Evaluating rock mass strength for exploratory adit of Dong Nai 4 hydropower project Daknong Province Tay Nguyen Area in Vietnam

THONG, Nguyen Huynh, Prof. Dr. Dwikorita Karnawati

2009 | Tesis | S2 Teknik Geologi

Estimating rock mass strength for exploratory adit with width 2 m, length 80 m is one of the important articles in Dong Nai 4th hydropower project, DakNong province, Tay Nguyen area in Viet Nam. Based on the analyses and results, solution for water conduit tunnelling excavation and powerhouse foundation was suggested to improve stability and save cost. Assessment on various rock engineering parameters such as discontinuity conditions with a number of sets, spacing, orientation, roughness, infilling as well as unconfined compressive strength, water condition along adit was considered and analysed. Based on the empirical analysis method, RMR and Q values were determined which conducted RMR values 41-60 (fair rock at span 0-50 m and 55- 80 m), 61-80 (good rock at span 50-55 m) and Q index 0.4-0.88 (very poor rock at span 0-35 m and 40-75 m), 1-4 (poor good at span 35-40 m and 75-80 m). Finally, the rock mass quality gets low values (fair, poor or very poor) because of discontinuity conditions. Therefore, if there are more existing discontinuities, the quality of rock mass will get low. Moreover, rock mass properties was applied to construct factory foundation, which cohesion varied 0.31-0.53 MPa, 44-52 degree for internal friction angle, and 0.26-0.74 GPa for deformation modulus by using RocLab tool. Accordingly, rockbolt support system was suggested with bolt length 1.5 m for adit and 2.4 m for tunnel. Bolt spacing in unshotcrete area of spans varied 1.0- 1.3 m. Bolt spacing in shotcrete area varied 1.5-1.7 m. Steel fibre reinforced shotcrete of spans varied 4.3-5.0 cm (adit) and 5.0-8.5 cm (tunnel).

Kata Kunci : Exploratory adit,Rock mass strength,Discontinuity condition