ADJUSTMENT OF ROCK MASS CLASSIFICATION BASED ON STATISTIC MECHANICS OF ROCK MASS(SMRM)TAKING GUANSHAN RAILWAY TUNNEL AS EXAMPLE

Unlike well predicting by specification method on rock mass classification in shallow project before excavation, in the tunnel excavation of jointed rock mass in large depth and high in situ stress, there are great change of rock mass parameters and structure, revealing not only the degradation of rock mass quality also the significant anisotropy of rock mass. Because the micro fracture or closed rock structural plane under high in situ stress will re-open and develop quickly during stress field change due to the excavation, which affects the stability and quality of rock mass. The rock mass classification before excavation is not suitable anymore. Therefore, for the purpose of describing the degradation of rock mass quality after excavation objectively and quantitatively, SMRM takes into account the anisotropy of rock mass affected by structural plane in the rock mass classification, fully considering the different structural plane parameters after excavation. For further discussion, taking the deeply buried Guanshan railway tunnel under high in situ stresses as an example, according to the statistic analysis of the rock structural plane, this paper applied SMRM to analysis the outstanding anisotropy of rock mass after the excavation. Finally, suggestions of rock mass classification adjustment is offered to catch up with the degradation of rock mass after excavation.