The National Monitoring Center for Ground and Underground Risks of Ineris, located at the School of Mines of Nancy, France, carries out research, expertise and early warning capabilities applied to field observation, monitoring and alert services related to ground and underground risks.
The CENARIS aims to develop, in the frame of both scientific and operational projects, innovative tools, methods and resources enabling to improve our understanding of physical processes linked to instabilities and disasters, to enhance forecasting capabilities as well as expertise applied to risk management.
- mines, quarries, and cavities,
- rockfalls, landslides and faults,
- structural engineering, dams and embankments,
- geological storage, rock reservoirs.
Cloud monitoring solutions, based on the e.CENARIS platform, are designed and implemented thanks to an extensive experience, providing optimally customized multi-parameter early warning systems. These include microseismic and advanced GPS-RTK geodetic measurement capabilities and feature a unique advanced website interface.
« Cloud Monitoring » presents a universe of tools, integrated and dematerialized services, which make project monitoring and information exchange for its members very simple.
The concept covers hazard and risk expertise, technical conception and feasibility of the project, observations and surveillance deployment systems. These cover: architecture and data acquisition, transmission, follow-up, control and data expertise.
Furthermore, Ineris conceives maintenance, vigilance and warning procedures, led consular crisis management exercises, and assures continuous feedback collaboration with the lead risk manager.
What is the « Cloud Monitoring » purpose?
As an integrated platform of observing and warning (fast and early) systems, data availability and accessibility are the main purpose of Cloud Monitoring. These are recognized as an efficient approach to highly reduce the population’s and property’s vulnerability, as well as improving its reactivity and resilience to hazards. The ability to operate global-scale geological and geotechnical surveillance, prevention and management solutions, constitute a major scientific and technical challenge in a generally complex context (with respect to anthropogenic activity, extreme climatic events effects, etc.).
What are the benefits of the e.cenaris platform?
The e.cenaris platform offers a high level of acquisition tools, management, data analysis and exchange, enabling optimized solution conception for every project case study.
Multi-parameter telemetry systems (SYTGEM) directly connected to the database with high-speed internet,
An automatic management infrastructure of the multi-parameter database (near real-time) with data teleprocessing and analyzing software, as well as alarm management structures,
A secure web-monitoring site for easy and fast access to data, metadata and associated results, with sharing conveniences between the project’s stakeholders.
To whom does the « Cloud Monitoring » address?
The E.CENARIS platform is meant for all bodies and partner research laboratories, communities, manufacturers, infrastructure managers, engineering offices, as well as decentralized departments in charge of telemetry and surveillance projects, linked to surface and subsurface problems.
Multi-parameter monitoring consists in deploying a system which allows to measure with the best resolution possible relevant variables with various natures (seismic, microseismic, geotechnical, geodesic, hydrological, meteorological, etc.) in order to detect not only hazard occurrence (rupture, collapse, sliding) but also to predict it. This implies the measure of triggering factors, for example exceptional pluviometry, increase of the interstitial pressure in grounds, a strong seismic excitation, and warning signs such as intense microseismic activity or the appearance of large deformations.
The multi-parameter monitoring system is possible thanks to the considerable technological progress made over these past years, concerning:
New generation acquisition,
Technology and radio transmission network developments and wireless connection,
Increased computer processing power, constantly becoming cheaper.
Global supervision of risks covers hazards, and, if necessary, the most vulnerable material stakes which are bound to it. Stakes supervision – buildings, works, infrastructures, etc. – when possible, can considerably improve the evaluation and the management of a crisis and post-crisis situation.
Integration under e.cenaris of a new module for more reliable operational monitoring through the management of alarms.
e.cenaris is an e-Infrastructure under continuous development, dedicated to the scientific observation and the instrumental monitoring for geotechnical and geological risk hazards. It enables the automatic management of data acquired by a high variety of sensors installed in vulnerable areas. By clicking on « Monitoring » on the home page, experts and site managers can access the online database, visualize the data, and get information on the general working state of the network. Data are displayed as graphs, tables, maps or 3D views to ensure a quick and efficient checking, adjustable to monitoring requirements and to stakeholders’ needs.
Data treated by custom time-series processing routines make it possible to work in near real-time on new transformed variables, which are easier to exploit by filtering, weighted moving average, daily cumulated data, etc. e.cenaris can also integrate independent variables coming from external sensors or databases related to industrial (flow, pressure, blast load,…) or natural (pore pressure, pluviometry, …) forcing processes, which facilitate regression analysis.
Data fusion technologies and the definition of complex alarms have lately been implemented into the platform as advanced decision-support tools. The latter is based on combining transformed-variable alarms associated with Boolean operators. This high level of alarm design and management enables a more efficient control not only of network working state but also of computed parameters variability and their coherence level, to ensure more relevant and more reliable alarm settings (e.g. determining the correlation between forcing variables and incident occurrence).
Microseismic surveillance is a non-intrusive passive technique which consists in detecting and recording the seismic waves emitted during fracturing and cracking of a rock mass. The principle is identical to the one implemented in seismology, except that the scale is reduced by some order of magnitude (lower than 2). The processing, analysis and interpretation of the sequences of microseismic events, in terms of their spatiotemporal distribution, rupture mechanisms, released source energies and frequency contents, supply essential information for ground movement hazard management.
Especially, observation and microseismic monitoring find very numerous applications in the fields of natural and industrial risk prevention. It is particularly well developed in the contexts of mine exploitation and hydrocarbon reservoirs, extractive activities generating important stress constraint redistribution (i.e. microseismic activities), and it also finds numerous other applications, such as:
Natural risk prevention: underground cavities, rock and landslides, faults,
Geologic storage monitoring
Reservoir surveillance of fluid injections/extractions in deep drillings,
Civil engineering: dams, engineering works, tunnels,
Acoustic monitoring of an underground cavity is a passive technique used to detect and record the sounds (areal and aquatic pressure waves) emitted during a block fall or fracturing of the cavity roof or pillars. Easily implemented, this method requires favorable environment conditions for the diffusion of these acoustic waves. Usually, it is best adapted for large abandoned and quiet underground cavities. A microphone, correctly implanted inside the cavity, enables to survey over an area of several tens to hundreds of meters diameter, depending on the context. Acoustic monitoring is a pertinent complement to geotechnical surveys in the context of extensive, complex and abandoned underground cavities presenting the risk of evolving vertically towards the surface (i.e. localized collapse or subsidence).
The cost and benefits of this technique are particularly advantageous, and instrumentation is relatively safe considering that the sensors (microphones and/or hydrophones) are not emplaced directly in the zones of strongest deformation. In cases where the cavity is inaccessible, acoustic monitoring of the cavity is equally possible by means of bore drilling, whereby the sensors are inserted inside boreholes. Subsequent analyses and processing of data enable to discriminate between the parasitic acoustic signals and those triggered by the geotechnical deterioration.
Geodetic monitoring by GPS-RTK network supplies all the quantitative data necessary for the complete analysis of the displacement field. To obtain the best possible precisions, while keeping the most essential “real-time” aspect within the framework of an operational ground movement monitoring, the involved principle is the real-time differential GPS precise RTK (Real Time Kinematic) measure.
This principle is based on a referenced marker placed in a stable zone: all the variations in position registered by this marker are considered, by definition, as measurement errors (mainly due to the crossing of the atmosphere by the signal or to terrestrial tides). These variations can then be communicated by radio transmission, in real-time, with one or several measurement markers in the hazard zone, and thus, can be affected by the same measurement errors that allow to drastically reduce the measurement uncertainties.
Furthermore, the RTK method, based on the comparison of the signal phases and not on its binary code, allows to measure much more precisely and also faster. It is then possible to obtain at least a centimetric (differential) precision, even with short measurement cycles (typically from 5 to 30 minutes) and without any treatment in retrospect, which allows to run it in near real-time conditions for the ground movement hazard management.
Measured variations recorded at the referenced marker (i.e. in stable zone) are transmitted in corrected format to the measurement marker located in the zone experiencing ground motion.
Ineris has developed a platform dedicated to geotechnical tests and to the management of risks linked to the presence of cavities. This platform is located inside the former limestone cave of Saint Maximin (Oise, France), which was exploited using the room-and-pillar mining method.
This platform extends over ~3 hectares, it is situated between 10 and 20 m depth, with accesses available from the hillsides. Security conditions, access and equipment facilities are suitable for the performance of tests and training activities.
There Ineris carries out studies on the stability of underground engineering structures as well as on deformation and rupture mechanisms through rock complexes. Experiments are also led to tests in real conditions some tools and methods used for the risk management, such as wall stabilization, landfilling, or monitoring.
Download presentation leaflet: Underground platform for geotechnical tests and for the management of hazards linked to cavities
Or contact: firstname.lastname@example.org
Among the stakeholders the most likely to deal with risks management, local authorities are especially concerned by instabilities of underground cavities such as sinkhole, local and large-scale collapse phenomena. These ground instabilities may have a high impact on public safety, properties and environment. It is then necessary for the decision-makers, and in some cases in emergency situations, to find out solutions to ensure public safety and the protection of structures, property and assets.
Options to eliminate the risks generally rely on expensive time-consuming solutions (backfilling, expropriation). In some cases, using appropriate monitoring tools as an early warning system offers a standstill strategy of great help while entering into large projects with management and decision making are not compatible with fast response and public safety.
Strongly recognized with a long experience in the auscultation and monitoring of underground structures (mines, quarries, underground storage), Ineris has developed and implemented specific methods and tools that can be adapted to a wide range of situations at risks:
Typical instabilities of ancient subsurface cavities: sinkhole and localized collapses,
Instabilities of deep large cavities: large-scale subsidence or generalized collapses.
Ineris’s approach is based on well-known monitoring methods, ranging from visual inspection, geotechnical, acoustic, geodesic or even microseismic monitoring.
Such methods can be used independently or in combination, depending on the situation and issues. Ineris also owns a high-level monitoring infrastructure, which enables to manage monitoring data in a seamless way and in quasi real-time, and to administrate multi-parameter early warning systems.
Feasability analysis, design and construction of the monitoring solution,
Continuous monitoring for permanent networks,
Remote monitoring and data management, metrological and functioning control,
Data processing and analysis, interpretation and expertise,
Monitoring procedures, trainings on crisis situations.
Monitoring of active, abandoned or revamped underground quarries; e.g. the investigation of a limestone quarry converted into thermal baths, by means of automated convergence analysis
Monitoring of shallow or deep mine structures; e.g. the investigation of a salt mine subject to sudden collapse and situated close to inhabited areas, by means of acoustic, microseismic and geotechnical methods
Monitoring of a mine subsidence phenomenon due to the exploitation of the water stored inside the mine; e.g. the automatic monitoring by means of differential GPS technology
High experience in field investigations and monitoring of areas subjects to ground deformations,
About forty monitoring networks deployed in France and abroad,
Quality of our activities approved by our clients and partners (EDF, Andra, IRSN, collectivities…),
Experienced working team able to carry on monitoring and alert systems and ready to respond to the needs of stakeholders and risk managers (24/24 operational). All these services are achieved within the framework of the CENARIS (National Monitoring Center for Ground and Underground Risks).
To meet your needs of diagnosis and performance assessment of underground engineering structures and infrastructures, Ineris designs, develops and implements innovative, stand-alone or coupled, geotechnical (strain and stress monitoring, tilt, displacement) and geophysical methodologies (passive acoustics, active tomography) to help your decision-making. Since each project is characterized by its specific setting, it is necessary to customize the solution, including the execution and the tools on a case-by-case basis.
It is essential to analyze the monitoring data and their evolution with time in order to assess the correct response or not of the geostructure to quasi static or dynamic solicitations. Whenever necessary, a numerical model is used to optimize the layout of the sensors. Field data also enable to check the reliability of the prediction model, which estimates the structure response to the solicitations.
Feasibility analysis, design and definition of the best diagnosis method and of the monitoring planning (periodic, continuous),
Three-dimensional geomechanical and geophysical modeling, including hydro-thermo-mechanical quasi static and dynamic solicitation,
Installation, remote monitoring and data management,
Data monitoring and analysis, interpretation and results assessment.
Well-known capabilities for field experimentation and operational monitoring of underground operations, managed through an experienced working team able to carry on multi-disciplinary projects with fast response to stakeholders, i.e. industries, state agencies and local authorities. All these activities are achieved within the framework of the CENARIS (National Monitoring Center for Ground and Underground Risks).
Ineris offers in situ measurement solutions to investigate, and if necessary to monitor in near-to-real time the static or dynamic stress fields exerting in your geostructure (rock-bedded structures, underground cavity, dam, etc) in order to provide a deeper insight in its stability conditions.
Ineris develops methods and specific tools on purpose for your site and according to the operating conditions of your engineered structure. Ineris identifies and sizes the most adapted stress monitoring solution in order to optimize the analysis and the interpretation of the measurement data.
The stability criteria of a geostructure is based on the fact that the stresses and the pressures exerting inside it, at its interfaces or all around it remain below its strength, all over the life cycle of the geostructure. In some cases where the engineered structures have been designed on an innovative way or for old structures subject to alterations or unexpected solicitations, it may be necessary to characterize the pre-existing stresses in order to control the actual stability conditions. In situ stress measurements are usually an important input parameter to set up and to run numerical models in order to analyze and predict the stability conditions of complex structures.
An instrumental solution can be based on the use of total pressure cells, interstitial pressure sensors, flat jack cells, strain sensors, deformation gauges and hollow cells, clinometers, extensometers, or if necessary on a combination of these complementary methods. Ineris also developed its own solution under the SYTGEOstress® designation (ROck Stress Analysis System).
The tools that are used to analyze the measured stress fields amplitudes and orientations enable to have an accurate overview of the global stress field, including gradient and concentrations areas. The devices are designed for long-term purposes and generally set with auto-calibration and auto-diagnosis functions.
Mines and quarries, engineering structures, deep storage areas, rock masses…
Analysis of feasibility, conception and sizing of the stress monitoring application considering two-dimension, three-dimension, static and dynamic models and using a predictive approach by means of hydro-mechanical numerical modeling,
Field monitoring campaigns,
Continuous monitoring for permanent networks,
Remote monitoring and data management,
Data monitoring and analysis, interpretation and results assessment,
Consulting and assistance.
Ineris has developed its competences in situ and for operational monitoring of underground structures thanks to its experienced working team able to carry on monitoring and alert system operations and ready to respond to the concrete needs of operators, State entities, territorial collectivities and engineering structures managers. All these activities are achieved within the framework of the CENARIS (National Monitoring Center for Ground and Underground Risks).
More specifically, Ineris has carried out in situ stress monitoring operations for more than 25 years (overcoring, doorstopper, flat jack…) and realized such surveys in numerous geo-engineering structures (deep mines, underground structures, dams…).
Date : Le 17 octobre 2019.
Lieu : La Grotte de la roche aux fées - 2 Rue de Rochecorbon - 37100 Tours
Date : Le 04 Avril 2019
Lieu : Mines Nancy, Campus ARTEM, France.
Date : Le 14 MARS 2019
Lieu : Paris, France.
Date : February 05, 2019
Lieu : Mines Nancy, Campus ARTEM, France.
prestation.event.workshop2018.descDate prestation.event.workshop2018.descLieu prestation.event.workshop2018.descLink
prestation.event.scan3D.descDate prestation.event.scan3D.descLieu prestation.event.scan3D.descLink
Dans le cadre du programme d’appui au Ministère de la Transition écologique et solidaire relatif à la prévention des risques naturels, l’Ineris exerce une veille scientifique vis-à-vis de dispositifs de mesures émergents et novateurs sur le marché.
En 2016 et 2017, l’Ineris a testé un dispositif conçu pour la télésurveillance instrumentale de mouvements de terrain.
Le dispositif se compose d’un réseau de modules GPS, permettant l’acquisition des signaux GNSS, et d’une station de base assurant les calculs des positions et la connexion GSM ou Ethernet. L’ensemble des éléments sont autonomes (alimentés par panneaux solaires). La transmission des données entre les modules GPS et la station de base est assurée par une communication radio.
À comparer aux technologies existantes basées sur la mesure GPS, ce type de dispositif se veut innovant de par son coût très maîtrisé, sa mise en oeuvre simplifiée et une précision centimétrique.
Les tests ont été réalisés sur les bordures des effondrements (exploitation de sel) du site de SOLVAY à Cerville et Haraucourt (54). Des modules GPS ont été implantés dans des zones connues comme actives ou considérées comme stabilisées. Un test « forcé et en aveugle » a également été réalisé.
L’objectif de cette instrumentation a été d’évaluer :
• la précision des mesures de position ;
• la mise oeuvre du dispositif sur site ;
• la gestion du suivi à distance ;
• la fiabilité des mesures et la robustesse du matériel dans le temps ;
• les limites éventuelles du système.
Les mouvements de grands versants font partie des risques naturels majeurs, dès lors que les populations et les infrastructures sont menacées. La prévention de tels mouvements n’est pas aisée, dans la mesure où les phénomènes sont amples et les mécanismes physiques sont complexes, parfois brutaux, difficiles à observer en continu et à étudier.
Le mouvement de versant « des Ruines de Séchilienne » est à ce titre emblématique. Il est situé à une vingtaine de kilomètres au sud-est de Grenoble, en rive droite de la vallée de la Romanche. Son instabilité en masse pouvait notamment conduire à l’obstruction de la rivière, ainsi que la coupure de la route départementale 1091 (ex RN 91) desservant les stations de l’Alpe d’Huez et des Deux-Alpes, ainsi que le col du Lautaret et Briançon.
Dès 1985, le site a fait l’objet d’investigations techniques et scientifiques dont les résultats ont permis de faire une première évaluation de l’aléa géologique et hydraulique. En 1986, au vu d’une accélération du phénomène, un dispositif d’alerte opérationnel a été installé par le CETE de Lyon (actuel Cerema Centre-Est) à la demande de l’Etat.
Entre 2009 et 2016, l’Ineris, dans le cadre de son programme d’appui au Ministère de la Transition écologique et solidaire, et en partenariat avec le Cerema, a contribué aux investigations sur ce mouvement de versant par la mise en œuvre d’un dispositif automatique d’observation multi-paramètres (géodésique, géotechnique et microsismique) en quasi temps réel, et placé en bordure ouest du secteur actif.
Le présent rapport, destiné aux acteurs qui interviennent dans la gestion du risque de « mouvement de versant » par la surveillance, décrit les apports technologiques et méthodologiques de l’observation menée par l’Ineris, et fait la synthèse des enseignements qui ont été tirés.
keywords: Industry, mines, hydrocarbons, geothermal, seismicity, hazard, risk, management, social acceptance.
The relation between underground industrial activity and seismicity has been highlighted at the beginning of the twentieth century in the deep gold mines of South Africa. Today, as the demand for mineral resources and energy keeps increasing, the number and size of industrial projects as well as new emerging underground industries that can potentially induce seismicity is also raising. Some of the most illustrating cases are presented in this report. This report also deals with the issues related to seismic hazard assessment, risk mitigation and emerging regulations in the context of anthropogenic seismicity.
The mechanisms of anthropogenic seismicity are now relatively well understood, and researchers suggest distinguishing induced events which results from the anthropogenic underground disturbance itself, from triggered events, which are related to the reactivation of natural geological faults due to industrial activity. In some extreme situations, anthropogenic seismicity can endanger public safety, especially when man-triggered earthquakes occur in regions with low natural seismicity and poor seismic prescription and sensitivity of the populations. In addition, social acceptability can quickly be challenged, and lead to the cessation or abandonment of industrial projects even when only rare earthquakes with very low intensity are felt. In some cases, induced seismicity can persist long after the ending of the underground operations. It can even occur several kilometers from the operations. These situations have been observed especially during fluid injection and extraction activities. The so-called triggered seismicity remains the potentially most destructive threat to public safety.
Currently microseismic monitoring has become a prominent tool for managing the risk of anthropogenic seismicity. The near to real-time processing of microseismic data, coupled with the monitoring of industrial parameters offers a helpful approach to decision making. Similarly, solutions exist to reduce the vulnerability of buildings and infrastructures, when the relocation of the project is not possible. Regarding the safety of minors at work, operators have developed numerous approaches to limit worker exposure.
Both the world of industry and the world of research are nevertheless facing several challenges. One of them concerns the characterization of the anthropogenic seismic hazard and the capability to distinguish natural earthquakes from anthropogenic earthquakes. This is of obvious interest for all parties involved; it may also have a significant impact in terms of responsibility of the operator. The success of future deep projects depends obviously on how well anthropogenic seismicity is managed and communicated to be acceptable to all stakeholders.
keywords: Underground cavities, natural and anthropic seismicity, gravity hazards
French territory is largely exposed to the risks of underground cavities. Some of them are subjected to anthropic or natural solicitations like seismic vibrations that could affect their stability in the long term. The objective of this study is to estimate the impact of those vibrations on shallow underground cavities and on the underground space located between the surface and several tens of meters deep, as they may induce ground movements (subsidence, crown-hole, sinkhole, etc.).
Based on a wide national and international bibliographic study, vibratory sources that may affect the stability of underground cavities (earthquakes, explosions, machines, traffic) are presented and discussed. We then describe the dynamic phenomena involved.
Among the different vibratory sources, it turns out that major earthquakes have the potential to destabilize the underground cavities during a single event and that a weaker but repeated seismic event can damage a little more a rock mass already fractured. Mechanical models for room-and-pillar underground excavation make it possible to estimate this impact, and the probability to collapse the pillar or the roof of an underground mine as a function of its depth and the intensity of the seismic loads.
Vehicles and construction equipment can also induce significant stresses when located in the immediate vicinity of underground cavities (particle velocity greater than the prescribed particle velocity of 10 mm/s). The traffic generates movements of low particle velocity (less than 3 mm/s) even at very short distances; it can only affect very sensitive structures or already close to ruin.
This document finally presents the preventive actions that could be envisaged to limit the impact of vibrations. It also shows the importance to consider the fatigue of underground and underground structures abandoned at low depths.
Keywords: monitoring – underground cavities – rockfall – treatment - methods
Wide areas and tens of thousands of communes in France are concerned by the risks related to underground anthropogenic (i.e. human-built) cavities. Sustainable solutions do exist, such as voids landfilling. Monitoring underground cavities can be used as a palliative and transitory tool, though.
The guide for the monitoring of underground anthropogenic cavities is a document produced by Ineris for the French Ministry of the Environment, the Ecology and the Sea (“MEEM”) to be addressed to the territorial collectivities and any field project manager that might face whether to use monitoring technologies or not.
This guide mentions the points that may be discussed before considering monitoring. First, the feared instability phenomenon must be known and correctly assessed. Second, how long monitoring will be performed should be considered: either for emergency, for short-term, or for more sustainable periods, before more stable risk management solutions are fixed. Then, access conditions and facilities to the site, security rules and transmission ways should be considered to decide whether to implement monitoring locally or in a remote way.
The monitoring project can start once these preliminary points are well understood. Several equipment solutions area available. They are briefly presented in the main section of the guide and are detailed in didactic documents in appendix.
Visual surveys are fundamental and to be performed as soon as it is possible to access to the site in acceptable security conditions; they are by the way often considered. Using additional tools such as photogrammetry or laser scanner is sometimes necessary to observe some evolutions which are hardly visible to the naked eye. In addition, geotechnical measures enable to directly assess local physical characteristics such as displacements, pressures, water levels… while geophysical sensors are used to monitor wider areas, thanks to remote measurements, i.e. by detecting the waves linked to any evolution and instability through the rocks or the underground voids.
To be effective, not only monitoring must be operational, but also all its constituting elements must be mastered: measurement devices, data transfer processes, maintenance and organization procedures. Monitoring might be based on meaningful alarm thresholds, corresponding to a possible prejudicial instability evolution, in order to alert the project managers or collectivities if necessary. The maintenance and the continuous follow-up of the equipment should also enable to detect any dysfunction along the measurement chain. Data sharing and transmission finally facilitate more rapid analysis and thus provide with feedbacks by taking into account the historical data.
Keywords: underground cavities – rock fall - surface effects - treatment - methods
Ineris provides people involved in land use and planning with a technical guide on procedures to ensure safety of the fields located over abandoned underground cavities. This guide was produced in the framework of the French National program for the prevention of risks related to collapse of underground cavities (“Cavity National Plan”).
This guide is addressed to local administrations and politicians, sites stakeholders and managers. It presents the most used processing methods to make surface fields secured, which are exposed to collapse hazard because of the presence of abandoned human-excavated cavities: carries, chalk mines, underground shelters, troglodyte houses, war sapping structures, etc. These methods are applicable not only for prevention (i.e. the presence of underground voids is known, however no disorder has affected the surface yet) but also for managing collapsing incidents (e.g. sinkhole formation). They are classified into two categories: the first methods consist in directly working on the cavity, the second ones are used to limit the surface effects induced by the presence of the cavity.
Underground cavities are at the origin of various risks of ground movements such as collapses and subsidences. A sinkhole is a “located” collapse, a phenomenon peculiar to cavities situated at shallow depths. This kind of risk, which widely affects most of the national territorial regions, covers the main part of the natural and anthropological cavities: post-mining, abandoned quarries, marlpits, karsts, tunnels and abandoned civil works, etc.
Nowadays, the supervision of these phenomena is essentially realized by visual inspection and by conventional geotechnical instrumentation. These steps present limits, particularly in terms of appreciation of the phenomena kinetics. In the context of a research operation financed by the Ministry of the Environment, and of Sustainable Development and Energy (“MEDDE”) as well as the European Regional Development Fund (ERDF), the institute Ineris tested and estimated acoustic detection as an innovative instrumental technique used for the cave-in risk evaluation. The present report synthesizes these works by detailing more-or-less:
the conception of equipments necessary for the underground cavity measurements;
full-scale tests on a pilot site and operational feedback experience;
identification of the advantages and limitations of this technique.
Keywords: microseismic monitoring - mining collapse - signes précurseurs - mécanismes de rupture - atténuation - interaction fluide / roche
In some cases, site supervision appears as the best compromise for the post-mining risk management for several types of ground movements. It mainly leans on systems of real time microseismic surveillance of the concerned zones. The purpose is to detect the acoustic emissions which may present precursor signals for a large-scale collapse phenomenon. Applied to public security since 1998, this type of supervision method was employed on more than about thirty networks destined for real time microseismic supervision within the Lorraine ferriferous mining region.
The present report aims to exploit and highlight the information contained in the microseismic signals, in correlation with other types of measurements whenever available, in order to:
progress in the identification of the precursor signs for an eventual collapse;
characterize mechanisms and dynamics of the collapse , particularly the presence of a stiff rock layer in the cavity overburden structure;
emit recommendations for the operational supervision management.
This report joins within the framework of the research project PR190 “Phenomenology of the geological instabilities in full-scale and precursor signs” introduced in 2007 and continued since 2010 within the framework of the research COSMOS (Comprehension, Modeling and Supervision of the deformation style of rock ruptures).
Keywords: unstable slopes - ground-based monitoring - interferometric radar - scan ground laser - risk-management - mobiles systèmes
For the protection of populations and infrastructures, the principal management actions for hillside risk instabilities, often rest on active hazard supervision, by regular field inspections and also implementation of in situ instrumentations.<br>The present report makes a review of the innovative supervision methods of full-scale hillside instabilities, compatible with portability requirements and operational supervision. The study is focused on interferometry RADAR and long-range laser ground measurement techniques , already widely used internationally by open air mine and quarrie exploitations, in the evaluation of instability evolutions, and also by public organizations for natural risks prevention.
This report shows that the conditions of implementation and performances of these two techniques are very different from one another, particularly in their data processing methods; although both are based on a common principle (the device emits signals which are reflected back at the surface of the imaged object. This report specifies the characteristics, the advantages and limitations of each technique across illustrations stemming from the scientific and technical literature. It also supplies elements of costs and recommendations for the optimal conditions of implementation of each method.
This study is registered in the framework of the entitled program EAT-DRS06 “National Supervision Center of Ground and Underground Risks”. It is a program of technical support for the Directorate General for Risk Prevention of the Ministry of Ecology, Sustainable Development and Energy.