1,721,195 research outputs found
A rheological model for the description of boulder impacts on granular strata
No full textThis paper considers the mechanics of rock boulders
impacting on granular strata. The study is aimed at
improving the numerical methods devoted both to describing
boulder trajectories along slopes and designing
preventive structures in mountain regions. The problem
is analysed by using a simplified approach inspired by
the lumped mass method. This is based on (a) the macroelement
concept, (b) the definition of generalised stresses
and displacements, and (c) delayed plasticity theory. Both
vertical and inclined impacts on horizontal strata and
vertical impacts on inclined slopes are discussed. The
numerical results are obtained by using a finite difference
numerical discretisation to integrate, over time, a coupled
system of two-dimensional differential equations. Most of
the input data requested by the model are basic and
geotechnically meaningful, and comparison of the numerical
results with the experimental data seems to be quite
promising
Progettazione, esecuzione e controllo di rilevati leggeri realizzati in argilla espansa
No full textIl ricorso all’impiego delle argille espanse, spesso abbinato alla tecnica della compensazione dei carichi, è oramai una
pratica comune nella realizzazione di rilevati stradali e/o ferroviari in presenza di strati di terreno cedevole di elevato spessore.
Le argille espanse, grazie ad un peso per unità di volume sensibilmente inferiore a quello dei comuni inerti di cava,
consentono di ridurre i cedimenti associati alla realizzazione dell’opera, incrementare la durabilità della stessa e ridurre i
costi di manutenzione da parte dell’ente gestore. In questa nota, è fornita una panoramica delle principali problematiche
geotecniche attinenti la progettazione di tali opere, con particolare attenzione alla risposta sismica delle stesse. Dopo una
breve introduzione riguardante le caratteristiche delle argille espanse alla micro-scala ed il loro comportamento alla mesoscala,
sono discussi in dettaglio alcuni aspetti di rilevanza pratica, quali le analisi di stabilità, la stima dei cedimenti attesi, le
tecniche di messa in opera e le metodologie di controllo dei manufatti. La nota evidenzia in particolare come l’utilizzo di tali
materiali permetta di ridurre sensibilmente anche i cedimenti permanenti associati a scosse sismiche di elevata intensità
Soil-pipe interaction under monotonic and cyclic loads: experimental and numerical modelling
No full textDiscrete numerical investigation of the ratcheting phenomenonin granular materials
No full textSeveral relevant geotechnical works, such as railway and road embankments, offshore foundations and vibrating machine foundations, are affected by the progressive accumulation of irreversible settlements. These latter represent the acroscopic evidence of the progressive rearrangement of particles under cycling loading, which is commonly referred to, in the literature, as ratcheting. This phenomenon is well known, but it is quite difficult to describe it by means of an appropriate constitutive model. As a consequence, the evaluation of durability of the aforementioned structures remains an open problem. In
this article, the phenomenon will be approached by employing a Distinct Element model capable of describing the evolution of the microstructure induced by cyclic mechanical perturbations. Several analyses are performed in order to stress the influence of both the stress level and loading history on the mechanical response of a numerical model of a sand specimen. The numerical analyses are intended to provide an experimental background for conceiving a simplified macro approach based on generalised plasticity theory. In particular by means of probe test the plastic potential and the hardening parameters will be defined
as a function of the current stress state and loading history
Mechanical behaviour of geo-encased sand columns: small scaleexperimental tests and numerical modelling
No full textThis paper presents experimental monotonic and cyclic test results on small scale sand columns reinforced by means of geosynthetics. The influence of the stiffness of the georeinforcement on the system mechanical response is discussed as well as that of the previous loading history. The experimental test results have also been numerically simulated by employing a 3D finite difference commercial code. A parametric study concerning the georeinforcement stiffness and the soil-column interface friction angle is presented. The results prove the influence of the encasing geosynthetic on the overall stiffness of the system, as well as of the stiffening effect induced by a possible preload applied on the column. The effect of shear stresses at column-soil interface is also observed to play a non negligible role, which is expected to become even more evident for real scale geo-encased columns. Numerical approaches based on standard constitutive models are able to capture the behaviour of the system under virgin load, but they totally fail in reproducing the unload-reloading response
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