Both quick cyclic and slow cyclic shear tests are performed on saturated sand to investigate the process of liquefaction under the condition of constant mean principal stress. Special tests with varying amplitude of cyclic shear stress are also performed to estimate the change in excess pore water pressure during irregular cyclic loading. The pore water pressure increment during each loading cycle may be expressed as a function of the shear stress and the normal stress on the shear plane. This relation is likely to be applicable to the case of irregular cyclic loading which simulates the actual timehistory of shear stress during an earthquake. The number of stress cycles required to cause the initial liquefaction may also be expressed in terms of the ratio of cyclic shear stress to normal stress. In so far as the sand and glass beads used here are concerned, the pore water pressure tends to increase during unloading and vice versa at the time when initial liquefaction occurs, and the angle of internal friction mobilized at that time has a close relation with the true angle of friction of granular materials.
