Influence of pressure, saturation, and temperature on the behaviour of unsaturated sand-bentonite

Triaxial compression tests were performed on unsaturated sand-bentonite buffer at elevated temperatures and pressures. Air and water drainage lines from the specimen were generally kept closed through (i) heating, (ii) pressuring, and (iii) shearing. The tests can therefore be characterized as undrained-undrained-undrained tests. Effects of open drainage were also explored. Confining pressures ranged from 0.2 to 3.0 MPa at temperatures of 26, 65, and 100 degrees C. Specimens were statically compacted to a constant dry density of 1.67 Mg/m(3), and to degrees of saturation between 35 and 98%. Suction water content relationships were established to determine the initial total suction before testing. Results indicate that undrained strengths increase with decreasing degree of saturation (50 less than or equal to S-r less than or equal to 100%), with increasing confining pressure, and with decreasing temperature. The normalized compression modulus E-50/s(u) does not respond 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 - suction space.