Search

Electrical resistivity is sensitive to various properties of concrete, such as water content. Usually used on the surface of old structures, devices for measuring such properties could also be adapted in order to be embedded inside the constitutive concrete of the linings of new tunnels or in new bridges, to contribute to structural health monitoring. This paper introduces a novel multi-electrode embedded sensor for monitoring the resistivity profile over depth in order to quantify concrete durability. The paper focuses on the design of the sensor as a printed circuit board (PCB), which brings several advantages, including geometric accuracy and mitigation of wiring issues, thus reducing invasiveness. The study also presents the numerical modeling of the sensor electrical response and its ability to assess an imposed resistivity profile, together with experimental validations using (i) saline solutions of known conductivity and (ii) concrete specimens subjected to drying. The results demonstrate the capability of the sensor to evaluate resistivity profiles in concrete with centimeter resolution.

Ballast deterioration, under dynamic loads, remains an important issue on high-speed tracks that can lead to high maintenance costs. This ballast deterioration leads to settlements. Several studies have shown that these settlements were linked to high accelerations produced in the ballast by high-speed train (HST) passages. The solution with bituminous underlayment was used since 1980s in several countries like United States, Italy, Spain, especially on high-traffic and high-speed lines (HSL). In France, the interest in this technique is recent. Following the East European HSL satisfactory behavior, a layer of asphalt concrete was used under the ballast layer of the Bretagne-Pays de la Loire (BPL) HSL. It is intended, in addition to the schedule savings and the protection of the subgrade during the construction phase, to reduce acceleration amplitudes produced at the passage of HST, to ensure moisture stability in the subgrade and thereby to decrease the maintenance costs of the tracks. BPL HSL includes 105 km of innovative track with an asphalt concrete (GB) ballast sublayer, and 77 km with a granular layer under the ballast (UGM). Out of the instrumented sections of the BPL track, 3 sections are constructed with GB subballast layer and one with a layer of UGM as a subballast layer. A total of 127 sensors that includes accelerometers, anchored displacement sensors, temperature and humidity probes, and extensometers are used. Sensors are placed at various positions and depths in the track structures. Data were first acquired during a speed up test phase, under controlled conditions, with the same train passing at speeds ranging from 160 to 352 km/h. This paper presents the different sensors used for the instrumentation as well as the acquisition system installed to collect all measurements. Data treatment and processing is explained in details. Finally, results obtained for different speeds are presented, with a focus on accelerometer and anchored displacement sensor measurements, on two sections, allowing, among others, comparisons between the response of structures with and without asphalt concrete. The role of the GB, as a subballast layer, in damping the vertical displacement of the sub ballast structure and reducing the accelerations peaks in the ballast layer for ballasted tracks is demonstrated.

The phenomena of packing and wear of the ballast, under dynamic stresses lead to high frequencies and high maintenance costs. It has been demonstrated that the settlements in the ballast were linked to the high accelerations produced in this layer by the passage of high-speed trains. The solution with bituminous underlay was used since the 1980s in several countries like the United States, Italy, Spain, especially on high-traffic and high-speed lines (HSL). In France, the interest in this technique is recent. Following the satisfactory behavior of the East European HSL, a layer of asphalt concrete was made under the ballast layer on a high scale lane, the Bretagne-Pays de la Loire (BPL) fast lane. It is intended, among other things, to reduce the amplitude of the accelerations produced at the passage of the HST. The HSL BPL has 105 km of innovative track with an asphalt concrete (GB) sublayer under the ballast, and 77 km with a granular under layer. In order to study the dynamic responses of these different structures and to understand the effect of the different layers on the dynamic response, four sections were instrumented (3 with asphalt concrete, and one on a standard granular structure) using, among others, accelerometers, strain gauges, temperature probes, etc. More than 100 sensors have been installed on the structure in different positions and depths. The acquisition of the data is made during the speed up test phase under controlled conditions with the same train passing with speeds going up from 160 to 352 Km/h. In a later phase, measurements of all the sensors will be treated under actual traffic. The BPL lane is subjected to commercial traffic since July 2017. The main idea of the project and the expected results for the first phase are to analyze the measurements in the database created and determine the responses of the different sections and the variations of the various parameters measured: Vertical displacements, accelerations at different levels, horizontal deformations in the bituminous layer, etc. In this paper, a description of the railway track “Bretagne pays De la Loire”, the instrumentation of the different sections and the acquisition system are detailed. The processing and treatment method used for the registered data is explained. The variation of the speed of the trains is also expected to be carried out in this paper to evaluate the behavior of the structures in section 4 with bituminous underlayment in terms of vertical acceleration.

Heavy commercial vehicle (HCV) overloads contribute to premature deterioration of infrastructure and increase road unsafety and unfair competition between transport modes and operators. Public authorities and road operators must therefore implement an efficient checking system to enforce weights and dimensions at an affordable cost. A large scale project was launched in 2014 by the French Ministry of Ecology, Sustainable Development and Sea, in charge of Transport, carried out by French Institute of Science and Technology for Transport (IFSTTAR) and Centre D’etudes et D’expertise sur les Risques, L’environnement, la Mobilite et L’amenagement (CEREMA), to demonstrate the feasibility of using high speed weigh-in-motion (WIM) systems for direct enforcement of overloaded HCVs. This ambitious challenge requires overcoming technological and metrological gaps, and modifying the current legislation. The required tolerances are ±5% for the gross vehicle weight, and ±10% for axle loads. None of the existing WIM system matches this accuracy for 100% of the vehicles. Therefore the objective is to set up some sorting criteria and algorithms, eliminating the weighings outside these tolerances. The project is divided into 5 WPs, to characterize WIM sensor response under controlled environment and loading conditions and to develop fiber optic WIM sensors, to assess the capability of multiple sensor (MS-) and bridge (B-) WIM systems to meet the requirements, to carry long term road tests and to develop type approval procedures for direct enforcement. This paper presents results gathered on the accelerated pavement testing facility of IFSTTAR in 2014 with 10 WIM sensors. Some results of B-WIM systems are also reported. Perspectives are given how to achieve a WIM system type approval procedure for direct enforcement.

The phenomena of settlement and wear of the ballast under dynamic stresses lead to high frequencies and high maintenance costs on high-speed railway lines. Studies have shown that these settlements are linked to high accelerations produced in the ballast by the passage of high-speed trains (HST). A layer of asphalt concrete (GB) was introduced under the ballast layer on the high-speed line Bretagne-Pays de Loire (BPL HSL). It is intended, among other things, to reduce the amplitude of accelerations produced at the passage of the HST and thus improve the durability of the track. The BPL HSL spans 105 km, with a sublayer of asphalt concrete under the ballast and 77 km with a granular sublayer (UGM). To evaluate the performance of the structures with bituminous sublayer and to compare it with traditional structures with granular sublayer, four track sections have been instrumented during construction. This article presents the different sensors of the instrumentation, as well as the acquisition system installed to collect measurements. The focus, in this study, concerns the temperature, water content, and vertical settlement measurements made on the instrumented sections. Temperature variations recorded during two years on the railway structure with bituminous sublayer were analyzed and compared with those measured on a classical bituminous pavement. Influence of the bituminous layer on water infiltration and track settlements has also been studied.

This article aims at modeling the WIM sensor electrical behavior to provide a better understanding of the mechanical and electrical proprieties of piezoelectric sensors. The model is considered in the frequency domain, supposing any sinusoidal solicitation with constant frequency or any other type of solicitation. Tests, having real WIM sensors placed on the pavement of a test track at IFSTTAR/Nantes was used to verify the nature of the electro-mechanical (EM) behavior of the real sensors over punching, flexural and extension effects. Also, two different pavement numerical simulations deliver the mechanical response using linear elasticity and viscoelastic proprieties. The output of these two simulations are compared with two WIM signals obtained at same load and speed at two different temperature conditions.

ICWIM7 - 7th International Conference on Weigh-In-Motion, FOZ DO IGUACU, BRESIL, 07-/11/2016 - 10/11/2016; Heavy commercial vehicle overloads contribute to deterioration of infrastructure and increase road unsafety and unfair competition between transport modes and operators. An efficient enforcement system of weights and dimensions at an affordable cost is therefore required. A large scale project was launched by the French Ministry of Transport in 2014 in France, led by IFSTTAR, in cooperation with the Cerema, to demonstrate the feasibility of using high speed weigh-in-motion (HS-WIM) systems for direct enforcement of overloads. This ambitious challenge requires overcoming technological and metrological gaps, and modifying the current legislation. The required tolerances are ±5% for the gross vehicle weight, and ±10% for axle loads for 100% of the vehicles. The methodology is to develop sorting criteria and algorithms, eliminating the outliers, that is to say the weighing data outside these tolerances. The project organization and management is described and the first results are presented in this paper.

International audience; The paper deals with the results of an experimental campaign carried out on a post tensioned concrete beam with the aim of investigating the possibility to detect early warning signs of deterioration based on static and/or dynamic tests. The beam was tested in several configurations aimed to reproduce 5 different phases of the ‘life‘ of the beam: in the original undamaged state, un-der increasing loss of tension in the post tensioning cables, during and after the formation of cracks at mid span, after a strengthening intervention carried out by means of a second tension cable, dur-ing and after the formation of further cracks on the strengthened beam. Responses of the beam were measured by an extensive set of instruments consisting of accelerometers, inclinometers, displace-ment transducers, strain gauges and optical fibers. In this paper data from accelerometers and dis-placement transducers have been exploited. The paper presents the test program and the dynamic characterization of the beam in the different damage scenarios in terms of the first modal frequency, identified from dynamic tests and of the bending stiffness monitored during static tests.

The article aims at detecting and quantifying early structural damages using deterministic and probabilistic model updating techniques. To achieve this purpose, local information in a form of optical strain measurement is employed. The strategy consists in updating physical parameters associated to damages, such as Young’s modulus, in order to minimize the gap between the numerical strain obtained from finite element solves and the strain sensor outputs. Generally, the damage estimation is an ill-posed inverse problem, and hence requires regularization. Herein, three model updating techniques are considered involving different type of regularization: classical Tikhonov regularization, Constitutive Relation Error based updating method and Bayesian approach. An illustration of these three approaches is proposed for localizing and quantifying an early damage in a real 8 meter post-tensioned concrete beam. Numerical results show that all the methods properly localize the damaged area and give similar estimation of the damage level

This paper presents an experiment, performed on the IFSTTAR circular accelerated testing facility, to evaluate the performance of different weight in motion (WIM) sensors. This project, carried out with the French ministry of transport, aims at improving the performance of these WIM sensors, to allow automated overload control. Four different types of sensors were evaluated in the project: piezo-quartz sensors (2 types), piezo-ceramic sensors and piezo-polymer sensors. The full scale experiment was performed on a thick bituminous pavement. A total of 10 WIM sensors were installed, as well as other sensors (temperature probes, vertical displacement transducers, geophones). Accelerometers were also used to monitor dynamic load variations. The response of the sensors was evaluated under a wide variety of loading conditions (different loading speeds, temperatures and lateral positions of the wheels). In the first phase of the experiment, the 4 arms of the carrousel were all equipped with single wheels (with wheel loads of 45 or 55 kN). In a second phase, different wheel configurations were tested, on each arm of the testing facility (single wheel, dual wheels, tandem, tridem). A large database, of about 30000 WIM signals, was collected. The full scale tests have allowed to evaluate the repeatability of the different types of sensors, and the influence of different loading conditions (temperature, load type, loading speed..). The results indicate that the sensitivity of the different types of transducers to loading conditions is very different. Recommendations for correcting and improving WIM sensor response have been made.

The device presented herein consists of an electromagnetic horizontal impact device. The use of a steel ball serves to avoid friction of the impact mass within the guide tube, and the presence of a slight back-slope easily leads the ball back to its initial position after bouncing on the target structure. Repeated impacts can then be triggered and tuned while in-flight. The obtained impact force duration is shorter than the impact of a truck on bridge piles; however, the required level of momentum transmitted to the pile could be attained, as could the other requirements such as remote control, reproducibility and tunability. This device produces sharp impacts that enable modeling the free vibration response of structures or the impulse response in modal terms. Two applications are presented here in order to demonstrate both the versatility of the device and the types of observations it yields: a study of the inertial pile response; and a study of structure-soil-structure interactions, as part of an effort to describe the “site-city interaction”.

International audience; In this paper are reported the results of an experimental campaign carried out on a post tensioned concrete beam with the aim of investigating the possibility to detect early warning signs of deterioration basing on static and/or dynamic tests. The beam was tested in several configurations aimed to reproduce several different phases of the 'life' of the beam: the original undamaged state, increasing loss of tension in the post tensioning cables, a strengthening intervention carried out by means of a second tension cable, formation of further cracks on the strengthened beam. Responses of the beam were measured by an extensive set of instruments consisting of accelerometers, inclinometers, displacement transducers, strain gauges and optical fibres. The paper discusses the tests program and the dynamic characterization of the beam in the different damage scenarios. The modal properties of the beam in the different phases were recovered basing on the responses recorded on the beam during sine-sweep and impact hammer tests. The variation of the first modal frequency was studied to investigate the sensitivity of this parameter to both the cracking of the concrete section and the tension in the cables and also to compare results given by different types of experimental tests.

International audience; Une méthode pour la détection et la quantification de l'endommagement est proposée. Elle est fondée sur le recalage des paramètres de modèle caractéristiques de l'endommagement, i.e. le module d'Young, à partir de mesures de déformation par fibres optiques. L'information locale apportée par la mesure de déformation permet une détection précoce de l'endommagement. La méthode a été appliquée sur une poutre en béton précontraint de 8m de long soumise à un chargement statique. Le problème de recalage pouvant s'écrire sous la forme d'un problème de minimisation, i.e. minimisation de l'écart entre déformation simulée et déformation mesurée, un algorithme de descente avec un calcul du gradient à moindre coût grâce à l'état adjoint est mis en \oe uvre. Cette méthode utilise les outils numériques standards de l'Ingénieur, e.g. un superviseur en langage Python et le code de calculs éléments finis Code_Aster. Concernant la poutre en béton précontraint, la méthode a permis de déterminer la zone endommagée et d'estimer l'endommagement à 10%.

Les prescriptions reglementaires et les imperatifs techniques necessitent une meilleure connaissance du fonctionnement reel des reseaux d'assainissement. Cette connaissance passe par celle de l'hydraulique d'unepart et par celle des polluants transportes d'autre part. Elle depend de la capacite d'un point de mesure a donner des resultats representatifs, et necessite la definition de criteres facilitant le choix de sites de mesure potentiels. Afin de definir ces parametres, un protocole d'aide a l'instrumentation, qui utilise les ressources de la mecanique des fluides numerique, est en cours de mise au point. Cela necessite des donnees experimentales. Cet article presente les echantillonneurs des champs de vitesses et de concentrations concus, developpes et utilises pour obtenir ces donnees de terrain ainsi que les resultats obtenus.

Presented in this paper are measurements from five different laboratories with four different probes to determine the moisture content of sand samples in flight on a geotechnical centrifuge. The sensors are resistivity probes, capacitance probes, TDR sensors and Geiger Müller tubes. Experiments were carried out with a sand-water-air system, resistivity probes and TDR sensors were additionally tested in the sand-water-NAPL system. All probes were fast responding and gave reliable and reproducible results during centrifuge tests at up to 40 g. The work presented in this paper was carried out as part of the NECER programme funded by the European Commission.

25 ème congrès de l'AIPCR, SEOUL, COREE, REPUBLIQUE DE, 02-/11/2015 - 05/11/2015; Heavy vehicle overloads contribute to premature deterioration of infrastructure and increase road unsafety and unfair competition between transport modes and operators. Public authorities and road operators must therefore implement an efficient checking system to enforce weights and dimensions at an affordable cost. WIM technologies are widely used for screening overloaded vehicles, and sometime to issue warnings to the violators. However, these systems are mostly not yet approved by the Legal Metrology for automated overload control and fining. With the traffic volume increase, the safety constraints and the downsizing of traffic officer staff, it becomes necessary to introduce automated overload control by WIM. The ongoing Automated Overloads Control (AOC) project, supported by the French Ministry of Transports (DGITM) and carried out by IFSTTAR and CEREMA, aims to demonstrate the feasibility of automated overload enforcement with adapted existing WIM technologies to be certified. The project is carried out in partnership with WIM vendors. Trials have been carried out in lab and on the large pavement testing facility of IFSTTAR in Nantes. Sorting algorithms will be developed to identify the vehicles weighed within the required tolerances and on road trials are planned to demonstrate the feasibility of the whole system.

International audience; Ballastless track structure are presently seen as an attractive alternative to conventional ballast. A new model was designed and a real-scale mockup was built and tested in fatigue test at IFSTTAR laboratory. To verify numerical simulations, the railway structure was monitored by conventional strain gages. A distributed fiber-optic strain sensing based on Rayleigh backscatter was also tested in this experiment. Fiber-optic cables were used as long-gage sensors and they were embedded in the concrete slabs of the structure. Firstly, we verified that the sensors were enough mechanical and chemical resistant for withstanding the stresses and the caustic environment experienced during concrete pouring process. Secondly, we validated the strain profiles measurements by comparison with the values obtained by strain gages. A good agreement was found throughout the duration of the fatigue test of 10 million cycles. Moreover, some cracks were observed early during the fatigue test. It is important to be able to monitor them during the service of ballastless track line. We showed that cracks can be detected and localized by fiber-optic distributed strain measurements. Finally, this experiment demonstrates that fiber-optic distributed strain sensing technique based on Rayleigh backscatter is a promising sensing technique to monitor ballastless track structures and more generally, civil engineering structures.

Prevenir l'ensablement des reseaux d'assainissement est un enjeu majeur alors que la norme europeenne NF EN 14654-1 mentionne explicitement le fait qu'il convient de se soucier d'empecher la sedimentation, que diverses etudes montrent que la remise en suspension de ces depots contribue aux deversements d'effluents non traites dans les milieux recepteurs dont le retour au bon etat ecologique est une echeance reglementaire pour 2015. Dans le meme temps on constate un manque de connaissances fondamentales sur les interactions ecoulement sediments. Afin de mieux comprendre les phenomenes physiques lies aux depots, a leur remise en suspension, il apparait important de pouvoir suivre en continu la hauteur des depots. Cette communication presente le cahier des charges du projet Furrina qui permettra la mesure en continu de la hauteur de sediment en un point d'une section transversale de collecteur d'assainissement. Les resultats des essais preliminaires sont presentes.

Road pavement bearing capacity is a crucial point for road maintenance and rehabilitation. Maximum deflection is usually measured discontinuously by mechanical sensors at low speed which implies safety problems. Pavement simulations showed that some parameters describing the deflection basin are more sensitive to pavement damages (cracking or delamination) than the maximum deflection. A direct measurement of surface deflection could be very useful to estimate such parameters. A new measurement system based on an imaging technology is presented. It consists in the projection of a structured pattern on the road surface A camera analyses the pattern deformation, which allows for measuring a surface deflection. The technique has been laboratory qualified in order to measure shapes, displacements and slopes on a road. A first experiment was carried out with a static system on the LCPC test track. The imaging technique was able to measure a surface deflection with satisfactory metrological performance.

Measuring flow-rate and pollutant discharges through sewer networks is required for legal, technical and management reasons. In order to achieve such measurements, a precise knowledge of the hydrodynamic conditions of each candidate measurement location proves critical. The LCPC has thereby become involved in a program on velocity and suspended matter concentration fields. This paper presents the devices developed to obtain 2D sampling of the velocities and pollutant concentrations. Mots-cles : vitesses, concentrations, echantillonnage spatial, assainissement.