Name¡§Yuta Sato
Thesis title¡§Development of triaxial tests on soils under undraind condition for pore-air phase using an active control
Supervisor: Hirofumi Toyota
Bishop tried to carry out the triaxial test of unsaturated soils under undraind condition for pore-air phase using mercury in the 1960's. Recently, this kind of test has not been done at all because of safety limitation of the handling of mercury although recent results with accurate measurements are expected to appear.
It is impossible to achieve the undraind condition for pore-air phase physically except for the use of mercury. Since there is the permeability of the air in membrane, the undraind condition for pore-air phase cannot be achieved strictly. Then, the method of the undraind condition for pore-air phase has not been standardised.
The method of the undraind condition for pore-air phase using an active control is discussed whether to perform the accurate undraind condition for pore-air phase without the use of mercury. Here, the active control means that volume of pore-air is measured by double cell system and air pressure, which is calculated from the volume change using the equation of state of ideal gas, is applied to the specimen.
The monotonic and cyclic triaxial tests were conducted to estimate the performance of the active control. The conclusions from the test results are shown as follows:
1. The shearing tests in a short time becomes close to the undrained condition for pore-air phase because the amount of the leakage of the pore-air is small.
2. Pore-air pressure decreases during a long time shearing because the pore-air diffuses into inner cell water through the membrane.
3. The test results using the active control is not related to the shearing rate, and becomes equivalent to the result in high strain rate shearing without the active control.
4. Pore-air pressure decreases because of the leakage of the pore-air. This derives the increase of the net mean stress, strength and volumetric strain in the specimens.
5. Chang of matric suction is small, although pore-air and pore-water pressure change during the active control. This is the reason that pore-water pressure changes dependently with the influence of the pore-air pressure.
6. When a ceramic disk of a high AEV value is used, the shearing should be conducted under low strain rate because of the delay of pore-water pressure transmission.
Thus, it is clear that the undrained condition for pore-air phase using the active control is effective method because it creates the equivalent condition with real undrained condition for pore-air phase.
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