Question

In an unconfined compression test, is the shear stregth (undrained) found also representative of the shear strength (undrained) at different confining pressures?

Answer 1

Before answering your question i just want to clear you the difference between unconfined compression test and triaxial test undrained (with various confining pressures)

unconfined compression test	confining test (triaxial test)
no confining pressure(all round stress) is applied .	confining pressure is applied with either water or sand.
sigma 3 (minor principle stress=0)	minor principle stress exists

comming to your question

shear strength in ucs is not representative of shear strength in confining tests.

reason : confinement in triaxial test ,condition of loading makes the difference with the values in both the tests.