1D Dynamic Non-Linear Numerical Analysis of Earth Slopes: The Role of Soil Ductility and Time-Sensitiveness

The mechanical response of dry granular slopes subjected to dynamic perturbations is tackled from a theoretical/numerical viewpoint. A 1D geometrical/numerical scheme is adopted to analyze infinitely long strata: the dynamic activation of shallow translational failure mechanisms (as well as the displacement performance far from collapse) is analyzed by means of a self-made FEM code. The soil mechanical behavior is described by means of a simplified viscoplastic one-dimensional constitutive model, capable of reproducing both ductile (hardening) and brittle (softening) mechanical responses. The dependence of numerical results on the soil “time-sensitiveness”, as well as the differences between viscoplasticity and standard rate-independent plasticity, is discussed. For the case of impulse-like loads (Ricker wavelets), the influence of the ratio between the dominant wavelength and the stratum thickness on the overall deformation mechanism is commented. The response of the slope to a real accelerometric record is finally illustrated

1D Dynamic Non-Linear Numerical Analysis of Earth Slopes: The Role of Soil Ductility and Time-Sensitiveness

The mechanical response of dry granular slopes subjected to dynamic perturbations is tackled from a theoretical/numerical viewpoint. A 1D geometrical/numerical scheme is adopted to analyze infinitely long strata: the dynamic activation of shallow translational failure mechanisms (as well as the displacement performance far from collapse) is analyzed by means of a self-made FEM code. The soil mechanical behavior is described by means of a simplified viscoplastic one-dimensional constitutive model, capable of reproducing both ductile (hardening) and brittle (softening) mechanical responses. The dependence of numerical results on the soil “time-sensitiveness”, as well as the differences between viscoplasticity and standard rate-independent plasticity, is discussed. For the case of impulse-like loads (Ricker wavelets), the influence of the ratio between the dominant wavelength and the stratum thickness on the overall deformation mechanism is commented. The response of the slope to a real accelerometric record is finally illustrated

Impact of dry granular masses on rigid barriers

This work concerns the impact of dry granular masses on rigid artificial obstacles. The authors approached the problem by performing an extensive campaign of numerical analyses with a commercial code based on the discrete element theory. The standard approaches employed to design sheltering structures are exclusively based on the assessment of the Maximum Impact Force (MIF) exerted by the soil mass on the obstacle, and the sheltering structure is usually designed according to simplified pseudo-static approaches. In a previous paper the authors considered the dependence of MIF on the Froude number and on a large series of both geometrical and mechanical parameters. Indeed, the impulsive nature of the force exerted by the soil onto the structure has to be considered in order to optimize the design of this type of structures. For this reason in this paper the evolution with time of the impact force and the mechanics of the phenomenon are investigated

ROCKFALL IMPACTS ON SHELTERING TUNNELS: REAL SCALE EXPERIMENTS

In this paper the results of a series of rockfall impact tests on a sheltering tunnel are discussed. A RC concrete sphere (mass 850 kg, diameter 0.9 m) was dropped (falling height ranging between 5 and 45 m) on a tunnel along a road in the Dolomites. This experimental campaign represents the extension of a previous one, performed at Politecnico di Milano (Campus Bovisa), when the same RC sphere was dropped on a circular pool filled with a loose sand stratum. Besides the mentioned differences, the new campaign is characterised by larger falling heights and the monitoring of the mechanical response of the shelter. A series of instruments have been employed to measure impact forces, stress propagation within the absorbing soil stratum on top of the shelter and its deflection. The results, which are in good agreement with available literature data, are presented with the aim of highlighting the features of the complex impact event and discussing the engineering factors to be considered for conceiving a realistic and reliable design approach. As to this point, the main conclusion is that the impact force is unaffected by the presence of the plate, and that the stress increment on the structure is slightly reduced by the structure deflection, which can be neglected for design purposes without unreasonable levels of conservatism being introduced

A multi-mechanism constitutive model for plastic adaption under cyclic loading

As is well known, granular soils under cyclic loading dissipate a large amount of energy and accumulate large irreversible strains. Usually, with time, this second effect reduces and the accumulation rate decreases with the number of cycles until obtaining a sort of ideal stationary cyclic state at which ratcheting disappears. In this paper, only this ideal state is taken into consideration and simulated by means of a multi-mechanism constitutive model for plastic adaptation. For this purpose, the concept of cycle is discussed, many different categories of cyclic stress/strain paths are considered and some theoretical issues concerning both the flow and the strain-hardening rules are tackled. Even though the paper focuses on soil behaviour, the conclusions can be extended to all materials exhibiting ratcheting due to volumetric behaviour. Copyrigh

DEFINIZIONE DEL DOMINIO DI INTERAZIONE DI MURI DI PLACCAGGIO MEDIANTE ANALISI NUMERICHE

La progettazione di opere strutturali per la messa in sicurezza di pendii potenzialmente instabili richiede un attento studio dell’interazione tra terreno e struttura, capace di tenere debitamente in conto i molteplici fattori che influenzano la risposta del sistema. Tali fattori (quali la complessità della geometria del pendio, l’incertezza circa la caratterizzazione meccanica dei materiali coinvolti, l’influenza del campo di spostamenti della massa di terreno instabile) non sempre rendono possibile l’impiego accurato dei metodi classici di progettazione, né l’utilizzo speditivo dei codici di calcolo attualmente disponibili in commercio. Tali limitazioni, particolarmente critiche durante le fasi di progettazione preliminare, possono essere in parte superate adottando metodi di progettazione basati sulla definizione di variabili generalizzate, e descrivendo l’interazione tra l’opera di sostegno e il terreno mediante molle concentrate gvernate da leggi costitutive non lineari. La corretta definizione del dominio di interazione per questi elementi risulta d fondamentale importanza per valutare la sicurezza del sistema sia in condizioni di esercizio, sia in condizioni ultime