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Trench Dug Alongside Footings

Discussion in 'Building' started by Mark-UK, 14 Aug 2019.

  1. Mark-UK

    Mark-UK

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    I've dug a trench right up against the footings on one side of my breeze block shed because I was having problems with rainwater pooling outside and getting inside the shed. The trench is roughly 16" deep and about a spade's width wide. A friend of mine said it's dangerous because the wall might shift. I guess he's right because I've not filled the trench in yet.

    He said I have to fill the trench with concrete. Problem is if I do that, the water getting into the shed is going to be worse than before, so the plan is to fill the trench to the level where the bottom of the wall starts, with 20 to 30mm sized stones and pack it all in tight.

    Will this render the wall safe again?

    Thanks all
     
  2. Notch7

    Notch7

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    If the block work is in good condition, it will be fine unless you leave the trench for a long time and allow it to fill with rainwater.

    Its water softening the foundation below the wall that causes the problem.

    Ive seen plenty of trenches dug up tight against a house wall with no problem.

    You probably need to apply a liquid DPM to the wall
     
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  3. Mark-UK

    Mark-UK

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    Thank Notch, I've decided to fill it in with poured concrete and dig a trench next to that.

    We've had a lot of heavy rainfall and it's been exposed for months. I need to get it done asap.
     
  4. StephenStephen

    StephenStephen

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    ...sorry to make an obvious point, but do slope the top of your concrete to send the water to where you want it to go.
     
  5. Mark-UK

    Mark-UK

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    You're absolutely right. The concrete-filled trench will have a slight gradient to channel the rainwater away from the wall. Will hopefully get it done within the next week at most.

    Thanks for the advice Stephen
     
  6. ^woody^

    ^woody^

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    Find a different friend, preferably one with a clue and some sense.
     
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  7. Mark-UK

    Mark-UK

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    Do you think the wall is safe as it is then? Right now it's a quarter full with drainage stones but the plan was to fill it full of them. The problem I've got is the water is sitting there in the trench; it's a pool. I've obviously not dug deep enough. That's my main worry; all that water getting under the footings.

    Perhaps I just need to dig deeper to go passed the clay.
     
  8. Notch7

    Notch7

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    It could prob stay like it for years TBH.
     
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  9. ^woody^

    ^woody^

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    In the trench, you should be laying a perforated pipe on a slight angle and extend the pipe past the extension somewhere for it to drain out of the end. If the ground is all clay, you need a pit at the end of the pipe as a soakaway, or extend the pipe for a few metres down the garden. Fill around the pipe with gravel or crushed stone.
     
  10. Mark-UK

    Mark-UK

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    And the trench to be filled with the drainage stones?
     
  11. Mark-UK

    Mark-UK

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  12. SpecialK

    SpecialK

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    30 bags??? How big is the hole! Remember these bags will make roughly their size in concrete. So if its 16" deep by a spade then 4 or 5 should fill it? You didnt say how long it was....
    As long as you have not dug underneath the foundation strip you should be fine without it.

    As said previously - Land drain pipe down a trench to a soak away further from the shed would be ideal. Back fill with stones and put the soil back on top (fill with stones to the top near foundation if required for quick drainage.)
     
  13. Mark-UK

    Mark-UK

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    Not sure why I posted 16" when I meant 16 foot. And apparently it's gone up to 40 bags!

    Trench: 16' long by (roughly) 9" wide by (roughly) 1' deep.

    I'll be digging a second trench next to the filled-in one and I'll be doing just as you say as concerns pipe/drainage.

    ---------------------------------------

    This is what I was told


    The approximate volume of concrete produced from a 40 pound sack is 0.3 ft³

    SOLUTION:
    CUFT Volume in the trench is divided by CUFT of concrete in one sack .

    TRENCH VOLUME: 19′x.75′x1′= 14.25 CUFT

    EQUATION: 14.25CUFT in trench/ .3 CUFT in one sack= 47 Sacks at 40lbs.

    -------------

    This is the product I'm looking at:
    www.wickes.co.uk/Blue-Circle-High-Strength-Ready-To-Use-Concrete-40N---20kg/p/133771#

    Says 100 bags covers m3 (which doesn't tell me much due to my poor math). Just found this info on the data sheet:

    PACKAGING & COVERAGE

    Tarmac High Strength Concrete (40N) is available in weatherproof and tear-resistant plastic packaging. One bag will typically produce around 0.01 m3 of fresh concrete (0.33m x 0.33m x 0.1m).
     
    Last edited: 19 Aug 2019
  14. Harry Bloomfield

    Harry Bloomfield

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  15. Mark-UK

    Mark-UK

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    Ascus (company) were pretty good when I used them for the concrete floor. I might look them up again and see what their fees are.

    Thank you
     
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