prevention of horizontal soil water movements, esp. in tree pits

Hi all of you,


Maybe one of you has a better idea and/or can support by giving further details.

This is my base text to raise a TQ with our Client.

This will (might) be for future use


Regarding capillarity breaker to prevent capillary movement of saline soil water to penetrate into planting medium.


In general specifications, detailed drawings and BoQs consider a capillarity breaker by spreading an adequate layer of coarse gravel covered by one layer of geotextile. This method is sufficient in horizontal and even moderately sloped areas but it does not prevent penetration of saline soil water from verticals i.e. tree pits, deeper planting beds, and the like.

A feasible solution in breaking the capillarity and at the same time allowing sufficient drainage effect is by installing a composite of geotextile/drainage net/geotextile.  This material is usually sturdy and stiff enough to allow a usage in the vertical. At the same time flexible enough to follow undulations in the landscape sub grading.

This sort of material is light weight, durable, easy to transport and store, and can be cut to fit, an ideal substitute to tedious drainage gravel transportation and spreading as well as insufficient geotextile overlapping due to heavy winds or consequent material installation.




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Take a look at this product, I've speced it for a project that never was built, so I can't really sya if it would work in your circumstances.

Good luck with the project.

Hi Ernst,

There are several manufacturers of drain mats that are used as underlayment in synthetic fields.  These systems completely block water from infiltrating where the soils are expansive as well as providing a structural layer.  I prefer Turfcore.  A woven Mirafi 500x liner may also be an option although some water will get through very slowly.  You could also combine the two for a possible solution.



Hi folks, thanks to the reply so far. I believe that I was not clear enough in my approach.

It is supposed to stop HORIZONTAL soil water movement. It is not about drainage. It should not seal completely to allow soil gas exchange. We have a high sodicity and sea salt content in the surrounding soils. I want to prevent the salt saturated soil water to move back into the planting medium by capillary movement.

Thanks, Ernst


I well understood what your problem is, that is why I suggested the above product.

did you even look at it?

Good morning Henry,

Yes, I did. The product you, as well as Brett, have proposed is a ground drainage matting and/or soil sealant. Both products are either permeable in both directions or not at all.

The idea is to keep the soil gas exchange and block capillary back flow of soil water, and that only on the sides, ground drain is no issue here.


These are also used in horizontal applications.


On horizontal the Client wants to have a 20 cm layer of coarse gravel with ordinary geotextile as soil seperator, that is OK, but no good and easy solution for the sides to install.

Correct me if I am wrong, but any larger porous material will separate capillary movement from a smaller pored material, such as those suggested above, would work without having to be water proof unless the soil reaches a saturated condition. A small pore space will not give up water to a larger pored material. Capillary movement will end right there.



What's the point?


I just got off the phone with Len Hopper, the editor of Landscape Architectural Graphics, asked him about the product that I suggested. Well I stand corrected, you are right it will not work.

So you have a big problem. How about constructing tree pits as if they are located on structure, out of concrete and waterproof both the exterior and interior of the pit.

Hallo friends,

It's not all about right or wrong. It is about brain sharing and not having to re-invent the wheel again and again.

I did not give up in trying to find a solution and/or product already invented. Please have a look:

Enjoy your day,


There is a lot on that web site. Is there a case study or product that matches what you are looking for? I'm interested in your solution.


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