Yes,you can do this,..several papers have been published on this,proceed with Google,..but you need to proceed with come UCS to validate this,..scale effect is not critical as you need around 20 tests on the same area,..

Yes, you can but you have to considerer: 

1) All tests to be performed at the same type of joint (roughness, filling materials etc.);

2) You will have to considerer the direction of testing (vertical upward and downward, horizontal)

3) I agree you Dr. Ballivy that the test is not scale  dependent

4) You can take  alook on the following papers:

Basu & Aydin (2004) Int. J. of Rock MEchanics, 41

McCarroll (1991). Earth Surface Processes and Landforms, V. 16

Demirdag, Yacuz & Altindag (2009); Int. J. of Rock Mechanics & Mining Sciences, N. 46

Aydin & basu (2005), Enginnering Geology, N. 81

There are several others that you can find at Google Scholar or other sites.

Thank you very much dear Prof. Ballivy and Marques  for sharing valuable information.