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ROCK MASS CLASSIFICATION - REVIEW | ROCK TUNNELLING


(i)


a ‘family tree’ of RMCS that relates all compiled systems to each other. This family tree facilitates a discussion of RMCS from a historical perspective as well as identification of trends, developments, research gaps, and allows to estimate future directions.


(ii) Surveys to investigate the international distribution of RMCS were conducted among the rock engineering community, and based on the results, ‘world maps’ of rock mass classification were created. A preliminary version of this survey was presented in Erharter et al. (2023). However, the herein presented results are more comprehensive as they include 435 more survey responses, thus covering larger parts of the world, and also present the results in more detail. Through the survey and additional literature research, a list of 37 RMCS for different underground and slope engineering purposes was set up, which is the most comprehensive overview of RMCS to date.


2 HISTORICAL DEVELOPMENT OF ROCK MASS CLASSIFICATION SYSTEMS The earliest systems for classifying geological formations have their roots in past centuries and initially arose from simple attempts to organise and record geological structures and were often related to mining activities. As also mentioned in Aydan et al. (2014), presumably the oldest formerly accessible RMCS was presented in Agricola (1556)—’De Re Metallica’ who differentiates four types of ore: ● “I call that ore “crumbling” which is composed of earth, and of soft solidified juices;”


● “that ore ‘hard’ which is composed of metallic minerals and moderately hard stones.”


● “I call that ore ‘harder’ when with those I have already mentioned are combined various sorts of quartz, or stones which easily melt in fire of the third degree, or pyrites, or cadmia, or very hard marble.”


● “I call that ore ‘hardest’, which is composed throughout the whole vein of these hard stones and compounds.”


These first attempts formed the natural scientific and technical basis for a modern identification and categorisation of soil and rock. After pioneering tunnelling work in the 19th Century


(Ritter 1879), the first ‘modern’ work about RMCS was conducted independently by Protodyakonov and Terzaghi. Protodyakonov introduced a classification system (Protodyakonov (1926) see also Ji et al. (2023)) that is considerably older than other known systems, providing initial insights critical for the development of rock mass classification in the fields of tunnelling and mining engineering. Protodyakonov’s methodology accounted for various


factors influencing rock mass behaviour, including the existence and condition of discontinuities. Terzaghi’s contributions to geotechnical engineering were marked by his capacity to integrate empirical data


with theoretical concepts in soil and rock mechanics. His research in the 1920s and 1930s laid the theoretical groundwork for understanding the stress behaviour of soil and rock, later influencing rock mechanics and tunnelling practices (Terzaghi 1946). In tunnelling-specific developments, Stini became a


key figure in rock mechanics and tunnelling, providing essential insights into the behaviour of rock mass during tunnel excavation (Stini 1950). Rabcewicz is credited with laying the conceptual


groundwork for the New Austrian Tunneling Method (NATM), introducing a strategy that tailored the support system to geotechnical conditions encountered during tunnel excavation (Rabcewicz 1957). The development of RMCS for tunnelling from the


1950s to the 2000s was characterised by significant innovations. In addition to Terzaghi’s contributions, Lauffer’s introduction of the concept of ‘standing time’ (Lauffer 1958) was a key moment in the dialogue on rock classification systems. Deere’s development of the Rock Quality Designation


(RQD) in 1963 focused on quantifying rock quality based on drill cores only. Subsequent decades saw the creation of comprehensive systems. Bieniawski’s Rock Mass Rating (RMR) system,


introduced in 1973, was revolutionary in offering a numerical rating correlated with tunnel support recommendations. Barton’s Q-system, starting in 1974, provided a detailed assessment framework for tunnelling projects, emphasising empirical data’s utility across varied rock conditions. The introduction of the Geological Strength Index (GSI) by Hoek and Brown (1997) marked a move towards a more direct visual, field-adapted, evaluation of rock mass properties without any direct numeric inputs. Slope-specific developments have been driven by


the unique challenges and objectives inherent in slope stability analysis. The divergence between classification systems for slopes and tunnels reflects the distinct stability issues encountered in each domain. While the GSI finds application in both tunnelling and slope stability analysis, its use in slopes often focuses more on the structural complexity and surface condition of the rock mass. The Slope Mass Rating (SMR) system, developed by Romana (1985), adapted the RMR system for rock slope assessment (SRMR), while the Q-system was adapted to Q-slope by Barton and Bar (2015). A remarkable parallel development that seems


detached from other RMCS that predominantly originate from the ‘West’ is the Chinese ‘Basic Quality’ (BQ) system that today is finding significant application internationally. BQ goes back to the ‘Z-System’ developed by Gu


and Huang (1979) and was subsequently adopted in the Chinese standard (Lin 1998; GB 50218–2014 (2014)). Further development goes into BQ, and it was recently modified to also account for anisotropy, thus becoming the ‘anisotropic-BQ’ system (A-BQ) (Guo et al. 2020) which combines BQ and Anisotropic RMR (ARMR) (Saroglou et al. 2019).


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