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

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
It can be performed under all three drainage conditions with complete control

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Soil Mechanics and Foundation
With the increase in the amount of compaction energy

optimum water content decreases but maximum dry density increases
both optimum water content and maximum dry density decrease[ES 93]
both optimum water content and maximum dry density increase
optimum water content increases but maximum dry density decreases

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