UKTC Archive

Re: Subsidence where foundations less than 300mm deep

Subject: Re: Subsidence where foundations less than 300mm deep
From: Jerry Ross
Date: Sep 13 2020 08:26:31
Thanks Wayne.
To paraphrase Edmund Tilney in his surprisingly early blog of 1566, "post in haste, regret at leisure". Words that we all (myself included) would be well advised to heed


From my mobile


On 12 September 2020 21:15:55 Wayne Tyson <wt750mv@xxxxxx.com> wrote:

I regret the post (against my own rule), but take full responsibility for
the content.

Wayne

On Fri, Sep 11, 2020 at 3:00 PM Jerry Ross <trees@xxxxxxxxxx.co.uk> wrote:

Wayne,
Oliver referred you to an article that ostensibly
refutes your assertion that clay shrinkage under the influence of tree
roots does not result in heave: how is that condescending or patronising,
let alone insulting? Despite your protestations of humility, there seems
to
be a touch of arrogance in your dismissal of the published works you have
been referred to, an arrogance exemplified by your insistence on placing
the word  "authorities" in inverted commas.
Be that as it may, dismissing as an insult Oliver's suggestion that you
consider one such authority is unjustified and unworthy.

From my mobile

On 11 September 2020 21:20:50 Wayne Tyson <wt750mv@xxxxxx.com> wrote:

Oliver et al:

I thought this was a forum for collegial discussion of tree-related
issues
amongst tree professionals. Others may do as they like, but I would never
respond to a discussion by asking someone to read a book instead of
personally responding with my own reasoning. I try not to be that
condescending/patronizing. I do appreciate points in refutation and the
citing of specific quotes from "authorities," and referrals to
peer-reviewed literature. I, too, have a lot (60+ years) of experience,
but
do not have the temerity to consider myself The Ultimate Authority on any
subject. I am always a student. I'm grateful to be informed, but it
shouldn't be necessary to merely insult me.

I continue to suspect that trees are not at fault in "subsidence" cases,
even though any Botany 101 student knows that roots can remove *a
fraction*
of the water (available water capacity--AWC) from any soil. Clay soils
tend
to hold more water under sufficient tension to prevent its passage
through
a root's semi-permeable membrane into the plant's vascular system, thus
limiting the soil water loss through absorption and transpiration. When
clay micelles expand, they create pressure in all directions (as it
were),
but in the absence of confinement, that pressure will be exerted against
an
area of *least *resistance, not the greatest, presumably a slab or a
foundation wall. Note that the lab experiments (please inform me of any
exceptions) that measure such pressure use confinement vessels,
presumably
rare or non-existent in the real world. Shrinkage *reduces* pressure,
creating a void into which forces may enter.

These aphorisms are submitted for consideration, not as The Final Word:

"The suspension of judgment is the highest exercise in intellectual
discipline." --Raymond Gilmore

"The most important thing to know is what you don't know." --Margaret
Mead

Wayne



On Thu, Sep 10, 2020 at 11:39 PM oliverhayes <olivernghayes@xxxxxx.com>
wrote:

Hi Wayne,

Jerry Ross provided evidence in the form of a research paper in his
previous reply. Biddle’s work is based on experimental evidence
collected
over decades.

Oliver

On Fri, 11 Sep 2020 at 01:31, Wayne Tyson <wt750mv@xxxxxx.com> wrote:

As "they" say, "one can't prove a negative." Please prove the positive.

Appeal to authority is a well established fallacy. Please show, on the

basis of evidence, how expansive soils like clay *can* move a building.

Ironically, I respectfully submit the following authority: 'One of the

great commandments of science is, "Mistrust arguments from authority."
...

Too many such arguments have proved too painfully wrong. Authorities
must

prove their contentions like everybody else.' --Carl Sagan



Actually, I'm interested in learning from the individuals on this
forum,

not from countless textbooks. However, a specific quote from a primary

source (peer-reviewed research) would contribute to a polite discussion
on

the subject. If anyone has a technically valid, specific point to make,

I'll be happy to become better educated.



I *suspect* that the real culprit is differential settling or
compression

caused, perhaps, by variations in soil moisture content, physical

structure, and texture. I also suspect that unconfined clays will tend
to

exert pressure where there is the least resistance. Confined clays, as
in

lab experiments may not translate to the real world where any
confinement

is variable and limited by the strength of the confining materials or

structures. I can imagine how one might make a valid observation but
reach

an invalid conclusion, which can lead to persistent myths. What we may
need

here, is a real research scientist in the area of soil mechanics, but
even

they apparently have differences. Of course, *context* always is
crucial. I

will be delighted to be enlightened.



Wayne



On Thu, Sep 10, 2020 at 2:28 PM oliverhayes <olivernghayes@xxxxxx.com>
wrote:



Hi Wayne,



Vegetation certainly can conserve soil moisture, but what is your
reason

for saying that clay is “too plastic” to move a building? Especially
after

having read the paper linked in the previous reply.



See also this quote from an important book on trees and soil in
relation
to

buildings:



“If the building is constructed on soil which already has a persistent

[moisture] deficit, and if inadequate precautions are taken in
foundation

design, it is inevitable that at some stage the soil drying will cease
and

the soil will rehydrate and swell. The swelling pressure which is
generated

will be equal to the suction, and is usually many times greater than
the

typical 100 kPa load of a two story building. The swelling of the soil
will

therefore lift the foundations; this upward (and sometimes lateral)

movement of the foundations is known as heave.” (Biddle, ‘Tree Root
Damage

to Buildings: vol. 1’, p111)



Soil drying may cease because vegetation has died or been removed;
some

other cause of drying has been removed; or because of inundation. If

rewetting is extreme the soil may dissolve or become displaced, which
could

cause subsidence. Up to that point, clay is capable of moving a
building
*

precisely because* it is plastic.



Oliver



On Thu, 10 Sep 2020 at 20:58, Wayne Tyson <wt750mv@xxxxxx.com> wrote:



I did make an error, but that wasn't it. Clays are too plastic to
move

much



of anything.







CORRECTION: It is not so much roots, but the shade and wind
protection



provided by the vegetation that slows shrinkage.







Wayne







On Thu, Sep 10, 2020 at 3:52 AM Jerry Ross <trees@xxxxxxxxxx.co.uk>

wrote:







"Expanding soils do not move buildings. "



https://is.gd/8BHnSz











On 10/09/2020 10:44, Wayne Tyson wrote:



Shrinkable soils without roots result in cracks, which allow

evaporation



to



the depth of the cracks in warm weather. They serve to replace
lost

water



when water enters the cracks. This cracking is largely prevented
by

the



presence of plant roots. Plant roots are opportunists that
develop

where



conditions are favorable (*available* water, very low soil
strength

or



pores at least as large as the root tip, and sufficient oxygen
for



respiration). Wet clay soils tend to be of variable strength, and
the



weight of a building can cause differential settling. Expanding
soils

do



not move buildings.







The soils may not be the only factors lacking competence. It's
about



*engineering*, not guessing and presuming. Sometimes correct

observations



can lead to incorrect conclusions.







Wayne







On Mon, Sep 7, 2020 at 4:04 AM "theapsy@xxxxxx.com" <



uktc@xxxxxx.tree-care.info> wrote:







Dear all,



I came across this unexpected sentence in a recent subsidence
report

and



wondered what they were trying to say:



"Where vegetation is involved it produces a characteristic

'seasonal'



pattern of foundation movement (subsidence through the summer,

recovery



through the winter); no other cause produces a similar pattern.
If

it

is



occurring - soil drying by vegetation must be involved, unless
the



foundations are less than 300mm in depth, which in this case
they

are



not."



Any thoughts?



Cheers







Trevor















--



The UK Tree Care mailing list



To unsubscribe send mailto:
uktc-unsubscribe@xxxxxx.tree-care.info







The UKTC forum is supported by Bosky Trees arboricultural

consultancy



and



Stockholm Tree Pits



https://www.stockholmtreepits.co.uk































--



The UK Tree Care mailing list



To unsubscribe send mailto:uktc-unsubscribe@xxxxxx.tree-care.info







The UKTC forum is supported by Bosky Trees arboricultural
consultancy

and



Stockholm Tree Pits



https://www.stockholmtreepits.co.uk



















--



The UK Tree Care mailing list



To unsubscribe send mailto:uktc-unsubscribe@xxxxxx.tree-care.info







The UKTC forum is supported by Bosky Trees arboricultural consultancy
and



Stockholm Tree Pits



https://www.stockholmtreepits.co.uk











--

The UK Tree Care mailing list

To unsubscribe send mailto:uktc-unsubscribe@xxxxxx.tree-care.info



The UKTC forum is supported by Bosky Trees arboricultural consultancy
and

Stockholm Tree Pits

https://www.stockholmtreepits.co.uk









--

The UK Tree Care mailing list

To unsubscribe send mailto:uktc-unsubscribe@xxxxxx.tree-care.info



The UKTC forum is supported by Bosky Trees arboricultural consultancy
and

Stockholm Tree Pits

https://www.stockholmtreepits.co.uk



--
The UK Tree Care mailing list
To unsubscribe send mailto:uktc-unsubscribe@xxxxxx.tree-care.info

The UKTC forum is supported by Bosky Trees arboricultural consultancy
and
Stockholm Tree Pits
https://www.stockholmtreepits.co.uk



--
The UK Tree Care mailing list
To unsubscribe send mailto:uktc-unsubscribe@xxxxxx.tree-care.info

The UKTC forum is supported by Bosky Trees arboricultural consultancy and
Stockholm Tree Pits
https://www.stockholmtreepits.co.uk




--
The UK Tree Care mailing list
To unsubscribe send mailto:uktc-unsubscribe@xxxxxx.tree-care.info

The UKTC forum is supported by Bosky Trees arboricultural consultancy and
Stockholm Tree Pits
https://www.stockholmtreepits.co.uk



--
The UK Tree Care mailing list
To unsubscribe send mailto:uktc-unsubscribe@xxxxxx.tree-care.info

The UKTC forum is supported by Bosky Trees arboricultural consultancy and
Stockholm Tree Pits
https://www.stockholmtreepits.co.uk




--
The UK Tree Care mailing list
To unsubscribe send mailto:uktc-unsubscribe@xxxxxx.tree-care.info

The UKTC forum is supported by Bosky Trees arboricultural consultancy and
Stockholm Tree Pits
https://www.stockholmtreepits.co.uk