SEMI-EMPIRICAL METHOD FOR DESIGN OF SUPPORTS IN UNDERGROUND EXCAVATIONS

Abstract

The design of an underground excavation is to a large extent, the design of underground support system. A semi-empirical method, has been developed by Singh et al (1994) for design of support systems for cavities excavated in poor rock mass. The support system may be consisting of rock bolts/anchors, shotcrete/fibre reinforced shotcrete, steel ribs and grouted arch. In this study, an attempt has been made to validate this method. For this, the data of 120 project sites spread across The globe has been compiled and analysed. The empirical co-relations have also been deduced for the mobilization factors for shotcrete and rock bolts/anchors (grouted and pretensioned) on the conservative side from extensive data of different underground power houses and tunnels. A correlation between span of the opening and the central half arch angle has also been deduced from the actual data. There is an acceptable correlation between empirical approach (Barton et al. 1974) and the proposed theory (Singh et al 1994) of estimating the support capacity, except for abnormal cases of design. The proposed method is quite simple for use in the field and is easily comprehensive.