Chemical soil stabilization legitimate?
Chemical soil stabilization legitimate?
(OP)
We have a facility in the south central Texas area were we are looking to expand the tankfarm (add two additional tanks). The area has fat clays and the geotech report recommends overexcavating 11 feet to replace the fat clays. An expensive process given the tank size and spacing. In preliminary talks with possible contractors, chemical injection was mentioned as being a less costly alternative to the overexcavating. Anyone have experience with this? Trying to get a little more educated before I call our geotech up to discuss. EcSS 3000 was a brand name of chemical specifically mentioned by one contractor but it seems to be more for residential looking at their literature.





RE: Chemical soil stabilization legitimate?
I might check on it with one of my contacts but it took a lot of closely spaced holes and sequential pumping (starting shallow and going deeper each time).
Some called it snake oil.
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RE: Chemical soil stabilization legitimate?
Other alternatives would include keeping the soil moisture constant by one means or another. Designing tanks to take differential support.
I'd be skeptical that 11 feet of replacement is an adequate treatment. Up here in Wisconsin the shrink=swell effect can readily go double that depth or deeper
RE: Chemical soil stabilization legitimate?
A good approach to chemical injection is two-fold. First, treat it just like water injection or moisture conditioning insofar as placing moisture barriers after injection to maintain the increased moisture conditions which will occur from the injection process. Keep trees and large bushes away. Second, advise the Client get warranties from the chemical injection contractor. While the contract may not be worth the paper it is written on, it directs liability to to the chemical injector. I happen to know EcSS has a warranty they can offer. This is critical since they use a proprietary process.
Subgrade modifications are alternatives to suspending structures on piers of full depth structural fill solutions. The Client should be educated on the risks associated with alternative methods.
Another point I would add is that based on the depth of improvement (11 ft) it sounds like the PVR is pretty high. In these cases you would likely want to place a 2 ft cap of non-expansive fill atop the 11 ft layer of chemical injection. Being the project is in south central Texas, is there any concern with limestone seams or layers which could cause early refusal to injection rods?
RE: Chemical soil stabilization legitimate?
RE: Chemical soil stabilization legitimate?
RE: Chemical soil stabilization legitimate?
My experience is that the depth of chemical injection is the same s water modification (moisture conditioning or water injection). A 2 ft cap of non-expansive fill (flex base would be better than select fill, but more expensive) with 10 ft to 12 ft of improved soils should get you to about an 1 inch PVR in 95 percent of cases. There are select geologic formations and geographic locations where you might assume slightly deeper, but I would leave that to the judgment of the geotech. If you subscribe to theory that the active depth of moisture change is about 15 ft, you will have modified 12 to 14 ft of the profile. The remaining portion below the improved depth contributes the least to the overall PVR due to the overburden pressures. Plus you've created a thick pad of relatively impermeable material. I won't get into a debate about the active depth of moisture change, because there are differing opinions and theories, capillary rise,etc. I've never had an issue using the assumption of 15 ft (in most cases) nor have the senior engineers in my firm.
RE: Chemical soil stabilization legitimate?
RE: Chemical soil stabilization legitimate?
Find out what the minimum level of product in the tank will be...this can help offset the swell potential. Additionally, have a solid estimate of the amount of new fill going on top of the subgrade...again will help offset swell potential and hopefully the geo will adjust the active zone depth from the new (higher grade). This likely won't do away with undercutting but it may reduce it quite a bit. Perhaps it shallows up enough that a few feet of the foundation can be stabilized with lime so import is reduced. If a ringwall is present for the tank, this can also help as a "vertical barrier". Lastly, confirm what the tolerance is for the tank...1" PVR may actually be 2"-3" for the tank bottom...but do also check the perimeter wall PVR at the base. If the perimeter wall is say <1" and the tank bottom is 2" (assuming that is the structural's confort level), then balance out how much select fill and stabilization is required.
Just keep in mind that the scenario is like trying to keep a dried out sponge from expanding in presence of water...more weight on top means less swell potential. Also keep in mind to cut off any select fill from surface water otherwise your active zone resets to the bottom of the select fill.
Talk to the geotech directly and involve the structural. I will gladly refer you to a geotech in that area if needed. Many times, the geo is given too little info to make these types of recommendations...heck, they may not even have actual loading information or have their hands tied if not being compensated for their time to assess the scenario.
In other words, I am not a fan of the inplace chemical stabilization based on my experience in that area.
RE: Chemical soil stabilization legitimate?
You might want to get another opinion on the PVR of 7".
RE: Chemical soil stabilization legitimate?
If the soil is prone to shrink-swell issues, it will be inherently low perm material. Injection of chemical and water is used all the time in low perm soils.
RE: Chemical soil stabilization legitimate?
I believe that using this method they only get the chemical on about 50% of the material so its effectiveness is limited.
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RE: Chemical soil stabilization legitimate?
However, it seems silly to insinuate that you should forgo the option for which it is specifically intended. What high perm soils need injection? None in my area. In fact, it is recommended to NOT use injection techniques in high perm soils since there is no way to verify once refusal is encountered (solution coming up at the ground surface away from the point of injection) because you can loose all the solution below grade.
It's like saying don't use drilled piers in rock because rock is hard to drill.