Bien que son utilisation requière plus de paramètres que les méthodes traditionnelles la méthode des éléments finis est de plus en plus utilisée pour la conception, des ouvrages géotechniques. Son utilisation nécessite notamment la définition du champ initial des contraintes qui reste très difficile à estimer et mesurer.Ce travail de thèse est une contribution à une meilleure connaissance de l'état initial des contraintes dans une pente. La thèse comporte des études numériques et expérimentales.Les études numériques évaluent, dans un premier temps, la variation des résultats des calculs par la méthode des éléments finis induite par l'incertitude sur l'état initial des contraintes. Dans un deuxième temps, la distribution des contraintes suite à la modélisation d'une pente au moyen du logiciel CESAR-LCPC est étudiée. L'influence des paramètres géologiques, géométriques et mécaniques sur le champ initial des contraintes est étudiée.L'objectif de l'étude expérimentale est de mesurer, avec des capteurs de pression totale fonçables, les contraintes horizontales dans une pente. La campagne expérimentale opte pour un suivi de la relaxation des contraintes horizontales jusqu'à la stabilisation des mesures. Des essais en laboratoire, réalisés au CEREMA à Aix en Provence, incluent des essais œdométriques à mesure de K0 qui donnent des valeurs du coefficient de pression des terres au repos mesuré en laboratoire. Les difficultés liées à la mesure du coefficient de pression des terres au repos et les paramètres qui peuvent l'influencer (nature des terrains, variations de teneur en eau, etc.) sont discutés / Though the finite element method requires more input data than traditional methods, it is increasingly used for the design of geotechnical structures. Its use needs to define initial stresses, which are difficult to estimate or to measure.This thesis is a contribution to a better understanding of the initial stresses in a slope. It consists of both numerical and experimental studies.The numerical studies focus on two issues. At first, they assess the effects of initial stresses on the results of calculations using finite element methods. Secondly, the distribution of stresses in a slope is analysed, using CESAR-LCPC finite elements software. The influence of geological, geometric and mechanical parameters on the state of stresses is studied.The objective of the experimental studies is to measure the lateral stresses in a slope using push-in total stress cells. The stresses are measured continuously in order to estimate the stresses in the ground after the dissipation of the effects of installation procedure. Laboratory tests made at CEREMA in Aix-en-Provence include “K0 oedometer tests” which provide measures of the coefficient of earth pressure at rest. The difficulties associated with the measurement of the coefficient of earth pressure at rest and the parameters that can influence it (type of soil, geometry of soil mass, water content ...) are discussed

Bien que son utilisation requière plus de paramètres que les méthodes traditionnelles la méthode des éléments finis est de plus en plus utilisée pour la conception, des ouvrages géotechniques. Son utilisation nécessite notamment la définition du champ initial des contraintes qui reste très difficile à estimer et mesurer.Ce travail de thèse est une contribution à une meilleure connaissance de l'état initial des contraintes dans une pente. La thèse comporte des études numériques et expérimentales.Les études numériques évaluent, dans un premier temps, la variation des résultats des calculs par la méthode des éléments finis induite par l'incertitude sur l'état initial des contraintes. Dans un deuxième temps, la distribution des contraintes suite à la modélisation d'une pente au moyen du logiciel CESAR-LCPC est étudiée. L'influence des paramètres géologiques, géométriques et mécaniques sur le champ initial des contraintes est étudiée.L'objectif de l'étude expérimentale est de mesurer, avec des capteurs de pression totale fonçables, les contraintes horizontales dans une pente. La campagne expérimentale opte pour un suivi de la relaxation des contraintes horizontales jusqu'à la stabilisation des mesures. Des essais en laboratoire, réalisés au CEREMA à Aix en Provence, incluent des essais œdométriques à mesure de K0 qui donnent des valeurs du coefficient de pression des terres au repos mesuré en laboratoire. Les difficultés liées à la mesure du coefficient de pression des terres au repos et les paramètres qui peuvent l'influencer (nature des terrains, variations de teneur en eau, etc.) sont discutés / Though the finite element method requires more input data than traditional methods, it is increasingly used for the design of geotechnical structures. Its use needs to define initial stresses, which are difficult to estimate or to measure.This thesis is a contribution to a better understanding of the initial stresses in a slope. It consists of both numerical and experimental studies.The numerical studies focus on two issues. At first, they assess the effects of initial stresses on the results of calculations using finite element methods. Secondly, the distribution of stresses in a slope is analysed, using CESAR-LCPC finite elements software. The influence of geological, geometric and mechanical parameters on the state of stresses is studied.The objective of the experimental studies is to measure the lateral stresses in a slope using push-in total stress cells. The stresses are measured continuously in order to estimate the stresses in the ground after the dissipation of the effects of installation procedure. Laboratory tests made at CEREMA in Aix-en-Provence include “K0 oedometer tests” which provide measures of the coefficient of earth pressure at rest. The difficulties associated with the measurement of the coefficient of earth pressure at rest and the parameters that can influence it (type of soil, geometry of soil mass, water content ...) are discussed

The magnitudes and relative pressure distributions transmitted to the crosstie-ballast interface of railroad track significantly influences the subsequent behavior and performance of the overall track structure. If the track structure is not properly designed to distribute the heavy-axle loads of freight cars and locomotives, deficiencies and inherent failures of the crossties, ballast, or underlying support layers can occur, requiring substantial and frequent maintenance activities to achieve requisite track geometrical standards. Incorporating an understanding of the pressure distribution at the crosstie-ballast interface, appropriate designs can be applied to adequately provide a high performing and long-lasting railroad track. Although this can be considered a simple concept, the magnitudes and distributions of pressures at the crosstie-ballast interface have historically proven to be difficult to quantifiably measure and assess over the years. This document describes the development and application of a method to measure average railroad track crosstie-ballast interfacial pressures using timber crossties and pressure cells specifically designed for granular materials. A procedure was specifically developed for recessing the cells in the bottoms of timber crossties. The validity of the test method was initially verified with a series of laboratory tests. These tests used controlled loads applied to sections of trackbed constructed in specifically designed resilient frames. The prototype trackbed section was intended to simulate typical in-track loading conditions and ballast response. Cells were subsequently installed at a test site on an NS Railway well-maintained mainline just east of Knoxville, TN. Six successive crossties were fitted with pressure cells at the ballast interface below the rail seat. Pressure cells were also installed at the center of two crossties where the ballast is typically not tamped or consolidated. Trackbed pressures at the crosstie-ballast interface were periodically measured for numerous revenue freight trains during a period of twenty-one months. After raising and surfacing the track, the ballast was permitted to further consolidate under normal train traffic before again measuring pressures. Having the ballast tightly and uniformly compacted under crossties is important to ensuring representative and reproducible pressure measurements. Measured maximum pressures under the rail at the crosstie-ballast interface ranged from 20 to 30 psi (140 to 210 kPa) for locomotives and loaded freight cars with smooth wheels producing negligible wheel/rail impacts. Crosstie-ballast interface pressures were typically 3 psi (20 kPa) maximum for empty freight cars with smooth wheels. Heavily loaded articulated intermodal car pressures for shared trucks tended to reach nearly 40 psi (280 kPa), actually higher than locomotive-produced pressures. The recorded pressures under the center of the ties were normally negligible, less than 1 psi (7 kPa) for locomotives and loaded freight cars. Wheel-Rail force parameters measured by nearby wheel-impact load detectors (WILD) were compared to crosstie-ballast pressure data for the same trains traversing the test site. Increases in peak WILD forces, either due to heavier wheel loads or increased impacts, were determined to relate favorably to increases in recorded trackbed pressures with a power relationship. The ratios between the peak and nominal wheel forces and trackbed pressures also have strong relationships.

Recent developments in constructions have heightened the need for protecting existing buried infrastructure. New roads and buildings may be constructed over already existing buried infrastructures e.g. buried utility pipes, leading to excessive loads threatening their stability and longevity. Additionally applied loads over water mains led to catastrophic damage, which result in severe damage to the infrastructure surrounding these mains. Therefore, providing protection to these existing buried infrastructure against increased loads due to new constructions is important and necessary. In this research, a solution was proposed and assessed, where the protection concept would be achieved through the inclusion process of geogrid-reinforcing layers in the soil cover above the buried infrastructure. The controlling parameters for the inclusion of geogrid-reinforcing layers was assessed experimentally and numerically. Twenty-three laboratory tests were conducted on buried flexible and rigid pipes under unreinforced and geogrid-reinforced sand beds. All the investigated systems were subjected to incrementally increasing cyclic loading, where the contribution of varying the burial depth of the pipe and the number of the geogrid-reinforcing layers on the overall behaviour of the systems was investigated. To further investigate the contribution of the controlling parameters in the pipe-soil systems performance, thirty-five numerical models were performed using Abaqus software. The contribution of increasing the amplitude of the applied cyclic loading, the number of the geogrid-reinforcing layers, the burial depth of the pipe and the unit-weight of the backfill soil was investigated numerically. The inclusion of the geogrid-reinforcing layers in the investigated pipe-soil systems had a significant influence on decreasing the transferred pressure to the crown of the pipe, generated strains along its crown, invert and spring-line, and its deformation, where reinforcing-layers sustained tensile strains. Concerning rigid pipes, the inclusion of the reinforcing-layers controlled the rebound that occurred in their invert deformation. With respect to the numerical investigation, increasing the number of the reinforcing-layers, the burial depth of the pipe and the unit-weight of the backfill soil had positive effect in decreasing the generated deformations, stresses and strains in the system, until reaching an optimum value for each parameter. Increasing the amplitude of the applied loading profile resulted in remarkable increase in the deformations, stresses and strains generated in the system. Moreover, the location of the maximum tensile strain generated in the soil was varied, as well as the reinforcing-layer, which suffered the maximum tensile strain. / Government of Egypt