The constitutive modeling of cyclic plasticity of soils has made great progress, especially in the area of sands liquefaction modeling. Nowadays, the problem of rutting of flexible pavements linked to permanent deformations occurring in the unbound layers is taken into account only by empirical formulas. This paper presents an elastoplastic model with both isotropic and kinematic hardening. The yield surface, plastic potential, and isotropic hardening are based on a model for sands, which takes into account the influence of the initial void ratio and of the mean stress on the mechanical behavior. A kinematic hardening has been added in order to take into account the mechanical behavior of the material for large cycle numbers. A complete model is then developed, simulations are presented, and comparisons with repeated load triaxial tests carried out on a subgrade soil (clayey sand), have been made. These comparisons underline the capabilities of the model to take into account the monotonic, cyclic, and rat...

Reinforcement using an interlayer system has been demonstrated for more than four decades as a multi-purpose solution to improve performance, to extend service life and thus to reduce maintenance costs of road pavements. Among a large number of existing interlayer systems, glass fibre grids have shown effective use in pavement reinforcement with a hot mix asphalt overlay. Recently they have received increasing attention from the pavement community. However, as for other types of interlayer systems, the mechanisms underlying the effectiveness and proper installation of this type of reinforcement system are still not fully understood, and the choice of the most appropriate grid (e.g. mesh size, tensile strength) and its optimal location in the pavement system are mainly based on experience. This article presents firstly a literature review on the use of glass fibre grids in pavement reinforcement. Then some results of recent full-scale tests on the accelerated pavement testing facility of the IFSTTAR are presented. They confirm that glass fibre grid properly installed near the bottom of the asphalt layer improves significantly the fatigue life of the reinforced pavement. They also demonstrate the efficiency of glass grid use under only a thin asphalt overlay. Finally, first results obtained using an original instrumentation of glass grid strands by means of strain gages, to understand better the mechanical behaviour of the glass fibre reinforcement in a new pavement structure are described.

Classically, measurements on instrumented pavements are performed on site, under known load conditions. In such conditions, data interpretation and modelling of the pavement are relatively easy. However, on-site measurements are time consuming and costly to perform, because they require using a dedicated vehicle and closing the lane to traffic. This paper presents an experiment, where an instrumented bituminous pavement motorway section has been followed by remote monitoring, under normal traffic. The section, instrumented with strain gages, temperature probes and geophones, has been monitored continuously during 18 months. Signal sorting procedures have been developed for reducing the quantity of recorded data, and for analysing the structural response of the pavement, under highly variable loading conditions. The results of the strain gage measurements, made at different depths within the pavement, have shown that the response of the pavement presents large variations with temperature, and in particular, that the degree of bonding between layers can decreases at high temperatures, leading to sliding between pavement layers. The mechanical response of this section has been analysed using a classical multi-layer linear elastic pavement model and also a viscoelastic model. The best predictions have been achieved with the viscoelastic model. Different approaches for describing the behaviour of pavement layer interfaces have also been evaluated.

This paper presents a complete experimental study of the fatigue behaviour of a glass-fibre-reinforced asphalt concrete, respecting EN 12697-24:2012, Annex D. The study is based on 38 four point bending tests, performed on 18 non-reinforced asphalt specimens and 20 geogrid-reinforced asphalt specimens. Both non-reinforced and reinforced asphalt specimens are tri-layered beams. The reinforced specimens contain two glass fibre grids, each one placed at the interface between two asphalt concrete layers. The objectives of the study were: (1) to characterise the fatigue behaviour of reinforced asphalt concrete, and to determine fatigue parameters, which can be used for pavement design, following the French pavement design method, (2) to show that glass fibre grid delays fatigue crack propagation and (3) to estimate the gain in fatigue due to the geogrid. The comparison of the fatigue curves of non-reinforced and reinforced asphalt concrete indicates that the geogrid increases fatigue life for the testing conditions, which were: fully reverse loading, displacement control, sinusoidal waveform, T = 10°C and f = 25 Hz.