Modelling the early age behaviour of a low heat concrete bulkhead sealing an underground tunnel

Abstract

A major experiment - the tunnel sealing experiment, related to the disposal of heat generating radioactive wastes in geological formations and supported by government organizations from Japan, France, U.S.A., and Canada, is being carried out at the Underground Research Laboratory of Atomic Energy of Canada Limited in Manitoba, Canada. Through a systematic process, the results from the experiment will be used to validate numerical models for the early age behaviour of high mass concrete bulkheads. A numerical model, based on the CESAR-LCPC finite element code equipped with the modules TEXO and MEXO, has been developed and used to predict the behaviour of a concrete bulkhead which will be built as part of the experiment. The TEXO-based component of the model which describes temperature changes has been validated. A maximum temperature rise in the concrete of 19%C is calculated. This will occur about 4 days after the concrete is cast. The temperature rise is low. This arises from the use of a specially developed low cement content concrete. Despite uncertainties in the MEXO-based model, which is used to describe the chemo-mechanical behaviour of the system, results indicate that it is unlikely that the concrete will crack, but a gap of 0.5 mm or more will develop between the bulkhead and the rock. Water leakage around the bulkhead through this gap could be significant and measures to seal this gap are advised. The modelling results recorded here will be tested against measurements made in the experiment. Thus, the numerical model will be formally validated and bounds to its use will be defined.