Soil Mechanics and Foundation
If the water table rises upto ground surface, then the

effective stress is reduced due to increase in pore water pressure only but total stress does not change
total stress is reduced due to increase in pore water pressure only but effective stress does not change
effective stress is reduced due to decrease in total stress only but pore water pressure does not change
total stress is increased due to decrease in pore water pressure but effective stress does not change

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Soil Mechanics and Foundation
A tri-axial shear test is preferred to direct shear test, because

It can be performed under all three drainage conditions with complete control
Stress distribution on the failure plane, is non uniform
Precise measurement of pore pressure and change in volume during test, is not possible
None of these

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