UKTC Archive

Re: Subsidence where foundations less than 300mm deep

Subject: Re: Subsidence where foundations less than 300mm deep
From: oliverhayes
Date: Sep 11 2020 06:39:38
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