INFLUENCE OF PRESSURE, SATURATION, AND TEMPERATURE ON THE BEHAVIOR OFUNSATURATED SAND-BENTONITE

Triaxial compression tests were performed on unsaturated sand-bentonit e buffer at elevated temperatures and pressures. Air and water drainag e lines from the specimen were generally kept closed through (i) heati ng, (ii) pressuring, and (iii) shearing. The tests can therefore be ch aracterized as undrained-undrained-undrained tests. Effects of open dr ainage were also explored. Confining pressures ranged from 0.2 to 3.0 MPa at temperatures of 26, 65, and 100 degrees C. Specimens were stati cally compacted to a constant dry density of 1.67 Mg/m(3), and to degr ees of saturation between 35 and 98%. Suction water content relationsh ips were established to determine the initial total suction before tes ting. Results indicate that undrained strengths increase with decreasi ng degree of saturation (50 less than or equal to S-r less than or equ al to 100%), with increasing confining pressure, and with decreasing t emperature. The normalized compression modulus E-50/s(u) does not resp ond monotonically to changes in saturation, pressure, and temperature. Changes in strength and stiffness have been described in relation to net mean stress and suction in shear strength - net mean stress - suct ion space.