[CANUFNET] pavement construction near large trees

[2vojka at rogers.com]

Thank you for your input Jeremy,

Most likeley, our actions will be like you described in your steps 4 - 6.

Best regrds, Vojka




________________________________
From: Jeremy Gye <jgye at shaw.ca>
To: Canadian Urban Forest Network <canufnet at list.web.net>
Sent: Wednesday, February 4, 2009 12:59:12 PM
Subject: Re: [CANUFNET] pavement construction near large trees


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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