ABSTRACT:

Contrasting geophysical, rock mechanics and rock engineering experience in basalts, caused by either exceedingly low or extremely high stress are described, from projects in the USA and Brazil. The first involves a nuclear waste characterization project in Hanford basalts in the USA, and the second describes, in much more detail, stress-fracturing problems in numerous large tunnels at the 1450 MW Ita hydroelectric project in SE Brazil's basalts. Particular phenomena that were noted, include linear stress-strain loading curves when columnar basalt is loaded horizontally, and a k0 value reaching about 20–25 at Ita HEP.

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