Bentonite hydro-mechanics

Based on the characterization of the bentonite and on the details of the process of test installation, a thermo-hydro-mechanical model for the bentonite barrier and the heaters was to be prepared. Using this model, the thermo-hydro-mechanical response of the bentonite barrier as a result of the heat released by the heaters and the hydration from the host rock was required. Local field variables such as temperature, relative humidity, pore water pressure, stresses and displacements, as well as global... 

PART B THERMO-HYDRO-MECHANICAL ANALYSIS OF THE BENTONITE BEHAVIOUR. 

Villar, M.V., Thermo-hydro-mechanical character-rization of a bentonite from Cabo de Gata. A study applied to the use of bentonite sealing material in high level radioactive waste repositories. PhD Dissertation and Enresa Technical Publication 01/2002. Madrid. 

Abstract The Canadian Nuclear Safety Commission (CNSC) used the finite element code FRACON to perform blind predictions of the FEBEX heater experiment. The FRACON code numerically solves the extended equations of Biot s poro-elasticity. The rock was assumed to be linearly elastic, however, the poro-elastic coefficients of variably saturated bentonite were expressed as functions of net stress and void ratio using the state surface equation obtained from suction-controlled oedometer tests. In this paper, we will summarize our approach and predictive results for the Thermo-Hydro-Mechanical response of the bentonite. It is shown that the model correctly predicts drying of the bentonite near the heaters and re-saturation near the rock interface. The evolution of temperature and the heater thermal output were reasonably well predicted by the model. The trends in the total stresses developed in the bentonite were also correctly predicted, however the absolute values were underestimated probably due to the neglect of pore pressure build-up in the rock mass. 

The research teams participating in the DECOVALEX III project were asked to predict the Thermo-Hydro-Mechanical (THM) response of both the bentonite and the rock mass after the commencement of the heating (from day 0). This paper summarizes the approach and results from the CNSC team for the bentonite response. 

UPC, 2000, Task definition DECOVALEX III, Task 1 Modelling of FEBEX in-situ test. Part B Thermo-hydro-mechanical analysis of the bentonite behaviour. Polytechnical University of Catalonia, Barcelona, Spain. 

Other termo-hydro-mechanical and geochemical characteristics of the FEBEX bentonite are detailed in ENRESA (2000) and Villar (2002). 

Villar, M.V. Lloret, A. 2002. Temperature influence on the hydro-mechanical behaviour of a compacted bentonite. Proc. Int. Meeting Clays in Natural and Engineered Barriers for Radioactive Waste Confinement. ANDRA, Reims. 

The initial conditions of the bentonite were as follows dry density 1,7 g/cm and water content 14.4%. This results in an initial degree of saturation of 0.65 and an initial suction of 115 MPa. Both the bentonite (solid phase and interstitial water) and the hydration water were subjected to a full chemical characterization. The thermo-hydro-mechanical parameters were determined in an independent laboratory testing programme. 

In the near-field of a HLW repository, the coupled thermo -hydro -mechanical and chemical (T-H-M-C) processes will occur, involving the interactive processes among radioactive decay heat from the vitrified waste, infiltration of groundwater into bentonite, swelling pressure of bentonite due... 

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