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Steel spacing for hollow block retaining wall


 
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D4dog

from United Kingdom

Joined: 15 Apr 2008
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Location: Derbyshire,
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PostPosted: Fri Jun 18, 2010 4:03 pm Reply with quote

I am building a 22m long retaining wall from 9" hollow block, which will be reinforced with steel hooked into a reinforced foundation. My question is, at what centres do I need to insert 12mm re-bar? I had estimated about 1 every metre - is this sufficient?

second question - Wall will be 440 thick for first course, 220mm thick for remainder on a 600 wide foundation. Hiegth will be 1.6m Do I need to fill the hollow blocks compeltely, or will filling those cells in which the re-bar sits suffice?

Any advice welcome
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themiddleagedun

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PostPosted: Sat Jun 19, 2010 7:23 am Reply with quote

I wouldn't bother with 440 in the bottom, but would put pillars on either end, and maybe every 2250 or so.

It's a fair old wall, so i'd use a bar in every block. These should be in a dead straight line. vertically plumb and at 450 centres (important) so a bar goes in every block.

You'd be better filling every block with concrete, but obviously the ones with the bar for certain.

you may need an exp. joint or two in that length of wall. (pillar either side)

22040mm will give you a wall 49 block long.
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themiddleagedun

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PostPosted: Sat Jun 19, 2010 7:48 am Reply with quote

Should also have said the foundation width is a bit on the small side. i'd increase it to 900mm if I were you, and go down nice & deep too.

Good luck.
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D4dog

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Location: Derbyshire,
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PostPosted: Sat Jun 19, 2010 9:59 pm Reply with quote

Many thanks middleagedun. Would like to have avoided pillars if possible - may well place one internal at the back of the wall, rather than buttressing at the front - I would think it would probably work, especially if tied in with a bit of steel.

I will be re-inforcing the foundation, and laying it in a single go - do you think an expansion joint really necessary?
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D4dog

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PostPosted: Sun Jun 20, 2010 8:53 am Reply with quote

Sorry - forgot to ask. What size gap should I leave for an expansion joint for say each 7m of wall? Would you recommend dowelling it, or would an expansion joint compound suffice? If so, any recommendations on the best product?
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mikric

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PostPosted: Sun Jun 20, 2010 8:56 am Reply with quote

How much earth is the wall retaining ?
Have you given any thought to drainage behind the wall ?
Expansion on a wall that length must be considered.
If retaining more than 1m of earth then as said above a 900mm foundation width should be used.
A rule of thumb for retaining walls is for the retaining height to lie between 2 and 4 times the wall thickness..
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Static

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PostPosted: Mon Jun 21, 2010 9:03 am Reply with quote

Some fairly good advice above but would add,.

900mm for a 1600 retained height is probably too small would normally look around the 1200 wide base region anything less may well sink..

Also for a height of that you will need a bar in every pocket as well as some in the base..

Im assuming your just retaining your garden and nothing else.. and that your putting in weepholes and sensible drainage..

Go for half debonded dowels at the movement joints that way the finishes will stay nice and flush.. (but dowels arent vital for the wall to stay up)

Answer mikric's questions will help give a better idea of what you propose;
Also, what soil are you retaining/bearing onto?
Are you just retaining a patch of garden (anything with 45 deg of proposed footing)?
Do you intend to put a handrail or fence ontop?
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D4dog

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Location: Derbyshire,
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PostPosted: Mon Jun 21, 2010 6:44 pm Reply with quote

Thanks all for assistance.

The current situation is that there is nothing holding a 45 degree bank, which itself sits atop a retaining wall. I am cutting the ground back 2 meters, and therefore the footing of the new wall will be will be square to the ground level, with a 30 deg shear line going through the footing of the original retaining wall.

Ground is fairly solid, and I beleive sits on significant outcrops of rock. Retained height will be about 1.4m, the additional height will be a capping stones.

Drainage will be a combination of 100mm corrugated slotted pipe at the rear running the enitre length, with weep holes in the bottom layer of the wall.

I note your comments re footing width - will increase to 900mm, and probably to 200mm thick - I wouldnt expect sinkage, but intend reinforcing the entire length in any case just in case.

My original plan was to make the base of the wall 440 wide, up to the 600mm point - assuming apporx 1/4 of the height at its base.

It is only retaining garden, and a patio (in fact this already exisits, supported by nothing more than the 45 degree soil slope!).

Ill take some photos once dug out - would be grateful for comment. Dowling noted - using standard 12mm rebar, what do you recommend for sleeving - 15mm plastic conduit ok?

Cheers
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Static

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PostPosted: Tue Jun 22, 2010 8:55 am Reply with quote

D4dog wrote:
The current situation is that there is nothing holding a 45 degree bank, which itself sits atop a retaining wall. I am cutting the ground back 2 meters, and therefore the footing of the new wall will be will be square to the ground level, with a 30 deg shear line going through the footing of the original retaining wall.

Is the 30deg line from the back of existing retaining walls footing?
So something like:

Added a house at top side assuming the patio backs onto something?

A 440 wide wall at the base would be more robust and would be less prone to slidding and overturning..

Depending on the age of the 45deg bank but you may find that its been engineered and there is something holding it in place (ie teram) but wont find out till you start diggin
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