Coal as backfill a bad idea? 2

[dirtsqueezer]

I was just wondering if anyone has had any bad experiences using coal as backfill. The situation is a cut/fill operation for a plat on a slope overlooking a valley, with a great view of Mt. Ranier, I might add. Coal is being considered for use below 4 feet, mainly for backfill below residences. Any thoughts or concerns?

 

[GeoPaveTraffic]

I would not recommend coal for backfill for the following reasons:

1. generally low strength
2. compressible
3. will degrade with time (run some slake durability tests)
4. sulfer content (what is the runnoff going to contain)

This just generally sounds like a bad idea. Also, why would someone want to use a material that has market worth for fill?

 

[Focht3]

A uniformly bad idea - for lots of reasons. I'd tell the developer "NO!" quickly -



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[MPENN]

I have read of sub-surface fires caused by lightning strikes. Would the coal fill also be capable of a smoldering fire? If so, safety concerns should rule out the use of coal.

 

[BigH]

MPENN gets my for today!

 

[dirtsqueezer]

Lightning strikes, my lord! This site is on a nice, high hillside...

I actually recieved this recommendation from 'on high', so it's out of my influence now. I was thinking originally that coal is only about a dinosaur's age away from being peat, and neither material do I associate with being 'firm and stable'. But not much I can say. It's only my second day on the project, and actually with my new company. They're using most of their fill, so no good system for exporting I can use to sneak out major volumes. I haven't seen any major layers go in yet, but I'm watching out for fragments with my nuke.

Anyway, thanks for the good input.

 

[Dirtmaster]

Sell the coal & by fill dirt

 

[iandig]

Just a quick point with using an NDM on the fill material, don't be surprised if you start to get 'strange' moisture contents. Material like coal, unburnt coal shale, ash and PFA can all effect the reading, and give values twice what they 'really' are.

 

[treg]

Coal will degrade with water, and, will tend to burn when loose. Coal steam plants usually figure 30 - 90 days max. in a compacted stockpile before the coal ignites.

 

[Robert168]

I would not buy a house sitting on such kind of soils unless a raft or frame structure foundation is used.

 

[MPENN]

Beyond the obvious structural and safety issues, word will spread that the development is founded on a coal base. Would an insurance company be likely to overlook the increase in risk and write homeowners policies?

Are there real estate disclosure laws that would reveal the risk posed by the use of coal as a fill and contribute to an uninsurable developed property?