Attard G.,National School of Public Civil Engineering |
Rossier Y.,Grenoble Institute of Technology |
Journal of Hydrology | Year: 2016
In this paper, underground structures are shown to have a major influence on the groundwater mean age distribution described as a dispersive piston effect. Urban underground development does not occur without impacts on subsoil resources. In particular, groundwater resources can be vulnerable and generate disturbances when this space is exploited. Groundwater age spatial distribution data are fundamental for resource management as it can provide operational sustainability indicators. However, the application of groundwater age modeling is neglected regarding the potential effect of underground structures in urban areas. A three dimensional modeling approach was conducted to quantify the impact of two underground structures: (1) an impervious structure and (2) a draining structure. Both structures are shown to cause significant mixing processes occurring between shallow and deeper aquifers. The design technique used for draining structures is shown to have the greatest impact, generating a decrease in mean age of more than 80% under the structure. Groundwater age modeling is shown to be relevant for highlighting the role played by underground structures in advective-dispersive flows in urban areas. © 2016 Elsevier B.V.
Gerthoffert J.,STAC |
Cerezo V.,IFSTTAR |
Bouteldja M.,Cerema |
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology | Year: 2015
The paper deals with the modeling of friction between aircraft tires and contaminated runway surfaces. Wet, snow- and ice-covered surfaces are considered. A tire Brush model developed for aircraft braking on dry runways is adapted to take into account the effect of contaminants. Compared with a dry surface, contaminants are assumed to affect the static and dynamic friction coefficients, the tire stiffness, the tire slip ratio, and the length of the contact patch. Linear relationship is established between static and dynamic friction coefficients. The dynamic friction coefficient is reduced using an empirical model for wet surfaces and experimental fitting for snow- and ice-covered surfaces. The tire stiffness is modified considering the frequency and temperature dependence of the tire mechanical properties. Values on snow and ice are lower than those on wet and dry surfaces. A physical model is developed to calculate the length of the wet contact patch. Finally, it is assumed that the aircraft effective slip ratio is surface-dependent, and values are determined for each of the studied contaminants. Theoretical friction-slip curves are realistic in terms of shape and differentiation between surface conditions. The model is applied to a Falcon 20 aircraft and a runway monitoring device called IMAG (Instrument de Mesure Automatique de Glissance). Friction-slip and friction-speed curves are calculated and compared to experimental data. It was found that the model can be used to relate ground friction to aircraft braking performance with enough reliability. © Institution of Mechanical Engineers.
Rosey F.,Cerema |
Auberlet J.-M.,University Paris Est Creteil
Transportation Research Part F: Traffic Psychology and Behaviour | Year: 2014
We carried out two studies to evaluate the impact of a message posted on a variable message sign (VMS) ahead of a rural four-way intersection with reduced sight distance on the major road. In the first study, 23 participants drove a desktop driving simulator and in the second, 24 different participants drove a fixed-base full cab driving simulator, using the same 3D virtual database. Two identical situations were involved in both studies. We took this opportunity to study the impact of the Driving Simulator Configuration (DSC) on the participants' driving responses in terms of lateral position, speed and gas pedal use, as well as on their level of control. Our aim was to determine whether both a desktop Driving Simulator (DS) and a full cab DS reliably replicate drivers' behaviors and level of control. The results essentially show that on the desktop DS the participants' approaches to the intersection were not smooth (a lack of anticipation) unlike those of the participants in the full cab DS. Furthermore, although for gas pedal use the participants using the two DSCs performed similarly, they drove at a higher speed on the desktop DS than in the full cab DS. Although the familiarization phase was exactly the same for both the studies, the results also show that the impact of the DSC varies according to the variable studied: the participants' control of each variable depends on the driving simulator. In the full cab DS, the control of action is more fine-grained than on the desktop DS. From our results, given the widespread use of driving simulators in the field of transportation research, the choice of a DSC and the content of the familiarization phase are not trivial. Consequently, the familiarization process should be considered with as much care as the other aspects of driving simulator use. © 2014 Elsevier Ltd. All rights reserved.
Accident Analysis and Prevention | Year: 2015
Context: The objective of divided roads is to increase users safety by posting unidirectional traffic flows. It happens however that drivers proceed in the wrong direction, endangering themselves as well as other users. The crashes caused by wrong-way drivers are generally spotlighted by the media and call for public intervention. Objectives: This paper proposes a characterization of wrong-way driving crashes occurring on French divided road on the 2008-2012 period. The objective is to identify the actors that delineate between wrong-way driving crashes and other crashes. Method: Building on the national injury road crash database, 266 crashes involving a wrong-way driver were identified. Their characteristics (related to timing, location, vehicle and driver) are compared to those of the 22,120 other crashes that occurred on the same roads over the same period. The comparison relies on descriptive statistics, completed by a logistic regression. Results: Wrong-way driving crashes are rare but severe. They are more likely to occur during night hours and on non-freeway roads than other crashes. Wrong-way drivers are older, more likely to be intoxicated, to be locals, to drive older vehicles, mainly passenger cars without passengers, than other drivers. Perspectives: The differences observed across networks can help prioritizing public intervention. Most of the identified WW-driving factors deal with cognitive impairment. Therefore, the specific countermeasures such as alternative road signs should be designed for and tested on cognitively impaired drivers. Nevertheless, WW-driving factors are also risk factors for other types of crashes (e.g. elderly driving, drunk driving and age of the vehicle). This suggest that, instead of (or in addition to) developing WW-driving specific countermeasures, managing these risk factors would help reducing a larger number of crashes. © 2014 Elsevier Ltd. All rights reserved.
Deliniere R.,Cerema |
Aubert J.E.,CNRS Materials and Construction Durability Laboratory |
Rojat F.,Cerema |
Building and Environment | Year: 2014
The use of clay plasters with or without plant fibers (straw, hemp or other) inside buildings is currently showing considerable growth in many countries. Despite this development, there are very few data in the literature on the characteristics of clay plasters. This paper deals with the characterization of five ready-mixed clay plasters from French brickworks using the recent German standard. The work essentially consisted in measuring the flow of fresh clay plasters and their characteristics after hardening (shrinkage, and compressive, flexural and adhesive strength). The characterization of the samples showed that the granular characteristics were practically the same and that the main difference concerned the nature of the clayey minerals they contained: four samples were essentially composed of montmorillonite, chlorite and illite whereas one was only composed of kaolinite. Despite this difference, the flow of fresh clay plasters and their characteristics after hardening (shrinkage, compressive and flexural strength) were very similar and were comparable to the values given by the standard. However, the measurement of the adhesive strength led to two significant problems: the dispersion of the values was very high and the results were markedly different from the values given by the standard. For these reasons, it seems necessary to complete and adapt the procedure for measuring adhesive strength and it could be interesting to develop new tests for the measurement of this important characteristic, either in the laboratory or on building sites. © 2014 Elsevier Ltd.