Grout to ground bond stresses in Green Bay, WI

[Geo1337]

Hello all,

I have a question as to where I can find some desktop information about grout to bind stresses for micro pile foundations in Green Bay. A geotechnical investigation report has been prepared for this project but the data suggests extremely low bond stresses. I would like to verify this information if at all possible. After a cursory Internet search, I have not been able to find much. Any help with any type of information would be greatly appreciated.

Thanks

 

[JedClampett]

The "Recommendations for Prestressed Rock and Soil Anchors" by PTI had values for grout against soil and rock. Depending on the soil or rock, they vary between 5 psi (clays) to 450 psi for granite. Pressure grouted anchors fare better against soil.

 

[Geo1337]

Thanks JedClampett. We are definitely going with pressure grouted anchors and I am looking at 5 psi. I was hoping to find some info out there that would justify using 10 psi.

Thanks again for the quick response.

 

[PEinc]

Geo1337, before you say you are "going with pressure grouted" micropiles, you better talk with a local micropile contractor if that is not you.
Will the bonded length be in soil or rock? What type soil or rock? Pressure grouting does not work in impermeable soil or rock.
FHWA has a publication on micropiles. PennDOT has their Design Manual DM-4 on line. Its Appendix O addresses micropiles.
As JedClampett said, PTI has recommended range of ultimate bond values for various soils and rock. If you are designing any type of ground anchors or micropiles, you should have the PTI and FHWA references and manuals.

http://www.PeirceEngineering.com

 

[PEinc]

Also, check to see if the geotech report is giving ultimate or allowable bond stresses.

http://www.PeirceEngineering.com

 

[Geo1337]

Thanks PEinc.

I am the micropile drilling contractor but we are not local to Green Bay. We anticipate bonding in clay soils. Unconfined compressive strength at our bonding depth is about 5 tsf. I am really just looking for some information that may justify me using higher than 5 psi.

 

[DenseSand]

I am pretty sure you will get much higher than 5 psi if the unconfined strength is 5 tsf

 

[PEinc]

If bonding in clay, pressure grouting won't work but post-grouting with re-grout tubes will work. Your clay is stiff. You should get an ultimate bond of at least 10 PSI. If you use re-grout tubes, make sure that your grout hoses, plastic re-grout tubes, and your grout pump have sufficient pressure ratings.

http://www.PeirceEngineering.com

 

[PEinc]

Actually, at 5 tsf, your clay is hard. Re-grouting may be also.

http://www.PeirceEngineering.com

 

[DougHole]

If you have some undrained shear strength readings in the clay from pilcon shear vanes tests (or pocket pens or torvanes) then you could use an alpha.Cu chart to get a design bond in the clay. The alpha value ("adhesion") is based on Tomlinson's chart but you can also find it in the Canadian Foundation Engineering Manual. For example, if you have an undrained shear strength in the clay of 100 kPa then look up what alpha you can use (let's say it is alpha=0.4). then you can use a bond of 40 kPa (100 kPa x 0.4). This is the ultimate value and you would have to multiply by a resistance factor if working in Limit state design or a Factor of Safety if using Allowable stress design. Good luck

Doug Hole
Junior Geotechnical Engineer

 

[Ingenuity]

Doug Hole
Junior Geotechnical Engineer

Doug, I am sure it has been said to you many times before, but with a first name of "dug" and a last name of "hole" you were destined to be a geotech engineer...or a grave digger.

Sorry for the hijack...carry on...

“…structural engineering isn’t rocket science. Evidently, it is considerably more difficult.”
Norbert J. Delatte, Jr., PhD, PE. 2009. Re Harbour Cay Condominium Collapse, March 27, 1981.