Pullout (Bond Strenght) on Slide 6.0 from Rocscience

[Jatego]

Hi everyone,

Regarding the input of Bond Strenght values for Soil Nails PullOut strenght on software Slide from Rocscience... should I consider the ULTIMATE bond strenght(qu) or the ALLOWED bond strenght(qu x FoS) as the required input?

Thanks so much for your help.

Xavier

 

[jimstructures]

What does the software ask for?

What is the context that the question is asked?

It is very hard to answer any questions when we can't see what you are seeing?

You might ask this question at the software's help desk or support number.

Jim

 

[Jatego]

The software asks for "Bond Strenght" no specifics. Hence my doubt. This is the adherence between grout and soil in a soil nail or anchor.

 

[PEinc]

I would enter allowable grout to soil bond stress and then make sure the stability analysis gives the required global stability safety factor.

http://www.PeirceEngineering.com

 

[Jatego]

Hi PEinc,

This is the official answer from Rocscience tech support.

Hello Javier,

Thank you for your email. Soil Nails are considered Passive Support and as such, both the support forces and the soil strength are divided by the factor of safety calculated during the analysis. Therefore you should use the ULTIMATE properties as opposed to the ALLOWABLE properties when using soil nail.

Please find more information on the implementation of soil nails here:

https://www.rocscience.com/help/slide2/slide_model/support/Soil_Nail.htm

and more information on Force application (Passive VS Active) here:

https://www.rocscience.com/help/slide2/slide_model/support/Active_Passive_Force_Application.htm

 

[PEinc]

I understand that; but, it is standard to use a higher safety factor (about 2.0) on the ground anchor bond stress for the grout to soil or rock than it is for the global safety factor (maybe 1.35 to 1.5). Therefore, you may not have a high enough bond safety factor if you use the ultimate bond.

http://www.PeirceEngineering.com

 

[GeoEnvGuy]

Your question reminds me of liner design life versus strength see image below. My understanding of soil nails is that the nails degrade over time so the thickness and spacing is determined by the expected strength at the end of the design life.

 

[PEinc]

GeoEnvGuy, that is not true. The soil nails for permanent walls are coated or encapsulated, or both for corrosion protection.

http://www.PeirceEngineering.com

 

[GeoEnvGuy]

PEInc, thank you for correcting me. I do have a follow up question regarding the service life of soil nail walls for permanent walls or reinforcement. The new global tailings standard requires facilities to be designed to 1 in 10,000 year seismic and flood events if they are to put in a state of passive closure. Is the service life of permanent soil nails or ground anchors applicable to a site where after a period of monitoring the intent is for the owner to walk away from the property and let nature take over?

 

[PEinc]

I don't know what all of that means. However, various agencies may specify a design life of an anchored wall, usually 50 or 100 years. This would apply to corrosion of steel members. I never saw anyone worry about longevity except for the ground anchors and their hardware. Therefore, the anchors and hardware are protected by some combination of grout, concrete, plastic encapsulation, grease, or coatings such as epoxy or HDG.

http://www.PeirceEngineering.com

 

[EngMan40]

I second PEinc. Global stability analysis is a service limit not ultimate limit state so all input values should be allowable. You don't want the slope FOS to be the material and bond FOS also, this is not safe!