Pierre Philippe

Analysis by x-ray microtomography of a granular packing undergoing compaction

Several acquisitions of x-ray microtomography have been performed on a beads packing while it compacts under vertical vibrations. An image analysis allows to study the evolution of the packing structure during its progressive densification. In particular, the volume distribution of the pores reveals a large tail, compatible to an exponential law, which slowly reduces as the system gets more compact. This is quite consistent, for large pores, with the free volume theory. These results are also in very good agreement with those obtained by a previous numerical model of granular compaction.

On the existence of stationary states during granular compaction

Abstract.When submitted to gentle mechanical taps a granular packing slowly compacts until it reaches a stationary state that depends on the tap characteristics. The properties of such stationary states are experimentally investigated. The influence of the initial state, taps properties and tapping protocol are studied. The compactivity of the packings is determinated. Our results strongly support the idea that the stationary states are genuine thermodynamic states.

Slow compaction of granular systems

The dynamics of granular compaction under vertical tapping is experimentally and numerically studied for isotropic and anisotropic grains. It is shown that if convection takes place in the medium, it has a strong influence on the compaction dynamics. The local behaviour of the grains during compaction and the consequences for the global properties of the medium are investigated.

Effects of Suffusion on the Soil’s Mechanical Behavior: Experimental Investigations

This study presents an experimental approach to investigate the impact of suffusion on the soil’s mechanical properties. A newly developed suffusion permeameter is used allowing separate erosion and mechanical tests. The effect of the initial density of the soil on the erosion process is examined. Thereafter, the influence of suffusion on the mechanical properties of the soil is investigated through drained and undrained monotonic triaxial compression tests. The results suggest that the shear strength of eroded soils may either decrease or increase or even may not be affected depending, among others, on the soil’s initial density. In addition, in all cases, slightly more dilative volumetric deformations seem to occur during shearing after erosion. Understanding the mechanical behavior of eroded soils depends on the combined effect of the global void ratio, the inter-granular void ratio and the final fines content after suffusion. Taking into account such a combined effect, an approach to estimate the shear strength of eroded soils is proposed.