Experimental tests on shallow foundations of onshore wind turbine towers

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

LCA Towards Sustainable Agriculture: The Case Study of Cupuaçu Jam from Agroforestry

Appropriate design of agricultural systems for the regeneration of deforested lands in critical areas, like the Amazon, may be an effective action to restore forest ecosystem functions and to mitigate biodiversity loss and climate change. Among the possible strategies, agroforestry may represent a viable trade-off between economic and environmental aspects. In this study, the production of a jam made of fruits from agroforestry was analysed from a Life Cycle Assessment (LCA) perspective. The agroforestry system investigated was implemented in a reforested area of the Peruvian Amazon. A cradle-to-grave approach, from the cultivation phase to the end-of-life of the jam, was adopted. Additionally to LCA, the focus is on the agricultural phase and, in particular, on the comparison of alternative agro-ecosystems from an environmental viewpoint. Therefore, LCA indicators are integrated with biodiversity indicators to account for the ecological dimension. Preliminary results highlight the benefits of producing jam from fruits harvested in an area of the Amazon reforested via agroforestry, as well as the high variability of environmental impacts due to the differences in the alternative agricultural systems considered

Three-Dimensional Constitutive Model for Dry Granular Materials Under Different Flow Regimes

The numerical simulations of granular materials, in the framework of continuum mechanics, is quite challenging since the constitutive model should be capable of reproducing the transition from solid- to fluid like regimes and vice versa. In this paper a constitutive model, valid under general three dimensional evolving conditions, and capable of describing the material response under both quasi-static and dynamic regimes is presented. The model is calibrated by employing a series of true triaxial DEM numerical simulations performed on a periodic cell. The comparison between model predictions and DEM results highlights that the capability of the constitutive relationship of taking into account the dependence of the mechanical behaviour of the dry granular material on Lode angle, strain rate, void ratio and confining pressure

A New Constitutive Approach for Simulating Solid- to Fluid-like Phase Transition in Dry and Saturated Granular Media

The authors focus on constitutive modelling of solid to fluid phase transition in granular soils. A new constitutive approach conceived to capture such a transition in either dry or saturated granular material is validated against DEM numerical simulations for steady conditions and discussed in the framework of the μ-e-I rheology. The approach considers granular and liquid phases separately, assuming the two phases work in parallel, as it is according to the effective stress principle in case of quasi-static conditions. The authors emphasize the importance of considering separately the two phase contributions and the limitations of the μ-e-I rheology, in particular in relation to the volumetric response of the material

A New Strategy for Mitigating Pipeline Uplift in Liquefied Soils

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

Fondazioni superficiali di torri eoliche su terraferma: studio sperimentale e interpretazione teorica

Per la produzione di energia elettrica è comune utilizzare torri eoliche di notevole altezza. Nel caso di opere realizzate su terraferma le fondazioni sono in generale superficiali e sono progettate principalmente in fun-zione delle sollecitazioni da vento. Gli autori hanno eseguito una serie di prove sperimentali su modello con rapporto di scala 1:15 al fine di comprendere il comportamento meccanico del sistema terreno-struttura. In particolare, si è considerato il ca-so di una fondazione superficiale posta su di uno strato omogeneo di materiale granulare secco. Il sistema è stato caricato ciclicamente mediante l’applicazione di una forza orizzontale in sommità. Al termine dei cicli di carico, si è monotonamente incrementato lo spostamento sommitale sino al raggiungimento della condi-zione di rottura del sistema. I risultati sperimentali mettono in evidenza che nella progettazione di queste opere sia necessario considerare il comportamento irreversibile sia per il terreno che per la fondazione