Showing papers by "Anh Minh Tang published in 2015"

Effects of aggregate size on water retention capacity and microstructure of lime-treated silty soil

Abstract: Lime treatment is a common technique of improving the workability and geotechnical properties of soils. In this study, the aggregate size effects on the water retention capacity and microstructure of lime-treated soil were investigated. Two soil powders with different maximum aggregate sizes (Dmax = 0·4 and 5 mm) were prepared and stabilised by 2% lime (by weight of dry soil). Soil samples were prepared by compaction at dry side of optimum water content (w = 17%) with a dry density of 1·65 Mg/m3. Suction and pore size distribution were determined after different curing periods. The results obtained show that: (a) the treated soil with smaller Dmax presents relatively smaller modal sizes and lower frequency of macropores (10–330 μm); (b) lime addition effectively improves the soil water retention capacity and decreases both the modal sizes of macro- and micropores gradually over time. Moreover, a higher air entry value and larger water retention capacity were also observed for a smaller Dmax value, in agre...

Assessment of conventional French railway sub-structure: a case study

Abstract: 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.

Experimental Investigation of Soil-Atmosphere Interaction in an Instrumented Embankment Constructed with Two Treated Clays

Abstract: This paper discusses the field monitoring of an experimental embankment divided into two symmetrical instrumented sections constructed with two clays treated with lime and/or cement in the northeast of France. The soil-atmosphere interaction is investigated in the monitored embankment. The field instrumentation included spatial and temporal changes of the soil suction, moisture, and temperature at predefined locations within the embankment, as well as measurements of meteorological data, collected from April to November 2011. The data show similarities in the suction daily variations trend in the two treated clays. Maximum changes in suction occur near ground surface. Even at the location of -0.75 m from the slope face the interchange of water between the atmosphere and the ground was observed in the daily soil suction measurements. No significant hydrologic response of the soils to rainfall was observed during the period of water deficit. The rainfall events showed a significant effect on the soil suction changes in the initial period of water surplus after a long period of water deficit. The comparison of the period of water deficit observed in the responses of the mean monthly suction and moisture measurements in the treated soils and the one estimated by simple water balance models based on standard meteorological observations in the region indicate that there is an overall qualitative agreement between the modelling and observational results.

Seismic Surface-wave Analysis for Railway Platform Auscultation

Abstract: The renewal of existent railways requires the characterisation of the mechanical properties of railway platforms (RP), thus raising the need to select appropriate maintenance actions. Conventional techniques (geotechnical soundings, coring) remain local, destructive, expensive and with low yields. Using non-destructive investigation techniques for local diagnosis and monitoring thus appears of great interest for enhancing RP control. Seismic surface-wave methods have been proposed to estimate in situ mechanical parameters of the superficial layers below railways. In this context, a joint geotechnical and seismic survey was carried out along the Northern Europe high-speed line (LGV) in order to precisely determine the origins of a phenomenon affecting the geometry of the track. Strong a priori knowledge of the RP structure allowed for inverting dispersion measurements for 1D VS models along the track. The results showed a contrast of VS in the loess lying below the RP, between areas where the phenomenon was observed and those it was not. This contrast was confirmed by Bender Elements measurements of VS performed on core drilling samples, and corresponded to the lateral variations observed along the track. These results encourage considering dispersion measurements as an appropriate tool of RP monitoring.

In-situ investigation of the behaviour of a French conventional railway platform

Abstract: Concerning the 30,000 km French conventional railway network (94% of the entire network), the speed is currently limited to 220 km/h as maximum, whereas for the 1,800 km high speed lines, the speed can go up to 250 - 320 km/h. Nowadays, there is a growing need to reduce the travel time and improve the service by increasing the speed limits on the conventional network. This paper aims to study the influence of train speed on the mechanical behaviour of an experimental site representative of the French conventional network. Emphasis is put on the behaviour of the interlayer soil. The selected experimentation site is located near Vierzon (Centre/FR). More than 40 sensors, including accelerometers and soil pressure gauges, have been installed. A testing campaign has been performed with a fully instrumented experimental intercity train composed of a locomotive and seven coaches running at different speeds (60 – 100 – 140 – 160 – 180 and 200 km/h). This campaign has revealed that when the train speed is increased, the loads transmitted to the platform increase. Moreover, these loads are amplified at the depth of interlayer soil. Indeed, the upgrade of limit speed of a line leads an increase of the vertical soil pressure and the vertical acceleration in the soil. The acceleration data obtained from the accelerometers will be used to determine the maximum vertical strain induced in the interlayer soil for different train speeds.

Anisotropy in Oedometer Test on Natural Boom Clay

Abstract: The mechanical behaviour of Boom Clay has been studied for many years in the context of geological disposal of radioactive waste in Belgium. The aim of this study is to investigate the anisotropic behaviour of Boom Clay in terms of compressibility and hydraulic conductivity. Oedometer tests (with effective vertical stress (\( \sigma_{v}^{{\prime }} \)) up to 32 MPa) were carried out on samples of various orientations: parallel, perpendicular and inclined 45° to the bedding plane. The compressibility index (C c ) and swelling index (C s ) were compared. Only a slight difference between these parameters was observed, suggesting that the anisotropic behaviour of Boom Clay cannot be revealed under the test conditions adopted. The hydraulic conductivity (k) was also determined by the Casagrande’s method for different values of vertical effective stress (\( \sigma_{v}^{{\prime }} \)). Unlike compressibility, the hydraulic conductivity, however, showed a clear anisotropic behaviour with k ver < k inc < k hor .

A New Apparatus for the Measurement of Swelling Pressure Under Constant Volume Condition

Abstract: A new constant volume cell was developed, allowing the measurement of swelling pressure without any strain adjustment and any effect of the stiffness of the testing device. By employing this new cell, the swelling behavior of compacted soil specimen under different suctions (57, 38, 9 and 0 MPa) was investigated. The results show good repeatability, indicating the reliability of the new cell and validating the test procedures adopted. Moreover, the developed cell is quite convenient to study the long-term swelling behavior of soil since no load adjustment is necessary. The obtained results show that, during the progressive wetting by applying successively the suctions of 57, 39, 9 and 0 MPa, the swelling pressure increases to 0.17, 0.31, 0.46 and 0.89 MPa, respectively. The swelling pressure and the time required to reach equilibrium are function of suction. Vapour-wetting and water-wetting show different hydration mechanisms and result in different swelling behavior: the swelling pressure develops slowly and gradually to finally reach stabilization upon vapour-wetting, while it increases quickly to a peak value and followed by a small decrease upon water-wetting.

Hydro-mechanical simulation in a deep excavation in Boom Clay

Abstract: [2] R. Charlier, R. Chambon, F. Collin, A. Dizier, S. Fauriel, B. Francois, J. Fokkens, B. Garitte, A. Gens, P. Gerard, et al. Timodaz report: Deliverable d13–simulation of lab and in situ tests. 2010. [3] P.Y. Hong. Development and explicit integration of a thermo-mechanical model for saturated clays. PhD Thesis, Universite Paris-Est, France 2013. 1 P. Y. Hong , hongp@cermes.enpc.fr Hydro-mechanical simulation in a deep excavation in Boom Clay P. Y. Hong 1,Y. J. Cui, J. M. Pereira, A. M. Tang, ENPC, France F. Collin, University of Liege, Belgium X.L. Li, ESV EURIDICE GIE , Belgium X. Sillen, ONDRAF/NIRAS, Belgium Context Brussels 2015 Poster No. P-09-03