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Duong T.V.,ParisTech National School of Bridges and Roads | Cui Y.-J.,ParisTech National School of Bridges and Roads | Tang A.M.,ParisTech National School of Bridges and Roads | Dupla J.-C.,ParisTech National School of Bridges and Roads | And 3 more authors.
Acta Geotechnica | Year: 2016

This paper deals with the resilient behavior of the interlayer soil which is created mainly by the interpenetration of ballast and subgrade soils. The interlayer soil studied was taken from a site in the southeast of France. Large-scale cyclic triaxial tests were carried out at three water contents (w = 4, 6 and 12 %) and three fines contents corresponding to 5, 10 % subgrade added to the natural interlayer soil and 10 % fine particles (<80 μm) removed from the natural interlayer soil. Soil specimens underwent various deviator stresses, and for each deviator stress, a large number of cycles was applied. The effects of deviator stress, number of cycles, water content and fines content on the resilient modulus (Mr) were analyzed. It appears that the effects of water content and fines content must be analyzed together because the two effects are closely linked. Under unsaturated conditions, the soil containing high fines content has higher resilient modulus due to the contribution of suction. When the soil approaches the saturated state, it loses its mechanical enhancement with a sharp decrease in resilient modulus. © 2015, Springer-Verlag Berlin Heidelberg.


Duong T.V.,ParisTech National School of Bridges and Roads | Cui Y.J.,ParisTech National School of Bridges and Roads | Tang A.M.,ParisTech National School of Bridges and Roads | Dupla J.C.,ParisTech National School of Bridges and Roads | And 3 more authors.
Geomechanics from Micro to Macro - Proceedings of the TC105 ISSMGE International Symposium on Geomechanics from Micro to Macro, IS-Cambridge 2014 | Year: 2015

This paper presents the driving factors for the interlayer creation and mud pumping phenomena in railway sub-structure. Physical model tests on a ballast layer overlying a sub-soil layer were carried out under different conditions in terms of water content, loading and sub-soil dry unit mass. The physical model was equipped with various sensors and devices allowing pore water pressure, axial displacement to be monitored. Visual observations were also made using a digital camera. It was observed that the ballast behavior depends on the sub-soil state. Both the interlayer creation and mud pumping are related to the migration of fine particles, and the water content of the sub-soil is the most important factor for this migration. Under the unsaturated conditions, the ballast/sub-soil interface did not change. On the contrary, under the near saturated conditions, significant migration of fine particles occurred. In case of low dry unit mass, the dissipation of high pore water pressure in the sub-soil gave rise to mud pumping. In case of higher dry unit mass, the excess pore water pressure was lower due to the smaller volume change of sub-soil. As a result, the effect of water pressure dissipation was limited and the upward migration of fine particles was only due to the penetration of ballast into the sub-soil, thereby, forming the interlayer. © 2015 Taylor & Francis Group.


Duong T.V.,ParisTech National School of Bridges and Roads | Cui Y.J.,ParisTech National School of Bridges and Roads | Tang A.M.,ParisTech National School of Bridges and Roads | Calon N.,French Railway Company SNCF | Robinet A.,French Railway Company SNCF
Bulletin of Engineering Geology and the Environment | Year: 2014

A statistical study was firstly undertaken on problems that occurred in a period of more than 1 year and were related to train circulation in the entire conventional French railway network. Emphasis was put on the degradation of track components. The analysis evidenced the particular importance of sub-grade quality in the performance of the whole track. After this general analysis, a conventional railway line in the West of France was investigated. In the sub-structure of this line, an interlayer was identified that was created mainly by interpenetration of ballast and sub-grade. In the analysis, the degradation rate of this line was correlated with different parameters, such as the nature of sub-grades involved along the line and the thickness of different layers. The results showed that the degradation rate is correlated to the thickness of various layers. Furthermore, it was observed that the interlayer plays an important role in the performance of tracks, as it represents a transition layer for the train-induced stress transmission to the sub-grade. © 2014, Springer-Verlag Berlin Heidelberg.


Duong T.V.,University of Paris Descartes | Cui Y.-J.,University of Paris Descartes | Tang A.M.,University of Paris Descartes | Dupla J.-C.,University of Paris Descartes | Calon N.,French Railway Company SNCF
Canadian Geotechnical Journal | Year: 2014

The conventional railway substructure in France was built by emplacing ballast directly on subgrade. Over years of operation, the interpenetration of ballast and subgrade created a soil layer between them. Under different conditions, this naturally formed layer, namely interlayer, can contain different quantities of fine particles, becoming more or less sensitive to changes in water content. As the water content changes are governed by the hydraulic behavior of the interlayer soil, assessing the influence of fine particle content on the hydraulic behavior of interlayer soil is of importance. To this end, the hydraulic behavior of an interlayer soil taken from Sénissiat (near Lyon, France) was investigated using two infiltration columns, a large-scale column equipped with tensiometers and a time domain reflectometer (TDR) for suction and volumetric water content measurements, respectively, and a smaller column equipped with high-capacity tensiometers only. Different fines contents were considered and wetting-drying cycles were applied to the soil specimens. The hydraulic conductivity was determined by applying the instantaneous profile method. The results obtained showed that (i) hysteresis exists for both the soil water retention curve and the hydraulic conductivity changes with suction; (ii) the effect of wetting-drying cycles is insignificant; (iii) adding 10% fine particles to the natural interlayer soil gives rise to changes in the soil water retention curve but does not induce significant changes in hydraulic conductivity; (iv) the unsaturated hydraulic conductivity of interlayer soil with 10% fine particles added is close to that of soil sieved at 2 mm, suggesting that the unsaturated hydraulic conductivity of interlayer soil is mainly governed by fine particles through the suction effect. By contrast, in a saturated state, the value for the interlayer soil with 10% fine particles added was found to be higher, suggesting that in this case the hydraulic conductivity is mainly governed by the water transfer through macropores. © 2014 Published by NRC Research Press.


Duong T.V.,ParisTech National School of Bridges and Roads | Cui Y.J.,ParisTech National School of Bridges and Roads | Tang A.M.,ParisTech National School of Bridges and Roads | Dupla J.C.,ParisTech National School of Bridges and Roads | And 5 more authors.
Geotechnical Testing Journal | Year: 2014

To study the interlayer creation and the mud-pumping phenomena in the conventional French railway substructure, a physical model was developed with a 160-mm-thick ballast layer overlaying a 220-mm-thick artificial silt layer (mixture of crushed sand and kaolin), both layers being compacted in a transparent cylinder of a 550-mm-inner diameter. One positive pore water pressure sensor, three tensiometers, and three time domain reflectometer (TDR) sensors were installed around the ballast/silt interface allowing the evolution of pore water pressure (negative or positive) and volumetric water content to be monitored, respectively. A digital camera was installed allowing direct monitoring of different movements (ballast, ballast/subsoil interface, etc.). The effects of loading (monotonic and cyclic loadings) and degree of saturation of subsoil (w1/416 %, Sr1/455 %, and near-saturation state) were investigated. It was found that the development of pore water pressure in the subsoil is the key factor causing the migration of fine particles, hence, resulting in the creation of interlayer, as well as mud pumping. In particular, the camera exposed the pumping up level of fine particles during the test, showing that the migration of fine particles was not only a result of the interpenetration of ballast particles and subsoil, but also of the pore water pressure that pushed the fine particle upward. The quality of the recorded data showed that the physical model developed worked well and the test protocol adopted for studying the mechanisms of intermixing of ballast and subsoil and mud pumping was appropriate. Copyright © 2014 by ASTM International.


Duong T.V.,ParisTech National School of Bridges and Roads | Cui Y.-J.,ParisTech National School of Bridges and Roads | Tang A.M.,ParisTech National School of Bridges and Roads | Dupla J.-C.,ParisTech National School of Bridges and Roads | And 3 more authors.
Engineering Geology | Year: 2014

This paper presents the driving factors for the interlayer creation and mud pumping phenomena in railway sub-structure. Physical model tests on a ballast layer overlying a sub-soil layer were carried out under different conditions in terms of water content, loading and sub-soil dry unit mass. The physical model was equipped with various sensors and devices allowing water content, pore water pressure, and axial displacement to be monitored. Visual observations were also made using a digital camera. It was observed that the ballast behavior depends on the sub-soil state. Both the interlayer creation and mud pumping are related to the migration of fine particles, and the water content of the sub-soil is the most important factor for this migration. Under the unsaturated conditions, the ballast/sub-soil interface did not change. On the contrary, under the near saturated conditions, significant migration of fine particles occurred. In case of low dry unit mass, the dissipation of high pore water pressure in the sub-soil gave rise to mud pumping. In case of higher dry unit mass, the excess pore water pressure was lower due to the smaller volume change of sub-soil. As a result, the effect of water pressure dissipation was limited and the upward migration of fine particles was only due to the penetration of ballast into the sub-soil, thereby, forming the interlayer. © 2014 Elsevier B.V.

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