Clay Soil - Property Foundation Issues - Advice.

[JonnyRFT]

Looking for advice...

 

I've been called out to an issue where a property is suffering from ground heave. Immediately north there's a row substantially lapsed Leyland Cypress hedging. To the west, an old Cypress (no doubt another Leyland) stump which looks older than 5 years since it's dismantlement.

 

The cracks inside and outside the property widen and close throughout the year suggesting desiccation of the soil caused by the trees. My desk study from SoilScapes shows the area where the property is situated is in fact "clay with impeded drainage." Heave happens throughout the summer months suggesting a dramatically reduced moisture content which, in turn suggests the possibility of clay soil.

 

Over the past few years I've had a handful of cases with mature broad leaf species along the clay belt in Norfolk causing ground heave. We have dismantled the trees over the course of 3 years in dormant months reducing radical moisture content changes within the ground.

 

Year 1: Pollard to secondary scaffold.

Year 2: Pollard to primary scaffold.

Year 3: Remove.

 

So far its worked on properties without substantial foundation footings (but still monitoring) resulting with manageable outcomes where our repairs company can rectify the issues.

 

Now, in this case we have a substantial amount of conifer. To my understanding; conifers are never fully dormant although the winter months have shown less water demand with the cracks closing on the external wall. I cannot carry out the same procedure to these Conifers as by pollarding will ultimately lead to its terminal decline near instantly. So with that in mind I should remove the trees to ground level in one go.

 

My question is simply; When is the best time? The evidence suggests winter but...

 

My concern is if the ground has impeded drainage and I've left the area with a substantial amount of moisture, can the clay swell causing a more positive heave? I have information given to me from our consulting engineers whom state that elsewhere in the village is 20m thick boulder clay. If there wasn't so much boulder clay in the area then I would've just removed the trees in winter and rectified the property issues.

 

Am I over thinking this? Part of me is thinking "what ever happens...happens" as I can't see many options.

 

 

 

 

[Andrew McEwan]

I'd get an experienced local consultant that has PI insurance for subs reports/advice to review any geotech and claim history and write the work spec if you're not covered.

[Khriss]

Hmmm,  hope that recent tiled roof hasn't played a part in this  ( extra loading )  That cracking whilst significant ain't as bad as many I have seen.  K

[kevinjohnsonmbe]

2 hours ago, JonnyRFT said:

Heave happens throughout the summer months suggesting a dramatically reduced moisture content which, in turn suggests the possibility of clay soil.

Am I reading that upside down?

[JonnyRFT]

Just now, kevinjohnsonmbe said:

Am I reading that upside down?

Yes. I mean subsidence 

[kevinjohnsonmbe]

1 minute ago, JonnyRFT said:

Yes. I mean subsidence 

That's a relief....  Thought I'd started on the cider a bit early ?

[JonnyRFT]

Just now, kevinjohnsonmbe said:

That's a relief....  Thought I'd started on the cider a bit early ?

I’m way ahead of you apparently 

[tree77]

If the customer has building insurance why not let there insurance provider carry out the investigation and then act on their recommendations.

 

 

 

[Wolfie]

So the cracks and annual movement is related to subsidence rather than heave.
I’ve never actually witnessed a case of heave, I think it’s a very rare occurrence.
From reading up on heave, I gather it can only happen when all these factors come into play:
1. Clay soil
2. Tree(s) have to predate the building
3 building has been constructed upon soil which is already water deficient due to the tree roots.

Open to being corrected.
Don’t know how old that building is but Leylandii grow pretty quick.

[daltontrees]

That pattern of racking of brickwork looks thermal to me. I can't see round conrers but I cannot imagine a scenario where it's subsidence or heave related.

 

If I'm wrong, you can add to your list that the clay soils have to be shrinkable. not all clay soils are significantly shrinkable. Boulder clays notably aren't often shrinkable. Also add tha tthere has to be a climat ethat would resoult in persistent soil moisture deficits. Also add that the foundations need to be substandard in depth relative to modern standards. Also add the buiding needs to be within the zone of influence of the trees, with regard to species, size, age and water demand.

 

I believe the estabished view is that gradual removal of trees will not reduce heave. If anything oyu could say you're better to do it in one go, experience the heave then make good. Slow recovery delays the time when you can safely do final repairs. And repairing too early follwng by seasonal movements can make the situation worse.

 

As such, there's no best time.