Borehole, shaft, and tunnel sealing of rock repositories

Precompacted blocks of Na bentonite powder absorb water and swell to several times their original size when exposed to low- and moderately saline water under unconfined conditions. On application in boreholes, shafts or tunnels, they can only undergo moderate swelling, which yields a homogeneous seal with high density and very low hydraulic conductivity. The swelling pressure exerted on the confining rock creates an intimate clay/rock contact and an effective mechanical rock support. By this, flow through the plugs and along the rock/bentonite interface is negligible and flow through the rock adjacent to the plugs is also diminished by self-sealing through penetration of clay into wider fractures and by the fracture-closing effect of the swelling pressure