Activité microsismique et caractérisation de la détectabilité des réseaux de surveillance du bassin houiller de Gardanne

National audienceMining in Provence have left many underground voids that may cause subsidence or collapse in areas of high population density. Microseismic monitoring networks have been deployed to prevent this risk. Here we present the post-mining microseismic records between 2008 and 2012 and the characterization of networks detectability at different scales.L'activité minière en Provence a laissé de nombreux vides souterrains qui peuvent provoquer la subsidence des terrains ou des effondrements dans des zones à forte densité de population. Pour prévenir ces risques, une surveillance microsismique a été mise en place dans les zones à fort enjeux. Ainsi depuis l'arrêt des concessions minières de Provence, l'INERIS a installé 5 réseaux de surveillance microsismique sur le bassin houiller de Gardanne qui était exploité par Charbonnages de France. Puis, le BRGM-DPSM en tant que Maître d'ouvrage délégué de l'Etat, a demandé à l'INERIS la poursuite de la surveillance microsismique

Surveillance des risques d'effondrement dans l'après-mine, besoins, méthodes : apport de la microsismique

National audienceDuring the exploitation, the stability of the underground mining works mainly directed towards the safety of the staff and the safeguard of the mine, were practised with methods adapted to accessible and maintained buildings. Following the closure of the mines, these conditions not being more assured and the objectives of public safety resolutely turned towards the safeguard the people and the overlying structures (such as urbanised areas and all kind of infrastructures), result in remotely seeking applicable total methods and from surface. Among those, we develop the typical example of the microsismicity which, before being applied to the monitoring of the risks of mining collapse had to answer a precise schedule of conditions to be qualified then validated. An example of its use successfully for the moni'.oring of the pillar of Nondkeil (Ottange, 57) is proposed.Lors de l'exploitation, la stabilité des ouvrages miniers principalement orientée vers la sécurité des mineurs et la sauvegarde de la mine était pratiquée avec des méthodes adaptées à des édifices accessibles et entretenus. Suite à la fermeture des mines, ces conditions n'étant plus assurées et les objectifs de sécurité publique résolument tournés vers la sauvegarde des personnes et des biens en surface conduisent à rechercher des méthodes globales applicables à distance et depuis la surface. Parmi cellesci, nous développons l'exemple type de la microsismicité qui, avant d'être appliquée à la surveillance des risques d'effondrement minier, a dû répondre à un cahier des charges précis pour être qualifiée puis validée. Un exemple de son utilisation avec succès pour la surveillance du stot de Nondkeil (Ottange, 57) est proposé

Real-time Microseismic Monitoring : Automatic Wave Processing and Multilayered Velocity Model for Accurate Event Location

International audienceMine-induced seismicity is a well-known phenomena wherever mining activities take place at great depths. At Provence colliery, France, longwall mining at 1100 meters deep induces numerous, daily tremors, triggered by the caving proeess above the tabular onebody. Many factors play an important part in this seismic activit

Surveillance des risques d'effondrement dans l'après mine, besoins, méthodes

International audienceAt the time of the exploitation, the stability of the mining works mainly directed towards the safety of the minors and the safeguard of the mine, were practised with methods adapted to accessible and maintained buildings. Following the closing of the mines, these conditions not being more assured and the objectives of public safety resolutely tumed towards the safeguard the people and the goods on the surface, resuit in remotely seeking applicable total methods and from surface. Among those, we develop the typical example of the microsismicity which, before being applied to the monitoring of the risks of mining collapse had to answer a precise schedule of conditions to be qualified then validated. An example of its use successfully for the monitoring of the pillar of Nondkeil (Ottange, 57) is proposed.Lors de l'exploitation, la stabilité des ouvrages miniers principalement orientée vers la sécurité des mineurs et la sauvegarde de la mine, était pratiquée avec des méthodes adaptées à des édifices accessibles et entretenus. Suite à la fermeture des mines, ces conditions n 'étant plus assurées et les objectifs de sécurité publique résolument tournés vers la sauvegarde des personnes et des biens en surface, conduisent à rechercher des méthodes globales applicables à distance et depuis la surface. Parmi celles-ci, nous développons l'exemple type de la microsismicité qui, avant d'être appliquée à la surveillance des risques d'effondrement minier a dû répondre à un cahier des charges précis pour être qualifiée puis validée. Un exemple de son utilisation avec succès pour la surveillance du stot de Nondkeil (Ottange -57) est proposé

3-Dimensional modeling of fault-slip rockbursting

International audienceA research program has been carried out at INERIS aiming to quantify rockburst potential from mining-induced fault-slip. As a part of the research, numerical modeling of fractured rock mass has been undertaken, using the three-dimensional distinct element code 3DEC. Results presented in this paper demonstrate a very good agreement between calculated deformations of modeled faults and the experienced rockburst sequence of the Estaque-sud district of the collier

Ecoute microsismique appliquée aux versants instables, exemple des ruines de Séchilienne (Isère, 38)

International audienceField observations and movements measured since 1985 by the Lyon CETE (Public works regional engineering office) monitoring system at the Ruines de Séchilienne show that the slope deformation and fault mechanisms are complex. To provide a deeper understanding of these mechanisms, INERIS has been investigating the site through the instrumentation of deep drillholes since 2009. An experimental multi-parameter monitoring system was installed on the western edge of the large active zone. It uses an integrated technology platform which combines microseismic, geotechnical, hydrogeological, meteorological and 3D displacements. The article outlines the objectives and the methodology applied by INERIS to meet the requirements of early warning multi-parameter systems applied to unstable rock slopes. The studied site and the main characteristics of the system are presented. Items dealing with the system calibration and characterization data are described and preliminary data are givenLes observations et les mouvements mesurés, depuis 1985, par le système de surveillance du CETE de Lyon sur le mouvement des Ruines de Séchilienne, montrent que les mécanismes de déformation et rupture du versant sont complexes. Pour progresser dans la compréhension de ces mécanismes, l'INERIS contribue depuis 2009 aux investigations menées sur le site par forages profonds. Un système d'observation multi-paramètres a ainsi été installé en bordure Ouest de la zone active. Il fait appel à une plateforme technologique intégrée qui combine des mesures microsismiques, géotechniques, hydrologiques, météorologiques et des mesures de déplacement tridimensionnel. L'article décrit les objectifs de la démarche et la méthodologie mise en oeuvre par l'INERIS pour répondre aux exigences des systèmes d'alerte précoce multi-paramètres, appliqués aux mouvements de versants instables. Le site d'étude et les principales caractéristiques du dispositif sont présentés. Des considérations sur le calibrage du système et la qualification des données sont décrites et les premières données sont présentées

Semi-automatic detection and localization of microseismicity induced by a "salt dissolution provoked" cavity collapse

Natural underground cavities, active or abandoned mine workings, particularly when they are shallow, can provoke large scale land subsidence and collapses attended by catastrophic social-economic impacts. The potential of passive microseismic monitoring to prevent such disasters was already indicated by several studies. Nonetheless, to further improve monitoring reliability a better understanding of associated seismicity is inevitable. In this context, within a large multi-parameter research project at Cerville-Buissoncourt in Lorraine, France, the growth of a single, shallow, about 150 m diameter salt cavity created by salt dissolution mining was surveyed from 2004 until 2009 when the cavity reached its critical size and a 'controlled' collapse was initiated. During the experiment, a large microseismic data set was recorded by a triggered, high resolution geophone monitoring system. Initial processing and data inspection reveal very unusual seismic signals mainly appearing in complex swarming sequences (Mercerat et al., 2010; Contrucci et al., 2011). To resolve spatio-temporal characteristics of associated seismicity we developed an semi-automatic seismic event detection and localization algorithm adressing these abnormal signal characteritics. The detector design is based on a spectral envelope function calculated for each seismogram. By this function, coherent signals are distinguished from signals comprising rather randomly distributed frequency proportions as noise or CODA waves. First application tests demonstrated highly improved event detection results when analysing seismic events of highly varying size and duration occurring in a swarming sequence. In addition, we localized the detected seismic events using inter-station amplitude ratios as introduced by Battaglia and Aki (2003) and Taisne et al. (2011). Within this approach, hypocenter source inversion relies on the decay of seismic wave amplitudes along the source-receiver path. As a result, no troublesome a priori phase segmentation is needed and the entire data set can be processed. To calibrate the local seismic attenuation law we used ~700 seismic events with known hypocenter locations found by previous studies (Klein et al., 2011). The final optimized localization algorithm sufficienty constrained the tendency of actual hypocenter source location in the cavity region. Taken all together, our detection and localization strategy provides an appropriate first order approximation to study spatio-temporal attributes of seismicity from huge data sets associated with seismic signals of unknown or complex signature as observed for Cerville-Buissoncourt

Methodology of research in the fight against rockbursts at the Provence colliery

International audienceA research program has been carried out at INERIS aiming to quantify rockburst potential at the Provence colliery. As a part of the research, numerical modeling of fractured rock mass has been undertaken, using the three-dimensional distinct element code 3DEC. Results presented in this paper demonstrate a very good agreement between calculated deformations of modeled faults and the rockburst sequence experienced at the Estaque-sud district of the colliery

Conception, numerical prediction and optimization of geomechanical measurements related to a vertical Mine-by-Test at the Meuse/Haute-Marne URL

International audienceAndra is conducting scientific experiments in the Meuse/Haute-Marne Underground Laboratory among which REP experiment is a vertical mine-by-test focusing on short and long term hydromechanical response of the argilite to the main shaft sinking. Displacements, strains, and pore pressures will be monitored while the shaft is passing down. Andra and INERIS intend to back-analyse most recorded geomechanical data based on under-excavation numerical technique in order to estimate pre-existing field stresses. The under-excavation interpretative technique consists in determining the pre-existing stress tensor related to a quite large volume of rock based on generalized inversion of geomechanical measurements recorded during the disturbance of the host rock (typically the excavation of an underground opening). In the framework a numerical study aiming to test accurately the sensitivity and numerical stability of this interpretative technique, 3D modelling of a step-by-step vertical mine-by-test, based on REP design, has been undertaken. One major step of the numerical procedure is to calculate each instrument response, coming up with a transient predicted measurement curve versus the progress of the shaft sinking. These important, intermediate results, on which this paper focuses, led the authors to several preliminary operational recommendations, e.g. relocation of sensors, which could not have been determined otherwise. These predictive numerical responses are of importance when a fast but efficient validation of the real data coming out from the field must be performed. More generally, the authors intend to show how a synthetic, 3D numerical conception of a under-excavation interpretative experiment reveals to be unique method to explore different instrumentation layouts and optimize numerous options offered to the engineer in charge of its final design

Apport de la mécanique des roches pour l'évaluation et la gestion des risques à long terme dans les exploitations minières abandonnées Cas des mines de fer de Lorraine

International audienceDue to its historical and economical evolution, we are now facing consequences of the end of mining in large sedimentary basins where it was the major regional activity during the last two Centuries. The contribution of Rock Mechanics in "after-mining" phases emerges nowadays, especially in the fields prediction and prevention of sudden collapses overlying partially mined areas. This paper present the example of closed iron mines in Lorraine (France) where different problems, at different scales have been identified : risk assessment, consequences for town-and-country planning and durable development.L'évolution historique et économique nous amène aujourd'hui à être confrontés aux conséquences de l'arrêt de l'exploitation de grands bassins miniers, qui a représenté l'activité dominante de certaines régions pendant un ou deux siècles. On commence à discerner ce que devra être aussi le rôle de la Mécanique des Roches pour la phase d'après-exploitation, notamment pour la prévision et la prévention des effondrements inopinés susceptibles de survenir lorsqu'ont été pratiquées des méthodes d'exploitation partielles. Le cas du bassin ferrifère lorrain, présenté dans cet article, illustre particulièrement bien les problèmes identifiés à différentes échelles : analyse et évaluation des risques, méthodes d'intervention avec les préoccupations d'un meilleur aménagement du territoire et d'un développement durable