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Rueil-Malmaison, France

Vibert C.,Tractebel Engineering | Vaskou P.,Geostock
Harmonising Rock Engineering and the Environment - Proceedings of the 12th ISRM International Congress on Rock Mechanics

The rapid spread of the use of geomechanical rock mass classifications (Q system, RMR and later developments such as the GSI made by Hoek and others) is a worldwide and irreversible trend driven by its applications in the profession. In particular, rock mechanical engineers value these tools in assessing characteristics and failure criteria of rock masses. Using case studies, the authors present an update on the benefits of the use of these classifications, such as providing a clear geological description of matrix and rock mass, and the possibility to compare and rank sites. In doing this, they emphasise the need for experienced engineering judgement at each step of the process to ensure the validity of results. Typical limits of classifications and their application are also presented. These include the risk of over-simplification by summarising a complex rock mass with a single figure, the scale effect, and how accounting for anisotropy and heterogeneity in tunnels and caverns design. In particular, attention is given to the risk of designing dams using the strict application of Hoek's approach for failure criteria using the GSI. Based on these case studies, recommendations are submitted for geologists/geotechnical engineers in charge of rock mass assessment, as well as for designers. © 2012 Taylor & Francis Group, London. Source

Kannan G.,Engineers India Ltd | Rath R.,Engineers India Ltd | Nanda A.,Engineers India Ltd | Vaskou P.,Geostock
Harmonising Rock Engineering and the Environment - Proceedings of the 12th ISRM International Congress on Rock Mechanics

Engineering geology plays a key role in planning, design and construction of underground cavern storage facilities. The geological assessment of the site is made not only during investigation but also corroborated and updated during construction. In case of cavern storage project, relatively smaller dimensioned water curtain tunnels, which lie above the main storage cavern, are always excavated in advance before excavation of the main large storage caverns. This water curtain tunnel acts as a pilot tunnel and helps assessment of the likely geological setting in advance. As part of the water curtain system, large numbers of boreholes are drilled from the water curtain tunnel and are hydraulically charged to maintain a saturated rock mass surrounding the storage caverns, revealing additional information about the geological and hydro-geological setting above the cavern. Thus a 3D geological (structural) model of the site is updated through an active design process with focus on geological hot spots intersecting the cavern. During construction of caverns, a careful approach is adopted along these hot spot segments. These adverse rock mass conditions are probed, assessed and supported in accordance with special design supports. The geological model is further updated during excavation of cavern heading and becomes useful for excavation of benching, for verification of the rock support in heading and in further optimisation of rock support during bench excavations. The paper presents two case studies of underground storage cavern sites, where in the active design process has been adopted for geological assessment of both the sites. © 2012 Taylor & Francis Group, London. Source

Duffaut P.,ISRM Commission on UNPP | Vaskou P.,Geostock
ISRM International Symposium - 8th Asian Rock Mechanics Symposium, ARMS 2014

In the fifties and sixties, some underground nuclear power plants, UNPP, have been built and operated in Europe and Siberia. It is clear that underground siting of any sensible and/or dangerous plant and depot will improve safety against external menaces (plane crash, bombing, etc.) as well as against consequences of internal accidents. The technical and economic feasibility of UNPP depends on various criteria, which are tentatively proposed herein, under main headings: i) Physiography (relief and water); ii) Geology (nature and structure of rocks, distance to geological hazards such as active faults, volcanism, glaciers, slope movements, tsunamis, etc.); iii) Population and Human activities (distance to large towns, industrial plants, agriculture, etc.); iv) existing service networks (harbors, roads and railways, transmission lines, etc.). All along the nuclear era, many advisers have called for siting reactors underground as had been often done for explosives and now, more and more, for sensible and nuclear wastes. Long before the accidents at Three Mile Island, Chernobyl and Fukushima, a partial core melt occurred in the underground Lucens plant, Switzerland, without any harm to people and environment. The practice of underground hydropower plants together with some other uses of man-made caverns, from hydrocarbon storage to the Norwegian ice rink and caverns needed for neutrino research are shortly recalled as they provide the bases for the design of caverns. The senior author has followed the cavern construction of the French plant Chooz (only second to Siberian plants as an underground nuclear plant with a significant output) and has attended the only international conference on the topic, organized by the government of Germany in Hannover in 1981, soon after the TMI accident. © 2014 by Japanese Committee for Rock Mechanics. Source

Renoux P.,Geostock
75th European Association of Geoscientists and Engineers Conference and Exhibition 2013 Incorporating SPE EUROPEC 2013: Changing Frontiers

The creation of an underground storage facility in salt leached caverns in Manosque for liquid hydrocarbons was decided in the mid-60s by the oil companies to meet regulatory obligations in terms of strategic reserve, imposed following the Suez crisis. The Salt of Manosque is of Oligocene age and was deposited after the Pyrenean orogenic phase. The origin of the salt is Triassic (Keuper) and results of dissolution of outcrops uplifted by orogeny tectonic movements, then evaporites, were deformed due to the tilting of the block inducing the sliding of the salt mass, and increasing locally the thickness of the salt depending on its initial deposit and structural location. The resulting thickness of the salt formation ranges between 200 to 1000 m. The average proportion of insoluble minerals is in the order of 15%. This study allows a better understanding of the mineralogical composition of the Manosque salt. It explains the occurrence of potassium detected in the leaching brine. The structural map indicates the salt thickness distribution and can be used for locating new caverns. A clear relationship is established between seismic activity and halokinetic phenomena. Copyright © (2012) by the European Association of Geoscientists & Engineers All rights reserved. Source

Vaskou P.,Geostock
Rock Characterisation, Modelling and Engineering Design Methods - Proceedings of the 3rd ISRM SINOROCK 2013 Symposium

Structural geology (a branch of geology aiming at describing the structures - joints, faults, folds, etc. - at various scales) can be used in the field of rock mechanics and rock engineering, and particularly in underground engineering works (tunnelling and rock caverns) to gather more reliable data for empirical stability analyses and deterministic calculation models. Methods of structural geology are presented and their applications in rock mechanics/rock engineering are highlighted in particular through the observation of faults and joints arrest. Structural geology allows a better understanding of the origin, the chronology and the mechanical behaviour of discontinuities, and therefore a more accurate rock mass characterization and rock mass classification, as well as a validation of the actual stress regime. Examples selected from different countries of using structural models are also given with emphasize on the necessity and the way to build a 3D model at each stage of an underground project, from site selection to investigation and construction, to ensure the quality and validity of rock mechanical data and assumptions. © 2013 Taylor & Francis Group. Source

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