Foundation performance 1

[cphi]

Please share your opinions on electrical resistive heating remediation of an environmentally impacted subsurface beneath building foundations and floor slabs. Thank you.

 

[Focht3]

Please give more details -



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[jdmm]

If this is the same process that I have seen it involves using an anode and cathode and passing current through the ground in order to raise the temperature of the ground in order to improve the mobility of some contaminants. The system uses larger currents to raise the ground temperature and vacuums to remove the contamination.

For the system that I looked at the contractor wanted to raise the temperature of the ground to 100 degrees C. The soil was clay and there was concern tha the heating of the ground might cause settlement, through shrinkage, of the buildings and slab above.

 

[cphi]

Thanks for your replies. Yes, jdmm, that is the process. Was the settlement your concern, and was the process done? If the electrical resistive heating process was done, can you share foundation and floor slab response information? The site I am analyzing as a geotechnical consultant is clayey glacial till. A recharge of water for cooling the anode (or cathode) and infiltration into the soils is proposed as part of the heating and vacuum treatment. I have my opinions and calculations, but was hoping to raise some independant and non-site-specific thought. Of course, time is running out.

 

[Focht3]

Are you relying on the location of the anode (or cathode) as the exit point of the contaminant, or is it sufficient to force the contaminants into vapor form? If you are counting on the contaminants collecting at one end of the circuit and some of the contaminants are volatile, I'd be worried about shrinkage cracks permitting the volatiles to escape at uncontrolled locations.

I have no experience with this process - can someone put some dimensions to this problem for me? Power consumption, effective treatment distance, etc. This is one of those processes that are described in the literature - but few of us have any real experience to share. Please educate us -



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[cphi]

Focht3 thanks for your reply and interest. I don't have the details that the prospective contractor provided with me now at home, but I'll explain from memory. I can check details if you want later. The process uses anodes and cathodes with a low voltage, but high current to heat the soil due to the electrical resistivity. The resistivity of the soil is pre-determined by lab testing soil samples and the resistivity is used to determine the voltage and current requirements, and the anode and cathode spacing (24 feet estimated)and diameter. The "plume size" determines volume of treated area. The cathode (or anode I don't remember electrical engineering terms anymore)that electrically charges the water to flow to the anode (or cathode)also is a water injection screen well, while the other is a dewatering well. The insitu and injected water along with the soil is heated to about boiling or below and develops steam. All this volatilizes contaminates for extraction by the dewatering anode or cathode, and also a vacuum is applied to the soil surface to collect vapor. The steam also "increases the permeability" (my emphasis)of the soil to help contaminate flow and extraction. I have my thoughts, what is yours on overlying foundation and floor performance during and after remediation? Thank you.

 

[Focht3]

At those temperatures, it's pretty risky -

Where is the site?



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[cphi]

Glacial clayey till, LL=35±, PL=15± w%=18 OCR>2 water table 13 ± to 20± feet deep