Induced seismicity monitoring of an underground salt cavity under a transient pressure experiment

International audienceWithin the framework of a research project launched to assess the feasibility of seismic monitoring of underground growing cavities, this specific work focus on the analysis of the induced microseismicity generated by a controlled pressure experiment recently carried out in a salt mine environment. A local seismic array has been installed over a stable underground cavity within a salt layer located in the Lorraine basin (north-east France). The array includes four 3D components and three 1D component geophones deployed at depths between 30 m to 125 m in cemented boreholes drilled in the vicinity of the study area. The underground cavity under monitoring is located within a salt layer at 180 m depth and it presents a rather irregular shape that can be approximated by a cylindrical volume of 50 m height and 180 m diameter. Presently, the cavity fully saturated with brine inducing a significant pressure on its walls (~2.5 MPa) to keep the overburden mechanically stable. Nevertheless some small microsesimic events were recorded by the array and analysed (~500 events in two years of recording). In October 2005, a controlled pressure transient experiment has been carried out in the cavity in order to analyse the mechanical response of the overburden by tracking the induced microseismicity. The recorded events are mainly grouped in clusters of 3 to 30 seconds of signal duration with non-emergent first arrivals and rather low frequency content (between 20 to 120 Hz). Some of these events have been spatially located by travel-time picking close to the actual cavity and its immediate roof. Preliminary spectral analysis suggests sources possibly related to resonant fluid-filled cracks, and/or cavitations due to the dynamic excitation of the brine-filled cavity. Rock-debris falling into the cavity from delamination of clayey marls in the immediate roof is possibly another source of seismic excitation. No clear evidence of classical brittle ruptures in the competent layers of the overburden has been observed up to now. Current work is focused on the discrimination of all these possible mechanisms to better understand the damage processes within the rock mass

Induced seismicity in a salt mine environment evaluated by a coupled continuum-discrete modelling

International audienceWith the objective to better understand the induced microseismicity in a salt mine environment due to an underground solution mining, an in situ experiment is undertaken by GISOS in the Lorraine salt basin. The overburden overlying the salt cavity is characterized by the presence of two competent layers where most microseismic events are expected. This paper presents a coupled continuum-discrete modelling to simulate the mechanics of fracture initiation and propagation in the rock mass overlying the cavity: discrete approach for the competent layers and continuum approach for marls, salt and other rocks and soils. For the competent layers, numerous calibrations of the model microparameters based on the laboratory results are firstly performed. The first coupled modelling results suggest that the mechanism of fracturing in the competent layers is predominantly tensile as it could be expected. The results also show that the microseismic events associated to the progressive damage in the competent layers through microcraks development can be modelled. This opens interesting perspectives to assess the feasibility of seismic monitoring of underground cavities by comparing, in the future, the numerical modelling results with the recorded seismicity of the study area.Dans l'objectif de mieux comprendre la microsismicité induite dans des mines de sel, une expérimentation in situ a été entreprise par le GISOS sur une cavité saline de la région Lorraine. Le recouvrement est caractérisé par la présence de deux bancs raides dans lesquels l'essentiel de l'activité microsismique est attendue lors de la reprise de l'exploitation. Ce papier présente une modélisation basée sur une approche couplée : continue (pour les marnes et le sel) et discrète (pour les bancs raides) pour évaluer les mécanismes de développement des fractures dans le recouvrement. De nombreuses calibrations des microparamètres du modèle discret à partir des paramètres macroscopiques ont été nécessaires. Les résultats de la modélisation montrent que le mécanisme de fracturation dans les bancs compétents résulte essentiellement d'efforts en traction. Les premiers résultats montrent aussi que les évènements microsismiques peuvent très bien être mesurés à travers la formation des microfissures. Ceci ouvre des perspectives intéressantes pour des confrontations avec les mesures qui seront enregistrées lors de l'effondrement provoqué

A large scale continuum-discrete numerical modelling : application to overburden damage of a salt cavern

International audienceWith the objective to better understand the evolution of overburden damage on top of an underground solution mining, an in-situ experiment is undertaken above a salt cavity in the Lorraine region (NE of France). The overburden overlying the salt cavity is characterized by a competent layer where most brittle damage, with the associated microseismicity, is expected. This work presents a coupled continuum-discrete modelling approach to simulate the mechanics of fracture initiation and propagation in the rock mass, a continuum approach for the marls and salt layers, and a discrete micromechanical approach for the competent layer. A methodology of a large scale coupled continuum-discrete modelling is proposed and applied to the site of Cerville-Buissoncourt. The numerical verification of the hybrid approach response is achieved by comparing the results with those from the fully continuum model at the site scale when the competent layers behave elastically. The first results of a large scale modelling based on the hybrid approach suggest that the fracture mechanisms in the competent layers are predominantly tensile. Finally, these explicit microcracking simulations open interesting perspectives for comparison with the observed microseismicity of the study area (transient pressure experiment or future final collapse).Dans l'objectif de mieux comprendre la microsismicité induite dans des mines de sel, une expérimentation in situ a été réalisée sur une cavité saline de la région Lorraine (Nord-Est de France). Le recouvrement est caractérisé par la présence d'un banc raide dans lequel l'essentiel de l'activité microsismique est attendue lors de la reprise de l'exploitation. Ce papier présente une modélisation basée sur une approche couplée : continue (pour les marnes et le sel) et discrète (pour les bancs raides) pour évaluer les mécanismes de développement des fractures dans le recouvrement. Une méthodologie de modélisation à grande échelle couplant les approches continue et discrète a d'abord été proposée, puis appliquée au site de Cerville-Buissoncourt. La validation numérique de cette approche hybride est réalisée par comparaison avec la réponse d'un calcul continu à l'échelle du site. Les premiers résultats de cette modélisation hybride à grande échelle montrent que les mécanismes de fracturation prédominants dans les bancs raides restent les tractions. Ceci ouvre des perspectives intéressantes pour des confrontations avec les mesures qui seront enregistrées lors de l'effondrement provoqué (essai de pression, future effondrement après la reprise de l'exploitation)

individual participant data meta-analysis of randomised trials study protocol

Introduction Parenteral anticoagulants may improve outcomes in patients with cancer by reducing risk of venous thromboembolic disease and through a direct antitumour effect. Study-level systematic reviews indicate a reduction in venous thromboembolism and provide moderate confidence that a small survival benefit exists. It remains unclear if any patient subgroups experience potential benefits. Methods and analysis First, we will perform a comprehensive systematic search of MEDLINE, EMBASE and The Cochrane Library, hand search scientific conference abstracts and check clinical trials registries for randomised control trials of participants with solid cancers who are administered parenteral anticoagulants. We anticipate identifying at least 15 trials, exceeding 9000 participants. Second, we will perform an individual participant data meta-analysis to explore the magnitude of survival benefit and address whether subgroups of patients are more likely to benefit from parenteral anticoagulants. All analyses will follow the intention-to- treat principle. For our primary outcome, mortality, we will use multivariable hierarchical models with patient-level variables as fixed effects and a categorical trial variable as a random effect. We will adjust analysis for important prognostic characteristics. To investigate whether intervention effects vary by predefined subgroups of patients, we will test interaction terms in the statistical model. Furthermore, we will develop a risk-prediction model for venous thromboembolism, with a focus on control patients of randomised trials. Ethics and dissemination Aside from maintaining participant anonymity, there are no major ethical concerns. This will be the first individual participant data meta-analysis addressing heparin use among patients with cancer and will directly influence recommendations in clinical practice guidelines. Major cancer guideline development organisations will use eventual results to inform their guideline recommendations. Several knowledge users will disseminate results through presentations at clinical rounds as well as national and international conferences. We will prepare an evidence brief and facilitate dialogue to engage policymakers and stakeholders in acting on findings. Trial registration number PROSPERO CRD4201300352

Energy Resolution Performance of the CMS Electromagnetic Calorimeter

The energy resolution performance of the CMS lead tungstate crystal electromagnetic calorimeter is presented. Measurements were made with an electron beam using a fully equipped supermodule of the calorimeter barrel. Results are given both for electrons incident on the centre of crystals and for electrons distributed uniformly over the calorimeter surface. The electron energy is reconstructed in matrices of 3 times 3 or 5 times 5 crystals centred on the crystal containing the maximum energy. Corrections for variations in the shower containment are applied in the case of uniform incidence. The resolution measured is consistent with the design goals

LINKING CATTLE GRAZING BEHAVIOR TO METHANE AND CARBON DIOXIDE DYNAMICS

Various methods are presently used to measure methane (CH4) emissions of ruminants on pasture. Those measurements are essential to evaluate nutritional strategies to mitigate enteric CH4 emissions as well as addressing the selection of low producing individuals. On pasture and in the barn, variations in CH4 emissions are observed depending on the time of the day. However, no studies have been made to link these diurnal fluctuations to behavioural phases, especially on pasture. The aim of this study was to understand the individual dynamics of CH4 production and their links to the grazing behaviour. For this purpose, a new tool was specifically developed. Five red-pied dry cows were equipped with infrared CH4 and carbon dioxide (CO2) sensors measuring concentrations in the exhaled air at 4 Hz. The animals were equipped with a heart rate belt (HR) and motion sensors to detect their feeding behaviours (grazing vs. rumination) for periods of 8 h/d. Wind speed (WS) was also monitor to verify interference with sampled gas concentrations. Results showed that using the CH4:CO2 ratio reduced the interference with WS that was observed on raw CH4 and CO2 concentration signals. CH4:CO2 ratio average over 5 min periods indicated that CH4 emissions were lower during grazing than rumination (P<0.01). The eructation frequency during grazing (0.48 eructation/min, P<0.01) was also lower than during rumination (0.65 eructation/min). HR was higher during grazing that rumination. Because HR is usually linked to metabolic CO2 production intensity, hence influencing the denominator of the CH4:CO2 ratio, further investigation should focus on the quantification of changes in fermentative and metabolic CO2 emissions along the day to estimate total CH4 production more accurately and the relationship between CH4 emissions patterns and post-feeding times.AgriGE