HAL-BRGM, les publications scientifiques en libre accès du BRGM
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On the use of thermal response tests for deep geothermal exploration in urban areas: A case study made on the Greater Montréal (Canada)
No full textInternational audienceExploring deep geothermal resources can be challenging in dense urban environments and therefore a preliminary screening for suitable target areas using existing data from, for example, the geothermal heat pump industry can help de-risk projects at the early exploration phase. Thermal response tests (TRTs) with initial ground temperature measurements can be used to estimate terrestrial heat flux, a metric to indicate suitable areas for deep geothermal development. The greater the heat flux value, the greater the area suitability. This does not replace deep geothermal exploration drilling for a more accurate assessment of the ground temperature but can help target areas of interest and provide a source of unexploited data. This hypothesis was tested in a study aiming to improve knowledge on deep geothermal resources over the Greater Montréal Area (Canada). TRT datasets were analyzed at 22 locations to estimate the terrestrial heat flux. The results were then compared to heat flux estimates made with bottom-hole temperature data and equilibrium temperature profiles from the 6 deep wells available in the area. Both datasets show a certain degree of correlation. To support these findings, a 400 m deep geothermal exploration well was drilled to provide an accurate equilibrium temperature profile in a zone of interest. The data retrieved from this well validated the results and confirmed that, in this setting, TRT can be used as a de-risking tool for deep geothermal exploration
Etat des lieux de la restauration écologique des milieux marins et littoraux en France : analyse des données issues de la plateforme LITTOREX
No full textNational audienceLa restauration écologique des milieux marins s'impose désormais comme une démarche incontournable pour la préservation de leur fonctionnement et des services qu'ils rendent aux sociétés. Elle s'inscrit notamment dans le cadre de la Décennie des Nations Unies pour la Restauration des Ecosystèmes (2021-2030) et le Règlement européen sur la Restauration de la Nature adopté en 2024. Afin de structurer les connaissances existantes, de partager les retours d'expérience et ainsi favoriser l'efficacité des opérations de restauration au niveau national, l'OFB et le BRGM développent depuis plusieurs années la plateforme LITTOREX dédiée au recensement des projets de restauration. L'analyse des 72 premiers retours d'expérience intégrés à cette plateforme constitue, à ce jour, l'un des états des lieux les plus complets sur les pratiques de restauration écologique en milieux marins et littoraux en France. Les actions recensées concernent majoritairement des écosystèmes de transition intertidaux (marais, herbiers, dunes) reflétant notamment la dynamique internationale de politiques publiques promouvant l'adaptation face au changement climatique. Les projets sur les milieux subtidaux sont aujourd'hui moins documentés soulignant l'importance de compléter le recensement. Par ailleurs, cette analyse montre que les dispositifs de suivi appliqués demeurent hétérogènes, de courte durée et rarement fondés sur des indicateurs traduisant la complexité structurelle, fonctionnelle et sociale de milieux restaurés. Cela a pour effet de limiter l'évaluation de l'efficacité des mesures employées ainsi que la comparabilité inter-sites. Ainsi, si la restauration écologique apparait comme un levier prometteur pour améliorer l'état de conservation des écosystèmes marins et littoraux, les résultats de cette étude révèlent la nécessité de renforcer les suivis à long terme, de mieux documenter les échecs et d'harmoniser les méthodes en définissant un cadre national d'évaluation scientifique. Elle met aussi en avant l'importance d'impliquer les acteurs afin d'enrichir LITTOREX et de capitaliser les retours d'expérience pour diffuser les bonnes pratiques
Multi-annual evolution of coastal dunes: Transition from fixed to transgressive dunes state
No full textInternational audienceMost of coastal dunes located in temperate latitudes, especially in the Northern Hemisphere, are relatively stable. However, along the Gironde coast (SW France) substantial dune remobilization has been observed over the last decade following major marine erosion events during the 2013-2014 winter. This study is based on the analysis of a robust dataset including (i) 10 high-resolution Digital Terrain Models (DTMs) derived from airborne LiDAR surveys conducted over a 12-year period (2011-2023) and (ii) 7 Satellite-derived Digital maps of dune vegetation cover derived from Sentinel-2 satellite images acquired between 2017 and 2023. These morphological and biological parameters are linked to forcing parameters derived from observed wind data, to provide a comprehensive analysis of coastal dune changes related to the transition from vegetation-fixed dunes to the development of transgressive dunes. For the first time, morphological and vegetation dynamics are explored over a large spatial scale (tens of km), covering a range of initial dune morphology and sediment supply.Dunes have transitioned from stable to transgressive states primarily driven by sediment stoss slope recycling process (cannibalism) across a gradient of alongshore variable dune sediment budget, ranging from slightly negative to notably positive (+10 to 15 m 3 /m/yr), Along this coast, transgressive dunes defined as dune migrating via similar stoss and lee slope migration rates, have tripled in number over the last 10 years (reaching ≈ 15 km or 17.3 % of the studied coast). At the center of the Gironde coast where dunes are heavily remobilised, the lee slope of the dune translates landward at a rate of several meters to more than 10 m/year. In the following years, dunes will probably continue to migrate and remobilise across a broader scale if no re-stabilization management plan is implemented
Towards recommendations for owners and geotechnical designers for adaptation of geotechnical structures to climate change
No full textInternational audienceAlmost all existing or planned geotechnical structures will have to cope over the coming decades with changes in the climate, whether gradual or sometimes sudden, which may have consequences ranging from a few disorders to the failure of the structure. Some questions need to be asked to adapt our civil works to these unprecedented changes. How does the climate change alter the properties and mechanical behaviour of soils? Where to find information on sea-level rise or climate projections for designing structures? Which of the IPCC scenarios can or should be considered? What effects might affect a road, a railway, a house, the foundations of an engineering structure, a retaining wall, or a coastal structure? How can we assess the vulnerability of existing structures and make them more resilient? What adaptation solutions are possible for each type of structure? How to make the design, keeping in mind that the climatic actions considered today will be obsolete in a few decades? To answer these questions, a working group (WG) called Geotechnics and Climate Change was launched in France in 2022 by the CFMS (French Society for Soil Mechanics and Geotechnics) and the CFGI (French Society for Engineering Geology). A Part of this WG, the Sub-Group 2, made up of around twenty members from the French geotechnical community, has been specifically dedicated to the adaptation of geotechnical structures to the effects of climate change, with the aim of drafting recommendations for owners and designers of geotechnical structures. The purpose of this paper is to describe the scope of the working group and to present the key points of the future recommendations, that will be published soon: reference scenarios and climate projections in France, effects of climate change and impacts on different types of structures, principles of adaptation strategies and design considerations
Nature-based solutions for water management: Pluridisciplinary state-of-the-art and research needs
No full textInternational audienceNature-based Solutions (NbS) offer a way to preserve, manage and restore ecosystems so as to better meet today's societal challenges, by combining benefits for society and the environment, including biodiversity. They are a response to current climate change-related challenges for water management. However, various barriers exist to the implementation of NbS, such as a lack of appropriation of the concept, as well as needs for knowledge and know-how. Focusing on societal challenges linked to water, we highlight the importance of implementing pluridisciplinary and transdisciplinary projects when trying to implement NbS projects. This requires new approaches in research, practice, and governance. This discussion allows identifying levers for a widespread use of NbS for water management
Effect of particle size on bioleaching of chalcopyrite at moderate temperature
No full textInternational audienceSeveral methods have been studied to overcome chalcopyrite passivation during bioleaching at atmospheric pressure. One such method is to reduce particle size to increase the reactive surface area of the mineral. However, little is known about the effect of fine particles on the performance of chalcopyrite bioleaching in terms of bacterial growth and activity. In this study, two size fractions were prepared by sieving a raw chalcopyrite concentrate to produce particles between 20 and 100 µm and particles below 20 µm. These three materials were used in batch bioleaching tests performed in 2 L stirred reactors at 42 • C, with a solid concentration of 10 %w/w and the BRGM-KCC microbial consortium. Redox potential and iron and copper concentrations were monitored over time to characterize the reaction progress. With the coarser materials, the redox potential increased to above 750 mV vs. SHE within a day, whereas particles below 20 µm took an additional day to reach this potential. This lag phase permitted faster copper dissolution, resulting in a yield of 35 % after two days. In contrast, a yield of 10-20 % copper was achieved in 15 days using coarser materials. In contrast to previous assumptions, fine particles did not hinder bacterial growth and activity. Rather, they promoted them by increasing the availability of substrates generated by greater sulfide oxidation. Bioleaching chalcopyrite particles < 20 µm produced higher copper yields thanks not only to their larger reactive surface, but also to the delayed increase in redox potential and subsequent chalcopyrite passivation
Monitoring of slopes, rock faces and masonry walls in a 19th century public park: the example of the Buttes Chaumont Park (Paris, France)
No full textInternational audienceDeveloped on former gypsum quarries, the Buttes Chaumont Park is a 25-hectare geotechnical complex that is unique in the world. After three years of heavy work to create, in particular, an artificial cave, a lake and an island, the park opened in 1867 and has suffered gravitational hazards ever since (landslides, rockfalls and sinkholes). The BRGM has worked with the Paris City Council since 2021 to characterize the geological and geotechnical context, identify major gravitational hazards, and monitor the evolution of instabilities in slopes and rock/masonry walls. In this context, the BRGM has proposed, defined and followed a geotechnical supervision scheme including four levels of monitoring: detailed quarterly site visits since March 2023, bimonthly tacheometric surveys (operating since December 2022), monthly manual gauges measurements (since January 2024), and automatic extensometers and temperatures measurements (since March 2024). The interpretation of the data allows to confirm and/or complement the gravitational hazard mapping that had been carried out in 2022. By analyzing the correlation between displacement measurements and meteorological conditions, we could also differentiate between seasonal/daily trends mainly associated with temperature variations, and displacements associated with gravitational processes. These results help mitigate risks in the Buttes Chaumont Park in its current state, and adapt works planned in the coming years to restore and secure the park
Morphological Development and Evolution of Barchanoid Dunes on the Cap Ferret Coastal Spit
No full textInternational audienceBarchans are crescent-shaped dunes with their convex side facing the wind and their horns pointing downwind, commonly observed in deserts but also in coastal environments. This study investigates the dune field of the Cap Ferret Spit (5-km wide, 23-km long; Atlantic Coast, SW France) including of series of barchanoids dunes, currently stabilized by forest cover. The aims are to classify each dune into distinct typologies and characterize their morphology in order to analyze their evolution. LiDAR-based analysis identified four distinct barchanoid dune types. Moreover, it revealed superimposed bedforms on the dunes, including draping and oscillating patterns, reflecting the influence of consistent wind regimes during dune development and migration. This study proposes an evolutionary sequence in which proto-barchans evolve into barchanoid ridges and eventually as mature isolated barchans. These findings provide insight into the geomorphological evolution of barchanoid dunes in a coastal context, and particularly their migration pattern on a coastal spit syste
Speleothem-based reconstruction of Holocene changes in monsoonal patterns and environmental conditions in Central Brazil
No full textInternational audienceThe east-west precipitation dipole that occurs in South America has been vastly investigated in previous studies using paleoclimate records from east and west of the continent, but the climate dynamics of central-eastern Brazil remains less understood. While δ18O values have been widely used to study past rainfall variability over South America, their ability to resolve local hydrological changes in central Brazil during the Holocene has been proven to be difficult. Recent studies in the region have used δ13C values and 87Sr/86Sr ratios from speleothems to assess local paleo-hydrology and environmental conditions. Here, we revisit this topic for the last 11,000 years based on a novel multi-proxy record (δ18O, δ13C, and 87Sr/86Sr) from a stalagmite collected in central Brazil at the northern side of the present day South Atlantic Convergence Zone (SACZ). The overall climate shifted from drier to wetter conditions throughout the Holocene, reflecting the increasing southern insolation and the monsoon-driven wetting trend based on the local and regional δ13C and pollen records. Changes in atmospheric circulation patterns during the Holocene might have been responsible for the increase in δ18O values through time. A north-eastern climate influence during the weaker monsoon phase from early-to-mid Holocene contrasts the late Holocene and present-day influence of SACZ over the area. Hence, a negative correlation between δ18O and δ13C indicates a decoupling of monsoon activity from local climate conditions. The Sr isotope signals in our site may be influenced by mixed lithology or increased dust input from nearby sandstone during drier periods, revealing the complexity of this proxy. The São Mateus record highlights the complex, non-stationary interplay between monsoon strength, SACZ dynamics, and atmospheric processes in shaping central Brazil's hydroclimate
Spectral induced polarization monitoring of chalcopyrite ore bioleaching: insights from laboratory column experiments
No full textInternational audienceBioleaching is a biologically facilitated process that helps to dissolve valuable metals in order to extract them from the mineral gangue. Applied in the field to heap ores, its efficiency mainly depends on solution flow inside the heterogeneous heaps, which is often tortuous and can remain stagnant in the pores and crevices between the particles. Methodologies that can help to monitor the bioleaching processes are therefore needed to improve operational efficiency. In this article, we present for the first time preliminary laboratory-scale investigations on spectral induced polarization (SIP) during the bioleaching of chalcopyrite (CuFeS2) containing ore material from a mine in Chile. Two column experiments representing different stages of the bioleaching process were monitored under un-saturated and highly acidic environment (pH ~2). Our objective was to explore the feasibility of SIP for detecting changes in electrical properties potentially associated with bioleaching-induced mineral dissolution and alteration. The results show a rapid decrease in SIP phase shift and imaginary conductivity during the early stage of bioleaching, while the real conductivity remains relatively stable. At a more advanced stage of bioleaching, the phase response is weaker and more stable. A relaxation time distribution (RTD) analysis was applied to further investigate changes in polarization mechanisms. Prior to bioleaching, the RTD exhibits a well-defined peak consistent with polarization controlled by sulfide mineral grains, whereas after one month of bioleaching the RTD broadens and shifts toward larger relaxation times, accompanied by a decrease in chargeability. This combined evolution suggests bioleaching-induced modifications of electrochemically active surfaces, potentially related to mineral dissolution and the formation of passivation layers. Estimated particle sizes derived from the RTD analysis are consistent with scanning electron microscopy observations. Although, the absence of a dedicated abiotic control column prevents us from attributing these changes unambiguously to bioleaching alone, these results highlight the potential of SIP as a non-invasive, real-time and integrative tool to monitor leaching processes and to identify zones that may remain weakly affected by leaching