Geological mapping and stand-up time estimation based on core drill evaluation using RMR89 on Tunnel 3 Sigli Banda Aceh Toll Road

Abstract

Tunnel 3 of the Sigli Banda Aceh Toll Road has been designed based on several site investigations. The site investigations have not included surface geological investigations. Subsurface geological investigations have been carried out but with less detailed drill core evaluation. This will cause less accuracy on the assessed tunnel stand-up time. This research aims to evaluate the engineering geological conditions at the tunnel construction site by conducting geological mapping with 1:5,000 scale and re-evaluating drill core using RMR89 method more thoroughly so that it can produce more accurate assessment of the tunnel stand-up time. The geological mapping result shows that the research area has three rock units, namely lapili, tuffaceous sandstones, and interbedded sandstone-siltstones, with moderate to fresh weathering degree. The drill core evaluation shows that research area has poor to good rock mass classes (34 – 67). The drill core evaluation results also indicate possible geological structures that may influence subsurface rock mass strength. The tunnel stand-up time obtained from the lowest RMR89 value for each drill core shows a value of 5 - 90 hours, implying immediate application of support system after tunnel excavation.