Geotechnical characteristics of the site for an underground research tunnel in KAERI

In order to design the underground tunnel for the validation of disposal system in KAERI, the geotechnical characteristics of the site should be investigated. In this study, the results from laboratory tests using the rock cores retrieved from the vertical and declined boreholes and those from in situ experiments in the boreholes were analyzed and the rock mass properties around the research modules were derived. The physical and mechanical properties of the rock and discontinuities could be determined from different laboratory tests using the NX size cores from the boreholes of 412m long. Rock mass classification could be done using the data from the vertical and declined boreholes. In order to investigate the rock condition inside the boreholes, Goodman Jack test, borehole shear test, water pressure test, hydraulic fracturing, and hole observation using BIPS and BHTV had been carried out. In the case of 252m long 10% declined borehole, hard rock is located from about 30m from the borehole entrance. The average RQD and RMR of the total zone including the weathered zone are 64.5 and 59, respectively, and could be classified as 'Fair rock'. The RQD and RMR values around the research modules are 89.5 and 76, respectively, and could be classified as 'Good rock'. About 24% of access tunnel will be located in 'Very good rock' according to RMR classification. When there are clear relationships between rock properties and depth, curve fitting equations were derived. From the relationships and the results from experiments, the rock properties at the location, where the research modules will be constructed, could be estimated. The rock mass properties will be used as input data for the thermal, mechanical, and hydraulic analysis for the underground facility in the future