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Journal Articles

Numerical analysis of the grout injection conducted in the ventilation shaft of the Horonobe Underground Research Laboratory

Nakashima, Hiroyoshi*; Koyama, Tomofumi*; Tatsuta, Keisuke*; Katayama, Tatsuo*; Aoyagi, Kazuhei

Dai-14-Kai Iwa No Rikigaku Kokunai Shimpojiumu Koen Rombunshu (Internet), 6 Pages, 2017/01

In this study, we created the three dimensional model based on equivalent continuum approach to study the penetration length and enhancement of the hydraulic conductivity of the rock mass. The developed numerical model was applied to the in situ grout injection conducted in the ventilation shaft of the Horonobe Underground Research Laboratory. We evaluated the hydraulic conductivity of the rock mass after the grout operation. As a result, hydraulic conductivity of the highly permeable fault was decreased in 4 orders of magnitude, which is almost consistent with the in situ hydraulic conductivity obtained from in situ Luegeon test after the grout injection. Thus the simulation method described in this paper can be applied to the evaluation of the efficiency of in situ grout injection.

Journal Articles

Numerical simulations and analysis for the $"A$sp$"o$ pillar stability experiment, 1; Continuum based approaches using finite element method and comparison with other analysis model

Chijimatsu, Masakazu*; Koyama, Tomofumi*; Shimizu, Hiroyuki*; Nakama, Shigeo; Fujita, Tomo

Dai-13-Kai Iwa No Rikigaku Kokunai Shimpojiumu Koen Rombunshu (CD-ROM), p.437 - 442, 2013/01

DECOVALEX-2011 is an international cooperation project for enhancing the numerical models of radioactive waste repositories. In Task B of DECOVALEX-2011 project, the failure mechanism during excavation, heating and destressing processes observed in the $"A$sp$"o$ pillar stability experiment (APSE), which carried out at the $"A$sp$"o$ Hard Rock Laboratory by the Swedish Nuclear Fuel and Waste Management Company (SKB), were simulated using Finite Element Method. When the calibrated parameters were used, simulation results agree qualitatively well with the experimental results. Therefore, it can be said that the spalling phenomenon is expressible even by the application with the continuum model by the use of the suitable parameters.

Journal Articles

Numerical simulations and analysis for the $"A$SP$"O$ pillar stability experiment, 2; Discontinuum based approaches using distinct element method

Shimizu, Hiroyuki*; Koyama, Tomofumi*; Chijimatsu, Masakazu*; Fujita, Tomo; Nakama, Shigeo

Dai-13-Kai Iwa No Rikigaku Kokunai Shimpojiumu Koen Rombunshu (CD-ROM), p.443 - 448, 2013/01

DECOVALEX-2011 is an international cooperation project for enhancing the numerical models of radioactive waste repositories. In Task B of DECOVALEX-2011 project, the failure mechanism during excavation, heating and destressing processes observed in the $"A$sp$"o$ pillar stability experiment (APSE), which carried out at the $"A$sp$"o$ Hard Rock Laboratory by the Swedish Nuclear Fuel and Waste Management Company (SKB), were simulated using two dimensional Distinct Element Method. As a result, it is found that the simulated crack generation and propagation during the destressing process by 2D-DEM agree qualitatively well with the observation at site.

Journal Articles

Development of grouting technologies for HLW disposal in Japan, 5; Development and application of numerical model for grout injection process during in-situ grouting test

Koyama, Tomofumi*; Katayama, Tatsuo*; Tanaka, Tatsuya*; Kuzuha, Yuji; Onishi, Yuzo*

Proceedings of 7th Asian Rock Mechanics Symposium (ARMS-7) (USB Flash Drive), p.712 - 720, 2012/10

Grouting is commonly used to decrease the hydraulic conductivity of the fractured rock masses and control the groundwater inflow. Since underground facilities were constructed in various geological conditions, different types of grout material and mixing/injection methods were developed for effective and economical grout injection. It is also important to evaluate the grout arrival distance and the range of altered hydraulic conductivity field after grout injection. However, the mechanism of grout injection process has not been clarified sufficiently yet due to complicated chemical and physical processes of grout. In this study, to simulate the grout injection process, the three-dimensional numerical model based on equivalent continuum approach was developed and applied to the in-situ grout injection tests at Grimsel test site, Switzerland. In the simulations, the injection pressure and/or injection rate was given as a boundary condition and total amount of injected grout (silica sol) was calculated. The simulation results were also compared with the ones obtained from in-situ measurements/monitoring and show qualitatively good agreement.

Journal Articles

The JAEA grouting test at the Grimsel test site; Numerical simulation of the grout injection process of silica sol in fractured rock mass

Koyama, Tomofumi*; Onishi, Yuzo*; Bruines, P.*; Tanaka, Tatsuya*; Hasui, Akinori*; Katayama, Tatsuo*; Kishi, Hirokazu; Kuzuha, Yuji

Proceedings of 2012 ISRM International Symposium; Rock Engineering and Technology for Sustainable Underground Construction (EUROCK 2012) (USB Flash Drive), 10 Pages, 2012/05

Grouting, which involves injection of grout material, is commonly used to decrease the hydraulic conductivity of the fractured rock masses and control the groundwater inflow. However, the mechanism of grout injection process has not been clarified sufficiently yet due to complicated chemical and physical processes of grout. In this study, to simulate the grout injection process, the three-dimensional numerical model based on equivalent continuum approach was developed.

Journal Articles

The JAEA grouting test at the Grimsel test site; Site characterization of a fractured rockmass and preparation of DFN model and its equivalent continuous porous media model

Bruines, P.*; Tanaka, Tatsuya*; Koyama, Tomofumi*; Kishi, Hirokazu; Nakanishi, Tatsuro; Onishi, Yuzo*

Proceedings of 2012 ISRM International Symposium; Rock Engineering and Technology for Sustainable Underground Construction (EUROCK 2012) (USB Flash Drive), 15 Pages, 2012/05

To better understand the grouting process and the effect of grouting on the performance of a nuclear waste repository, the Japanese Atomic Energy Agency (JAEA) has initiated a grouting test carried out in the fractured granite of the Grimsel Test Site (GTS) located in the Swiss Alps. This paper describes the characterization of the rock mass, how the data obtained has been used to make a discrete fracture network (DFN) model and how an up-scaled equivalent continuous porous media (ECPM) model for the purpose of numerical simulation of the grout injection process is generated. The generated DFN model and the up-scaled ECPM model was able to reproduce the measured fracture characteristics (e.g. orientation, density) as well as the hydraulic behavior observed in the field (e.g. transmissivity distribution, anisotropy, heterogeneity) and has proven to be suitable for modeling grouting behavior.

Journal Articles

Development of grouting technologies for geological disposal of high level waste in Japan, 3; Numerical simulation for grout injection using equivalent continuum model

Koyama, Tomofumi*; Katayama, Tatsuo*; Hasui, Akinori*; Tanaka, Tatsuya*; Kishi, Hirokazu; Onishi, Yuzo*

Dai-41-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koenshu (CD-ROM), p.83 - 88, 2012/01

In this study, to simulate the grout injection process, the 3-D numerical model based on equivalent continuum approach was developed. The viscosity measurements for silica sol was performed to measure the time-dependent viscosity. The developed numerical model was applied to the planned in-situ grout injection tests at Grimsel test site (GTS), Switzerland. The rock type is fractured granite and the equivalent porous media was created from the DFN (Discrete Fracture Network) based on the frature data obtained from the observation boreholes. The preliminary simulation was carried out to determine the suitable grout injection pressure and investigate the arrival distance of grout from injection boreholes.

Journal Articles

Distinct element analysis for mechanical behavior in HLW disposal tunnel considering pre-existing cracks

Shimizu, Hiroyuki*; Koyama, Tomofumi*; Chijimatsu, Masakazu*; Fujita, Tomo; Nakama, Shigeo

Doboku Gakkai Rombunshu, A2 (Oyo Rikigaku) (Internet), 68(2), p.I_477 - I_486, 2012/00

In this paper, the coupled thermal-mechanical processes in the $"A$sp$"o$ pillar stability experiments (APSE) were simulated using Distinct Element Method (DEM). By considering pre-existing cracks in the rock model, mechanical response of the rock during excavation phase and heating phase were successfully represented by DEM. Simulation results agree qualitatively well with the experimental results. However, the microcracks in the simulation were widely distributed around the heater and exfoliation of rock surfaces observed in the ${it in-situ}$ experiment was not formed accurately. To simulate more realistically the experimental results by the DEM models, the calibration of the microscopic parameters considering the model scale should be done. Moreover, more detailed discussion on the excavation damaged zone around the borehole and the distribution of pre-existing cracks are required.

Journal Articles

The Project for grouting development for high level radioactive waste repository, 7; A Study on clogging characteristics during grout injection in sand column

Ohashi, Hideki*; Koyama, Tomofumi*; Hasui, Akinori*; Katayama, Tatsuo*; Kuzuha, Yuji

Doboku Gakkai Heisei-23-Nendo Zenkoku Taikai Dai-66-Kai Nenji Gakujutsu Koenkai Koen Gaiyoshu (DVD-ROM), p.77 - 78, 2011/09

no abstracts in English

Journal Articles

The Project for grouting development for high level radioactive waste repository, 8; Prediction analysis of grout injection in equivalent porous media

Kuzuha, Yuji; Kishi, Hirokazu; Hasui, Akinori*; Katayama, Tatsuo*; Koyama, Tomofumi*

Doboku Gakkai Heisei-23-Nendo Zenkoku Taikai Dai-66-Kai Nenji Gakujutsu Koenkai Koen Gaiyoshu (DVD-ROM), p.79 - 80, 2011/09

no abstracts in English

Journal Articles

Distinct element modeling for Class II behavior of rock and hydraulic fracturing

Shimizu, Hiroyuki*; Koyama, Tomofumi*; Murata, Sumihiko*; Ishida, Tsuyoshi*; Chijimatsu, Masakazu*; Fujita, Tomo; Nakama, Shigeo

International Journal of the JCRM (Internet), 7(1), p.33 - 36, 2011/09

In this research, newly developed numerical approaches using the Distinct Element Method (DEM) were presented, and a series of DEM simulations were performed for better understanding the physical phenomena and mechanism for the following two fundamental issues in rock engineering field. The first issue is the Class II behavior of the brittle rocks under uniaxial compression. The radial strain control method for uniaxial compression tests was introduced in the DEM codes and the Class II behavior of rocks was simulated. The simulation results suggest that the DEM can reproduce the Class II behavior of the rock successfully and revealed that the loading condition of rocks will play an important role for the Class II behavior. The second issue is the hydraulic fracturing behavior in rocks. A series of simulations for hydraulic fracturing in rock was performed by using the flow-coupled DEM code. Simulation results clearly show that the fluid infiltration behavior depends on the fluid viscosity. The fluid infiltrates into the fracture immediately, when a low viscosity fluid is used and the fluid infiltrates slowly into the cracks after the fracture generation and propagation, when a high viscosity fluid is used. Moreover, the tensile cracks are dominantly generated in the DEM simulations as expected in the conventional theory. However, the energy released from tensile cracks becomes smaller due to the fact that the tensile strength of rock is usually smaller than the compressive one. Such a small AE events is not distinguishable from noise and hard to recognize during laboratory experiments. Therefore, in AE measurements, shear type AE events with large energy are dominantly observed.

Journal Articles

Distinct element approach for the analysis of coupled thermal-mechanical processes in the near field of the HLW repository

Koyama, Tomofumi*; Shimizu, Hiroyuki*; Chijimatsu, Masakazu*; Nakama, Shigeo; Fujita, Tomo

Proceedings of 2011 World Congress on Advances in Structural Engineering and Mechanics (ASEM '11plus) (USB Flash Drive), p.3759 - 3782, 2011/09

In this paper, the coupled thermal-mechanical processes in the $"A$sp$"o$ pillar stability experiments (APSE) carried out by the Swedish Nuclear Fuel and Waste Management Company (SKB) were simulated using 2 dimensional Distinct Element Method (2-D DEM) with particles. The main objective for large scale in-situ experiment is to investigate the yielding strength of crystalline rock and the formation of the excavation disturbed/damaged zone (EDZ) during excavation of two boreholes, pressurizing in one of the borehole and heating processes. For the simulations, the heat flow algorism was newly introduced into original DEM code to consider heating processes in the APSE. For the DEM simulations, one of the borehole cross sections (in 2-D) was selected and modeled as an assemblage of many particles bonded each other to investigate the failure mechanism during excavation and heating processes in detail including crack propagation at the borehole surface. The microscopic parameters used in the DEM simulations were determined by the calibration using the laboratory uniaxial/triaxial compression testing results. The calculated stress distribution, displacements and temperature distribution were compared with the ones obtained from in-situ measurements and 2-D, 3-D FEM simulations. The simulated crack propagation during the excavation, pressurizing and heating processes by DEM with particles agrees qualitatively well with the observation. The parametric study for initial microcracks was performed to reproduce the spalling phenomena observed in the APSE.

Journal Articles

Simulation of the spalling phenomena at the $"A$sp$"o$ Pillar Stability Experiment by the coupled T-H-M analysis using the damage model

Chijimatsu, Masakazu*; Koyama, Tomofumi*; Kobayashi, Akira*; Shimizu, Hiroyuki*; Nakama, Shigeo

Proceedings of 4th International Conference on Coupled T-H-M-C Processes in Geosystems: Fundamentals, Modeling, Experiments and Applications (GeoProc 2011) (CD-ROM), 13 Pages, 2011/07

The experiment was performed at the $"A$sp$"o$ Hard Rock Laboratory facility owned by the Swedish Nuclear Fuel and Waste Management Co. For the experiment an oval shape tunnel was excavated in which two large holes, $$phi$$ 1.75 m and depth 6.5 m, were excavated. The holes were placed so that a 1 m wide vertical pillar was created between them. The pillar volume was then heated to increase the tangential stress so that yielding could propagate along the borehole wall. Analysis of the coupled thermal, hydraulic and mechanical processes is carried out with the computer code named THAMES. In order to evaluate the spalling phenomena, the damage model was included in the computer code. In the damage mechanics, the change in mechanical behavior due to the growth of damage (cracks) in material is considered. The parameters of this damage model were determined by the unconfined compression test. When the parameters determined by laboratory test were used, the damage did not occur. This is because the parameters were determined from the experiment of the rock core, and it is thought that the parameter of actual bedrock is inferior to that of the rock core. Therefore, the calibration of the damage parameters was performed. When the calibrated parameters were used, simulation results agree qualitatively well with the experimental results. During the simulation of excavation, generating of damage is seen to similar to the observation by the in-situ experiment. Furthermore, temperature change during heating after the excavation of borehole also shows the good agreement between the measured and simulated results. Therefore, it can be said that the spalling phenomenon is expressible even by the application with the continuum model by the use of the suitable parameters.

Journal Articles

Numerical simulations for the coupled thermal-mechanical processes in $"A$sp$"o$ Pillar Stability Experiment; Continuum and discontinuum based approaches

Koyama, Tomofumi*; Shimizu, Hiroyuki*; Chijimatsu, Masakazu*; Kobayashi, Akira*; Nakama, Shigeo; Fujita, Tomo

Proceedings of 4th International Conference on Coupled T-H-M-C Processes in Geosystems: Fundamentals, Modeling, Experiments and Applications (GeoProc 2011) (CD-ROM), 11 Pages, 2011/07

In this paper, the coupled thermal-mechanical processes in the pillar stability experiments carried out at the $"A$sp$"o$ Hard Rock Laboratory by the Swedish Nuclear Fuel and Waste Management Company (SKB) were simulated using both Finite Element Method (FEM) and Distinct Element Method (DEM) with particles. The main purpose for in-situ experiment is to investigate the yielding strength of crystalline rock and the formation and growth of the excavation disturbed/damaged zone (EDZ) during excavation and heating processes. For the 3-D numerical simulations using FEM (called THAMES), the measured in-situ stress and its time evolutions (stress re-distribution) due to the tunnel and two borehole excavations, pressurize in one of the borehole as well as heating process were considered. On the other hand, in 2-D DEM simulations, one of the borehole cross sections (in 2-D) was selected and modeled as an assemblage of many particles bonded each other to investigate the failure mechanism during excavation and heating processes in detail including crack propagation at the borehole surface (spalling phenomena). The microscopic parameters used in the DEM simulations were determined by the calibration using the laboratory uniaxial/triaxial compression testing results. The calculation results such as stress distribution, displacements as well as temperature distribution were compared with the in-situ observation and measurements. The simulation results from 3-D FEM shows good agreement with the data obtained from the measurements. The simulated crack propagation during the excavation, pressurizing and heating processes by DEM with particles agrees qualitatively well with the observation. The findings obtained from two different types of numerical simulations can be used for the performance and safety assessment of nuclear waste disposal.

Journal Articles

Coupled thermo-mechanical simulations for HLW disposal tunnel using distinct element method

Shimizu, Hiroyuki; Koyama, Tomofumi*; Chijimatsu, Masakazu*; Fujita, Tomo; Nakama, Shigeo

Zairyo, 60(5), p.470 - 476, 2011/05

In this study, the thermal calculation algorism was newly developed and introduced to the original distinct element code, and the coupled thermo-mechanical behavior of rock mass around the HLW disposal tunnel was simulated. For the simulations, the experimental data was obtained from the pillar stability experiments with mechanical loading and heating at Aspo HRL (hard rock underground laboratory), Sweden and simulation results were compared with the measuring and observation results. The crack propagation process during heating can be successfully simulated and simulation results agree well with the measuring and observation results at the site. However, for the better agreement quantitatively, the further bonding parameter as a function of heat will be necessary.

Journal Articles

Discrete and continuum approaches for the analysis of coupled thermal-mechanical processes in the near field of a HLW repository

Shimizu, Hiroyuki; Koyama, Tomofumi*; Chijimatsu, Masakazu*; Fujita, Tomo; Nakama, Shigeo

Dai-40-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koen Rombunshu (CD-ROM), p.248 - 253, 2011/01

This paper reports on the results of the numerical simulations for the analysis of coupled thermal-mechanical processes in the near field of a HLW repository using Finite Element Method (FEM) and Distinct Element Method (DEM). The FEM approach provides quantitative information of the change of stress and strain during excavation and heating process. On the other hand, the DEM approach shows the crack propagation process at the borehole surface, and this result agrees qualitatively well with the experimental observation. By comparing these results obtained from both approaches, quantitative and qualitative insights into various aspects of the processes occurred in the near field can be obtained.

Journal Articles

Distinct element analysis for Class II behavior of rocks under uniaxial compression

Shimizu, Hiroyuki*; Koyama, Tomofumi*; Ishida, Tsuyoshi*; Chijimatsu, Masakazu*; Fujita, Tomo; Nakama, Shigeo

International Journal of Rock Mechanics and Mining Sciences, 47(2), p.323 - 333, 2010/02

Journal Articles

Bubble behavior in mercury cavitation

Naoe, Takashi; Futakawa, Masatoshi; Koyama, Tomofumi*; Kogawa, Hiroyuki

Jikken Rikigaku, 6(3), p.301 - 307, 2006/09

A mercury target for spallation neutron source is subject to pressure waves caused by proton bombarding mercury. The pressure wave propagation induces the cavitation in mercury that imposes pitting damage on the target vessel. In this paper, single micro-bubble behavior in mercury was evaluated using numerical calculation on the basis of bubble dynamics given by Rayleigh-Plesset. Impact pressure loading tests using an electro-Magnetic IMpact Testing Machine (MIMTM) were performed to measure the impact pressure and acoustic vibration. Additionally, in order to visualize micro-bubble behavior in mercury, high-speed video camera observation was carried out. As the result, we confirmed that the maximum bubble radius and lifetime of micro-bubble are dependent on the imposed pressure and the pressure saturate time and that the acoustic vibration with high frequency components above 15 kHz is exited by the micro-bubble collapse.

Journal Articles

Development of aluminum (Al5083)-clad ternary Ag-In-Cd alloy for JSNS decoupled moderator

Teshigawara, Makoto; Harada, Masahide; Saito, Shigeru; Oikawa, Kenichi; Maekawa, Fujio; Futakawa, Masatoshi; Kikuchi, Kenji; Kato, Takashi; Ikeda, Yujiro; Naoe, Takashi*; et al.

Journal of Nuclear Materials, 356(1-3), p.300 - 307, 2006/09

 Times Cited Count:9 Percentile:56.05(Materials Science, Multidisciplinary)

We adopted silver-indium-cadmium (Ag-In-Cd) alloy as a material of decoupler for decoupled moderator in JSNS. However, from the heat removal and corrosion protection points of view, the Ag-In-Cd alloy is needed to clad between Al alloys (Al5083). We attempted to obtain good bonding conditions for between Al5083 and ternary Ag-In-Cd alloys by HIPing tests. The good HIP condition was found for small test piece ($$Phi$$20mm). Though a hardened layer due to the formation of AlAg$$_{2}$$ was found in the bonding layer, the rupture strength of the bonding layer was more than 20 MPa, which was the calculated design stress. Bonding tests of a large size piece (200$$times$$200$$times$$30 mm$$^{3}$$), which simulated the real scale, were also performed according to the results of small size tests. The result also gave good bonding and enough required-mechanical-strength, however the rupture strength of the large size test was smaller than that of small one.

Journal Articles

Erosion damage evaluation using acoustic vibration induced by micro-bubble collapse

Naoe, Takashi*; Futakawa, Masatoshi; Koyama, Tomofumi*; Kogawa, Hiroyuki; Ikeda, Yujiro

Jikken Rikigaku, 5(3), p.280 - 285, 2005/09

no abstracts in English

24 (Records 1-20 displayed on this page)