Time effects in the compression of sands

Abstract

A simple extension of the compression model proposed by Prestana and Whittle (1995) is proposed to incorporate the time-dependent compression behaviour of sands. The formulation assumed that the elastic strain component is time-independent and therefore time effects are introduced through the plastic formulation only. Compression behaviour at high stresses is independent of initial formation density and is characterized by a unique, time-dependent locus referred to as the limiting compression curve (LCC), which is linear in a double logarithmic void ratio-effective stress space. The change in void ratio in the LCC regime is assumed to be described by a power law function of the elapsed time (with respect to a reference time) and results in parallel LCC loci in a log current void ratio - log mean effective stress space. The model describes two important features: (a) at low stress levels (transitional regime) the strain rate increases with both an increase in initial void ratio and an increase in effective stress, while in the LCC regime the strain rate converges for all formation densities and eventually decreases at large stress levels, and (b) the effective stress at the onset of significant strain rate is dependent on the initial formation density. The model, in its general form, uses five input parameters, but can be simplified in the transitional regime where the behaviour is primarily governed by the initial formation void ratio. (A)