Difference Between Simplied Janbu and Bishop Slope Stability Methods 2

[Saboral]

I understand that in Bishop Slope Stability Analysis we are determining a FS based on moment equilibrium. In the Janbu Method we are determining based on force equilibrium. What I am having trouble determining is the merits of each and when one method would prove more applicable than the other.

 

[GeoPaveTraffic]

With moderen slope stability software neither method is generally recommended or used. Although Bishop's method is occationally used. These older methods were used when calculations were done by hand.

Either Spencer's procedure or the Morgenstern-Price method is most commonly used since both these methods satisfy both force and moment equilibrium.



Mike Lambert

 

[Saboral]

I find that very interesting. In this region of the country (mid-atlantic) I have only ever seen Bishop method via GStable being utilized. Are there any references to specific jurisdictions, DOTs, or other organizations requiring Spencer's procedure or the Morgenstern-Price method in lieu of Bishop or Janbu?

 

[GeoPaveTraffic]

Most U.S. Army Corps of Engineer (USACE) Districts require Spenser's method. Spenser's is also recommended by the USACE Engineering Manual. California Department of Natural Resources requires either Spencer's or M-P, don't remember which off the top of my head.

If you are using a moderen slope stability program, I'm not familiar with GStable, there is no reason not to use a moderen analysis method. The only time I conider using Bishop's method is when I have a small slope with high undrained shear strength that is stable by inspection, but I have to determine and report a factor of safety (usually in the 4 to 10 range). Bishop's method will happly report a FS when more exact methods will indicate a tension crack is required that is deeper than the slope is high.

Mike Lambert

 

[Saboral]

I was looking at some examples in Virginia. VDOT calls out the use of Modified Bishop, simplified Janbu, or Spencer Methods. I can say that in my 8 years in the industry I don't think I've seen a Spencer Method analysis in a report.

Can anyone recommend any good specific literature or references for global stability analyses? I have a good number of geotechnical references, but they are all kind of lacking in regard to global stability.

 

[GeoPaveTraffic]

I'm not sure what you are looking for. If you are looking for a reference that says use method A for situation X and method B for situation Y; then I think you are out of luck.

There is a lengthly discussion of different analysis methods in Appendix C of EM 1110-2-1902 which is the USACE slope stabiltity design manual. Page C-39 has a summary of several different methods. A copy of the manual can be downloaded here:

http://www.publications.usace.army.mil/USACEPublications/EngineerManuals.aspx

Other than the USACE manuals, I do not have a good reference for slope stability analysis. I will say that it takes a lot of experience to be good at it and that experience only comes from performing many hundreds of anlayses.

Let me know if you are looking form more specifics after you look at the EM and I'll try and help out.

mike



Mike Lambert

 

[moe333]

Watch this Terzaghi lecture by Stephen Wright. I would always use the Spencer method.

https://www.youtube.com/watch?v=Q_6aOU7msBM

 

[Saboral]

moe333, thank you for that video. It was fantastic and offered some great insights.