1,721,069 research outputs found
Micromechanical investigation of the visco-plastic behaviour of granular materials
No full textStarting from the original formulation of the Granta-Gravel and Cam-Clay constitutive models, the framework of elasto-plasticity has been successfully applied to describe the geomaterials behaviour. Thanks to the modifications proposed by different authors, several aspects of the granular materials behaviour were progressively taken into account, such as the non associated flow rule and the effects of induced anisotropy. Recently, a series of triaxial laboratory tests performed by di Prisco and Imposimato (1996) has put in evidence an aspect which is disregarded in elasto-plasticity: the time dependency of the mechanical behaviour of loose sand specimens. The same authors proposed to interpret the observed behaviour within the framework of visco-plasticity.
In this paper, the non reversible behaviour of an idealised granular material composed of a 2D stack of disks is analysed by performing a series of Distinct Element numerical simulations (PFC-2D code). Starting from different stress levels (from isotropic to close to failure) previously recorded during a biaxial compression simulation, a series of finite stress probes is applied to the numerical specimen. All the probes have the same (small) magnitude, but they differ in direction in the principal stress plane. For each probe, the stress increments are applied to the boundary plates in an unique finite step, and the corresponding strain increments are recorded during the following time period. The obtained results show that the transient state is reached passing through two phases: a first one, where mainly elastic strains take place as the stress increment propagates within the specimen followed by a second one where the measured strains (non reversible) increase under constant stress; The duration of both phases considerably increases as the initial stress state approaches to failure. These results, which confirm the adequacy of a visco-plastic flow rule, are put in relation to the specimen structure progressive rearrangement caused by the applied stress-increment
Experimental and numerical analysis of a 2-D granular material
No full textPietruszczak and Pande eds., Balkema, Rotterdam
Rockfall shelters covered by granular layers. Experiments and design approach
No full textThis paper describes an uncoupled approach for the design of rockfall protection tunnels. More precisely, this approach concerns tunnels covered by soil layers, and it derives from the interpretation of real scale tests. Within this approach tools are provided for evaluating the impact force acting at the boulder-soil interface and for describing the propagation of stresses through the soil stratum. The experimental basis and the modelling tools are described in dedicated sections. Engineering considerations about the dynamic excitation of the sheltering tunnel are also suggested on the basis of the behaviour observed during experiments. Finally, a section is devoted to an application of the method
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