[CANUFNET] Normes de sécurité concernant l'excavation et les arbres / Safety standards for trees and excavation

Thu Nov 24 13:27:17 EST 2022

Robert,

This could be a scenario where an instrument guided pulling test could help.
Pull the tree before the root cutting to establish the baseline stability of
the tree and then pull the same tree to the same load after and see if the
reactions are different. The resultant stability after root cutting can be
modelled with the data collected during the test. That way there is no
longer guessing, you know if the tree is stable or not and if not, what
crown reduction may be required to achieve a reasonable safety factor.

I am a member of the SAG Baumstaik group in Europe, an association of tree
risk experts , many long time practitioners of the elasto-inclino pulling
method initiated by Lothar Wessolly and Gunther Sinn. I have been doing
these pulling tests in North America since 2004 and have done over a 1000
tests. 

If there is going to be a one-sided straight line excavation we often talk
about the critical distance being 1.5 X DBH. Any closer and stability will
likely be compromised. Outside that at 1.5 x dbh you still have a
significant proportion of the anchorage-associated structural roots and the
tree may well stay stable. The affect on the future health of the tree is
another matter and the loss of soil volume, fine root system and good
rooting space may be a significant matter that also needs to be factored in.
This is the arboricultural consultant side of things, not for the engineer
to decide

But of course it all depends on the specific arrangement of the structural
roots on the tree you are interested in. In an urban situation there may be
no roots in some directions and then an unexpected mass of roots in another
location.

We do need to stop the engineers from taking “simple” and drastic measures
to work around a tree. We can identify the constraints and they can work
with them. Its just easier, and historically what they are used to, to just
cut the tree and get it out of the way
but we know that it is not simple and
that when they cavalierly cut down the tree, the community loses a
significant asset and will not be able to adequately replace it for many,
many years
if at all. I doubt the success of much of the proposed
compensation planting I have seen over the years.

The engineers are amazing at solving problems and finding solutions
when
there is a gas main they have to work around it and they do. Maybe we need
to call all structural roots “gas mains” to get their attention. Then they
will carefully and successfully work around them.

If we don’t stand up to the engineers, they will keep the straight line
thinking mentality forever.

Since the tree pulling test is an engineering based approach, we have often
had success talking to engineers with our data. They speak the same language
then.

Maybe this might help?

Cheers,

Philip

Philip van Wassenaer, B.SC., MFC

Urban Forest Innovations Inc.

1331 Northaven Drive

Mississauga ON L5G 4E8

Tel:  (905) 274-1022

Cell: (647) 221-3046

Fax: (905) 274-2170

 <http://www.urbanforestinnovations.com/> www.urbanforestinnovations.com

From: CANUFNET <canufnet-bounces at list.web.net> On Behalf Of Liveanu, Robert
via CANUFNET
Sent: November 24, 2022 12:29 PM
To: Canadian Urban Forest Network <canufnet at list.web.net>
Cc: Liveanu, Robert <r.liveanu at laval.ca>
Subject: [CANUFNET] Normes de sécurité concernant l'excavation et les arbres
/ Safety standards for trees and excavation

Bonjour-Hi

English follows below.

Est-ce que quelqu'un sait s'il existe une norme CNESST spécifique en lien
avec les excavations à proximité des arbres? Nous avons un cas où les
ingénieurs exigent l’abattage d’un arbre comme mesure de sécurité pour les
travailleurs, tandis qu’à la Foresterie, nous sommes d’opinion que compte
tenu de l’essence et le DHP de l’arbre, et la distance et nature de
l’excavation, l’ancrage de l’arbre ne sera pas compromis, surtout si
l’effort (peut-être superflu) est mis pour soutenir l’arbre comme dans cette
photo-ci <https://www.ebing.ca/EBing-Projet-Support-de-poteaux-3.jpg> . Le
problème se présente puisqu’à notre connaissance, la norme du CNESST
concernant les arbres est une approche unique qui traite les arbres comme un
poteau ou lampadaire, peu importe l’essence, son DHP, l’environnement, etc.

___

Hello,

This age-old question is mostly targeted to Quebec professionals, but any
insight from other provinces is appreciated as well as it’ll be interesting
to compare. Does anyone know if there is a specific CNESST – Quebec’s
occupational health and safety governing body – standard related to
excavations near trees? Or what does your own province’s safety body have to
say? We have a case where the city engineers are asking to remove a tree as
a safety measure for the workers, while at the Forestry department we’re of
the opinion that given the species and DBH of the tree, and the distance and
nature of the excavation, the stability of the tree wouldn’t be compromised,
especially if the (perhaps superfluous) effort is put into supporting the
tree as in this photo
<https://www.ebing.ca/EBing-Projet-Support-de-poteaux-3.jpg> . The problem
arises because, to our knowledge, the CNESST standard for trees is a
one-size-fits-all approach that treats trees like a pole or lamp post,
regardless of the species, DBH, its growing environment, etc.

Merci, thank you!

___

Robert Liveanu, MFC, B.Sc.

Arboriculteur certifié de l’ISA

Technicien à la foresterie

Division Foresterie & Horticulture

Service des travaux publics

Tél. 450-978-6888 poste 4775

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