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Réunion Island
First results of muon tomography of a giant cliff — The Maido rampart
Truffert, Catherine (IRIS Instruments) | Bouteille, Simon (IRIS Instruments) | Le Moigne, Benoit (BRGM, French Geological Survey) | Martea, J. (IP2I) | Hueber, Nicole (BRGM, French Geological Survey) | Samyn, Kevin (BRGM, French Geological Survey)
Muography is gradually making its way into the field of Earth sciences, notably with the imaging of large objects such as volcanoes (Portal et al., 2013) or the detection of density variations in the subsurface (Truffert et al, 2021). However, its use to monitor opacity/density variations with time is less popular (Jourde et al., 2015). The aim of the experiment was to test muography to assess the risk of rock falls from the top of the Maïdo rampart (La Réunion Island) without intervening in the zone of instability. The primary objective of this experiment was to establish a 3D map of the average density of the gigantic geological object in all directions to which the measuring device is sensitive. The second objective was to provide unique information about the cliff and potential instabilities by studying temporal variations in muon fluxes that have passed through the massif. This paper illustrates the first results of the use of muography to monitor the density variation with respect to time from a single view-point (the telescope).
ABSTRACT Marine reinforced concrete structures are expected to suffer from chloride-induced Corrosion during their service life. The use of in-built cathodic protection system (referred as Cathodic Prevention (CPrev)) can be used to prevent corrosion by maintaining steel passivity. Such a CPrev system has been implemented on a 5.4 km long marine viaduct exposed to aggressive environment in the Indian Ocean. The tidal and submerged parts of the 48 piers were selected to receive this enhanced corrosion protection. The paper emphasizes particularly on the anode design, anode zone configuration and installation practices. Innovative solutions with respect to the anode type and configurations were implemented to meet with the specific requirements of the viaduct construction scheme. The results of initial performance and early polarization behavior between the submerged and tidal parts are also described and discussed. INTRODUCTION Cathodic prevention (CPrev) systems are now often specified for new reinforced concrete structures that are to be exposed to chloride containing environments. The mechanisms and theory of cathodic prevention is comprehensively described elsewhere in the literature. The object of this paper is to present the field application and data for the CPrev system implemented on a 5.4 km long marine viaduct in the tropical environment at the Reunion Island off the coast of East Africa. This paper gives account of further data and methodology most particularly with respect to field data such as anodic and steel potentials, and CP circuit resistance after concreting on-shore and after the concrete elements were placed offshore. An innovative anode system for the concrete submerged part is also presented. PROJECT BACKGROUND In 2013, The Conseil Régional de la Réunion (The public authority of Reunion Island) let a contract for the construction of a 12.5 km long coastal road connecting the two main cities of Reunion Island, Saint-Denis and La Possession. Known as the MT3 project, part of this roadway consists of a 5.4 km long marine viaduct along the coastal perimeter of the island. Standing between 20 m and 30 m above sea level, and located 70 m away from the coast, the elevated highway serves to accommodate buses, cars, pedestrians and bicycles across a dual three-lane configuration, as shown in figures 1 and 2 below.
- Europe (1.00)
- Africa > Réunion Island (0.65)
- North America > United States > Texas > Harris County > Houston (0.16)
- Construction & Engineering (1.00)
- Materials > Construction Materials (0.95)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (0.86)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (0.86)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (0.56)
Abstract Rockfalls are major and essentially unpredictable sources of danger, particularly along transportation routes (roads and railways). Thus, the assessment of their probability of occurrence is a major challenge for risk management. From a qualitative perspective, it is known that rockfalls occur mainly during periods of rain, snowmelt, or freeze-thaw. Nevertheless, from a quantitative perspective, these generally assumed correlations between rockfalls and their possible meteorological triggering events are often difficult to identify because i) rockfalls are too rare for the use of classical statistical analysis techniques and ii) all intensities of triggering factors do not have the same probability. In this study, we propose a new approach to investigate the correlation of rockfalls with rain, freezing periods, and strong temperature variations. This approach is tested on three French rockfall databases, the first of which exhibits an outstandingly high frequency of rockfalls (approximately 950 events over 11 years), whereas the other two databases are more typical (approximately 140 events over 11 years). These databases come fromthe national highway RN1 on La Réunion Island, a railway in the Bourgogne-Franche Comté region, and a railway in the Auvergne region. Whereas a basic correlation analysis is only able to highlight an already obvious correlation in the case of the "rich" database, the newly suggested method appears to detect correlations even in the "poor" ones. Indeed, the use of this method confirms the positive correlation between rainfalls and rockfalls on La Réunion Island database. This method highlights a correlation between cumulative rainfalls and rockfalls in the Bourgogne region, and it detects a correlation between the daily minimum temperature and rockfalls in the Auvergne region. This new approach is easy to use and also serves to determine the conditional probability of rockfall function of a given meteorological factor. This approach will help to optimize risk management in the studied areas based on their meteorological conditions. Nevertheless, even if some rockfalls are correlated to meteorological factors, other seems to occur independently of these factors, which highlights the unpredictability of rockfall hazard.
- North America > Canada (0.49)
- Africa > Réunion Island (0.48)
- Europe > France > Bourgogne-Franche-Comté (0.24)
- Overview > Innovation (0.55)
- Research Report > New Finding (0.48)
- Research Report > Experimental Study (0.35)
- Geology > Geological Subdiscipline (0.48)
- Geology > Rock Type (0.46)
- Geology > Structural Geology > Tectonics (0.46)
Surface geophysics has been used for a number of years to solve a variety of major groundwater exploration problems in coastal and island regions. The electrical properties of nearsurface rocks are highly dependent on porosity, degree of saturation, and pore fluid resistivity Keller and Frischknecht, 1966. Because the resistivity of the formations decreases with increasing salinity of the water content, electrical methods, such as vertical electrical soundings, timedomain electromagnetic soundings, and audiomagnetotellurics AMT, are wellsuited for mapping changes in groundwater salinity and, in particular, for detecting a fresh watersalt water interface.
- Geology > Geological Subdiscipline > Volcanology (0.31)
- Geology > Rock Type > Igneous Rock (0.30)
- Reservoir Description and Dynamics > Formation Evaluation & Management (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.50)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.46)