Empirical rock mechanical site-descriptive modeling (RMSDM) for the Korea Atomic Energy Research Institute Underground Research Tunnel (KURT)

Abstract

As part of master plan, when preparing to construct the second stage of the Korea Atomic Energy Research Institute Underground Research Tunnel (KURT-2), site investigations were carried out to characterize the rock mass and its related geophysical nature. The rock mass at the study site was divided into rock units depending on a rock type and fracture developments in rock. The rock mass quality for each rock unit was evaluated, using rock mass classification systems, such as Q, rock mass rating (RMR), and rock mass index (RMi). The mechanical properties of rock units were empirically estimated with associated rock mass classification systems, including deformation modulus, uniaxial compressive strength, and cohesion and friction angles. Ultimately, a rock mechanical site-descriptive model (RMSDM) covering the block size of 85 m × 120 m × 80 m was developed by combining the analysis of rock units. Rock block consists of granite, dike, and fault, being divided into six rock units, such as G1, G2, G3, D1, D3, and F3. G1 and D1 rock units were classified as good rock masses, and the rock mass quality of G2 is fair. G3 and D3 rock units were classified as poor rock masses, and the F3 rock unit was very poor. The mechanical properties of rock unit G1 and D1 were almost considered similar and best, and those of G2 were considered middle class. G3 and D3 rock units had poor mechanical properties and those of F3 were the worst. G1 occupies most of block volume, but other rock units were distributed as small portions. Two-dimensional distributions of rock mass from modeling and face mapping at the elevation of the tunnel excavation exhibited that predicted distributions well fit to those observed. Therefore, RMSDM will be of help with the geoscientific understanding of site investigation and designing of a site and construction of a site, similar to KURT-2, and ultimately, it will become a scientific base to future-related research and development projects of the Korea Atomic Energy Research Institute (KAERI).