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Abstract Due to existence of various unfavorable geological bodies，assessment results of rock mass quality are often varied at different stages of construction，and induce some arguments. In order to assist in rock engineering aims，the engineering geological rock grouping is necessary to carry out on analyses of lithology and physi- mechanical features，for differentiation of main components of engineering geological zonation and evaluation. The widely applied rock mass quality classification is useful in rock engineering design and construction for surrounding rock stability purpose. The former comes from the viewpoint of rock mass structural control and takes account of rock mass types from a large range，while the latter adopting single or multiple parameters for assessment rock mass quality，including rock mass itself and surrounding environment. At different stages and layers，the two methods play distinctive roles，as for large scale geological forecast and engineering design，respectively，but with somewhat joints and overlays. The obvious differences of rock mass quality indices obtained at various stages of construction，can be clarified and interpreted from views of engineering geological rock group，with respect to unfavorable geological bodies. Taking the Yanmenguan Tunnel as one case example，their roles and application process are presented and discussed. The different advantages of the two systems and obtained results could be used in other rock engineering projects.
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Received: 05 November 2012
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2013, Vol. 32 
