Sheet Piles and Trees

[ace_mcgraw]

So here's a question - does anyone have any experience / evidence relating to sheet piling and the damage (or otherwise) they cause to tree roots. 

There are plans to put a retaining wall within the RPA of a tree. The Arb Method Statement outlined hand-digging and severance of roots to the edge of the cutting etc. The client has now suggested that sheet piling is to be used instead. Does anyone have any case studies where this has been done? Were the roots severed cleanly? Were the roots shattered and severely damaged? 

 

My inclination is that on larger roots the sheets could cause significant damage to the trees, but I'd be interested if anyone else has other knowledge / evidence. 

[daltontrees]

It may be difficult to establish the type of damage sheet liping does, since its very nature is to drive steel sheets into the ground rather than excavate then retain. The severed end of tree roots will always remain covered on the retained side.

 

Shhet piles are typically 20mm steel sheets, hardly a Silky for clean cuts. Likely to mash anything in their way.

 

Remember, RPA is a rooting volume for ongoing vitality, and BS 5837 says (constructively) nothing about avoiding tree roots. Apart from slow hand-digging to identify roots before they are damaged, there is no precaoution against wholesale severance by the likes of sheet piling.

 

5837 doesn't mention sheet piling but the generality is that

"5.3.1 The default position should be that structures (see 3.10) are located outside the RPAs of trees to be retained. However, where there is an overriding justification for construction within the RPA, technical solutions might be available that prevent damage to the tree(s) (see Clause 7). If operations within the RPA are proposed, the project arboriculturist should:

a) demonstrate that the tree(s) can remain viable and that the area lost to encroachment can be compensated for elsewhere, contiguous with its RPA;

b) propose a series of mitigation measures to improve the soil environment that is used by the tree for growth."

I suspect you're at that point now. "technical solutions might be available that prevent damage to the tree(s)" are a non-starter, as it will be like getting a haircut with a hatchet. "demonstrating th the trees can remain viable" may include arguments about vitaity in the face of likely pathogen colonisation of several crush wounds below ground in an unreadable quasi-anaerobic environment where pathogens lurk at their finest. In that context, compensation of rooting volume elsewhere would be cold comfort to a tree, or to an amenity-conservant LPA.

Good luck with it.

 

[Gary Prentice]

Is there any literature about that shows a significant difference in pathogen colonisation between cleanly cut roots and those that aren’t? 

 

I just wonder if we’re a bit obsessive in clean cuts, particularly of smaller diameter roots.

[Gary Prentice]

11 hours ago, daltontrees said:

like getting a haircut with a hatchet

 sounds like my barber!

[ace_mcgraw]

I'm sure I've heard of some research relating to the shattering of roots encouraging compensatory root growth - much like how hedgerows come back after being smashed back by a flail. If this does happen, does this counteract any potential ingress of pathogens? 

 

[daltontrees]

6 hours ago, Gary Prentice said:

Is there any literature about that shows a significant difference in pathogen colonisation between cleanly cut roots and those that aren’t? 

 

I haven't been able to find any such literature.

[daltontrees]

3 hours ago, EdwardC said:

Shattered roots provide a larger surface area for pathogen colonisation. Also, clean cut roots are better at absorbing water than shattered roots.

 

 

And presumably a bigger surface area to have to callus over?

 

Oddly enough, Shigo in Modern Arboriculture says small damaged roots should be followed back to where they are at least 1-2cm diameter and cut there. Suggesting a bigger wound is better.