The Experts below are selected from a list of 1089 Experts worldwide ranked by ideXlab platform
Uotinen Lauri - One of the best experts on this subject based on the ideXlab platform.
-
Kallion jännitystilavaurioiden ennustaminen käytetyn ydinpolttoaineen loppusijoitustiloissa ja syvissä kaivoksissa
'Springer Science and Business Media LLC', 2018Co-Authors: Uotinen LauriAbstract:Nuclear plants have existed since the 1950s, and they provide 11 % of the world's electricity production. Worldwide, 30 countries are operating 448 nuclear reactors for electricity generation, and 57 new nuclear plants are under construction in 15 countries. Measured by deaths per terawatt hour, nuclear power is the safest method to provide energy, but it does produce a range of radioactive waste, which must be disposed of safely and responsibly. The deep geological repository is currently the only acceptable long-term solution for high-level nuclear waste. The two most common causes of rock mass failure are structurally controlled gravity-driven failure and stress-induced failure. Usually, surface and near-surface rock excavations are subject to structurally controlled gravity-driven problems, but in deep rock spaces, the in-situ stress of the rock mass increases and the risk of stress-driven problems grows. The five most common stress-driven damage mechanisms are i) rockburst, ii) spalling, iii) convergence, iv) shearing and v) seismic. Excessive convergence is rarely a problem in hard, massive rock mass. In this thesis, the remaining four mechanisms are addressed. The goals of the research were to discover the damage-reducing capability of thin sprayed Concrete Liners, to define the strength of long rock joints, and to develop a real-time risk management concept. Numerical modelling was used to design an in-situ Concrete spalling experiment, the ICSE. Laboratory scale mortar rock joint replicas were used to study the scale effect, and large 2.00 m by 0.95 m (ASPERT) and 0.50 m by 0.25 m rock joints were sheared to validate the methods. A new real-time formulation of the Geotechnical Risk Management (GRM) concept was studied using both example cases and case data. New methods were developed for the photogrammetric capture of rock joint surfaces and shear testing of large rock samples. The numerical modelling predictions for the in-situ experiment show that the thin Concrete Liner produces up to 3 MPa of support pressure and using polyaxial Ottosen criterion the Liner is not damaged during the heating stage. Both the replica shear tests and the large shear tests results show a weak negative scale effect. Based on the initial analyses using example data, Bayesian networks appear compatible with the Observational Method, and the approach is ready to be tested using real data. The three main conclusions each address the stress-driven damage prediction and mitigation. The stress-driven damage can be reduced using support pressure generated by thin Concrete Liners. A new method was developed to capture rock joint geometry using photogrammetry and to manufacture mortar replicas for laboratory scale shear testing. The use of Bayesian networks, together with the real-time geotechnical risk management concept, was demonstrated. The results contribute towards predicting stress-driven damage in deep underground spaces.Ydinenergialaitoksia on ollut olemassa 1950-luvulta lähtien, ja ne tuottavat 11 % maailman sähköntarpeesta. Maailmanlaajuisesti 30 maata käyttää 448:aa ydinreaktoria sähköntuotantoon, ja 57 uutta reaktoria on rakenteilla 15 maassa. Mitattuna kuolemantapauksilla terawattituntia kohden ydinenergia on turvallisin tapa tuottaa energiaa, mutta se tuottaa myös erilaisia ydinjätteitä, joista täytyy huolehtia turvallisesti ja vastuullisesti. Syvä geologinen säilö on tällä hetkellä ainoa hyväksytty pitkäaikainen ratkaisu korkea-aktiiviselle ydinjätteelle. Kalliotilojen sortumat voivat tapahtua useista eri syistä, mutta kaksi yleisintä syytä ovat rakenteellinen painovoimainen murtuma ja jännityksen aiheuttama murtuma. Yleensä pinnassa ja lähellä pintaa tehtävissä louhinnoissa on kyse rakenteellisista painovoimaisista murtumista, mutta syvemmissä kalliotiloissa maankuoren jännitys ja jännitysvaurioiden todennäköisyys kasvavat. Viisi yleisintä jännitysvauriomekanismia ovat i) kallioräiske, ii) hilseily, iii) siirtymä, iv) leikkautuminen, v) seisminen. Liiallinen siirtymä on harvoin ongelma kovassa, massiivisessa kalliossa. Tässä väitöskirjassa käsitellään jäljelle jäävää neljää mekanismia. Tutkimuksen päätavoitteina on selvittää ohuiden ruiskubetonikuorien jännitysvaurioita vähentävän vaikutuksen suuruus, määrittää pitkien rakojen mekaaniset ominaisuudet ja kehittää reaaliaikainen riskienhallintakonsepti. Numeerista mallintamista käytettiin betonin hilseilyn in situ -kokeen (ICSE) suunnittelemiseksi. Laboratoriomittakaavan rakojen laastijäljenteitä käytettiin mittakaavavaikutuksen tutkimiseksi, ja ison mittakaavan 2,00 m kertaa 0,95 m (ASPERT) sekä 0,50 m kertaa 0,25 m rakonäytteet leikkauskuormitettiin menetelmien varmentamiseksi. Uutta reaaliaikaista geoteknistä riskienhallintakonseptia (GRM) tutkittiin esimerkkitapauksia sekä tapaustietoja käyttäen. Uusia menetelmiä kehitettiin kallion rakopintojen fotogrammetriseen tallentamiseen ja suurten rakonäytteiden leikkauskoestamiseen. Numeerisen mallinnuksen ennusteet ICSElle osoittavat, että ohut betonikuori tuottaa enintään 3 MPa tukipaineen, ja käyttämällä moniaksiaalista Ottosen murtokriteeriä betonikuori ei vaurioidu lämmitysvaiheen aikana. Sekä replikaleikkauskoesarjassa että isommissa leikkauskokeissa havaittiin negatiivinen mittakaavavaikutus. Esimerkkiaineiston alustavien analyysien perusteella Bayes-verkot vaikuttavat yhteensopivilta seurantamenetelmän kanssa, ja lähestymistapa on valmis testattavaksi todellisella datalla. Kaikki kolme pääjohtopäätöstä liittyvät jännitysvaurioitumiseen sekä sen vähentämiseen. Jännitysvaurioita voidaan vähentää ohuiden betonikuorien tukipaineen avulla. Uusi menetelmä kehitettiin kalliorakojen geometrian digitoimiseksi ja laastijäljenteiden valmistamiseksi laboratoriomittakaavan rasialeikkauskokeita varten. Bayes-verkkojen käyttöä havainnollistettiin yhdessä reaaliaikaisen geoteknisen riskienhallintakonseptin kanssa
-
Elastoplastic Modelling of an In Situ Concrete Spalling Experiment using the Ottosen Failure Criterion
'Hindawi Limited', 2017Co-Authors: Uotinen Lauri, Siren TopiasAbstract:An in situ Concrete spalling experiment will be carried out in the ONKALO rock characterization facility. The purpose is to establish the failure strength of a thin Concrete Liner on prestressed rock surface, when the stress states in both rock and Concrete are increased by heating. A cylindrical hole 1.5 m in diameter and 7.2 m in depth is reinforced with a 40 mm thin Concrete Liner from level -3 m down. Eight 6 m long 4 kW electrical heaters are installed around the hole 1 m away. The experiment setup is described and results from predictive numerical modelling are shown. Elastoplastic modelling using the Ottosen failure criterion predicts damage initiation on week 5 and the Concrete ultimate strain limit of 0.0035 is exceeded on week 10. The support pressure generated by the Liner is 3.2 MPa and the tangential stress of rock is reduced by -33 %. In 2D fracture mechanical simulations, the support pressure is 3 MPa and small localized damage occurs after week 3 and damage process slowly continues during week9 of the heating period. In conclusion, external heating is a potent way of inducing damage and thin Concrete Liner significantly reduces the amount of damage.Peer reviewe
Byunghee Choi - One of the best experts on this subject based on the ideXlab platform.
-
Probability-based structural design of lined rock caverns to resist high internal gas pressure
Engineering Geology, 2013Co-Authors: Dohyun Park, Byunghee Choi, Hyung-mok Kim, Dong-woo Ryu, Kong-chang HanAbstract:Abstract This paper describes a probability-based structural design approach to underground, lined rock caverns for the bulk storage of pressurized gas, such as compressed air, compressed natural gas, or compressed gaseous hydrogen. Our design approach is based on a combination of a point estimate method and a deterministic numerical analysis code. In the present study, we demonstrate the validity of this numerical approach in the design of underground structures by comparing it with a theoretical solution for a lined-tunnel problem. Our design approach is then applied to the preliminary structural design of a lined rock cavern for storing compressed natural gas at a high pressure of 15 MPa, where structural support for ensuring gas-tightness and the cavern's mechanical stability is supplied by both steel and Concrete Liners. In this application, a probability-based design chart for determining the strength and thickness of the steel Liner is presented, and the structural performance of the Concrete Liner is evaluated in a probabilistic manner.
-
exploring the concept of compressed air energy storage caes in lined rock caverns at shallow depth a modeling study of air tightness and energy balance
Applied Energy, 2012Co-Authors: Jonny Rutqvist, Byunghee Choi, Choon Sunwoo, Wonkyong SongAbstract:This paper presents a numerical modeling study of coupled thermodynamic, multiphase fluid flow and heat transport associated with underground compressed air energy storage (CAES) in lined rock caverns. Specifically, we explored the concept of using Concrete lined caverns at a relatively shallow depth for which constructing and operation costs may be reduced if air tightness and stability can be assured. Our analysis showed that the key parameter to assure long-term air tightness in such a system was the permeability of both the Concrete lining and the surrounding rock. The analysis also indicated that a Concrete lining with a permeability of less than 1×10−18m2 would result in an acceptable air leakage rate of less than 1%, with the operation pressure range between 5 and 8MPa at a depth of 100m. It was further noted that capillary retention properties and the initial liquid saturation of the lining were very important. Indeed, air leakage could be effectively prevented when the air-entry pressure of the Concrete lining is higher than the operation air pressure and when the lining is kept at relatively high moisture content. Our subsequent energy-balance analysis demonstrated that the energy loss for a daily compression and decompression cycle is governed by the air-pressure loss, as well as heat loss by conduction to the Concrete Liner and surrounding rock. For a sufficiently tight system, i.e., for a Concrete permeability of less than 1×10−18m2, heat loss by heat conduction tends to become proportionally more important. However, the energy loss by heat conduction can be minimized by keeping the air-injection temperature of compressed air closer to the ambient temperature of the underground storage cavern. In such a case, almost all the heat loss during compression is gained back during subsequent decompression. Finally, our numerical simulation study showed that CAES in shallow rock caverns is feasible from a leakage and energy efficiency viewpoint. Our numerical approach and energy analysis will next be applied in designing and evaluating the performance of a planned full-scale pilot test of the proposed underground CAES concept.
-
stability analysis of Concrete Liner installed in a compressed air storage tunnel
Tunnel and Underground Space, 2009Co-Authors: Younkyou Lee, Kyungsoon Park, Wonkyong Song, Chulwhan Park, Byunghee ChoiAbstract:The stability assessment of a Concrete Liner of a compressed air storage tunnel should be performed by an approach which is different from that commonly used for the Liners of road tunnels, since the Liner is exposed to high air pressure. In this study, the stability analysis method for the Liner of compressed air storage tunnel is proposed based on the elastic and elasto-plastic solutions of the thick-walled cylinder problem. In case of elastic analysis, the yield initiation condition at the inner boundary is considered as the failure condition of the Liner, while the condition which results in the extension of yielding zone to a certain depth is taken as a failure indicator of the Liner in the elasto-plastic analysis taking Mohr-Coulomb criterion. The application of the proposed method revealed that the influence of the relative magnitude of boundary loads on the stability of Liner is considerable. In particular, noting that the estimation of the outer boundary load may be relatively difficult, it is thought that the precise prediction of outer boundary load is very important in the analysis. Accordingly, the emphasis is put on the selection of the Liner installation time, which may govern the magnitude of outer boundary load.
Dimitri E. Beskos - One of the best experts on this subject based on the ideXlab platform.
-
Soil–structure interaction effects on seismic inelastic analysis of 3-D tunnels
Soil Dynamics and Earthquake Engineering, 2010Co-Authors: George D. Hatzigeorgiou, Dimitri E. BeskosAbstract:Abstract This paper investigates the importance of seismic soil–structure interaction in three-dimensional lined tunnels, assuming inelastic material behaviour for both the Concrete Liner and the soft rock type of soil. The seismic response of the soil–structure system is determined by the finite element method (FEM) in the time domain. Viscous absorbing boundaries are used in conjunction with the discretization of the rock medium. Both the rock medium and the Concrete Liner are assumed to behave inelastically on the basis of the continuum damage mechanics theory. The seismic waves are assumed to have any arbitrary time variation and direction of propagation. The system is analysed with and without soil–structure interaction in order to assess its importance on the response of the system. Through parametric studies, the influence of the most critical parameters affecting the structural response is determined and critically discussed.
-
2D dynamic response of unlined and lined tunnels in poroelastic soil to harmonic body waves
Earthquake Engineering & Structural Dynamics, 2002Co-Authors: S.e. Kattis, Dimitri E. Beskos, A. H. D. ChengAbstract:The problem of harmonic wave diffraction by tunnels in an infinite poroelastic saturated soil obeying Biot's theory is studied numerically under conditions of plane strain and the effect of poroelasticity on the response is assessed through some parametric studies. The method is based on the theory of Mei and Foda, which considers the total field to be approximated by the superposition of an elastodynamic problem with modified elastic constants and mass density for the whole domain and a diffusion problem for the pore fluid pressure confined to a boundary layer at the free boundaries. Both problems are solved numerically by the boundary element method in the frequency domain. Results dealing with the response of a circular tunnel with and without an elastic Concrete Liner in an infinite poroelastic medium to incident harmonic P and SV plane waves are provided and compared against analytical ones as well as to those corresponding to linear elastic soil behaviour. Copyright © 2002 John Wiley & Sons, Ltd.
-
Inelastic response of 3-D underground structures in rock under seismic loading
WIT Transactions on the Built Environment, 2001Co-Authors: George D. Hatzigeorgiou, Dimitri E. BeskosAbstract:This paper describes the development of a numerical approach to compute the inelastic response of three-dimensional underground structures (mainly tunnels) to seismic loading. The solution is obtained using the finite element method for the surrounding rock medium and the boundary element method for the shell Liner, both in the time domain. It is assumed that there is no interaction between the rock medium and the Concrete Liner. This enables one to analyze the two different bodies separately and determine the response of the Liner by imposing on it the displacements of the rock cavity computed under the influence of the seismic waves. Both the rock medium and the Concrete Liner are assumed to behave inelastically on the basis of the continuum damage mechanics theory. The seismic waves are assumed to have any arbitrary time variation and direction of propagation. The proposed methodology is used to determine the response of various underground structures under various types of loading including the seismic one. Through parametric studies, the influence of the most critical parameters affecting the structural response is determined and critically discussed.
Siren Topias - One of the best experts on this subject based on the ideXlab platform.
-
Elastoplastic Modelling of an In Situ Concrete Spalling Experiment using the Ottosen Failure Criterion
'Hindawi Limited', 2017Co-Authors: Uotinen Lauri, Siren TopiasAbstract:An in situ Concrete spalling experiment will be carried out in the ONKALO rock characterization facility. The purpose is to establish the failure strength of a thin Concrete Liner on prestressed rock surface, when the stress states in both rock and Concrete are increased by heating. A cylindrical hole 1.5 m in diameter and 7.2 m in depth is reinforced with a 40 mm thin Concrete Liner from level -3 m down. Eight 6 m long 4 kW electrical heaters are installed around the hole 1 m away. The experiment setup is described and results from predictive numerical modelling are shown. Elastoplastic modelling using the Ottosen failure criterion predicts damage initiation on week 5 and the Concrete ultimate strain limit of 0.0035 is exceeded on week 10. The support pressure generated by the Liner is 3.2 MPa and the tangential stress of rock is reduced by -33 %. In 2D fracture mechanical simulations, the support pressure is 3 MPa and small localized damage occurs after week 3 and damage process slowly continues during week9 of the heating period. In conclusion, external heating is a potent way of inducing damage and thin Concrete Liner significantly reduces the amount of damage.Peer reviewe
Topias Siren - One of the best experts on this subject based on the ideXlab platform.
-
Elastoplastic Modelling of an In Situ Concrete Spalling Experiment using the Ottosen Failure Criterion
Journal of Engineering, 2017Co-Authors: Lauri Uotinen, Topias SirenAbstract:An in situ Concrete spalling experiment will be carried out in the ONKALO rock characterization facility. The purpose is to establish the failure strength of a thin Concrete Liner on prestressed rock surface, when the stress states in both rock and Concrete are increased by heating. A cylindrical hole 1.5 m in diameter and 7.2 m in depth is reinforced with a 40 mm thin Concrete Liner from level −3 m down. Eight 6 m long 4 kW electrical heaters are installed around the hole 1 m away. The experiment setup is described and results from predictive numerical modelling are shown. Elastoplastic modelling using the Ottosen failure criterion predicts damage initiation on week 5 and the Concrete ultimate strain limit of 0.0035 is exceeded on week 10. The support pressure generated by the Liner is 3.2 MPa and the tangential stress of rock is reduced by −33%. In 2D fracture mechanical simulations, the support pressure is 3 MPa and small localized damage occurs after week 3 and damage process slowly continues during week 9 of the heating period. In conclusion, external heating is a potent way of inducing damage and thin Concrete Liner significantly reduces the amount of damage.