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Grout UCS for sinkholes works

Grout UCS for sinkholes works

Grout UCS for sinkholes works


I am involved in a sinkhole reparation job in FL.

I noticed that for the LMD (limited mobility displacement) grout, the engineer specified 1000 psi as Unconfined compressive strength (UCS).

My question is, since these grout works are in order to fill the voids underneath, what role plays the UCS value of the grout in this situation?. I mean, to me, for these purposes, it would be the same a 100 psi grout and 1000 psi grout.

Obviously, 1000 psi grout will be more expensive than 100 psi.

Please let me know your thoughts,


RE: Grout UCS for sinkholes works

In our Pennsylvania karst areas, most of the grout used to fill the sinkholes is a mix of cement and soil (even topsoil). It is low mobility, less expensive grout but still pumpable. I'm not sure, but I suspect it is not 1000 psi minimum (= 144 ksf). This is very much stronger than usually needed to fill voids.


RE: Grout UCS for sinkholes works

pelelo - Since the work is in Florida, perhaps there is a high water table. If so, the grout may be stronger than needed to allow for potential dilution or cement loss in ground water. The same logic is used for high cement content concrete being used for cofferdam seals.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Grout UCS for sinkholes works

Thanks for your replies.

PE(inc), I didn't know that soil-grout mix tech, in FL, it is just cement+sand.

SlideRuleEra -> Here in FL area there are bunch of shallow and mid deep LMD grout jobs, I have seen the UCS requirements are around 50 psi, which is pretty much a low UCS value. Even a 40 psi LMD grout "would" stand a 50 ft overburden.

cvg-> thanks for the publications. I would go with the lower end (300 psi). The difference in cost between 300 and 1500 psi should be big, so grouting at 1000 or more, wouldn't make sense, cost wise.

RE: Grout UCS for sinkholes works

I would like to suggest that the OP watch the 2015 Terzaghi lecture. This might be enlightening to him as well as others . . .


RE: Grout UCS for sinkholes works


Thanks for posting this link. I engaged Donald Bruce as a consultant to a complex karst coral rock anchor project in Guam about 18 years ago. We was very good in his advice - nice to see him be awarded such a prestigious award.

We had 'grout takes' of 400 bags in holes that had a theoretical bore hole volume of 10 bags. It was a new concrete sea wall with a top of wall elev 10 ft above sea level. We drilled through an aquifer, hit underground caverns, lost several d-t-h hammers. All the grout was w/c=0.4 with anti-washout admixtures - US Navy specs. 100 each x 1-3/4" dia bar anchors total about 40 feet long. It was a challenging project, to say the least.

pelelo: Sorry to hijack your thread.

RE: Grout UCS for sinkholes works

Great Post BigH, Thanks a lot.

Not a problem Ingenuity, the idea is that all of us share as much as possible through this forum.

RE: Grout UCS for sinkholes works

Quote (pelelo)

Not a problem Ingenuity, the idea is that all of us share as much as possible through this forum.

In the spirit of sharing, a PDF copy of Donald Bruce's 2015 Terzaghi Lecture presentation is here: Link

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