As shown in Fig. 2, these two halves of the granite core
emplaced with the bentonite block faced each other and
they were joined by a urethane sleeve. The sleeve was
compressed by a highly pure nitrogen gas at about
3.0MPa and this pressure will hold the granite core tight so
as not to make the groundwater flow along the perimeter of
the granite core. This confining pressure by the nitrogen
gas is also needed to prevent the core from widening the
aperture between the two halves of the granite cylinder
when the bentonite swells due to a hydration.