TABLE OF CONTENTS MASOUD SHIROUYEH ARAGHI 1 , FEREIDOUN BAHRAMI SAMANI 2 and MOHAMMAD TORABI GOUDARZI 3
1 Engineers co, Iran, Tamavan Consulting Eng.
(masoudshirouyeh@tamvan.com )
2 Engineers co. Iran, Tamavan Consulting Eng.
(fbsamani@tamavan, com )
3 Engineers co. Iran, Lar Consulting Eng.
(goudarzi44@yahoo.com )
The RQD of Deere (1964) is considered as a quick and economical factor in most rock engineering classifications such as Q, RMR and even in calculation of some Rock Geotechnical parameters and support design. Besides its high applicability, RQD has some deficiencies, which should be considered; a) RQD method does not give any information for spacing more than 10 cm (4 inches); b) In case of 9 joints per meter, if 1 or 2 joints are added, the RQD will decrease from Excellent to Very poor class. Which shows non realistic sensitivity of RQD to joint numbers; c) Rock masses with 11, 20, and even 50 joints per meter have the same RQD. This is true, also, for fragmented or crushed rock masses, as well as cavities, RQD of all these rock masses are equal to zero. But, there is a distinct difference in Rock Quality for all above cases. So MRQD is suggested to correct and modify it for the best usage. This parameter could describe more completely the differences of various cases. The modified version of RQD (MRQD) is explained according to percentage of weak zone which includes discontinuities, core washed, core loss,...
