Tree removal close to property

[Wolfie]

I still fairly regularly get told by clients that their surveyor has recommended a staged removal.
I try and explain all the above but they rarely want to take the “risk”

[Jon Heuch]

On 12/03/2022 at 22:21, Mesterh said:

I've dropped many a tree due to subsidence but never been involved in or know anyone who has taken a tree out which had caused heave.

Made me laugh. Clearly, with subsidence you take the tree out after the subsidence has occurred. With heave, the reverse. The only way anyone would contact you is if they wished to sue you. They would need to prove quite a lot to show you had been negligent.....so it is most unlikely that they would. Unless you were stupid enough to put pen to paper and without any reference to professional or technical documents state that there was no potential problem and you would stake your bank balance, business, house and your reputation on the issue.

Does heave occur. Yes. Is it frequent. No. Two types of cases: a) removal of large tree immediatley prior to foundation laying. Ground given no time to "rest" following tree removal. These cases become NHBC claims. The trees have gone. Only a need for specialists to advise. b) removal of large old trees (big oaks in particular) that easily predate the property. It requires a geotechnical engineer to assess the risk, following a site investigation to 4 metres depth preferably. Otherwise keep your mouth closed. Heave won't occur until at least one winter after tree removal. Has the tree surgeon put pen to paper (as above). If not, they won't come chasing you on the grounds of what you told someone in their back garden.

Records of heave cases are buried in insurers and their agents. Only in a few cases will heave be diagnosed directly. It will probably take a year of monitoring before the absence of a tree and continuing upwards movement confirms heave. Even less likely that someone will come looking for the tree surgeon who removed the tree.

[daltontrees]

Here's the thing. Clay 'soils' are not the sort of dirt that plants are normally grown in. They are closer to rock substrate than the porous plant-friendly stuff that has 'field capacity' for seasonal water. Dry clay is pretty much waterproof unless subject to long slow soaks. The change in its volume that causes heave or subsidence takes a long time (months or years) and takes persistent soil moisture defecits or near-permanent soil misture increases (such as can happen when thirsty trees have been removed).

Basically, it takes more than summer to winter weather changes to casue subsidence or heave.

[doobin]

On 12/03/2022 at 16:46, peds said:

That's just anecdotal evidence and really shouldn't hold any sway in the big picture, and without concrete proof of it being a swan, who's to say what happened. Could have just been a load of ducks taped together. 

So that’s what that well known brand of heavy duty tape is for?! I always wondered! 

[Jon Heuch]

12 hours ago, daltontrees said:

Here's the thing. Clay 'soils' are not the sort of dirt that plants are normally grown in. They are closer to rock substrate than the porous plant-friendly stuff that has 'field capacity' for seasonal water. Dry clay is pretty much waterproof unless subject to long slow soaks. The change in its volume that causes heave or subsidence takes a long time (months or years) and takes persistent soil moisture defecits or near-permanent soil misture increases (such as can happen when thirsty trees have been removed).

Basically, it takes more than summer to winter weather changes to casue subsidence or heave.

You may want to pay a visit to SE England where clay soils are very common. Oak trees grow best on clay soils. Dry clay soil cracks and fissures. Easily penetrated by water, until it swells at which point it is not so dry. Subsidence takes months......well yes....but a good hot dry summer can do the trick forcing trees to use roots under houses or forcing them to extend their roots under houses. Subsidence does not require a persistent soil moisture deficit. Heave (of any significance) does. The occurrence of (tree related) subsidence is weather related; the occurrence of heave is not. 

[openspaceman]

13 hours ago, daltontrees said:

The change in its volume that causes heave or subsidence takes a long time (months or years)

Aren't clay subsoils in the SE still recovering from having water squeezed out of them by the weight of ice 10000 years ago?

[Stubby]

7 hours ago, openspaceman said:

Aren't clay subsoils in the SE still recovering from having water squeezed out of them by the weight of ice 10000 years ago?

Yep I was around then and remember it happening . 👍

[openspaceman]

2 minutes ago, Stubby said:

Yep I was around then and remember it happening . 👍

Strange I only remember as far back as the coronation😉

[Khriss]

9 hours ago, openspaceman said:

Aren't clay subsoils in the SE still recovering from having water squeezed out of them by the weight of ice 10000 years ago?

Not when there is chalk under them. K

[Canal Navvy]

Overcampacted clays are pretty resistant to water being able to get through. 

Plant roots (not just trees) can desicate clay to the point that rehydration is into years or decades. 

I have worked on structures that have sunk on desicated clays and are still supported on boulders of dry clay with cracks that water and the odd root use as a passage to the moister clay below. 

Old houses would have a well in the cellar so the water level would have been artificially lowered. 

Rain water butts and watered gardens were fairly normal. 

 

Old houses get bought by a different sort of people and adapted, ground water level rises and the building experiences changes that it hasn't seen in a a couple of centuries and people are alarmed to see a few cracks. 

 

Generally the problem is in the building industry particularly since it's been possible to get ground works signed off by an independent surveyor with no local knowledge of the local pockets of soil types, rather than the good old local building control. 

 

On puddle clay liners of canals it takes water something like six years to get from the top of a two foot layer to the bottom!

 

Different types of clay have very different behaviours, some are good engineering materials, some are unreliable and some are destructive. 

 

It is quite easy to get a bit obsessed by clays 🙄