Bentonite sealing of rock excavations

Blocks of precompacted Na bentonite powder are strongly hydrophilic and tend to swell to several times their original size when exposed to low- and moderately saline water under unconfined conditions. If they are used to fill up the space between waste canisters and the rock in drilled deposition holes, or applied as plugs in a borehole, shaft or tunnel, they undergo moderate swelling and ultimately form a dense homogeneous seal with a high density and extremely low hydraulic conductivity. The swelling pressure exerted on the confining rock creates an intimate clay/rock contact and an effective mechanical rock support