No Dig Construction in RPA

[jacquemontii]

What does anyone consider to be the maximum depth of build up for a ‘no dig’ permeable drive construction without causing compaction damage to the soils below? Currently looking at a scheme to create a new drive (using 3D Cellular Confinement System products backfilled with clean aggregate) which crosses through root protection areas of mature birch and sycamore.  The ‘no dig’ element is not a problem as the site levels are lower than the adjacent highway, so it will be possible to tie in to the road without any excavation.  However, the engineering solution (designed by the project engineer) will create a level change of 700mm above the existing soils at one particular point along its course.

My feeling is that at a depth of 700mm the weight of stone will consolidate the soil of the RPA below, regardless of being laid onto Geo-grid/geo-web products.  After all, tree roots tend to grow in the top 600mm to 1m of soil, because at greater depths the conditions become less favourable…..I think I may have answered my own question….

[Gary Prentice]

I had this conversation with a fellow giving a talk from Cellweb, after he'd shown some pictures of a site where they had layered to a depth of four or five feet. 

 

IIRC it was a question that he couldn't really answer, even as an arboriculturist. 

 

I'd imagine that the underlying soil structure would make a lot of difference. Soils with high silt or clay contents suffering the affects of the weight more than sandy soils.

 

I'd try to have a chat with the engineers at cellweb.

[Arborist]

Hmmm, this is an interesting question and seeing as i haven't started my IRP yet, i may well give this a think. 

[jacquemontii]

Just found this useful case study:  http://www.geosyn.co.uk/wp-content/uploads/2016/08/Case-Study-Cellweb-TRP-69-Church-Lane-Extended-CS-1.pdf

 

 

[Gary Prentice]

As an aside, 

 

at the workshop/lecture/sales pitch we were told that Cellweb would guarantee the health of a tree for ten years where their product was used (useful for TPO trees) as long as they were involved from the start.

 

I don't know the specifics but the angle is that they've done the r&d to have the confidence to give one. 

 

Personally I've only had a couple of dealings with them, some basic  requirements that they resolved easily & efficiently, but their specificying department are supposed to know their onions.