1. A tensiometer is used to measure a compacted soil in the field that has a matric suction of 200 kPa under atmospheric conditions. The pore-water pressure measurement in the tensiometer reaches -99 kPa and suddenly increases to zero. Briefly explain the problem encountered in this measurement.
2. A tensiomater is used to measure a soil specimen in the labaratory that has a constant matric suction of 30 kPa under atmospheric conditions. In the beginning the pore-water pressure measurement in the tensiometer reaches -30 kPa, but after a few days the meausrement drifts to a higher pore-water pressure. Briefly explain the problem encountered in this measurement.
3. A homogeneous coarse sand deposit has a water table at 10 m depth. The water coefficient of permeability of the sand is found to vary significantly with height above the water table even though the sand deposit is homogeneous. Briefly explain the reason for the variation of the water coefficient of permeability above the water table.
4. A soil is to be compacted on a site and it is expected that the soil contains a high percentage of montmorillonite.
(i) Briefly explain the working principles of two test that can be carried out to ascertain the presence of montmorillonite in the soil.
(ii) Should the soil be compacted at the dry of optimum or at the wet of optimum condition in order to minimize swelling potential? Briefly explain the reason for your answer.
5. Measurements of pore-water pressure in soils are affected by time lag, cavitation and air diffusion. Briefly explain the meaning of these processes and how they affect the pore-water pressure measurements.