An experimental investigation of the independent effect of suction and degree of saturation on very small-strain stiffness of unsaturated sand

The paper presents an experimental investigation of very small strain stiffness of unsaturated sand. A triaxial test apparatus was equipped with bender elements and compression discs in order to assess the stiffness at very small strains by measuring the velocity of propagation of shear and compression waves through an unsaturated sample. The negative water column method was adopted to apply suction at the base of the sample. The experiments were designed to investigate the independent effect of suction and degree of saturation on the wave propagation velocities. This was achieved by testing the sand sample on both the drying and wetting path

Feasibility of luminescent multilayer sol-gel thermal barrier coating manufacturing for future applications in through-thickness temperature gradient sensing

This paper investigates the feasibility of manufacturing sol-gel multilayer thermal barrier coatings (TBC) functionalized with different lanthanide ions Ln3 + having distinct photo-luminescence emission wavelengths (Ln = Sm, Eu, Dy, Er, Tm) for future applications in temperature gradient sensing. Ln3 + doped 9.75 mol% yttria stabilized zirconia (YSZ) powders were produced to study the effect of activator concentration on luminescence intensity and host matrix crystal structure. Self-quenching was found to limit the maximum signal-to-noise ratio achievable with Sm3 +, Dy3 +, Er3 + and Tm3 + activators, which was not the case for Eu3 + in the 1–10 mol% range. The increase in activator was found to affect the crystal structure of YSZ. A solution was proposed that suppressed this effect while significantly increasing the luminescence intensity of all activators. Finally a TBC sensor prototype integrating Eu3 +, Er3 + and Dy3 + doped layers distributed throughout the thickness was successfully deposited by a dip-coating sol-gel process and showed promising through-thickness luminescence sensing capabilities

Groundwater quality index as a hydrochemical tool for monitoring saltwater intrusion into coastal freshwater aquifer of Eastern Dahomey Basin, Southwestern Nigeria

Saltwater intrusion into coastal freshwater aquifers is a threat to groundwater quality globally. This study aims to determine the extent of saltwater intrusion into the coastal freshwater aquifer of the Eastern Dahomey Basin (EDB), Nigeria. Groundwater chemistry was sampled and analysed for ionic ratios and interpreted using a hydrochemical facie evolution diagram (HFE-D), the saltwater mixing index (SMI) and the Groundwater quality index for saltwater intrusion (GQIswi). High EC and TDS and the concentration of dissolved ions showed increased salinity as a result of seawater intrusion in wells located around communities in Seme, Lekki, Eleko, Okun-Ajah, Ode-Mahin and Igbokoda. Correlation of ions in the wet season also suggests higher salinities which originate partly from industrial and municipal effluents especially from wells which are close to river channels, while dry season groundwater shows the dominant influence of seawater intrusion. HFE-D revealed that mixed groundwater of Na + Ca–HCO3, Na–Cl and Ca–Cl dominate the area due to gravity-driven flow leading to groundwater freshening inland from the coastline towards the northern part of the basin. The groundwater quality index from SMI and GQIswi shows areas within 3 km from the coastline that are more sensitive to saltwater intrusion based on abstraction rate and depth of the wells. The present study provides information of value to planners and policy-makers for the sustainable management and protection of coastal groundwater resources in the Eastern Dahomey Basin

Apparent Interfacial Toughness of Undoped and Photoluminescent Eu3+-Doped Yttria-Stabilized Zirconia Thermal Barrier Coatings

Most photoluminescence methods for the diagnostic of thermal barrier coatings (TBC) rely on the functionalization of yttria-stabilized zirconia (YSZ) with trivalent lanthanide ions. It consists in determining temperature and detecting preventively damages within the volume of the TBC prior to ceramic topcoat spallation. The latter depends on the interfacial toughness, which is an important factor to address thermal barrier coating’s performance and durability. In this paper, the influence of the addition of rare earth elements (Eu3+) on the interfacial toughness of TBC deposited by atmospheric plasma spray is investigated. Two types of coatings are deposited and investigated: (1) Type I: coating deposited using Eu3+-doped YSZ powder (2 mol.%), (2) Type II: coating deposited using undoped YSZ powder. Both types of coatings are heat-treated at 1100 °C under isothermal conditions using different oxidation exposure times: 100, 300 and 800 h. The morphology of the interface between the topcoat (TBC) and the bond coat is analyzed by scanning electron microscopy. The apparent interfacial toughness is investigated using indentation. It is shown that the interfacial apparent toughness decreases as the oxidation exposure time increases. Concomitantly, the thickness of the thermally grown oxide (TGO) layer between the bond coat and the topcoat increases. Results show as well that the partial substitution of Y3+ ions by a low amount of Eu3+ ions (2 mol.%) does not have influence on the microstructure and the interfacial toughness of the YSZ coatings. In addition, energy dispersive spectrometry reveals that there is no diffusion of Eu3+ into the TGO layer. It is therefore concluded that the use of Eu3+ for damage diagnostic based on photoluminescence methods will not induce any kind of degradation of the properties of TBCs

Subsurface condition assessment of critical dam infrastructure with non-invasive geophysical sensing

Recent cases of dam failures indicate that the safe operation and proactive maintenance of critical infrastructure is of significant importance considering the growing number of ageing dams and the increase in intensity and frequency of extreme climatic events. The current procedures to assess the performance of dam infrastructure, usually based on geodetic and geotechnical instrumentation, do not provide repeatable and reliable information with regard to subsurface hazards that evolve within the body of earth-fill dams that could compromise the integrity of the structure. This increases the risk of failure with significant socio-economic impacts and long-term disruption on downstream communities. On the contrary, geophysical methods can provide advanced information about subsurface hazards and can therefore significantly assist to define the safety level of dam infrastructure. This will enable early remedial maintenance and repair actions to be carried out enhancing public safety and eventually reducing costs for asset owners. This study presents for the first time the investigation of the condition of three reservoir dams in Scotland with the application of two complementary non-invasive geophysical methods coupled with visual inspection. Electromagnetic (EM) sensing was initially employed to provide an assessment of the upper soil layers of the crest and downstream shoulder of the dam. Electrical Resistivity Tomography (ERT) arrays were then installed on the crest to assess the subsurface conditions of the dam based on the resistivity signatures. The analysis of the geophysical models identified weak zones within the body of dams associated with high-resistivity patterns associated with potential animal burrowing activity and fissuring on the crest of the dam. The electrical resistivity surveys revealed low-resistivity zones influenced by seepage conditions inside the body of dams but also provided an indication of potential internal erosion areas. Finally, the geophysical models provided an insight of the homogeneity of the fill material and determined the dam foundation characteristics. The geophysical results presented in this investigation provide important baseline measurements and key information about the current condition and on-going performance of dam infrastructure

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Fonctionnalisation de barrières thermiques sol-gel YSZ pour la mesure de température et le CND par fluorescence

International audienc

Fonctionnalisation de barrières thermiques sol-gel YSZ pour la mesure de température et le CND par fluorescence

International audienc