SPTs in hydraulic fill
SPTs in hydraulic fill
(OP)
I'm dealing with an old (~100 years) hydraulic fill dam in a seismically active area. Among my difficulties is interpreting SPTs with very low recovery (mostly 30-50 percent, some much lower and almost none above 70 percent). The low recovery is concerning because the fines and PIs in the recovered material suggest that the stuff might not be so bad in medium-size earthquakes, but I'm not convinced that the recovered material is representative. Seems to me that the clayiest stuff is the least likely to be lost out of the sampler. Unfortunately, the data are all "past tense," with no potential to get more or to talk with the drillers. Not completely sure about drilling methods. They were done with hollow-stem augers, and I THINK the hole was advanced ahead of the augers with a rotary bit and clear water. I don't know how careful they were about keeping the augers full, not tripping out too quickly, etc. Pretty sure they did not use catchers in the sampler. The raw blow counts, N, are generally very low (many in single digits at depths over 50 feet).
I have a few CPTs, but none the full depth of the hydraulic fill. qc is quite low in much of the embankment. However, Ic is very high there, mostly 2.5 - 3.5 (implying that it's clayey), but if the layering is thin, Ic might not mean a whole lot. The qc trace suggests layering with thickness 1/2 to 1 foot thick.
Have any experience with SPTs or CPTs in hydraulic fill?
I have very limited information about the construction practices, but that's a different headache.
Cheers!
DRG
I have a few CPTs, but none the full depth of the hydraulic fill. qc is quite low in much of the embankment. However, Ic is very high there, mostly 2.5 - 3.5 (implying that it's clayey), but if the layering is thin, Ic might not mean a whole lot. The qc trace suggests layering with thickness 1/2 to 1 foot thick.
Have any experience with SPTs or CPTs in hydraulic fill?
I have very limited information about the construction practices, but that's a different headache.
Cheers!
DRG





RE: SPTs in hydraulic fill
I have no problem understanding the low blow counts in a hydraulic fill - the water would not escape fast enough leaving a very metastable compacted structure - similar, I would guess to some fill placed up in the tar sands of Alberta years ago when the recovered sample was referred to as sandy ice . . . when it thawed it was very loose.
RE: SPTs in hydraulic fill
RE: SPTs in hydraulic fill
The SPTs and CPT qc values are reasonably compatible with each other in the places where I have both, so the SPTs may not have been fouled up by disturbance very much. In the clayey layers, they are consistent with normal consolidation, which is what you would expect in the central part of the dam, the way it was built.
Any ideas on the least plastic material being more prone to getting lost, affecting the material classification, or whether the high Ic values are reliable in an apparently layered hydraulic fill?
RE: SPTs in hydraulic fill
I assume you are looking at liquefaction potential. If so, I'd be conservative with the little info you have and not stretch the interpretation....I would probably neglect the clayey material.
RE: SPTs in hydraulic fill
All in all you, and the project, appear to be on the short end of a bad situation. Once they see the cost to remidiate this dam, there just might be money for another round of careful drilling to determine the real magnitude of the problem, if there really is a problem.
The most likely material to loose out of a split spoon without a catcher is clean sand.
Not sure where the project is located, but in the mid-west, the driller would have advanced the auger with a plug, quickly pulled the plug, maybe filled the auger with water, then drove the spoon. Sometimes this results in low blow counts, sometimes not. Depends on the material.
I don't see that you have any real option to but to assume that the SPTs are acurate and do your analysis based on that assumption and the data. Best of luck and hopefully you will be able to control the next round of drilling.
Mike Lambert
RE: SPTs in hydraulic fill
Now I understand folks doing irregular stuff. Seen it a bunch. But, in an agency setting usually the service contracts are so prescriptive, I'd think you'd have some recourse to get the contracted level of work.
I'd bring in a dilatometer though. . .
f-d
¡papá gordo ain’t no madre flaca!
RE: SPTs in hydraulic fill
I don't know what was actually in the contract (long story, not one for this kind of forum). Is it any wonder I'm becoming more and more of a control freak in my old age?
On the dilatometer, I'm inclined not to, for several reasons, including the material being so variable from point to point that I think getting more CPTs would be a better investment, for trying to pin down boundaries between materials. The best thing of all would be a 3/4 million CY test trench from crest to foundation, toe to toe, the full length of the dam. Then I could backfill it with compacted core and filter material, and all the questions would be answered or made irrelevant.
RE: SPTs in hydraulic fill
RE: SPTs in hydraulic fill
SWV predictably low (<150 m/s) in places in the "pool" area, high in others, probably in dike fill and/or areas where coarser material was left behind when the fines were sluiced out. (Still waiting for the construction records so I can see how it was done, with less guesswork.)
The u2 measurements look good, with sharp response at material changes. Haven't yet picked through the CPT data much, however. The layering is thin enough that there isn't anything like a "typical interval" I can focus on. u2 does show some spikes in clay layers above the piezometric level, indicating that the hydraulic fill clay is still saturated and didn't drain by gravity (again, predictable).
DRG