Sampling Disturbance in Champlain Clays

A comparison of the results of laboratory tests on block and tube samples shows that the “cemented” sensitive clays are disturbed severely by conventional thin-wall tube sampling. The undrained shear strength is reduced to 50 to 60 percent of its original value, and the recompression index at pressures smaller than the preconsolidation pressure is doubled. Even the effective stress parameters at low stress level are greatly affected by sampling. This effect is attributed to the presence at the contact between the clay particles of “cementation bonds” which have a high sensitivity to strain.