Wichit Sriwisead creator Noppadol Phien-Wej Chairperson Bergado, Dennes T. Examination Committee Sugimoto, M. Examination committee text th Bangkok Asian Institute of Technology 1996 monographic eng

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235 leaves The engineering geological mapping along the access tunnel to powerhouse and to top gallery was carried out which helped classify the rock mass according to the most popular classification systems namely RMR ,Q-system and EPDC. The rock mass turned out to be mostly of fair quality and good quality for sandstone section. The deformation modulus, cohesion and frictional angle, Hoek and Brown's m ands strength parameter and others rock mass properties were approximated. The support recommendation from RMR and Q-system were estimated that could be compared with the actually installed which was recommed by EPDC. The convergence measurement was monitored and collected data were analyzed, interpreted and the rock mass modulus of deformation was back calculated by using the Phases analysis. The results of back calculation modulus of deformation of sandstone was higher than siltstone (1.4-4 GPa for reddish siltstone and 4.3-42 GPa for sandstone) and the intercalated of sandstone and siltstone showed high value. Modulus deformation estimated from Phases analysis would be related well with modulus from Q system. The plastic zone was developed deeper behind inve1t and crown for highly weathered siltstone and sandy siltstone up to 4-5 m. The rock mass showed time-dependent behavior but the convergence rate decreased with time that insignificant. The estimated of the convergence rate was less than the lower value for squeezing ground (0.07% at 1000 days for siltstone (0.042 mm/day), 0.09% at 1000 days (0.0054 mm/day) for sanstone and 0.15% at 1000 day or 0.006 mm/day for intercalated of both layer. Ground responses were observed that several types were identified such as loosening, slaking, swelling, stress slabbing, delayed fracturing etc. The Loosening was the most prominent as failure was governed both by discontinuity systems and the low strength of rock mass itself. Slaking though being very drastic outside the tunnel was not so severe inside of both access tunnels. Stress slabbing including delayed with depth became noticeable due to excessive strength ratio. The excavation and support performance was described of several suppo1t types. The main supporting types was used of the system rockbolt and shotcrete that was proved to be most suitable for each ground section. A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science, School of Civil Engineering Thesis (M. Sc.) - Asian Institute of Technology, 1996 Lam Ta Khong Project Asian Institute of Technology. http://203.159.5.9/ait-thesis/detail.php?q=B15152 http://203.159.5.9/ait-thesis/detail.php?q=B15152 20260818112829.0