STUDY OF ROCK MASS STRENGTH BASED ON LAB TESTING OF EGYPTIAN ROCKS

A mohr-coulom failure criterion is a function of the apparent cohesion (tau0) and the angle of internal friction (φ). the evaluation of these two parameters requires testing many rock samples, where these tests are more expensive and consume more time for triaxial testing set-up. hoek-brown failure criterion for rock masses is widely accepted and has been applied in large number of projects around the world. while, in general, it has been found to be satisfactory, there are some uncertainties and inaccuracies that have made this criterion inconvenient to apply, and incorporate into numerical models and limit equilibrium programs. in practice, the difficulty of finding an acceptable equivalent friction angle and cohesive strength for a given rock mass has been a problem since the publication of the criterion in 1980. this study is based or laboratory data of more than 70 rock samples of different kgyptian rocks collected from several mining sites and quarries. these laboratory data represent the mechanical properties of these rocks, obtained from the uniaxial and triaxial tests, and then these data used in rocklab computations to define the required all rock properties. the new rock strength relations were determined by using the previous rocklab computed properties to obtain the adequate equations, which show new representations for the peak and post-peak behavior of rock masses.