SIA- the tree pulling test/theory

[Steve Bullman]

Now here's a thing...

 

How bizarre!

[Gary Prentice]

This made me laugh, for the second time round

 

Sure dude:lol::lol:

[sloth]

How is Tony anyway? Anyone in touch with him, is he still lording it up in Bulgaria?

[David Humphries]

Plenty of food for thought in the earlier pages of this thread so no need to start a new one.

 

Last week we were kindly invited along by our colleagues at the London Borough of Islington to witness a tree pulling assessment on a particularly impressive London plane which has a colonisation by the giant polypore (Meripilus giganteus) Possibly due to surface level changes during the building of the playground some years before.

 

This was the second tree pulling event I had attended (first one was in 2011) both carried out by the consultants at the Bristol based Tree Works Environmental Practice.

 

The tree is in the middle of a well used playground (which is due for refurbishment) and is the largest of its type in that borough. It has a CAVAT value in the hundreds of thousands of pounds and has the appearance of high vitality.

 

 

 

 

A pull line with a dynameter was set up about halfway up in the target tree and attached to a base anchor and then winched under relatively small tension to simulate a load.

 

 

 

 

Various meters (for elasticity and incline) were set up around the base of the tree to measure against micro changes in relation to the potential for stem breakage and root plate tilt. 

 

 

 

The operation was then repeated at a perpendicular angle to test the load from a different direction. The data gets transmitted from the meters and added in to the equation of (amongst many other things) the trees dimensions, locality, direction of wind load, exposure, expected wood strength etc.....and this then arrives at a calculation with gives the Safety Factor.

 

We were informed that the lower limit of threshold for a tree and a situation like this would be to have a safety factor of 1,5 or above and although I couldn't stay for the entire session (so didn't hear the second set of results) it was looking like this tree had a safety factor exceeding the threshold.

 

I haven't heard exactly what the borough plan to do with the information but I suspect it will give them the confidence to keep on managing the tree.

 

Prior to the static load assessments the tree had a canopy reduction undertaken last year to lessen the impact of the wind upon it.

 

A very interesting morning 

 

 

[Steve Bullman]

seems an odd location to do a pull test?

[David Humphries]

7 hours ago, Steve Bullman said:

seems an odd location to do a pull test?

Good double entendre there Mr Bullman 

 

Or do you refer to the high level of target specifically?

 

 

 

 

 

 

 

 

 

 

 

[Darrin Turnbull]

Are there any notable measurement differences between wet soil and dry .
After two days of heavy rain on the 5 of October 2017 here in Berlin a storm uprooted many trees maybe the wet soil/conditions made things worse.

[Paul Barton]

Interesting post, thanks for sharing David.  I don't have any first hand experience with pull-tests, but a few questions!  As already asked by Darin above, do you know how the test and interpretation of results accounts for soil and rooting conditions.  Obviously the stretch of wood fibres under tension is measurable, but surely the cohesion of fine and structural roots to the soil medium is critical when considering whole tree failure?

 

Are the values provided by the test compared with some kind of benchmark data - e.g. the 'normal' elasticity of Platanus wood? 

 

I notice that the tree was a multi-stemmed tree but that the cable was attached to one of the stems rather than linked to all of them.  How does the test allow for the flexure of that stem at its junction with the primary trunk?  I would have thought that this junction would flex and therefore dissipate some of the load from the base - or would that only be true of a dynamic test rather than a static load?

 

I realise that you were an attendee rather than the demonstrator - but you're about the smartest tree nerd I know so I reckon you'll have something to say in return 

[Khriss]

Fascination stuff- but am dubious of what is shows , with wind and climate being so varioable plus the actual expense of the test. Would be good to see test  carried out on a ropey old thing with some die back and root compaction , RE 1987 storms and veteran tree survival rates against semi-matures nearby , K

[Mark Bolam]

I bet they didn’t pull very hard with the Greenpeace building being just down the road.