Impact of Dry Granular Flows on a Rigid Wall: Discrete and Continuum Approach

Numerical 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

MPM simulations of the impact of fast landslides on retaining dams

Possible 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

Analysis of piezocone penetration under different drainage conditions with the two-phase Material Point Method

The piezocone penetration test (CPTU) is commonly used to identify the soil profile and to estimate material properties. Depending on the soil type, ranging from clay to sand, undrained, partially drained or drained conditions may occur during cone penetration. In silt and sand-clay mixtures the CPTU penetration is characterized by partially drained conditions, which are often neglected in data interpretation. The effect of drainage on CPTU measurements has been mainly studied experimentally. Numerical analyses are rare because taking into account large soil deformations, soil-water and soil-structure interactions, as well as non-linear soil behaviour is still a challenging task. This paper presents and discusses numerical simulations of CPTU in saturated soils with the two-phase Material Point Method. Soil behaviour is described with the Modified Cam Clay model. This study investigates the effects of pore pressure dissipation during penetration, cone roughness and horizontal stress state, comparing the results with experimental data. The paper discusses the effect of neglecting partial drainage in deriving the shear strength parameters for silty soils and suggests a procedure to estimate the consolidation coefficient performing CPTU at different penetration rates

Modelling soil-water interaction with the Material Point Method. Evaluation of single-point and double-point formulations

Many problems in geotechnical engineering involve large deformations and soil-water interactions, which pose challenging issues in computational geomechanics. In the last decade, the Material Point Method (MPM) has been successfully applied in a number of large-deformation geotechnical problems and multi-phase MPM formulations have been recently proposed. In particular, there exist two advanced coupled hy-dro-mechanical MPM approaches to model the interaction between solid grains and pore fluids: the single-point and the double-point formulation. The first discretizes the soil-water mixture with a single set of ma-terial points (MP) which moves according to the solid velocity field. The latter uses two sets of MP one for the fluid phase and the other for the solid phase and they move according to the respective velocity field. The aims of this work is to present and compare the two theories, to emphasize their limitations and poten-tialities, and to discuss their applicability in the geotechnical field. To this end, the results of two numerical examples carried out by using both formulations are presented: a 1D-consolidation problem and a saturated column collapse problem

Numerically based design of protection systems against landslides. Workshop Numeric in Geotechnology

fast flow-like landslides are the one of the most dangerous natural hazards. Rigid or flexible structures are often used to stop, deviate or slow down the flow. Because of the complexity of the landslide-barrier interaction, the design of these defence structures is still based on oversimplified and empirical approaches. Numerical methods able to cap-ture the essential features of the phenomenon can offer a valuable tool to gain a better understanding of the impact process and to support the design. This paper shows the potentialities of the MPM in this field. The run-up of the landslide and the dynamic forces on the structure are some of the fundamental parameters to define the properties of the barrier

Study of large deformation geomechanical problems with the Material Point Method

The 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

A constitutive active MAPK/ERK pathway due to BRAFV600E positively regulates AHR pathway in PTC

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor mediating the toxicity and tumor-promoting properties of dioxin. AHR has been reported to be overexpressed and constitutively active in a variety of solid tumors, but few data are currently available concerning its role in thyroid cancer. In this study we quantitatively explored a series of 51 paired-normal and papillary thyroid carcinoma (PTC) tissues for AHR-related genes. We identified an increased AHR expression/activity in PTC, independently from its nuclear dimerization partner and repressor but strictly related to a constitutive active MAPK/ERK pathway. The AHR up-regulation followed by an increased expression of AHR target genes was confirmed by a meta-analysis of published microarray data, suggesting a ligand-independent active AHR pathway in PTC. In-vitro studies using a PTC-derived cell line (BCPAP) and HEK293 cells showed that BRAF(V600E) may directly modulate AHR localization, induce AHR expression and activity in an exogenous ligand-independent manner. The AHR pathway might represent a potential novel therapeutic target for PTC in the clinical practice