The road base is normally situated above the water table and thus in unsaturated state. Experimental results show that the accumulated strains of the unsaturated road base aggregate under high‐cycle traffic loads are significantly influenced by the matric suction. To predict the accumulated strain of unsaturated road base aggregate under high‐cycle traffic loads, a constitutive model was developed based on the Barcelona Basic Model (BBM) and the shakedown concept. In this model, the shakedown and plastic creep boundaries of the aggregate under cyclic loads were supposed to exist and to have the same shape as the “static” yield surface in BBM. The strain accumulation rates were described as an exponential function of the distance between the peak cyclic stress point and the conjugated point at the current cyclic yield surface. An explicit calculation methodology was adopted to avoid large calculation errors and to improve the calculation efficiency of the model. Comparison between model predictions and testing results proved the accuracy of the proposed model, which can be used as a basic model to predict the long‐term deformation of unsaturated road base aggregate under high‐cycle traffic loads.

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Monitoring structural behavior of earth structures during construction and in service is a common practice done for safety reasons, consolidation control and maintenance needs. Several are the techniques available for measuring displacements, water pressures and total stresses, not only in these geotechnical structures but also at their foundations. Materials testing has been used for calibrating models for structural design and behavior prediction, and these models can be validated with instrumentation data as well. Relatively recent investigation on the behavior of these materials considering their degree of saturation focuses on monitoring the evolution of water content or suction as function of soil-atmosphere interaction, necessary to predict cyclic and/or accumulated displacements, and has huge potential to predict

The paper describes the heave experienced by two embankments providing access to a bridge located in a high-speed railway line. The compacted soil, a mixture of a low plasticity clay, sand and gravel, had a significant sulphate content (2 – 2.5%). The embankments received a reinforcing treatment by mixing the soil with cement in the proximity of the bridge abutments. In addition, a grid of grouting columns provided more stiffness to the embankments. The embankments experienced a fast heaving rate (around 4 mm/month) in the areas improved by cement mixing. Precision extensometers indicated that heave concentrated in the upper 6 – 8 m of the embankments. The sulphate content reduced sharply to 0.25% at increasing depth. No heave was detected in these deeper zones. The swelling was found to be associated with the development of thaumasite and ettringite minerals. The presence of clay, cement and sulphates in the compacted soils and the infiltration of water from rainfall events are ideal conditions for the growth of the mentioned minerals. Long-term tests performed on compacted samples provided a good evidence of the phenomena developing in situ. A chemical modelling of the mineral changes at the soil-cement interface provided an additional insight into the development of swelling, which could last for a long time (several years). Accordingly, it was decided to underpin the railway track and to excavate the upper active volume of the embankments. This solution went in parallel with train service, which was never interrupted.