[CANUFNET] pavement construction near large trees

[Jeremy Gye]

Hi Vojka,
Here is how I might approach this challenge:
1. Establish what the actual vertical soil and root profile is beneath the
lane (or immediately adjacent to it on the tree side).  
2. If there is a significant density of woody transport roots (>20mm in
diameter) within the proposed excavation depth, I would begin by doing
everything possible to persuade the engineers to reconsider their road
profile and sub-grades.  Can the road be crowned up gently in the area
immediately opposite the trees?  Would the engineers consider a reduced base
course in order to avoid having to excavate so deeply within the critical
root area of the tree?
3. Once you have modified the road design as much as possible in favour of
the trees, re-assess the residual anticipated impacts to the tree roots. 
4.  If the anticipated root impacts remain unacceptable, a modified
excavation workplan is required to minimize root impacts.  I would begin by
supervising some initial grading back of the existing road base with an
excavator with a clearing bucket and a competent operator.  Once you
encounter the root horizon in earnest, stop.
5.  Whatever depth still remains to be excavated to achieve an adequate
bearing/frost-free depth should now be excavated through the root horizon
either hydraulically or pneumatically.  My weapons of choice are a septic
truck with a high-pressure pump and hose with a variable-pitch nozzle and a
pair of hand-pruners.  Work together with the hose operators to remove
smaller roots to facilatate better access to soils further down.  Play with
the volume and pressure of the water to minimize tissue damage to the roots
as much as possible.
6.  Once your road bed depth has been achieved, back fill with a structural
material(s).  Work with the engineers to come up with a base material
profile that will work for both the roots and the road.
 
This is messy, slow work, but can often mean the difference between a viable
tree after road construction and a dead one.
 
Good luck,
 
Jeremy Gye
 
Gye and Associates - Urban Forestry Consultants Ltd
Victoria, BC
Tel: (250) 544-1700
Cell: (250) 883-4533
Fax: (250) 544-2059
 

  _____  

From: canufnet-bounces at list.web.net [mailto:canufnet-bounces at list.web.net]
On Behalf Of 2vojka at rogers.com
Sent: February-04-09 8:34 AM
To: Canadian Urban Forest Network
Subject: [CANUFNET] pavement construction near large trees


Hello Canufnet,
 
I am reviewing a proposal to repave a  lane in a well vegetated residential
area. Curently, the lane is paved with gravel and it is proposed to replace
the gravel with asfalt paving. The lane elevation may no change, therefore,
the asfalt paving when finished must be at axisting grade, requiring at
least 35cm deep excavation. There are a number of large trees (the largest
are two silver maples with diameter greater than 100cm)  in the close
proximity of the lane. The excavation for the asfalt bed will result in
severing a great portion of the root system of those trees.
 
The engineers are prepared to hand excavate around the trees and ensure that
no roots are severed....but they would like to have the root protection
requirements written in a form of construction specifications.
 
I was wondering if anyone has dealt with a similar situation and may have
available construction specs addressing the above described problem.
 
Thanks in advance.
 
Best regrds, 
Vojka Miladinovic
Urban Forestry Planner
City of Toronto
 

 
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