Organics (tree stumps) under house

[JAE]

So my cousin has a problem (see photo attached).
A whole lot of tree stumps under their house - discovered recently after a small sink hole formed beside their house.
After poking around a bit, then digging with a backhoe, they started finding lots of organics, tree stumps, roots, etc.

The attached photo shows the amazing redundancy in a concrete masonry foundation (this is a foundation wall for a crawlspace situation)
I think in this case the brick veneer is holding it all up

Anyway - based on the red soil at the site (this is near the Carolinas) - do tree stumps eventually deteriorate and cause problems in red clay?
Or does the red clay keep oxygen away from the stumps and minimize future settlements?

I'll post another photo next. This is one is early in the game and the next one is after 18 feet of digging.

 

[JAE]

Here's the "big dig" photo:

 

[hokie66]

I think all types of tree stumps found in that part of the world will eventually rot out. In the meantime, they will attract termites.

And get out of that hole!

 

[Ron]

Yes, they will eventually rot; however, a few things on the positive side....

Water table is apparently low, so the available moisture in the soil is low...thus less opportunity for rotting.
Much of the area has pine trees of a variety of species, which are often high in pine sap...fire hazard when above grade, but will also prevent decay.

Foundation will obviously bridge small areas of loss.

Soils do not appear to be "organic" though interspersed with roots and stumps...big difference in foundation response. Not as much probability of settlement or failure, unless large accumulation under large area of foundation.

 

[Patgeotech]

Yes, they will rot - natural groundwater not likely to be a problem then make sure runoff from roof is taken well away from house. Wetting and drying cycles will increase the rotting time.

Our experience with pine trees is that they can absorb quite a bit of water out of the ground and keep the soil moisture in check (botha good and a bad aspect depending on the conditions), but following fires, which destroyed the trees, the natural groundwater regime changed in certain areas. Areas where soil moisture content in clayey ground was changed resulted in movement of the soils (expansive soils) and highlighted areas underlain by organic material.

We have been involved in several such residential scenarios where organic material was buried beneath homes and all required underpinning (most of the time micro-piles) to secure the house and reduce the settlment. One house we investigated was a single storey residential home, which demonstrated the ability of the brickwork to span localised areas (uncracked but no subsoil support) as well as severe movement at other parts of the home (whole walls moved) - we did not know the full extent of the organics below the home but it was evident by the nature of the different cracking patterns that it was highly variable. The decision was taken to underpin the entire home rather than "wait" for the problem to occur.