Retaining Wall, Reinforced - Am I safe?

burgerxv · 19 Mar 2009

Hi All

I am planning to build a retaining wall 1900mm high, by the advice of this site (http://www.diydoctor.org.uk/projects/retainingwall.htm) and the hight being 4 times the thickness that would mean it needs to be 475mm thick which is huge.

However it says that reinforcing the wall doubles it strength. Does that really mean i can halve the width to 237mm? If this is the case I was thinking of 2 block skins 100mm wide with a 50mm gap with reinforced steel and filled with concrete.

Am I correct and this will be OK?

I am sure that my math is OK but what I want to check is that by reinforcing the wall I can actually half the width of it. It seems too easy an answer.

If I am, the foundations need to be twice the width of the wall so 500mm?

stuart45 · 19 Mar 2009

It would be better to use the hollow block system, and put vertical and horizontal re-inforcing into it.

burgerxv · 19 Mar 2009

stuart45 said:
It would be better to use the hollow block system, and put vertical and horizontal re-inforcing into it.

Hi Thanks I had thought about this system as well but again not sure how the reinforcing effects the required thickness the wall needs to be. Any idea?

For the horizontal reinforcement I presume you mean mesh. I can't remember it's exact name.

Matt

stuart45 · 19 Mar 2009

I have built retaining walls about 2M high using hollow blocks with re-bar and concrete fill. If you want to use horizontal re-bar as well as vertical put some cuts in the bottom of some blocks and knock out the piece. When filled with concrete this forms a concrete bonding beam.
When you concrete the foundations set out the blockwork so you can put the steel in the right places. Bend the re-bar over so it hooks into the concrete. Don't make the vertical bars too high as you will have to lift the blocks over them. Use shorter pieces and tie more as you go up as well as to the horizontal bars. You can also put in wall ties and face with brickwork.

PaulJR · 19 Mar 2009

A couple of points.

Rebar needs about 40 times its diameter at each lap to be effective.
It also needs the same at its anchorage - bends are worth about 12D

The reason for the massive thickness of the wall is that it needs the weight (I should say mass I know) to hold back the ground behind it.

There is another post I have just replied to where the author is looking at interlocking systems - they will have an off the shelf design that will cope.

Frankly a 1.9m high retaining wall is getting into the realms of proper Civil Engineering and I really dont think you should just bung some steel reinforcing in ad hoc, it will only stiffen the wall panel, it will not stop the whole wall sliding out at its base, or falling over etc.

You will be getting something like 4 Tonnes pressure per metre run along the base, so it needs a bit of thought.

stuart45 · 19 Mar 2009

burgerxv,
It might be a good idea to put on the pictures that are on the other forum.
ultimatehandyman

burgerxv · 19 Mar 2009

stuart45 said:
burgerxv,
It might be a good idea to put on the pictures that are on the other forum.
ultimatehandyman

Hi See below

The cross section of the wall is a design I was given for a 2.4m wall, using hollow blocks reinforced, the foundations 900mm with 500mm out front and a 1m re-bar running through it and up into the slab and also has a reinforced mesh across the whole of the foundation. This is a lot bigger foundation than I was planning but makes sense.

It will also have a horizontal reinforcements around the sides and into the return walls running 3.8meters back (as in diagrams) which will help hold it back at the top and mid way down.

In fairness the desgin I was given had a stone cladding front to it but I'm not sure if that actually adds to the strength. I am trying to find out if it does at which point I could include an run of 100mm blocks on the front, maybe not the full hight.

To finish the wall I'm planning on a sand stone colour render.

All thoughts welcome, naturally

Untitled

burgerxv
19 Mar 2009
1

Untitled

burgerxv
19 Mar 2009
1

Untitled

burgerxv
19 Mar 2009
1

PaulJR · 20 Mar 2009

Ok, I can see the logic behind this system.

To make it work best - use Ø10 or Ø12mm reinforcing rods and bend the ends to give yourself a 300x1200mm "L" bar. Sit the short leg on you mesh when you concrete the foundation - use a bit of 4"x"2 or similar to keep them in line/vertical. aim to have them at about 150 crs. At the front edge of the foundation dig a 300mm wide trench an additional 300mm deep - this "toe" will stop the whole thing sliding if you get the sort of deluge we've all being suffering the last few "summers" Stick a strip of mesh vertically in it.

Use brick reinforcing mesh in the mortar beds for the height of the vertical bars.

As I put in the other post - take a lot of care with the drainage - wrap any stone in a geotextile - terram or similar and leave weep holes. It is water that causes most failures in retaining walls.

burgerxv · 21 Mar 2009

PaulJR said:
Ok, I can see the logic behind this system.

To make it work best - use Ø10 or Ø12mm reinforcing rods and bend the ends to give yourself a 300x1200mm "L" bar. Sit the short leg on you mesh when you concrete the foundation - use a bit of 4"x"2 or similar to keep them in line/vertical. aim to have them at about 150 crs. At the front edge of the foundation dig a 300mm wide trench an additional 300mm deep - this "toe" will stop the whole thing sliding if you get the sort of deluge we've all being suffering the last few "summers" Stick a strip of mesh vertically in it.

Use brick reinforcing mesh in the mortar beds for the height of the vertical bars.

As I put in the other post - take a lot of care with the drainage - wrap any stone in a geotextile - terram or similar and leave weep holes. It is water that causes most failures in retaining walls.

Thanks Paul, very usefull advice, I definitely tink you are right about the 'toe'.

The drainage is going to be quite hefty with 2 cubicmeters of stone and 110mm drainage pipe as you say. I actually hope to catch the run off to use in the garden.
Matt

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Retaining Wall, Reinforced - Am I safe?

Similar threads