UKTC Archive

RE: Subsidence where foundations less than 300mm deep

Subject: RE: Subsidence where foundations less than 300mm deep
From: Tim Moya
Date: Sep 07 2020 14:38:30
Trevor
I suspect that the author was trying to convey that seasonal building 
movement on clay soils can occur without the influence of vegetation. The 
Institution of Structural Engineers publication "Subsidence of Low Rise 
Buildings" states "research indicates that the effects of evaporation to the 
atmosphere in firm clay soils are largely restricted to the uppermost 0.5m of 
the soil." And goes on to say that grass and other low growing vegetation can 
influence soil to 1-1.5m and trees to greater depth.

The BRE publication "Subsidence damage to domestic buildings" says that 
slight movements of buildings on clay soils are inevitable. While these 
movements may be slight they can be enough to cause differential movement, 
particularly in some circumstances - for example where exposed soil to the 
south of the building is dried more than shaded soil to the north.

Obviously, these effects are more likely where the building is on very show 
foundations 

Tim Moya 
-----Original Message-----
From: uktc-request@xxxxxx.tree-care.info <uktc-request@xxxxxx.tree-care.info> 
On Behalf Of "theapsy@xxxxxx.com"
Sent: 07 September 2020 12:04
To: UK Tree Care <uktc@xxxxxx.tree-care.info>
Subject: Subsidence where foundations less than 300mm deep

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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