Abandon des exploitations souterraines CdF Méthodes géophysiques appliquées à la recherche d'anciens travaux miniers

National audienceLes risques potentiels d'instabilité induits par les ouvrages souterrains abandonnés constituent un héritage du passé dont il faut tenir compte sur le plan de la sécurité des biens et des personnes, particulièrement dans et à la périphérie des zones urbanisées et industrialisées. La détection des vides miniers, proches de la surface et susceptibles d'évoluer plus ou moins rapidement vers le fontis, représente un élément essentiel des investigations géotechniques à mettre en oeuvre dans les régions sous-minées. Si la campagne de sondages est la méthodologie la plus répandue et bien souvent la plus fiable, la prospection par des méthodes géophysiques simples, rapides et non destructives, peut parfois apporter des informations très importantes sur la localisation et l'état de vieux travaux miniers superficiels. Elle peut également guider le choix de l'implantation des sondages. La présente étude bibliographique a consisté à inventorier et à comparer les meilleures techniques existant actuellement dans ce domaine et à tester certaines d'entre elles sur site

Comportement des terrains au-dessus des exploitations partielles Diagnostic de stabilité et organisation de la surveillance des exploitations partielles abandonnées Cas des carrières de la région Nord-Pas-de-Calais

Les exploitations souterraines dites partielles ont pour particularité de laisser subsister des vides en profondeur après exploitation. Nous nous intéressons ici au cas des exploitations partielles développées en terrains sédimentaires, dans des gisements peu pentes. Les principales méthodes d'exploitation partielle dans ce type de gisement sont les méthodes par chambres et piliers abandonnés (figure 1) et les méthodes par îlots où alternent bandes fermes et bandes dépilées. Ces méthodes posent le délicat problème de l'évolution à long terme de la stabilité des terrains dans lesquels sont creusées ces excavations et des risques engendrés en surface pour les personnes et les biens

The use of forward rate agreements in Canada

In this article, the authors identify forward rate agreements, or FRAs, as short-term interest rate guarantee instruments negotiated by two parties, one of which is typically a bank. In outlining the main features of FRAs, the authors contrast them with BAX contracts (futures contracts on bankers' acceptances that are negotiated through the Montreal Exchange). The article then describes how market participants use FRAs to cover short-term interest rate risk. The final section deals with the way the Bank of Canada uses information from the FRA market as an indicator of interest rate expectations. Econometric models used to retrieve information from FRA rates, as well as the underlying assumptions, are discussed in an appendix.

Method for reclaiming opencast sites in the central and southern coalfields (HBCM, groupe Charbonnages de France)

The activities presented are the result of collaboration between HBCM, INERIS, responsible for the coordination of the studies of the sites within the context of an ECSC research project, "Rehabilitation of old mine workings", and SIR AS, a branch of CNR, responsible for managing the restoration project in the mining sites belonging to the Herault Operations Unit. The mining deposit of Graissessac basin extends over 20km and is in the form of a syncline, 2km wide in the area being mined. The underground workings were shut down in 1962 after a total coal production of 30 million tonnes. The mining was developed mainly along the north flank of the syncline, in 7 to 8 seams of between 30° and 50° dip. Since 1956, 4.6 million tonnes of coal with 29 million m3 of overburden were extracted by open-pit on 5 mountain massives (Plaisance, Rive Gauche, Rive Droite, Cap Negre, and Orb). The mining ended in 1993. The pits situated at mountains tops, were worked in benches, frequently leaving as such, with no backfilling, while the overburden materials were dumped on hillsides, at limit of equilibrium at heights of 40 to 250 metres. Altogether, the sites to be reclaimed represent an extend of 400 hectares. The provisional duration of the work is 4 years. CdF has decided to carry out a particularly exemplary restoration on the Herault sites and has procured the necessary financial and technical means

Observation and auscultation of the geotechnical behaviour of a slope in an open cast mine influenced by old underground mining (South-western part of France)

International audienceThe final slopes of a French open pit mine of the "Charbonnage de France" Company which final depth will be 300 metres, have been designed after a Standard geotechnical survey. This one has taken into account the geomechanical, hydrogeological, structural parameters äs well äs the" decohesion", induced by former mining subsidence. However some slopes can locally present risks of slipping (increasing with the depth of the pit) induced by old Underground mining. A methodology has been defined concerning the slope auscultation and its behaviour including the use of numerous measuring tools (topographic measurement, inclinometer, equipped cable bolts...). Two auscultation cases are presented, one on a slope slipping, another one on a potential slide. In the first case, the instrumentation checked that the reinforcement is satisfactory. In the second case, the instrumentation allows to analyse that the correct measures have been taken to prevent any risk

Surveillance et auscultation du comportement géotechnique de talus de mine à ciel ouvert influencés par des travaux souterrains (application à la fosse Ste Marie)

National audienceLes flancs definitifs de l'exploitadon ä ciel ouvert des H.B.C.M, U.E Tarn, qui aura une profondeur finale de 300 metres, ont ete dimensionnes apres une etude geotechnique classique prenant en compte les divers parametres geomecaniques, hydrogeologiques, structuraux ainsi que la decohesion liee a l'influence d'anciens affaissements miniers. Cependant certains flancs d'exploitaüon influences par la reprise d'affaissements miniers en liaison avec l'enfoncement de l'exploitation ä ciel ouvert, presentent localement des configuraüons de risque de glissement biplanaire. Aussi a t-il ete mis en place toute une methodologie pour ausculter et surveiller au plus pres le comportement de ces talus : suivi topographique, inclinometres et extensometres en sondages, indicateurs de rupture de bancs, jauges de contrainte sur boulons-cables de renforcement. Deux cas d'auscultation sont presentes et analyses: l'un sur un glissement declare, l'autre sur une configuration a risque. L'instrumentation a permis dans le premier cas de s'assurer que les moyens de confortement mis en oeuvre etaient satisfaisants et dans le second cas de controler que les mesures adoptees pour prevenir ce risque etaient correctes

New geochronological history of the Mbuji-Mayi Supergroup (Proterozoic, DRC) through U-Pb and Sm-Nd dating

peer reviewe

How to date a sedimentary serie: Different approaches to better constrain the diversification of early eukaryotes in Central Africa (Mbuji-Mayi Supergroup, Proterozoic, DRCongo)

Peer reviewe

Managing understory light conditions in boreal mixedwoods through variation in the intensity and spatial pattern of harvest: A modelling approach

In the context of partial harvesting, adequately managing post-harvest light conditions are essential to obtain a desired composition of tree species regeneration. The objective of this study was to determine how varying the intensity and spatial pattern of harvest would affect understory light conditions in boreal mixedwood stands of northwestern Quebec using the spatially explicit SORTIE-ND light model. The model was evaluated based on comparisons of observed and predicted light levels in both mapped and un-mapped plots. In mapped plots, reasonably accurate predictions of the overall variation in light levels were obtained, but predictions tended to lack spatial precision. In un-mapped plots, SORTIE-ND accurately predicted stand-level mean GLI (Gap Light Index) under a range of harvest intensities. The model was then used to simulate nine silvicultural treatments based on combinations of three intensities of overstory removal (30%, 45% and 60% of basal area) and three harvest patterns (uniform, narrow strips, large gaps). Simulations showed that increasing overstory removal had less impact on light conditions with uniform harvests, and a more marked effect with more aggregated harvest patterns. Whatever the harvest intensity, uniform cuts almost never created high light conditions (GLI > 50%). Gap cuts, on the other hand, resulted in up to 40% of microsites receiving GLI > 50%. Our results suggest that either a 30% strip or gap cut or a 45–60% uniform partial harvest could be used to accelerate the transition from an aspen dominated composition to a mixedwood stand because both types of cut generate the greatest proportion of moderately low light levels (e.g., 15–40% GLI). These light levels tend to favour an accelerated growth response among shade-tolerant conifers, while preventing excessive recruitment of shade-intolerant species. A better understanding of how spatial patterns of harvest interact with tree removal intensity to affect understory light conditions can provide opportunities for designing silvicultural prescriptions that are tailored to species’ traits and better suited to meet a variety of management objectives

Personalized Risk Assessment for Prevention and Early Detection of Breast Cancer: Integration and Implementation (PERSPECTIVE I&I).

Early detection of breast cancer through screening reduces breast cancer mortality. The benefits of screening must also be considered within the context of potential harms (e.g., false positives, overdiagnosis). Furthermore, while breast cancer risk is highly variable within the population, most screening programs use age to determine eligibility. A risk-based approach is expected to improve the benefit-harm ratio of breast cancer screening programs. The PERSPECTIVE I&I (Personalized Risk Assessment for Prevention and Early Detection of Breast Cancer: Integration and Implementation) project seeks to improve personalized risk assessment to allow for a cost-effective, population-based approach to risk-based screening and determine best practices for implementation in Canada. This commentary describes the four inter-related activities that comprise the PERSPECTIVE I&I project. 1: Identification and validation of novel moderate to high-risk susceptibility genes. 2: Improvement, validation, and adaptation of a risk prediction web-tool for the Canadian context. 3: Development and piloting of a socio-ethical framework to support implementation of risk-based breast cancer screening. 4: Economic analysis to optimize the implementation of risk-based screening. Risk-based screening and prevention is expected to benefit all women, empowering them to work with their healthcare provider to make informed decisions about screening and prevention