In order to study the hydraulic behavior of fouled ballast, an infiltration column of 600 mm high and 300 mm in diameter was developed. Five TDR sensors and five tensiometers were installed at various levels, allowing the measurement of volumetric water content and matric suction, respectively. The material studied was fouled ballast that was formed in the railway track-bed by penetration of finegrained soil into the ballast. This material is characterized by a high contrast of size between the largest and the smallest particles. During the test, three stages were followed: saturation, drainage, and evaporation. Based on the test results, the water retention curve and the unsaturated hydraulic conductivity were determined. The quality of the results shows the capacity of this large-scale infiltration column in studying the unsaturated hydraulic properties of such fouled ballast.

Résumé Characterisation of constitutive materials of old railway platform AbstractIn order to better understand the structure of an old platform and especially the structure of the intermediate layer that was created mainly by interpenetration of subgrade under trains action, the constitutive materials of an old railway platform situated in Sénissiat (near Lyon) were characterised in laboratory. The Atterberg limits, methylene blue value and mineralogy were determined on the fine-grained portion, whereas analysis of the pore size distribution covered the whole grain elements of different dimensions for both the intermediate soil and the soil subgrade. The results show that the intermediate soil corresponds to a heterogeneous material that is very compact and constituted of large grain elements and of fine grains from subgrade. The compaction properties of intermediate soil under Modified Proctor energy was also studied using the portion after clipped to 20 mm. The required corrections were made to account for the effect of large grain elements. It was observed that the maximum dry density obtained in laboratory (2.28 Mg/m3) is slightly lower than that measured in field condition (2.39 Mg/m3), showing the difficulties related to the preparation of representative soil samples in laboratory by compaction.

Abstract:In order to better understand the heave observed on the railway roadbed of the French high-speed train (TGV) at Chabrillan in southern France, the swelling behaviour of the involved expansive clayey marl taken from the site by coring was investigated. The aim the study is to analyse the part of heave induced by the soil swelling. First, the swell potential was determined by flooding the soil specimen in an oedometer under its in-situ overburden stress. On the other hand, in order to assess the swell induced by the excavation undertaken during the construction of the railway, a second method was applied. The soil was first loaded to its in situ overburden stress existing before the excavation. It was then flooded and unloaded to its current overburden stress (after the excavation). The swell induced by this unloading was considered. Finally, the experimental results obtained were analyzed, together with the results from other laboratory tests performed previously and the data collected from the field monitoring. This study allowed estimating the heave induced by soil swelling. Subsequently, the part of heave due to landslide could be estimated which corresponds to the difference between the monitored heave and the swelling heave.

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