The Geomechanics Classification of rock masses was proposed in 1973 and has since been applied to such varied rock engineering projects as tunnels, caverns, slopes and foundations in civil engineering and to haulages and chambers in mining. The classification is based on six parameters: the uniaxial compressive strength of the rock material, drill core quality RQD, spacing, orientation and condition of discontinuities and groundwater conditions. Importance ratings are allocated to each parameter and total rock mass ratings (RMR) for five rock mass classes are specified. This paper summarizes the experience gained with this classification in the past five years.
La Classification Geomecanique, une classification pour l'ingenieur des masses de roches fracturees, a ete proposee en 1973 et a ete applique en ingenierie civil et minière. Elle depend de six paramètres: la resistance à la qualite des carrottes de sondage obtenues (valeur RQD), espacement, orientation et etat des fissures" et les venues d'eau souterraine. On definie des valeur relatives pour chaque paramètre et des valeurs totales pour la masse rocheuse (RMR). Cette communication pourvoit un resume de experience avec cette classification pendent les derniers cinq ans.
Die Geomechanische Gebirgsklassifizierung, eine fuer den Ingenieur bestimmte Klassifizierung fuer klueftiges Gebirge wird vorgeschlagen in 1973 und im Bauingenieurwesen und Bergbau angewendet wird. Sie grundet sich auf sechs Parameter: die einachsige Gesteindruckfestigkeit, die Qualitat der gewonnenen Bohrkerne (RQD - Wert), den Kluftabstand, die Kluftstellund und den Zustand der Kluefte, sowie auf den Grundwasserzufluss. Jeder Parameter wird nach seiner relatives Wichtigkeit bewertet und die Gesamtberwertung des Gebirges (RMR) wird definiert. Dieser Aufsatz zusammenfasst die Erfahrung mit dieser Klassifizierung wahrend die vergangene fuenf Jahre.
Engineering classifications of rock masses are acknowledged today as a necessary adjunct for assessing rock mass conditions for engineering purposes. This subject has received considerable attention following the pioneering work by Terzaghi (1946), Lauffer (1958) and Deere (1964). More recently, three classification systems have been extensively employed particularly in the field of tunneling. These were: the RSR Concept by Wickham et al. (1972), the Geomechanics Classification by Bieniawski (1973) and the Q-System by Barton et al. (1974). A number of comparative studies have been conducted aiming at assessing these, classification systems from the point of view of the ease of application, the accuracy of prediction and any possible correlation, Houghton, 1975, Bieniawski, 1976, Barton, 1976 and Rutledge, 1978.
Notable developments in the last few years concerning rock mass classifications fall under seven items:
Although the main applications of rock mass classifications have traditionally been in tunneling, the Geomechanics Classification is an exception having been also applied to other projects and not only to tunnels and chambers. This inc1ud~ rock slopes (Steffen, 1976, K. W: John, 1978), dam foundations (Bieniawski and Orr, 1976), foundation bearing pressures (Newton, 1975), ground rippability (Weaver, 1975) as well as mining applications: caveability of ore (Laubscher, 1976) and haulage stability (Fergason, 1977). Most recently, the Geomechanics Classification is being applied by the author to assess mine roof stability in a number of coal mines in the USA.
A trend has emerged to select engineering geological parameters on the basis of borehole data alone which would be sufficient for rock mass classification purposes without the need for tests in edits or pilot tunnels. 2.3 Special rock conditions The situations involving poor rock conditions such as swelling and squeezing rock can now be handled by both the Geomechanics Classification and the Q-System. In the case of the former, Olivier (1977) has presented a rock durability system for use in conjunction with the Geomechanics Classification.
Although some classification systems tend to rely exclusively on the accumulated case study experience, it is more appropriate to back support prediction based on rock mass classifications with a monitoring program during construction. The New Austrian Tunneling Method is a success story of the benefits that can be derived by combining rock classifications with monitoring.
The traditional concepts of primary (temporary) and secondary (permanent) support for rock tunnels are loosing their meaning as the modern tendency is toward a single support system, that is rock reinforcement necessary to maintain tunnel stability for the life of the project. This raises the question as to the need for massive concrete linings which are featured on some tunneling projects.
The analytical techniques in the field of rock mechanics have experienced a tremendous growth and although analytical design cannot as yet replace empirical and observational designs (mainly due to the difficulty in providing reliable input data for the mathematical models), the value of the analytical techniques should not be overlooked. Progress can only be maintained if empirical approaches are backed by analytical studies.