Experiment and validation of numerical simulation of coupled thermal, hydraulic and mechanical behaviour in the engineered buffer materials

• Published in: International journal for numerical and analytical methods in geomechanics Vol. 24; no. 4; pp. 403 - 424
• Main Authors: Chijimatsu, Masakazu, Fujita, Tomoo, Kobayashi, Akira, Nakano, Masashi
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 10.04.2000; Wiley
• Subjects: Applied sciences; bentonite buffer material; Buildings. Public works; Computation methods. Tables. Charts; coupled problem; Exact sciences and technology; Geotechnics; high-level radioactive waste disposal; large-scale experiment; numerical simulation; Pollution; Radioactive wastes; Soil mechanics. Rocks mechanics; Structural analysis. Stresses; Wastes; Buffer layer; Water infiltration; Radioactive waste; Experimental test; Swelling; Measurement sensor; Pressure distribution; Thermomechanical properties; Soil mechanics; Waste management; Temperature measurement; Water content; Bentonite; Numerical simulation; Thermohydraulics; Water barrier; Heat transfer
• ISSN: 0363-9061; 1096-9853
• DOI: 10.1002/(SICI)1096-9853(20000410)24:4<403::AID-NAG73>3.0.CO;2-E

Evaluation of the coupled heat transfer, water flow and stress changes in the engineered clay barrier is an important issue in the performance assessment of the high‐level radioactive waste disposal. To demonstrate the function of the engineered barrier system, the large‐scale experiment is conducted, which is called Big Bentonite facility (BIG‐BEN). The facility consists of an electric heater surrounded by glass beads, carbon steel overpack, buffer material and man‐made rock. The buffer is a mixture of bentonite and sand. The heater is operated at 0·8 kW. Water is injected from the interface between the buffer and the man‐made rocks at the pressure of 0·05 MPa. The duration of the experiment is 20 months. The change in temperature and swelling pressure are continuously monitored and gravimetric water content is measured by sampling. The coupled thermal, hydraulic and mechanical processes are simulated with a finite element code THAMES, which can simulate the fully coupled phenomena in the saturated and unsaturated clay under anisothermal condition. To examine the validity of the code, all the parameters used in the model are evaluated from the other laboratory tests. The simulated results are compared with the measured ones without calibration of the parameter values using the results from the BIG‐BEN experiment. It can be concluded that the changes in temperature and gravimetric water content within the buffer can be simulated reasonably well and that the mechanical effect such as swelling pressure is difficult to realize. Copyright © 2000 John Wiley & Sons, Ltd.