Viscous behaviour of dry sand

Abstract

SUMMARYTests on air-dried Hostun sand were performed on a newly developed triaxial apparatus, which allows static and dynamic measurements at 'Département Génie Civil et Bâtiment' (DGCB) of ENTPE. The prototype was designed to perform tests in order to investigate the viscous effects of sand from small strain (some 10 −5 m/m) up to intermediate strain (some 10 −3 m/m). The accuracy of the measuring system is ensured by the use of local non-contact displacements transducers and by the use of an internal load cell. The viscous behaviour of sand is experimentally studied for loose and dense specimens for confining pressure values from 80 up to 400 kPa and considering different histories of loading. Three types of viscous loading: creep periods; stress relaxation periods; and paths with stepwise changes in the strain rate are specifically analysed. The proposed viscous modelling is issued from a three-component general framework and is able to reproduce the experimental observations. More specifically, the peculiar behaviour of sand observed during a stepwise increase or decrease in the strain rate is detailed and modelled by the viscous evanescent (VE) model, developed at DGCB/ENTPE. Based on the three types of viscous tests, a simple relation is finally proposed for the viscous parameters of the VE model. Comparisons between data and simulations validate the approach.

Elasto-plastic model for sand including time effect

“…Time effects on granular soils -time dependent strains under constant stress (creep), time dependent reduction of stresses under constant strain (relaxation) and rate dependency -have been observed in laboratory tests by Lacerda and Houston (1973), Murayama et al (1984), Delage et al (1990), Lade (1994), Tatsuoka et al (1997), Di Benedetto and Tatsuoka (1997), (2002), Cazacliu and Di Benedetto (1997), Matsushita et al (1999), Di Benedetto et al (1999), (2005), Howie et al (2002), Kuwano and Jardine (2002), Bowman and Soga (2003), Van Bang et al (2007) but also on some field applications reported by Mitchell & Solymar (1984), Mesri et al (1990), Schmertmann (1991), Jardine et al (2006). The soil response is affected by the extent of time over which the effective stress (or strain) has been sustained.…”

Predictive potential of Perzyna viscoplastic modelling for granular geomaterials

“…With the same set of elasto‐plastic parameters (Tables and ), the viscous parameters of Hostun loose and dense sand have been separately identified through the drained creep test results from di Prisco and Imposimato and Pham Van Bang et al…”

“…The viscous parameters for Hostun dense sand ( D r = 71%) have been then derived based on the experimental results from Pham Van Bang et al and reported in Table . It should be noted that the same value of α (ie, same shape of Φ) has been used for both loose and dense Hostun sand (see Tables and ) to reduce the number of free parameters.…”

“…TXD on air‐dried loose Hostun sand ( e 0 = 0.95) performed, respectively, at a strain rate of = 0.06%/min, test 400.95 1i and = 0.6%/min, test 400.95 10i (data from Pham Van Bang ).…”

“…The microstructural rearrangements that cause macroscopic deformations take place over time frames sometimes in the order of minutes—such as in the case of loose sands . Laboratory investigations regarding strain rate effects, creep, and relaxation in sand have been presented in previous studies . In light of those experimental observations, the mathematical modelling of granular soil behaviour may be successfully tackled in the framework of delayed plasticity theories—also referred to as viscoplasticity—or through a viscous evanescent relationship.…”