UKTC Archive

Re: Subsidence where foundations less than 300mm deep

Subject: Re: Subsidence where foundations less than 300mm deep
From: Wayne Tyson
Date: Sep 10 2020 09:45:13
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



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