The factors affecting the onset of unstable behaviour in saturated loose sand loaded under drained stress-controlled conditions are not as well known as those involved in its undrained behaviour, which has been analysed in detail.
This paper is intended as a first step towards a better understanding of the onset of instability in drained stress-controlled tests and reports on the analysis of certain factors affecting the unstable behaviour of saturated loose sand samples subjected to drained stress-controlled triaxial compression tests. The samples are loaded continuously at a constant loading rate and the results are compared with those obtained by other authors who discontinuously applied a load using finite increments.
A special experimental apparatus was designed so that the axial load could be applied in various proportions by a dead weight and by a pneumatic cylinder in a triaxial cell with no friction on the loading ram.
The paper focuses first on the influence of the load application method (i.e. by dead weights and by a pneumatic cylinder), which proves important, since the sample always collapses at a more or less constantly low mobilized friction angle when loaded with dead loads, whereas it may have unstable strain jumps starting from a high value of the mobilised friction angle, but may even be stable up to the steady state of deformation, when the axial load is applied by a pneumatic cylinder.