Retaining Wall - Sanity Check Pls...

[rdwessex]

OK, I'm about to build my retaining wall - never done any brickwork before. My plan is this... does it sound OK?

- I've got (what I think is) a decent footing - concrete - -150mm deep and 450mm wide
- wall is going to be 550mm high, concrete blocks at back, facing bricks at front
- going to slurry the back of the concrete blocks for water proofing before backfilling
- going to tie to concrete blocks to the facing bricks at regular intervals (do the back and front walls need tying together?)
- my mortar mix is going to be -1:4 (is the mix the same for both the facing bricks and concrete blocks?)
- going to add drop holes every few meters or so along the bottom of the wall

Questions - is the gap between the back bricks (the concrete blocks) and the front bricks (the facing bricks) simply determined by the length of the facing brick, which I plan on using on their side as the top of the wall..?

Thanks!

 

[^woody^]

Ok to all of that except the slurry - that's a waste of time, and ties aren't necessary for that height.

 

[martygturner]

retaining walls only retain the 45 degrees of earth from roughly the middle of a wall to the soil height of the mass above it. Gravity only works downwards, All you are retaining is the bit liable to slippage.

See below, unless you are trying to retain a highly sloped garden then consider if you actually need the blocks as they are there to provide mass.

 

[rdwessex]

Thanks. Yeh, I was going to use bricks but blocks were cheaper. Garden not sloped at all, it's just tidying the height difference between an old lawn and a new one.

 

[martygturner]

Thanks. Yeh, I was going to use bricks but blocks were cheaper. Garden not sloped at all, it's just tidying the height difference between an old lawn and a new one.

Then why bother with the blocks.. just a single skin wall will do.

 

[rdwessex]

Because I've everything I've read says anything over 450mm should be double skin...

 

[Dereekoo]

Then why bother with the blocks.. just a single skin wall will do.

Depending on what you mean by the thickness of single skin wall even with a 550 wall 215 thick with a density of 2000kg/m3 and assuming the design was based on no tension developing in the wall itself and a nominal internal angle of friction of the retained material of 35 degrees the overturning force would be greater than the resting force hence it would fail. Granted the design could be based on a permissible tensile stress of 0.7N/mm2 or heavier/thicker wall or greater angle of friction but just saying a single skin wall will do is finger in the air design. A bit of light reading, page17 is a starter for 10.

 

[Ivor Windybottom]

You won't regret overdoing it (other than while building it!), you'll definitely regret underdoing it.

It's as much art as science, there are a million variables including drainage, soil type and plants. Make it tank-proof!

 

[martygturner]

Depending on what you mean by the thickness of single skin wall even with a 550 wall 215 thick with a density of 2000kg/m3 and assuming the design was based on no tension developing in the wall itself and Granted the design could be based on a permissible tensile stress of 0.7N/mm2 or heavier/thicker wall or greater angle of friction but just saying a single skin wall will do is finger in the air design. A bit of light reading, page17 is a starter for 10.

As the Op pointed out its not a retaining wall.... and in as for finger in the air rubbish, its not retaining jack. so is purely decorative. So single skin is perfectly acceptable, its not retaining anything. As for walls over 450mm need to be double skin...what ? its a garden wall and as such its ok to build upto 1m high, which is a rule of thumb but has stood the test of time.

 

[rdwessex]

It's difficult when lots of people give lots of different answers! Thanks, though, appreciate the feedback.

 

[Dereekoo]

As the Op pointed out its not a retaining wall.... and in as for finger in the air rubbish, its not retaining jack. so is purely decorative. So single skin is perfectly acceptable, its not retaining anything. As for walls over 450mm need to be double skin...what ? its a garden wall and as such its ok to build upto 1m high, which is a rule of thumb but has stood the test of time.

OK, I'm about to build my retaining wall -

????

 

[Ivor Windybottom]

As the Op pointed out its not a retaining wall.... and in as for finger in the air rubbish, its not retaining jack. so is purely decorative. So single skin is perfectly acceptable, its not retaining anything. As for walls over 450mm need to be double skin...what ? its a garden wall and as such its ok to build upto 1m high, which is a rule of thumb but has stood the test of time.

Please ignore every word of the above! Utter rubbish.

 

[Dereekoo]

It's difficult when lots of people give lots of different answers! Thanks, though, appreciate the feedback.

?? Except for one confused individual everyone else seems more or less agreeable with your initial proposal