Simulated Hydraulic Response of AECL's Isothermal Test and Comparison with Measured Data

A large in-ground experiment, the Isothermal Test (ITT), was conducted in the Underground Research Laboratory to examine how a large mass of dense sand-bentonite buffer would take on water from a surrounding rock mass. The ITT was installed in a 1.24-m-diameter by 5-m-deep borehole in granite. The bottom two metres were filled with an in situ compacted sand-bentonite material. This material was capped by a 1.25-m-thick mass of concrete and was left undisturbed for 6.5 years. During this period, the pore water pressures in the buffer and the surrounding rock were continuously monitored. Numerical simulations were conducted using the commercially available finite-element program CODE_BRIGHT in an attempt to model the evolution of the pore water pressure in the unsaturated sand-bentonite buffer and the surrounding rock. The influence of the excavation-induced damage zone on the evolution of the hydraulic response in the sand-bentonite material and the rock was also examined. The water seepage from the rock to the borehole and the pore water pressure in the rock and the buffer were compared with the measured data.