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cariboo (Geotechnical) (OP)
8 Jan 09 11:22
Is there a relation or correlation between RMR and Factor of safety? or what's the best way to "build" a new design? We have 10m of wheatered rock covering a intact bedrock. So, what's is your opinion: how can i design a new slope with a good factor of safety? and which parameters  should i use c, phi, w, etc? And for weathered rocks what's construction methods to increase factor of safety?

thank you.
BigH (Geotechnical)
9 Jan 09 1:29
Cariboo - get Hoek's book.  note that in rock, joints will be a major issue (maybe not if you consider the weathered rock separately) but even then joints, slickensides on the joints, etc. are crucial - as is the water table.  Those much more knowledgable about rock slopes will fill you in on the details. There are a couple of books out there on rock slopes too.
dmwbnd (Geotechnical)
9 Jan 09 17:26
Yes, step one is definitely to get Hoek's classic rock mechanics book.

I also agree that rock joints and water table will be the greater issue.  Rock jointing can be quantified using the rock GSI.  RocScience (www.rocscience.com) has some good publications on the GSI system and how to use it.  They also have a nice little program called RocLab (http://www.rocscience.com/products/RocLab.asp) that assists in picking the appropriate GSI.  RocLab can also use the Hoek and Brown strength model (which does a better job at modeling rock strength than MC) to determine equivalent phi and c values for the rock mass. This is handy because once you have equivalent phi and c values, any limit equilibrium slope stability method and/or program can be used (i.e. PCStable, GeoSlope, Slide, etc).

Hope this helps.
moe333 (Geotechnical)
9 Jan 09 17:56
The GSI system is used in situations where discrete rock joints or other discontinuities do not control the stability of the slope, such as in moderately to extremely fractured/weathered rock.  Where predominant discontinuites forming critical planes or wedges do control the stability of the slope, you should look at stereonet analyses.  Hoek and Rocscience are great resources for this.  Many of Hoek's papers can be downloaded from the Rocscience website.  
Mccoy (Geotechnical)
17 Jan 09 17:36

Quote (moe333):

The GSI system is used in situations where discrete rock joints or other discontinuities do not control the stability of the slope, such as in moderately to extremely fractured/weathered rock.  Where predominant discontinuites forming critical planes or wedges do control the stability of the slope, you should look at stereonet analyses.

Also, it's the scale which governs isotropy.

A joint field which is anisotropic at a small-medium scale may be isotropic (hence evaluated by roclab) at a larger scale.

As a rule, as far as detailed jobs are concerned, roclab will not make everyone happy.

One situation where it's just about the only choice though it's very high quarry faces. You can't survey them by ordinary means, you just evaluate GSI by binoculars and use roclab...
 
mudman54 (Geotechnical)
13 Feb 09 9:29
i think you'd be pleasantly surprised at how much help an engineering geologist could provide on this type of project.
cvg (Civil/Environmental)
13 Feb 09 11:51
geologist should assist with the design and should also be present during the excavation. you never know what you will find when you excavate your rock.

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