Effect of Principal Stress Direction on Undrained Cyclic Shear Behaviour of Dense Sand

摘要

The stress conditions for soil elements subjected to cyclic loading such as those beneath the foundations of breakwater and offshore structures are very complex. Based on this fact, the authors have performed an elastic stress analysis for the wave-induced stress distribution and stress states in the seabed underneath a breakwater. The results of the analysis indicate that the angle of principal stress direction of the stress path during wave actions is different depending on the location of the ground beneath the breakwater. Following above results, a series of undrained torsional shear tests were carried out to investigate the effect of the principal stress direction on strength and deformation (Sato et al., 1996, 1997). Results of experiment show that (1) each effective stress path is influenced by the principal stress direction a at the initial time of cyclic loading. This behaviour is especially observed in the stress paths from the initial effective mean principal stress to the phase transformation line, and (2) development of the excess pore water pressure and shear strain with increasing number of load cycles is remarkable for principal stress direction a between 45°and 60°. In the present paper, in order to further examine the above situation, a family of undrained cyclic torsional shear tests has been carried out to investigate the effect of initial fabric anisotropy on liquefaction characteristics.