Drywell / Sinkhole Using Plastic Pipe Rather Than Rubble

Discussion in 'Builders' Talk' started by Axel, Nov 28, 2012.

  1. Axel

    Axel New Member

    Hi,

    I need to install a drywell in an area between a garage and a small retaining wall, a path about 900 wide and ponding at the low point near the centre.  There is no room to dig a decent sized soakaway so I am thinking of a dry well or sinkhole, formed with a 150mm post auger, to take the surface water below the clay level into subsoil that will allow it to percolate away.  Most of the advice and videos online suggest a drainage sleeve or fabric filled with gravel or stones.  Does anyone see a problem with simply sinking a plastic drain pipe, say 1200mm or whatever is needed, down to some gravel then fitting a drainage gully to the top of the pipe.  I fail to see the point of the rubble, as I am not trying to drain the surrounding subsoil, as you would in a lawn, but simply trying to get the water away from the concrete surface, below the clay and percolate off as quickly as possible.  Rubble or gravel will take away volume that could be used for storage of water if necessary and I believe the vertical plastic pipe would be more efficient.  Also a solid plastic pipe with no holes in it is not going to silt up and the water cannot go sideways to the garage or wall foundations.

    Any thoughts would be appreciated.

    Axel      
     
  2. Captain Leaky

    Captain Leaky New Member

    Do it properly Axel. What you propose will not work.
     
  3. Axel

    Axel New Member

    Sorry for being dumb, but why "will it not work" and what does "do it properly mean" ? 
     
  4. G Brown

    G Brown New Member

    Properly means digging a decent sized soak-away constructed correctly.

    A pipe going into the ground will simply be unable to cope when the rain is heavy and will soon silt up.
     
  5. Axel

    Axel New Member

    Thanks for the input, however you have not read the original question or appreciated the problem.  There is no room to build a "decent soakaway".  The question is whether or not the solid PVC vertical pipe would be a better solution than the dry well solution with a drainage sleeve filled with gravel.

    Axel
     
  6. G Brown

    G Brown New Member

    I doubt it very much. Can't you divert the water elsewhere?
     
  7. Axel

    Axel New Member

    Unfortunately the problem here is gravity and there are there are only two ways to divert the water.

    1.  Drain it into a sump and then install a pump to take it back up and into to a drainage system.

    2. Create at path to allow it to continue on it's downward journey to the water table and leave the surface dry.

    I am only looking at option 2 and still need a reason why the vertical, empty plastic pipe would be inferior to the traditional drywell sytem with rubble infill.

    Axel     
     
  8. jack101

    jack101 New Member

    it wont percolate fast enough and  it wont work because it isnt big enough to deal with a heavy downpour and it will silt up over time and the voids will fill up with fines. i have some experience of drainage and soakaways and my advice would be to over engineer the solution every time to cope over time. there is always a way to divert the water or design the system correctly. i would also advise drilling 20mm holes into the pipe at various depths to give the water more than one escape route as often the front of the pipe gets blocked. you should terram somewhere in the design and also you can use perforated pipe to help divert the water away. use free draining stone/rubble to create a french drain. there is always a solution. also the pumped system is not that expensive.
     

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