The phenomenon and cause of non-uniform distribution of pore water pressure in the torsional and triaxial shear tests are theoretically discussed in detail at first. According to the laboratorial studying and theoretical inferring

we then concluded that the critical axial strain in the triaxial shear tests is 0.15% and the critical shear strain in the torsional shear tests is 5.2% if the silt samples are subjected to a cyclic loading with the period of 8 second. Therefore

in the triaxial shear tests

we had better measure the pore water pressure at the center of silt samples

or rectify the pore water pressure measured at the basement. But in the torsional shear tests

it is feasible to measure the pore water pressure directly at the basement of the samples.