I have recently started digging and laying the base for a patio with pavers. Its roughly 300 sqft and the soil is made of clay. I dug around 7" deep to have 4" gravel layer, 1" sand an 2" for the pavers and noticed that after compacting (using a plate compactor) the clay and the 4" gravel on top there are a couple of spots that are roughly 2x2 ft that act as a liquid when I step on them. I think its called "liquefaction". There was quite a bit of water in the clay due to a few days of rain but no standing water.

I do not want to lay anything on top until I stabilize it and wanted to get an opinion on whether its just a matter of drying it, or whether it's ok to proceed and it will harder or settler, or if I can add something to give it more stability.

P.S. the gravel is "A" type gravel, and the rest of the patio space is extremely rigid except the two spots.

Thank you!

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    May 7, 2019 at 3:11

1 Answer 1


You’ll continue to have that “liquid” action until you remove the water.

I’d provide a way for the water to “runoff”, like a perimeter drain, drain rock at the perimeter, etc. that will remove the excess liquid. (I’d make sure the drainpipe extends to a ditch or something, to carry the water away. Water will run in the direction of least resistance.)

Your Class A gravel will give you a good base and the sand will provide a layer for you to set the bricks level, but I’d provide a filter fabric between the sand and the gravel. Otherwise, the fines in the sand will “wash” down into the gravel and the bricks will soon be uneven.

  • Thank you! I forgot to mention I installed a geo-textile between the clay and gravel so that the gravel wont be driven in too much into the clay. Would you recommend another layer between gravel and the sand on top? I think most of the water came from a week of rain. If I install the pavers, and it rains for a few days, do you see the effect coming back? I will have the pavers reinforced with polymeric sand and can seal them if needed, and they are at roughly 1.5% grading so would most of the water just roll off instead of being absorbed in and again causing this issue?
    – Mike B.
    May 6, 2019 at 18:57
  • I like filter fabric between the sand and gravel to keep the sand from displacing. With your slope, I’m sure most of the water will run off. However, we design for the extreme conditions and you’ve already experienced this problem once.
    – Lee Sam
    May 6, 2019 at 19:34

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