Pierre-Yves Hicher

Experimental Data Highlighting the Role of Surface Fracture Energy in Quasi-Static Confined Comminution

Since the pioneering work of Griffith, Linear Elastic Fracture Mechanics has been widely experimentally validated and successfully developed in solid mechanics modeling. However, recent theoretical models applying the energy balance found in Griffith theory specifically for quasi-static confined comminution have until now not been systematically confronted to experiments. In this study, we analyze data of compression tests on crushable sand, where grain breakage has been triggered by flooding the initially dry material at constant stresses. We consider a partition of the dissipation between surface fracture energy and the rearrangement of fragments and grains surrounding crushed particles. Our results show that the role of the surface fracture energy is stressdependent and that its influence becomes less significant at high stresses.

Comportement mécanique des sols granulaires traités par injection

ABSTRACT This article describes the major themes treated in a research project led by SOLETANCHE, the RATP and the Ecole Centrale de Paris, to study the mechanical behaviour of granular soils, injected by various types of grouts. Such grouts are commonly used on building sites, in soil reinforcement as well as in watertightness treatment. First, this study investigates the mechanical behaviour improvement of a grouted soil at laboratory scale, as it can be approached through series of experiments in Soil Mechanics. The second part of the research presents an analysis of the mechanical behaviour improvement for an in situ grouted soil.

A probabilistic approach of confined comminution in polydisperse granular materials

We present a method to predict how grain size distribution (gsd) evolves during confined comminution. We describe particle breakage as a probabilistic phenomenon considering the single particle strength and the pdf of interparticle contact forces from DEM simulations. Our results show a good agreement with published experimental data.

Identifying soil parameters by inverse analysis of field testing

The identification of constitutive parameters by inverse analysis of limited experimental information is investigated. In order to ensure the quality of measurements, all the data come from a thick wall cylinder test performed on a saturated sand sample. A numerical FEM-simulation considering a linear elastic perfectly plastic model (Mohr-Coulomb) is carried out in order to determine the pressure – cavity deformation relationship. Two kinds of optimization algorithms, a deterministic and a stochastic one, are presented and implemented in the inverse procedure. The performance of theses algorithms taking for identifying three parameters (Young’s Modulus, friction angle and dilatancy angle) is compared. The two kinds of algorithms provide a quite similar response for the mathematical optimum, but some parameters sets did not have an acceptable physical meaning. Contrary to the deterministic algorithm, the genetic method provides an assembly of “satisfactory” individuals. Some of the parameters sets have acceptable physical meaning and the expert has to choose the best one considering his scientific and technical background.

Behavior of Granular Materials Affected by Grain Breakage

Abstract: In geotechnical and particularly in dam engineering, observations in the field and, in some cases, dramatic failures of structures have often incited research and increased knowledge. For instance, the first rockfill dams were elevated without any prior knowledge of the mechanical capacities of the rockfill mass. As natural and local resources are usually preferred for economic and environmental issues, their non-optimal properties can lead to potential severe damage to the hydraulic structure. Similarly, a basic principle of construction of rockfill dams or embankments consists in sluicing rockfill after deposition and before compaction: this recommendation has been adopted for a long time. However, the beneficial effects of such a practice have been understood only in light of recent studies on unsaturated soil and multi-scale analyses.

Clay Subjected to Cyclic Loading: Constitutive Model and Time Homogenization Technique

Numerical modeling of the behavior of geotechnical structures subjected to cyclic loading requires the consideration of two main aspects: the constitutive relationship and numerical strategy. The constitutive model has to be representative of the clay behavior, whereas the numerical strategy should be efficient in order to reduce the computation time. To simulate undrained triaxial cyclic tests on clay, a method of time homogenization is applied to a bounding surface plasticity model. This method of homogenization is based upon splitting time into two separate scales. The first scale relates to the period of cyclic loading and the second to the characteristic time of the material. Simulations of undrained triaxial cyclic tests on normally consolidated clay under one-way cyclic loading are carried out. The performance of time homogenization is numerically validated. The sensitivity of the time increment is also investigated.

Method to Evaluate the Shear Strength of Granular Material with Large Particles

Because of the lack of experimental devices for testing granular materials with large particles, the mechanical behavior of rockfill is not very well known. This lack of knowledge can lead to improper design of rockfill dams, and as a consequence, to severe accidents including dam failures. A method has been developed by Frossard (2005) for evaluating the shear strength of rockfill based on the estimation of size effect in granular materials, affected by grain breakage. Comparison between experimental results and numerical predictions shows that this method can estimate with good accuracy the strength of granular materials made of large particles.

Instability in Granular Materials with Internal Erosion

In this paper we study the influence of internal erosion on the development of instability in soil masses. A constitutive modeling method for granular materials based on particle level interactions has been developed using an homogenization technique. In the model, a simple elastic‐plastic behavior is assumed on each contact plane. A numerical analysis of the condition of instability expressed by the vanishing of the second‐order work is performed in the context of soil subjected to internal erosion. Special attention is given to constant deviatoric stress paths, which are representative of a change in hydraulic conditions within a soil element. Numerical results show that instability condition can be reached along such stress path when the soil undergoes internal erosion.