Piping/internal erosion
Piping/internal erosion
(OP)
How do you check:
-Piping ptential of a soil zone ( is there any piping potential criteria);
-FOS against piping from seepage analysis
Thanks
-Piping ptential of a soil zone ( is there any piping potential criteria);
-FOS against piping from seepage analysis
Thanks





RE: Piping/internal erosion
determine the exit gradient (let's call that ie).
determine the critical gradient (let's call that ic).
f=ie/ic
The are many references on this topic. I'd suggest you do some research and let us know what part of your studies have you confused.
f-d
¡papá gordo ain't no madre flaca!
RE: Piping/internal erosion
Make damned sure that you are applying the concept of critical gradient properly, as it really only applies to boiling and heave, not to initiation of internal erosion on non-vertical paths.
Beyond that, you must use filtering criteria such as have been developed by Terzaghi, Sherard, and plenty of others. Sherard's criteria from the late 1980s (ASCE JGE ~1988 or 1989) are probably the most widely used and accepted.
RE: Piping/internal erosion
f-d
¡papá gordo ain't no madre flaca!
RE: Piping/internal erosion
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RE: Piping/internal erosion
The issue of potential dispersive properties complicates the issue. As BigH notes, the examples can be spectacular. A note about the Pinhole test, ASTM D 4647:
It is a good test but, a review of the Standard, notably Sections 5 (Significance and Use) & 6 (Limitations) provides a reality check.
Dispersive Soils can be identified but no computation methods are produced. To my knowledge, you will continue to be on the 'Frontiers of Science" when dealing with soil piping. The above posting by fattdad to 'draw a flow net' is appropriate.
The Pinhole test, along with the Double Hydrometer (ASTM D 4221) and the Crumb (ASTM D 6572) methods can usually (note usually, not always) identify a Dispersive Soil. The problem comes when you have a soil with Dispersive-Like characteristics.
Regarding soil with Dispersive-Like characteristics, which has apparently been the condition I usually encounter, I have an old reference from my Father's Library.
ASTM STP 623, 1977, Dispersive Clays, Related Piping and Erosion in Geotechnical Projects, Sherard/Decker, editors.
The chapter by Daniel Resendiz, Relevance of Atterberg Limits in Evaluating Piping and Breaching Potential, has been helpful in my circumstances. The discussion section describes observations by Resendiz relating observed piping in small dams to values of clay activity (Skemptons Activity, [plasticity index / percent clay, 0.02mm]). Resendiz observed that "...all the dams whose failure was attributed to one of these mechanisms {piping and breaching} have clay activity between 0.3 and 1.1".
As my Father insisted on the Hydrometer analysis being required, I have 35 years of data in Western Colorado, Southwest Wyoning & Eastern Utah. In all cases of soil piping in soils with low water flows (at least initially) I find the Resendiz criteria of clay activity between 0.3 and 1.1 to be applicable for identifications of soil with Dispersive-Like characteristics.
Does anyone have any other published references???????
RE: Piping/internal erosion
I don't believe the Teton core was actually dispersive, and I couldn't find mention of that in the report of the independent review panel, which included R. Peck, A. Casagrande, H. Seed, and a few others. It didn't really need to be dispersive. It was aeolian silt, fine grained, mostly nonplastic, therefore very easily eroded and in need of a filter with D15 < 0.7 mm by Sherard's criteria. The volcanic bedrock at the site has wide open fissures, shrinkage cracks, etc., and the fill in the cutoff trench was probably exposed to high head, high velocity flow in rock that may have scoured the core material, high gradients, etc.
RE: Piping/internal erosion
RE: Piping/internal erosion
Mike Duncan (my professor) lectured on the Teton Dam failure and if I recall correctly, there were big seepage forces in the rock fractures of the abutments. This resulted in a very high gradient from the rock fracture through the embankment soil and toward the open air. I'd think this defines "piping" as the exit gradient exceeded the critical gradient. Now, how does "internal erosion" differ from "piping" in this scenario?
f-d
¡papá gordo ain't no madre flaca!
RE: Piping/internal erosion
Any of several things could have occurred at Teton. It's clear that there was erodible fill adjacent to very large discontinuities in the rock. What isn't known for sure is whether the internal erosion initiated as "classic piping" where there was v. high exit gradient out of core material in the cutoff into rock, or due to erosion by flow through a crack in the core (maybe associated with arching in the cutoff trench), or whether relatively high-velocity flow in the rock fractures adjacent to the fill started the erosion as scour. The evidence of exactly how it started was all washed away. JMD is correct - because the rock was so pervious, the gradient over the top of the grout cap was huge. You couldn't make things much worse if you tried. If ever in eastern Idaho (between Idaho Falls and Yellowstone), stop and look at the site, just a few miles off US 20 near Rexburg.
What do you mean by "critical gradient"? The only definition I know relates to upward flow causing blowout or boiling at the downstream toe of a dam or levee, not to anything like the more-or-less flow through Teton's cutoff trench.
RE: Piping/internal erosion
RE: Piping/internal erosion
Graham is Wayne Graham?
DRG
RE: Piping/internal erosion
RE: Piping/internal erosion
RE: Piping/internal erosion
The middle right picture on p. 12 (big fractures in rock) was probably taken after the failure. The two bottom pictures were, I think, taken during construction. The bottom left looks like a guy with a blowpipe cleaning the bedrock surface.
Remind me next week when I have more time, and I will scan some pictures from the review panel's report. I won't scan the whole report for you, as it is 1.3" thick, mostly double-sided.
RE: Piping/internal erosion
RE: Piping/internal erosion
I was wrong about the guy with a blowpipe. It was actually a compressed-air pogo stick compactor.
Regards,
DRG
RE: Piping/internal erosion
RE: Piping/internal erosion