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Retaining wall:footing is lower than grade. Should I add height on top of footing?

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  1. #1
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    Default Retaining wall:footing is lower than grade. Should I add height on top of footing?

    Greetings,
    Your help would be most appreciated.
    Please see diagram.
    I have a concrete footing already poured. However, it's top surface is lower than grade (paver level). In addition to an ago-pipe I would like to have pvc weeper pipes in the wall that will drain water on to the pavers.
    Do I will need to raise the level of the footing (approx 200mm) to place the agi pipe and for the weeper tubes to function correctly? I will be installing a new deck that will sit higher than the weeping holes.
    Would Besser blocks be suitable or just normal bricks? Is there an alternative plan?

    Thank you and kind regards, Bob
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    Hi Bilby, any reason you cant have it draining our one end?

  3. #3
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    Quote Originally Posted by Bart1080 View Post
    Hi Bilby, any reason you cant have it draining our one end?
    Hello Bart1080,
    Thank you for your your reply.
    I guess I could. I just liked the added security of have weeping hole pipes as well. Am I correct in thinking that weeping hole pipes at approx 220mm above the footing would not function and therefore no point in having them.

    If the agi-drain were to sit on 200mm of stones, would that be too high? The water would then be sitting below the agi-drain and directly on the footing without it flowing away- am thinking correctly?
    Bilby

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    I've built many retaining walls but never with weeping holes...all with aggi or slotted PVC pipe covered with scoria stone, geo-textile and drained out one end (the lower end ) and from a drainage perspective all has worked perfectly.

    Is there a specific design requirement for the wall stability or drainage your trying the meet or more around you think it would be better? ......sounds like the latter. If I was to think through what your wanting to build, logically I dont see any point in designing your wall with those drainage features (weep holes) 200mm above the base of the wall as they would serve no purpose however if its a double brick wall, whats the middle filled with ....depending on the answer, there may be a benefit to have weep holes to ensure it doesnt hold water. This could be simply the back of the wall feeding into the agi drain/free draining rock

    How high is your wall? ...looking at your diagram 600mm??

  5. #5
    4K Club Member Marc's Avatar
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    The retaining walls that stand the test of time are those with the best drain, not only with permeable backfill and pipes to take it away from behind it, but also those built with materials that allow water to come through the wall itself, when the amount of water is too much.

    That is why full brick or solid concrete or core filled walls don't do particularly well, and require wider footings to prevent toppling. Those footing you have in your diagram are for vertical load, and the wall needs to withstand mainly horizontal loads. Best you can do is build your retaining wall with blocks that sit on top of each other with no mortar. The backfill with aggregate and ag pipe is still required, and the excess water will come occasionally through the wall, anywhere it choses to. To try to channel that through little pvc pipes, is a hit and miss affair.

    By the way ... how high is the wall, and do you have vertical reo bars to link to the wall in the footing already?
    Real knowledge is to know the extent of one's ignorance
    Confucius

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    Quote Originally Posted by Bart1080 View Post
    I've built many retaining walls but never with weeping holes...all with aggi or slotted PVC pipe covered with scoria stone, geo-textile and drained out one end (the lower end ) and from a drainage perspective all has worked perfectly.

    Is there a specific design requirement for the wall stability or drainage your trying the meet or more around you think it would be better? ......sounds like the latter. If I was to think through what your wanting to build, logically I dont see any point in designing your wall with those drainage features (weep holes) 200mm above the base of the wall as they would serve no purpose however if its a double brick wall, whats the middle filled with ....depending on the answer, there may be a benefit to have weep holes to ensure it doesnt hold water. This could be simply the back of the wall feeding into the agi drain/free draining rock

    How high is your wall? ...looking at your diagram 600mm??
    Hello Bart,
    Thank you again.
    After your first reply I have thought again. I can have the ag pipes coming out both sides easily. I think I was just been over cautious by trying to have two systems ag pipe and weep holes. Weep holes just been an extra. I just didn't want a problem in future years. Previously I see that that the plastic ag pipe just gets squashed and distorted. But now I am clearer.
    I'll use a stronger pvc slotted pipe (100mm), graded 1:100, that will protrude out of the wall at its end. It is then only 1m to the storm water (downpipes). I think I will need to dig and insert a pit so as to collect sediment. That should not be too difficult. I will include Y-junction and access point to the agipipe to flush out if necessary.

    I am planning that the brick wall is core filled. It is about 750mm high. Mark might change my mind if I am convinced that brick/core filled is not a good idea for a retaining wall. Mark suggests that blocks are a better option as they can release water more easily. I can see that is ultimately true but wondering if a good ag-pipe drainage system will solve this issue.

    The footings are 500mm wide and even wider in some places. The vertical starter base are already in place.

    Thx so much for your advice,

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    Hello Marc,
    Thank you for your advice,.
    I am planning that the brick wall is core filled. It is about 750mm high. I might change my mind if I am convinced that brick/core filled is not a good idea for a retaining wall. I can see that blocks are a better option as they can release water more easily and and wondering if a good ag-pipe drainage system will solve this issue sufficiently.

    The footings are 500mm wide and even wider in some places. The vertical starter bars are already in place.

    Thx so much for your advice,

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