A series of undrained cyclic loading tests of three types of saturated and unsaturated soils were conducted on a triaxial apparatus. To overcome the difficulties of this type of test, cell pressure control system to maintain constant p, membrane filter technique to measure pore water pressure and double cell system to measure volumetric strain (εv) were introduced to the apparatus. Test results shown that the cell pressure control system reduced more than 60% variation of p which would be induced by applying vertical cyclic loading. The membrane filter technique could measure negative pore water pressure in a prompt manner and as a result suction of the unsaturated specimens was well monitored under the 0.1 Hz cyclic loading. The time delay problem of electric transducer employed in the εv measurement system, which may bring significant system error, was recognized and the measurement error of εv was discussed. Regarding the resistance against liquefaction of the unsaturated soils, the test results shown increase in resistance with reduction in degree of saturation and the p-constant condition was necessary to correctly evaluate the resistance for the unsaturated soils.
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