Collapsible Fly Ash?
Collapsible Fly Ash?
(OP)
Has anyone encountered collapsible coal fly ash placed as a backfill? I investing this sinkhole and the properties of the sampled fly ash from the site matches almost perfectly that properties of collapsible soil (loess), and that seems to be a good explanation of what is happening at the site, but I am still uncertain. Can anyone comment?
RE: Collapsible Fly Ash?
RE: Collapsible Fly Ash?
BigH, actually, it is the same situation, but I can't recall anyone explaining from the perspective that the soil might be collapsible-although one person mention that some flyash when wet can sort of liquify. Anyway, to be more specific, about 85% of the particles passes the #200 sive, and ther is less than 5% gravel and sand. The maximum density was about 100pcf, at about 12% moisture using AASHTO T-180. The density of the undisturbed sample was about 76pcf. A pin-hole dispersion test was not perform. GS= 2.2, PL = 26, LL = 30, and PI = 4.
RE: Collapsible Fly Ash?
I will close my case :)
RE: Collapsible Fly Ash?
RE: Collapsible Fly Ash?
RE: Collapsible Fly Ash?
Given the limited information we have, I think your instincts are likely spot on. If the fill was deposited wet of optimum and in relatively thick lifts the loads would have been primarily supported by the pore water pressures. However, you still have to work our why it happened now? What circumstances caused the PFA fill to become drained and collapse? An alternative explanation could be that the fill was deposited dry of optimum and became wet? That would definately lead to a collapse.
RE: Collapsible Fly Ash?