unprofessional for a wall only about 1 meter high. Further information could provide different picture.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Concrete filled brick retaining - wall max height
There is for any project an economical limit to the wall height where other types of soil retention would be less costly. Is that whar you mean?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Concrete filled brick retaining - wall max height
He wants to build a wall 1.8 metres high, per his second post. I see no problem with building a brick retaining wall his way...probably what the owner or architect wants to see.
RE: Concrete filled brick retaining - wall max height
Mike - no, it is a structural limit, I think the limit was mainly governed by concrete liquid pressure. I think I have a much better understanding now.
Thanks for all the replies.
The wall will be significantly better than the 1.8m high, unreinforced double brick retaining wall that is there at the moment! It has quite a lean to it..
I am going to specify brick ties at 300 centres.. leave out every second brick at base of external skin for cleanout... brickie to minimise dags at rear of internal skin... corefill in two lifts
RE: Concrete filled brick retaining - wall max height
Although it may work with central reinforcement, I would specify the bars to be toward the earth side. You know...design for central, tell the builder to put them on the earth side, hope he doesn't put them on the wrong side.
There are a lot of those leaning, unreinforced brick walls around.
RE: Concrete filled brick retaining - wall max height
With a 100mm cavity, they have to be central to get the necessary cover.
Concretemasonry,
This is fairly standard practice in parts of Australia, though I agree that it does not seems to be as proctical as using some CMU.
msquared48,
Australian codes are generally not that specific and leave those sorts of decisions up to the designer.
RE: Concrete filled brick retaining - wall max height
I think 20 mm cover is enough in a grouted core, and AS3700 agrees, even for aggressive soil exposure. So assuming a 20 mm bar, you could have the starter bars at 70/30 within the cavity. I would tend to dimension it at 60/40, and wouldn't accept 50/50. Too little tolerance? Many would agree, but good builders can do it.
RE: Concrete filled brick retaining - wall max height
The bricks add absolutely nothing to the durability of the bars. I would be surprised if 20mm would be enough, even in concrete masonry as these are quite porous.. But in this case it is really plain concrete with brick formwork as far as durability is concerned.
RE: Concrete filled brick retaining - wall max height
RE: Concrete filled brick retaining - wall max height
With regards to porosity, I was referring to the porosity of a typical Australian concrete block - too high to properly count on for protection.
RE: Concrete filled brick retaining - wall max height
RE: Concrete filled brick retaining - wall max height
Yes I saw it in the cmaa manual shortly after posting but did not want to double post (in case I got scalded by the fire and brimstone that would be sent my way).
Personally I would allow more than 20mm to concrete and deifnately more than 1/4" to clay masonry but that is a personal opinion.
RE: Concrete filled brick retaining - wall max height
RE: Concrete filled brick retaining - wall max height
would a double skinned brick retaining wall be able to support as high as 3m. and also what would be a recommended cavity width?