Problems and research performed
TC3 was defined based on a large scale laboratory experiment of the coupled THM processes of the engineered barrier system for GDRW, using the BIG–BEN (Big–Bentonite) facility at the Tokai Works, PNC, Japan. The aim of TC3 was to test and compare the capabilities of different numerical models and computer codes for simulating one of the test pits based on the current design. Figure 7a illustrates the BIG–BEN test facility with different components, and Figure 7b shows the test pit geometry and some monitoring point locations. Three research teams participated in TC3 and used different modeling approaches: CLAY (supported by SKB), CNWRA (supported by NRC, using code ABAQUS of FEM), and KPH (supported by PNC CNWRA (supported by NRC, using code THAMES of FEM). All teams used 2D axisymmetric models, but with different element types (4-noded and 8-noded) and mesh resolutions. Figure 7c and 7d show the results of the calculated and measured temperature and water content at different monitoring locations.
Main achievements and outstanding issues
The main findings were that the calculated results of temperature and water content agreed well with the measured data, but not the stress values among the teams, which may have been caused by different treatments of the swelling pressure phenomenon of the bentonite, and inadequate mechanical constitutive models for the bentonite materials.