1,721,046 research outputs found
Effect of wood degradation and soil creep on long-term behavior of historical wooden pile foundation in the historic city of Venice
Full text linkRun-up of granular avalanches on protective barriers: a numerical study with the Material Point Method
Full text linkNumerical study of partially drained penetration and pore pressure dissipation in piezocone test
No full textThe piezocone penetration test (CPTU) is commonly used as a fast and economical tool to identify soil profile and to estimate relevant material properties in soils ranging from fine to coarse-grained. Moreover, in the case of fine-grained soils (clays and silts) the consolidation coefficient and the permeability can be estimated through the dissipation test. Undrained conditions are commonly assumed for the interpretation of CPTU in fine-grained soils, but in soils such as silts, penetration may occur in partially drained conditions. This aspect is often neglected in data interpretation thus leading to an inaccurate estimate of soil properties. This paper investigates numerically the effect of partial drainage during penetration on the measured tip resistance and the subsequent pore pressure dissipation response contributing to a more accurate interpretation of field data. A realistic simulation of the cone penetration is achieved with the two-phase Material Point Method, modelling the soil response with the modified Cam Clay model. The approach takes into account large soil deformations induced by the advancing cone, soil-water and soil-structure interactions, as well as non-linear soil behaviour
Impact of Dry Granular Flows on a Rigid Wall: Discrete and Continuum Approach
Full text linkNumerical simulations of impacts of granular flows with structures are complex because they have to take into account large deformations, large strain rates and interactions with boundaries or structures. Moreover, the material response is governed by interactions between grains, which leads to a complex rheology. Discrete methods (DEM), which apply a micromechanical approach, appears very well suited to this purpose, but they can hardly deal with large-scale problems. In contrasts, continuum methods can handle large granular volumes because they use a macroscopic approach in which the material behaviour is described by a constitutive model. The aim of this paper it to compare the results obtained by a discrete and a continuum approach in simulating the impact of a dry granular flow on a rigid wall. The problem is simulated with a DEM code and with a software based on the Material Point Method
Granular Flow Impact Forces on Protection Structures: MPM Numerical Simulations with Different Constitutive Models
No full textAbstractFlows of granular materials are among the most destructive of all landslide phenomena. The assessment of the potential damage caused by the granular flow and the design of protection structures require the knowledge of the landslide-structure interaction. Numerical simulations of these phenomena are very complex because large displacements, soil-structure interaction and complex non-linear soil behavior have to be considered. A key issue in the simulation of these phenomena is the definition of a constitutive model able to describe the granular material response under a wide range of strain rates. This study examines and compares the results obtained by different constitutive models, namely the elastic perfectly plastic model with Mohr-Coulomb failure criterion, and the viscoplastic model with Drucker-Prager yielding condition. To this aim, we consider a finite volume of granular material instantaneously released from the top of an inclined channel; the material flows downslope and bumps a rigid wall on which the forces are measured
Study of landslide run-out and impact on protection structures with the Material Point Method
No full textReliable estimates of the impact forces induced by flow-like landslides on existing structures is
of great importance for hazard assessment. This is customarily obtained by means of
empirically based relationships but, significant differences may be encountered using the
existing approaches. Large scale experimental studies are expensive and difficult to set up; for
this reason a numerical technique able to simulate the material flow and its interaction with
structures would be helpful for the hazard assessment as well as for the design of mitigation
measures. This paper shows the applicability of the Material Point Method (MPM), a meshless
method specifically developed to describe large deformations of bodies, to the study of
granular flow propagation and impact forces on rigid structures. Complex shapes of the
structure as well as different soil-structure interface properties are considered. It is shown that
the MPM may represent a suitable tool to support the design of landslide mitigation measures
Study of large deformation geomechanical problems with the Material Point Method
Full text linkThe numerical simulation of real geomechanical problems often entails an high level of complexity; indeed they are often characterized by large deformations, soil-structure interaction and solid-fluid interaction.
Moreover, the constitutive behavior of soil is highly non-linear.
Landslides, dam failure, pile installation, and undrground excavation are typical examples of large deformation problems in which the interaction between solid a fluid phase as well as the contact between bodies are essential.
This thesis addresses the challenging issue of the numerical simulation of large deformation problems in geomechanics.
The standard lagrangian finite element methods are not well suited to treat extremely large deformations because of severe difficulties related with mesh distortions.
The need to overcome their drawbacks urged researchers to devote considerable effort to the development of more advanced computational techniques such as meshless methods and mesh based particle methods.
In this study, the Material Point Method (MPM), which is a mesh based particle method, is exploited to simulate large deformation problems in geomechanics.
The MPM simulates large displacements with Lagrangian material points (MP) moving through a fixed mesh.
The MP discretize the continuum body and carry all the information such as mass, velocity, acceleration, material properties, stress and strains, as well as external loads.
The mesh discretizes the domain where the body move through; it is used to solve the equations of motion, but it does not store any permanent information.
In undrained and drained conditions the presence of water can be simulated in a simplified way using the one-phase formulation.
However, in many cases the relative movement of the water respect to the soil skeleton must be taken into account, thus requiring the use of the two-phase formulation.
The contact between bodies is simulated with an algorithm specifically developed for the MPM at the beginning of the century.
This algorithm was originally formulated for the frictional contact. It extension to the adhesive contact is considered in this thesis, which is well suited to simulate soil-structure interaction in case of cohesive materials.
In this thesis typical geomechanical problems such as the collapse of a submerged slope and the simulation of cone penetration testing are considered.
Numerical results are successfully compared with experimental data thus confirming the capability of the MPM to simulate complex phenomena
MPM simulations of the impact of fast landslides on retaining dams
Full text linkPossible protection systems against flow-like landslides are earth dams built to stop or deviate the flow. The evaluation of impact forces on the structures is still based on oversimplified empirical approaches, which may lead to a very conservative design, with high costs and environmental impact. Numerical methods able to capture the essential features of the phenomenon can offer a valuable tool to support the design of protection measures. This paper shows the potentialities of the Material Point Method (MPM) in this field. A dry granular flow, modelled with the Mohr-Coulomb model is considered. The landslide is placed in front of the barrier with a prescribed velocity and the impact forces on the slanted face is monitored with time
Modellazione del collasso di un rilevato arginale con il metodo dei punti materiali per terreni parzialmente saturi
Full text linkNumerosi fenomeni di instabilità in pendii naturali o artificiali sono caratterizzati da grandi deformazioni. Le condizioni di saturazione dei terreni coinvolti giocano un ruolo fondamentale nelle fasi di innesco e propagazione. Entrambi questi aspetti sono inclusi in una recente formulazione del metodo dei punti materiali (MPM), detta 2Phase+suction, oggetto del presente contributo.
In questo contributo, viene brevemente presentata la formulazione e applicata all’instabilità di una scarpata arginale indotta da una combinazione di pioggia e piena prolungata, mettendo in luce le potenzialità dell’MPM in quanto permette di simulare il comportamento post-failure rispetto ai tradizionali metodi FEM e LEM
VALUTAZIONE DEGLI EFFETTI DI UNO SVASO RAPIDO SULLA STABILITÀ DEL PETTO ARGINALE CON IL METODO DEI PUNTI MATERIALI
Full text linkLe verifiche di sicurezza delle opere artificiali in terra e delle scarpate naturali si concretizzano nelle analisi di stabilità, di prassi condotte mediante metodi consolidati quali l’equilibrio limite e il metodo agli elementi
finiti.
Tuttavia, lo studio dell’evoluzione del collasso, caratterizzabile come un fenomeno di grande deformazione, non può essere compiutamente valutato mediante suddette tecniche.
A questo scopo è necessario adottare un metodo capace di modellare grandi spostamenti per una quantificazione effettiva dei volumi di terreno mobilitati e delle distanze percorse.
Il presente contributo mira ad esplorare le potenzialità del Metodo dei Punti Materiali per la valutazione di stabilità dei rilevati arginali.
In particolare viene adottata una formulazione multifase, la 2phase-Double Point (bifase a due punti), per analizzare e quantificare gli effetti di uno svaso rapido sulla stabilità del petto arginale; il confronto con il fattore di sicurezza FS risultante dalle analisi LEM e FEM permette di valutare il contributo effettivo del metodo ad una migliore quantificazione e comprensione del fenomeno
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