Unsaturated resilient behavior of a natural compacted sand

Granular materials are generally used in unbound layers of road pavement structures. The mechanical behavior of these materials is widely studied with repeated load triaxial tests (RLTT) in which the elastic response is defined as the resilient behavior. Usually observed under total stress conditions, the effect of pore pressure changes during loading are not usually included in design. Further, the unbound layers frequently exist under partially saturated conditions. The influence of the unsaturated state, i.e., the suction, on the mechanical behavior, of unbound granular materials for roads has not been sufficiently studied and is generally not taken into account in models used for these materials. This article presents an experimental study of the repeated load response of a compacted clayey natural sand, and describes a model for the response which includes the effects of soil suction. The response of the proposed model formulated in terms of effective stress is compared with a similar model formulated in terms of total stress. The results from both the effective stress model and the total stress model are compared with the measured volumetric and deviatoric response. It is suggested that since the model parameters for the effective stress formulation are relatively constant for all values of suction (water content), the resilient response can be best captured by an effective stress model

eRoads Group (from a pavement point of view)

International audienc

Modélisation de l'orniérage des chaussées à faible trafic

L'orniérage, dû aux déformations permanentes des matériaux non traités (assise en grave non traitée), est l'un des principaux modes de dégradations des chaussées souples. De nos jours, des lois d'élasticité linéaire sont utilisées pour le dimensionnement. Une méthode d'analyse limite pour la prédiction des déformations permanentes des graves non traitées soumises à un chargement cyclique a été développée et présentée dans le cadre de ce travail. Cette méthode, basée sur le concept de l'état limite (shakedown theory), est développée par Zarka (1979) pour les structures métalliques soumises à un chargement cyclique. L'état de contraintes initiales, la teneur en eau et l'anisotropie initiale des graves non traitées sont pris en compte dans la méthode proposée. Une procédure, basée sur les résultats d'essais triaxiaux à chargements répétés, a été développée pour la détermination des paramètres du modèle proposé. Les résultats de modélisation éléments finis, du comportement à long terme d'une structure de chaussée, obtenus avec le modèle sont présentés et comparés aux résultats issus de l'expérience du manège de fatigue du LCPC

Essais de fluage confinés et thermorégulés sur enrobés bitumineux : expérimentation et modélisation

Pour étudier les déformations permanentes des enrobés bitumineux, un essai triaxial thermorégulé à pression de confinement constante a été developpé. Des essais de fluage à contrainte imposée ont permis d'étudier l'influence des paramètres pression de confinement, déviateur de contraintes et température sur le comportement des enrobés. Ils ont aussi permis de valider le principe d'équivalence temps température en grandes déformations. Un modèle élasto-visco-plastique pouvant être intégré dans un calcul structurel, a été développé pour simuler les essais de fluage

Assessment of cracks detection in pavement by a distributed fiber optic sensing technology

International audienceThis paper presents the feasibility of damage detection in asphalt pavements by embedded fiber optics as a new non-destructive inspection technique. The distributed fiber optic sensing technology based on the Rayleigh scattering was used in this study. The main advantage of this technique is that it allows to measure strains over a long length of fiber optic with a high spatial resolution, less than 1 cm. By comparing strain profiles measured at different times, an attempt was made to link strain changes with the appearance of damage (cracking) in the pavement. This non-destructive method was evaluated on accelerated pavement testing facility, in a bituminous pavement. In our experimentation, the optical fibers were placed near the bottom of the asphalt layer. The application of 728 000 heavy vehicle loads (65 kN dual wheel loads) was simulated in the experiment. Optical fiber measurements were made at regular intervals and surface cracking of the pavement was surveyed. After some traffic, a significant increase of strains was detected by the optical fibers at different points in the pavement structure, before any damage was visible. Later, cracking developed in the zones where the strain profiles were modified, X. Chapeleau et al. thus indicating a clear relationship between the increased strains and crack initiation. These first tests demonstrate that distributed fiber optic sensors based on Rayleigh scattering can be used to detect crack initiation and propagation in pavements, by monitoring strain profiles in the bituminous layers

Guidelines for the implementation of SMARTI: Sustainable Multifunctional Automated Resilient Transport Infrastructure

The World's transport infrastructures (TI) network is facing fast changes due to population growth, mobility, business trades and globalization. More challenges are coming from unforeseen natural and human-induced hazards, including climate change's effects. Meanwhile, technology development continues apace, and new solutions from multi-disciplinary sectors could help solve the main challenges faced by the TI industry. This work presents “SMARTI”, a vision that aims at engineering and implementing concepts such as Sustainability, Multifunctionality, Automation and Resilience within the design, construction and management of TI. As a result, the paper provides roadmaps for each of the above-mentioned pillars, identifying aims, current practices and stepping stones that infrastructure managers, policymakers and governors should consider toward more sustainable TI within 2030

Water in road structures : Chapter 10, Water Influence on Mechanical Behaviour of Pavements : Experimental Investigation

This chapter presents laboratory and in-situ experimental techniques used to describe the mechanical behaviour of pavement material at different saturation stages. The use of repeated triaxial load testing to obtain stiffness characteristics as well as the ability of the material to withstand accumulation of permanent deformation during cyclic loading is considered. For unsaturated soils, in addition to mechanical variables, it is shown that a moisture/suction control should be added. Several techniques are described to assist in this. A brief presentation of model parameters and tests needed for model calibration are introduced. Evaluation of pavement structural capacity based on deflection measurements with non-destructive testing equipment are presented. Finally, some examples of laboratory and in-situ measurement are shown

Finite elements modelling of the long term behaviour of a full scale flexible pavement with the shakedown theory

Rutting, due to permanent deformations of unbound materials, is one of the principal damage modes of low-traffic pavements. Flexible pavement design methods remain empirical; they do not take into account the inelastic behaviour of pavement materials and do not predict the rutting under cyclic loading. A simplified method, based on the concept of the shakedown theory developed by Zarka for metallic structures under cyclic loadings, has been used to estimate the permanent deformations of unbound granular materials subjected to traffic loading. Based on repeated load triaxial tests, a general procedure has been developed for the determination of the material parameters of the constitutive model. Finally, the results of a finite elements modelling of the long-term behaviour of a flexible pavement with the simplified method are presented and compared with the results of a full-scale flexible pavement experiment performed by Laboratoire Central des Ponts et Chaussées. Finally, the calculation of the rut depth evolution with time is carried out

Water in road structures : Chapter 11, Modeling Coupled Mechanics, Moisture and Heat in Pavement Structures

Different physical problems have been analysed in the preceding chapters: they relate to water transfer, to heat tranfer, to pollutant transfer and to mechanical equilibrium