Granular materials are usually used in low-traffic pavement structure as base layer or sub-base layer. The influence of fine content on permanent axial deformation behaviour is significant as well as the water content. This study aims to investigate the permanent axial deformation behaviour of the granular material under cyclic loading at various water contents and various fine contents. A triaxial apparatus is used to obtain permanent axial deformation on the samples prepared with the same dry density at different water contents between 7% and 11% and at different fine contents of 4%, 7.5% and 15.3%. The results show the significant influence of water content and fine content on permanent axial deformation behaviour. The permanent axial deformation increases with the increase of water content while the influence of fine content depends on the water sensitivity of fine particles and their initial water contents. The modified empirical-analytical models are proposed for describing the evolution of permanent axial deformation based on the results in the single-stage test and the multi-stage tests. It takes into account the number of cycles, the stress level, the water content and the fine content of the granular material. Two approaches are used: one based on the water contents and fine contents and the other based on suction values. The approach based on suction values needs less number of parameters to describe permanent axial deformation compared with the approach based on the water contents and fine contents while the two approaches present more or less the same accuracy. The simulation results show a very good capacity of the proposed approaches. These findings reduce the number of tests required to predict permanent axial deformation.

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Granular materials are often used in pavement structures. The influence of anisotropy on the mechanical behaviour of granular materials is very important. The coupled effects of water content and fine content usually lead to more complex anisotropic behaviour. With a repeated load triaxial test (RLTT), it is possible to measure the anisotropic deformation behaviour of granular materials. This article initially presents an experimental study of the resilient repeated load response of a compacted clayey natural sand with three fine contents and different water contents. Based on anisotropic behaviour, the non-linear resilient model (Boyce model) is improved by the radial anisotropy coefficient γ3 instead of the axial anisotropy coefficient γ1. The results from both approaches (γ1 and γ3) are compared with the measured volumetric and deviatoric responses. These results confirm the capacity of the improved model to capture the general trend of the experiments. Finally, finite element calculations are performed with CAST3M in order to validate the improvement of the modified Boyce model (from γ1 to γ3). The modelling results indicate that the modified Boyce model with γ3 is more widely available in different water contents and different fine contents for this granular material. Besides, based on the results, the coupled effects of water content and fine content on the deflection of the structures can also be observed.

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The prediction of additional stresses in ballasted track due to subgrade deformation is the main objective of the present paper. In this context, a 2D finite element model of ballasted railway track was built using the ANSYS Workbench program. Based on this model, an investigation of stresses and deformation values of track elements was conducted in three cases with different contact types. It was found that the case introducing the status of a new track, which has frictional contacts between sleepers and ballast with bonded contacts between other elements, has lower stresses in most of the track elements. Moreover, this case was applied for studying the effect of the settlement on track elements. It was found that stresses increased with increasing the settlement value. The average percentages of increased stresses are 4.18%, 5.85%, and 7.21% in railhead, tie plate, and sleeper, respectively, due to a 1 mm increase in the settlement. Finally, a second-degree polynomial equation was derived to predict the additional stresses in each element due to track settlement. It is expected that this study would help to decrease the maintenance costs and extend the service life of the track elements by predicting the additional stresses in them.

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Granular materials are usually used in low traffic pavement structures as base layer or sub-base layer. The influence of the fine content on mechanical behavior is significant as well as the water content. In this study, based on the test results, a proposed empirical-analytical model was used to determine the permanent axial deformations of Missillac sand in Repeated Load Triaxial Tests (RLTTs). The model was also used to simulate the other experimental results existing in the literature. Globally, the results show a good capacity of model to estimate the permanent deformation behavior of granular materials.

This paper deals with the mechanical behaviour, especially the permanent deformation and resilient deformation of an unbound granular material (UGM) from Bréfauchet quarry which is used as base layer material in low traffic pavements for full-scale tests at IFSTTAR in France. Medium-scale repeated load triaxial tests (RLTT) are carried out at different water contents and the results show that both permanent and resilient deformations increase with water content. Besides, two techniques of fixing the sensors in materials with large particles for RLTTs are proposed and compared with each other. The results suggest that the tube method is more suitable for the UGM for an accurate measurement and a good adaptability is obtained during the RLTT. Based on the test results of UGM Bréfauchet, the modelling work is performed with improved models used previously for a sandy material. It appears that both the permanent and resilient behaviours of different unbound granular materials can be well captured by the proposed equations considering the effects of water content and anisotropy. This study is helpful to understand the evolution of permanent and resilient deformation in different granular layers, especially for the base layer, in low traffic pavements. The verified models can be used for other similar granular materials and this will lead to reducing the number of tests required to predict the deformation behaviour of granular materials.