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# How to built a stereographic net

## How to built a stereographic net

(OP)
I'm now doing on my thesis and the topic is 'Engineering Geological Properties'. Therefore, I must go to the site at one of our local new developed highway to take reading about dip and strike inclination, dip and strike direction and minor and major set of joint and fault. So, after all this, i must develope a stereographic net using the data. But the problem here is i don't have the data about angle of friction. So, my question is , can i built a complete stereographic net without the data about angle of friction depending oin the data about joint and faults only?

### RE: How to built a stereographic net

all you need is strike and dip to plot on a stereographic net...you will only need the friction information to do an analysis...you can estimate the friction in the field by breaking off two pieces of the outcrop, wet them, put one against the rock face at an angle then set the other one on it while letting it rest against the rock face...rotate the bottom one til the top one slides...when it starts to slide mark the angle...by using a trig you can determine an approx. friction angle...Richard Goodman has written several papers on the subject and he also mentions the subject in his Intro to Rock Mechanics text...hope that helps somewhat

### RE: How to built a stereographic net

gbbycu has covered the basics.  If you are interested in the orientation distribution of the fractures, strike and dip will do.  However, you must satisfy yourself on the consistency of the pattern in your mapping area.  Faults can separate volumes of rock mass with different fracture patterns or can be special fracture pattern volumes of their own.  These are "Structural Domains."  I take a mininmum of 120 strike and dip observations at a site within a single structural domain..

If you are analyzing stability, you will need the angles of internal friction of each fracture orientation set.  gbbycu gave a good description.  I do at least six or more repetitions of each fracture set from different samples to get some idea of a mean and variance.

It starts to get very complicated for critical slopes.  You must also consider roughness and fracture continuity in the analysis of stability.

Get a copy of Goodman's texts.

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