Sinkhole in an open field.
Sinkhole in an open field.
(OP)
Engineers,
I got a question about a depression that occurred in a piece of land.
There is nothing around, the depression ocurred after consecutive heavy rainy days.
Dimensions are 40 ft long, 33 ft wide and 15 ft deep. Per the borings, rock was detected at 20 ft.
The idea is to back fill the depression and grout in angles around the perimeter of the depression. Then, perform a grid of vertical grouts on top of the depression.
My question is, do you think a grid of 5 ft by 5 ft is ok or is it very conservative?. Same question is related to the angled grout around the perimeter. I plan to propose grout locstions every 5 ft around the perimeter.
Please let me know your thoughts, thanks.
I got a question about a depression that occurred in a piece of land.
There is nothing around, the depression ocurred after consecutive heavy rainy days.
Dimensions are 40 ft long, 33 ft wide and 15 ft deep. Per the borings, rock was detected at 20 ft.
The idea is to back fill the depression and grout in angles around the perimeter of the depression. Then, perform a grid of vertical grouts on top of the depression.
My question is, do you think a grid of 5 ft by 5 ft is ok or is it very conservative?. Same question is related to the angled grout around the perimeter. I plan to propose grout locstions every 5 ft around the perimeter.
Please let me know your thoughts, thanks.





RE: Sinkhole in an open field.
RE: Sinkhole in an open field.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Sinkhole in an open field.
The depression is in Lakeland, FL.
We don't have detailed information other than blowcounts. Usually for properties, we recommend 8 to 10 ft center for Limited mobility displacement (LMD) grout. But not sure if for this situation 5 ft on centers, we are too conservative.
RE: Sinkhole in an open field.
RE: Sinkhole in an open field.
http://www.ei.lehigh.edu/envirosci/enviroissue/sin...
Since you operate in a karst area, I think that may already know about that repair method.
RE: Sinkhole in an open field.
That solution would work if it is a shallow depression and if rock is shallow.
In my case, per the borings, rock is found at 50 feet deep. At the same time, the depression showed up on a parking lot.
RE: Sinkhole in an open field.
Let us know how it goes. I deal with karstic geology also and am curious how people deals with it in other locations.
RE: Sinkhole in an open field.
Sure, I will let you know, thanks fro your input.
On top of the limestone the borings show loose sands (SP), there is not Water table. There is a pipe, which was leaking, so yes, the pipe is part of the cause. LMD is what we use typically around here, what i was not sure of is if 5 feet spacing was very conservative.
RE: Sinkhole in an open field.
RE: Sinkhole in an open field.
Thanks. Yes, i agree with you.
RE: Sinkhole in an open field.
This method http://www.ei.lehigh.edu/envirosci/enviroissue/sin does work if you can find the opening and the opening is relatively small. To get down to the opening (sinkhole throat), we have had to use double track-hoes...one in the bottom of the hole digging "up" and another grabbing the lower track-hoes spoil and getting it out of the hole. The excavations can get very large especially following OSHA trench safety guidelines. We have dug to 48 feet below grade before using this method. A single sinkhole repair using this method on the 48 feet deep excavation took 7 full days with 2 track-hoes and a D-9 dozer. We also used 50 cyds of boulders and 20 cyds of concrete.
Sometimes, when the opening (sinkhole throat) is too large we will place a layer of boulders and concrete at the base of the hole. Then repeat - essentially gluing the boulders together with the concrete - but there are still openings in this repair method that will allow water to continue to seep into the sinkhole.
We have also used structural mats doweled into sound bedrock designed to hold the soil and live loads above - we do place weep holes in the structural mat to prevent water from ponding on the repair.
RE: Sinkhole in an open field.
Thanks for your reply.
At least here in Florida, when sinkhole occurs, no one is allowed to go down to the bottom of the depression and do any type of works. This is more for safety purposes.
Given that condition, in my case my remediation plans starts around the depression (to avoid it from continuing moving sideways) and then, after depression is backfilled, we proceed with grouting on top of it.
RE: Sinkhole in an open field.
Sinkholes in Florida are a whole different animal than what we deal with in Missouri. I am amazed how they can grow laterally over a short time.
Pressure grouting followed by compaction grouting, in my Missouri experience, is normally done when "filled sinkholes" are present (either ancient ones filled with younger weak rock or soft shale or filled by man with "whatever") in an attempt to stabilize them without performing any excavation. This method is very expensive, significantly more so than excavation and repair, and is typically only used when excavation and repair can't be done.
Thanks for sharing your repair method. No two sinkholes are alike and I am always learning.
RE: Sinkhole in an open field.
Does anyone have any sources for other remediation methods? I'm just trying to see if there is a more economical method (aside from building in another site).
this is for a new office campus which will have up to 4-story office buildings and parking lots / decks.
--morgwreck243
KN4DHC
RE: Sinkhole in an open field.
The OP describes rock at 20 ft and the longest dimension at 40 ft. In that instance, I would also consider a reverse graded filter first.
Later, there is a description that the rock is at 50 ft. So, that would suggest a reverse graded filter not likely.
Grout seems expensive, but. . . It may be what you need to do. It's not obvious whether 5 ft centers would be all you need; however. So, there'd need to be some consideration for primary, secondary and tertiary grout holes. That would require some performance level be written into the specs.
Will it be perfect? I mean at what point will you be confident enough to build a hospital or other such critical structure? Don't know. That said, the suspenders would be to complete the building pad by constructing the backfill as a soil raft. You know figuring out how thick and the demands that may be placed on the reinforcement.
I'm also curious about epikarst soils - you know the really soft lean clay that results from the inplace weathering of the limestone. We have that stuff and it'll trigger settlements as it's essentially normally consolidated.
On the more pedantic side. DOLOMITE IS NOT A ROCK! <rant over>
Dolostone is a rock, just as limestone is a rock. The principal mineral in limestone being calcite and the principal mineral in dolostone being dolomite.
f-d
ípapß gordo ainÆt no madre flaca!
RE: Sinkhole in an open field.
Once a cavity dome collapse occurs, drilling in the center or near the center of the depression will only tell you where the fractured rock is now or, if a clean collapse, where the bottom rock is. Going outside the perimeter of the sinkhole you can more likely tell where the rock WAS prior to the dome collapse. This is important. If you compare the inside boring and the outside borings and plot a profile in several directions, you can likely tell if there is still a void to be filled (by grouting). If there is not, and you feel reasonably certain of that, then you can fill the depression and be done with it.
You have a good foundation contractor, Hayward Baker, in Tampa. They have a variety of techniques that can be used for these situations.
For disclosure.....I am not an employee of Hayward Baker nor do I have any affiliation with them. As a consultant, I'm just familiar with their capabilities.
RE: Sinkhole in an open field.
Dolomite is indeed a rock. Limestone is calcium carbonate, dolomite is magnesium carbonate...both rock types are extensive here in the great state of Missouri. For instance, the Jefferson City formation is largely comprised of dolomite. Here is the Wiki link - https://en.wikipedia.org/wiki/Jefferson_City_Forma... the rock types are on the right in the box.
Dolostone and dolomite terminology is largely a function of geography with different parts of the country preferring one over the other.
RE: Sinkhole in an open field.