UKTC Archive

Re: Gabion wall within RPA

Subject: Re: Gabion wall within RPA
From: Julian Dunster
Date: Jul 29 2020 00:11:51
Level the ground, place a biaxial geogrid on that, place gabion on top. That is a fairly common approach out here and seems to accepted quite readily. The geogrids provide a lot of tensile strength and generally prevent subsidence. See Jim Urban's book Up By Roots for more info.

On Behalf of Dunster and Associates Environmental Consultants Ltd.


Dr. Julian A Dunster R.P.F., R.P.P.., M.C.I.P., ISA Certified Arborist,
ASCA Registered Consulting Arborist # 378,
ISA Tree Risk Assessment Qualified
Honourary Life Member ISA + PNWISA

North American distributor for Rinntech
www.dunster.ca
www.treelaw.info
www.rinntech.info

On Tue/7/28/2020 12:27 PM, Lee Davies wrote:
Evening all,

Thanks for the input. Interesting stuff!

The proposal is not part of a planning application. The client is
landscaping the garden and is keen to ensure they do not cause harm to
their neighbour's tree. The tree is an early-mature ash.

The purpose of the gabion is to act as a retaining wall along the rear
boundary, to enable a sharp drop at the end of the garden (approx. 1.5m) to
be raised and the lawn levelled.

I've tried to attach a basic sketch of the proposal but it doesn't seem to
have worked.

Thanks again,

Lee

On Mon, Jul 27, 2020 at 9:07 AM <admin@xxxxxxxxxxxxxxxxxxxxxxxxx.co.uk>
wrote:

Morning,

Really interesting thread with many informative contributions all of which
are entirely valid and well thought out.

Might I suggest that the starting point is the tree and not the
structure.  What species, age and condition?  Is it tolerant of root damage
due to species type e.g. Monterey Cypress or is it intolerant of damage
e.g. mature Beech.  Can you offset the RPA successfully.

This is also a third-party tree so you need to be mindful of avoiding any
harm which may lead to a decline in overall health / condition.

BS5837 has the default position of no structures being in the RPA without
a justification.  Is there an engineering requirement to install gabions in
the RPA for a scheme which has planning permission or is this just a design
proposal for landscaping etc.  A Tree Officer might object to this without
a reasonable justification.

Just throwing this in there to see if any more information is available.

Regards

Oliver Bennett  Prof Dip (RFS) M.Arbor.A
Arboricultural Consultant
Objective Tree Consultancy

Ph 01326 XXXXXX

Email: admin@xxxxxxxxxxxxxxxxxxxxxxxxx.co.uk
Website: www.objectivetreeconsultancy.co.uk







-----Original Message-----
From: uktc-request@xxxxxx.tree-care.info <uktc-request@xxxxxx.tree-care.info>
On Behalf Of Wayne Tyson
Sent: 24 July 2020 06:07
To: UK Tree Care <uktc@xxxxxx.tree-care.info>
Subject: Re: Gabion wall within RPA

Redundantly, perhaps, *context is everything. *Once one knows the
objective. Gabion manufacturers might be a good source of information.

Wayne

PS: I have used angular stones laid up dry (no mortar, they must maintain
porosity) with a significant batter where some people would insist on
gabion.

On Thu, Jul 23, 2020 at 8:23 AM Ben Rose <benrose@xxxx.co.uk> wrote:

Dear all,

I had an interesting conversation about this with an engineer. You can
convert loading per square metre into kPa quite easily (there are lots
of converters online if you want to try).

If the gabion is 1.7 metric tonnes (1700kgs) per m3 that converts to
16.7kPa per metre height of gabion. That ground pressure is between
the pressure exerted by a quad bike (14kPa) and a standing human
(55kPa). So, when considering static loading, I don't think that
building stone-filled gabions would cause serious ground compaction.

Ben


Sent: Thursday, July 23, 2020 at 12:29 PM
From: "Jon Kiely" <jk-tc@xxxxxxxx.com>
To: "UK Tree Care" <uktc@xxxxxx.tree-care.info>
Subject: Re: Gabion wall within RPA

Lady-boy mud wrestling aside, isn’t the load spreading idea with
cellular confinement systems based on passing point loads e.g.
stilettos, rather than static loads already spread in a wire basket?
The CCS solution isn’t a one-stop-shop. The details are key, as
suggested by others:
soil type
ground conditions
water table
root distribution
foundations
size of gabion

The baskets are generally about 0.5m wide and 1-2m long.
In any case the fill is typically about 1400-1700kgs per m3
depending on
material used.

Jon K



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