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The dynamic interaction between granular flowing masses and rigid obstacles is a complex phenomenon characterised by both large displacements and high strain rates. In case the flowing mass is modelled as a continuum, its numerical simulation requires both advanced computational tools and constitutive relationships capable of predicting the mechanical behaviour of the same material under both fluid and solid regimes. In this paper, the authors employed the open‐source ANURA3D code, based on the Material Point Method (MPM), and a multi‐regime constitutive model. A series of impacts characterised by different velocities, initial void ratios, front inclinations and impacting mass lengths have been simulated. The MPM numerical results are critically compared with those obtained by using a Discrete Element Method (DEM) numerical code. The model capability of simulating material regime transitions, from fluid to solid and vice versa, is shown to be crucial for reproducing the mechanical response of the flowing mass put in evidence by DEM data. [ABSTRACT FROM AUTHOR]

Seismic-induced liquefaction is one of the main hazards for pipelines buried in saturated granular materials. When soil is partially or completely fluidized, a lifeline, although installed in superficial trenches in which the coarse backfill soil usually is compacted, may experience a sudden uplift and damages. To reduce pipeline uplift and thus limit the associated risks, the authors propose a sustainable and original mitigation strategy, suitable for both existing and new lifelines, based on both the use of a geomembrane and the compaction of the soil surrounding the pipeline. According to the design method proposed, the intervention geometry is selected on the basis of the pipeline maximum admissible displacement, whereas the minimum required relative density can be designed, based on the site-specific seismic demand, to avoid cyclically induced local accumulation in excess pore-water pressure. To prove the effectiveness of this strategy, a series of 1-g small-scale laboratory tests was performed on a pipe buried in a fluidized sand layer. A simplified displacement-based design approach, which was validated against the experimental data, is proposed. [ABSTRACT FROM AUTHOR]

When studying, by using continuum-based approaches, liquefaction phenomena, granular flows and granular material reconsolidation, crucial is the correct modelling of the change in material behaviour due to water presence and force chains collapse. To this aim, in this paper, the authors outline a model based on an in-parallel scheme. Three stress contributions are defined: the one associated with force chains applied to the solid skeleton (the effective stress), the one related to particle collisions (dominating for large values of void ratios and when the system is agitated) and the liquid one (not necessarily isotropic for large deviatoric strain rates). The model is conceived to reproduce the material mechanical behaviour of granular media under three different regimes: solid like, fluid like and inertial. The transition from one regime to another, in the model, is governed by the evolution of two state variables: void ratio and granular temperature (a measure of the material agitation). In this paper, the saturated version of the multi-regime model, already conceived for dry granular materials, is proposed. Its capability of reproducing the material fluidization in undrained constant volume rheometer tests is illustrated by discussing the numerical results obtained by using a Material Point Method code. [ABSTRACT FROM AUTHOR]

During heating (loading characterised by a progressive increase in strain rate) and cooling (loading characterised by a progressive decrease in strain rate) numerical tests, performed by using Discrete Element codes, granular materials experience phase transition phenomena, named in this paper 'dry liquefaction' (when from solid the material starts behaving like a fluid) and 'dry resolidification' (freezing, when the material from fluid starts behaving like a solid). The aim of this paper consists in reproducing phase transition phenomena by using a strain hardening visco‐elastic‐plastic model based on the critical state concept and kinetic theories of granular gases. The authors demonstrate that crucial is the role of isotropic softening/hardening, which describes the size of the elastic domain and the capability of the solid skeleton of storing elastic energy according to permanent force chains. The main ingredients of the model are: (i) the additivity of quasi‐static and collisional stresses, (ii) the energy balance equation governing the evolution of the granular temperature, interpreted this latter as an additional internal variable for the system for the collisional contribution, (iii) the mixed isotropic and kinematic hardening characterising the quasi‐static incremental constitutive relationship. The model has been both calibrated and validated on Discrete Element Method (DEM) numerical results, obtained by testing dry assemblies of monodisperse spheres under true triaxial loading conditions. [ABSTRACT FROM AUTHOR]

In this paper, the authors analyse numerical and experimental results concerning either dry or saturated granular flows under steady, simple shear conditions. A new constitutive model is introduced, on the base of the mixture theory, according to which granular and liquid phases are considered separately. The constitutive relationship refers to the representative elementary volume and assumes that the mean values of all kinematic variables, of both granular and liquid phases, coincide. For the two phases, a parallel scheme is chosen. As regards the granular contribution, the authors employ an already conceived constitutive model where the critical state concept and the kinetic theory of granular gases are merged, and in which the granular temperature plays the role of state variable for the material. Under saturated conditions, the new model accounts for granular–liquid coupling effects. In fact, the liquid viscosity is a function of granular concentration, whereas the evolution of granular temperature is influenced by the liquid molecular viscosity. The model is validated against numerical results and critically discussed. For sufficiently small values of concentration, the transition from a Newtonian to a Bagnoldian regime, for increasing values of strain rate, is correctly reproduced. [ABSTRACT FROM AUTHOR]

The current effort towards the progressive switch from carbon‐based to renewable energy production is leading to a relevant spreading of both on‐ and off‐shore wind turbine towers. Regarding reinforced concrete shallow foundations of onshore wind turbine steel towers, possible reductions of reinforcement may increase their sustainability, speed of erection, and competitiveness. The article presents the results of an experimental program carried out at Politecnico di Milano concerning both cyclic and monotonic loading, simulating extreme wind conditions on 1:15 scaled models of wind turbine steel towers connected by stud bolt adapters to reinforced concrete shallow foundations embedded in a sandy soil. Three couples of foundation specimens were tested with different reinforcement layouts: (a) similar to current praxis, (b) without shear reinforcement, and (c) without shear reinforcement and with 50% of ordinary steel rebars replaced by steel fibers. Additional vertical loads were added to the small‐scale models in order to ensure similarity in terms of stresses. The test results allowed to (i) characterize the mechanical behavior of the foundation element considering soil‐structure interaction under both service and ultimate load conditions, (ii) assess the foundation failure mode, (iii) highlight the role of each typology of reinforcing bars forming the cage, and (iv) provide hints for the optimization of these latter. [ABSTRACT FROM AUTHOR]