Effects of temperature on strength and compressibility of sand-bentonite buffer

Dense sand-bentonite buffer (gamma(d) = 1.67 Mg/m(3)) has been proposed in Canada as one of several barriers for isolating nuclear fuel waste, The buffer will be required to function under conditions of high total pressures and elevated temperatures approaching 100 degrees C. Summary results are presented from two test programs: (1) isothermal consolidated undrained triaxial(CI(U) over bar) tests; and (2) isothermal drained constant-p' (CID) triaxial tests. Specimens were consolidated at effective stresses up to 9.0-MPa and temperatures up to 100 degrees C. The results indicate parallel hardening lines at systematically lower values of specific volume at elevated temperatures. In shear, increased temperatures produced lower values of maximum deviator stress q(f), and higher pore water pressure changes Delta u(f). The net result is curved peak strength envelopes in plots of qi versus p(f)' that are higher at elevated temperatures, even though the strengths, q(f) of individual specimens are lower. The critical state strength envelope is curved in q, p'-planes. The effect of drained heating on buffer to 100 degrees C. is not marked. Compressibilities, stiffnesses, strengths, and pore water pressure generation are all affected, but none of the changes are great.