Suncoh Consultants Co.

Tokyo, Japan

Suncoh Consultants Co.

Tokyo, Japan
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Yokota T.,Japan National Institute of Advanced Industrial Science and Technology | Jinguuji M.,Japan National Institute of Advanced Industrial Science and Technology | Yamanaka Y.,SUNCOH Consultants Co. | Murata K.,SUNCOH Consultants Co.
Exploration Geophysics | Year: 2017

Property damage results from liquefaction that occurs easily in soft sandy layers. Moreover, liquefaction damage tends to be more serious at locations where earthquake ground motions are locally amplified. It is commonly understood that ground stiffness is correlated with S-wave velocity (Vs); in addition, the structure of the local subsurface is important for predicting local earthquake ground motion. Surface wave and S-wave reflection surveys are efficient, non-destructive techniques used to obtain two-dimensional S-wave velocity distributions and to map subsurface structures. In this study, we performed surface wave and S-wave reflection surveys to investigate the Hinode area of Itako, Ibaraki, Japan. This area suffered serious liquefaction damage during the Great Eastern Japan Earthquake of 2011. Using subsurface boundaries imaged by the reflection surveys and the Vs structures obtained by surface wave analyses, it is possible to extrapolate geological and hydraulic information obtained by boring and cone penetration tests (CPTs). The combined information was used to delineate the layer in which liquefaction occurred, identified as an artificial layer of sandy dredged material, formed after 1970. The results of this study confirmed the effectiveness and applicability of geophysical surveys to the evaluation of the liquefaction potential. These methods enable us to predict the spatial distribution of liquefiable soils for future large earthquakes. © ASEG 2017.

Iwata N.,Chuden Engineering Consultants Co. | Sasaki T.,Suncoh Consultants Co. | Yoshinaka R.,Saitama University | Kurooka K.,Chugoku Electric Power Co.
International Journal of Rock Mechanics and Mining Sciences | Year: 2012

This paper describes the validity of the multiple yield model (MYM) based on a comparison between predictions by MYM analysis and in-situ measurements of two large-scale vertical excavations, about 30. m in depth and 100. m in width, for nuclear power plants. MYM is a finite element method for modeling the mechanical properties of intact rock and joint systems in rock mass. The method can analyze the non-linearity of deformation under loading and unloading stress paths. The analysis was conducted by determining the geometrical model of rock mass from test adit and borehole observations of discontinuities in conditions such as orientation, spacing, and persistence. The physical parameters of intact rock and discontinuities were determined by laboratory tests using sample specimens, taking the scale effect into account. The deformation mode and displacement value determined by the MYM analysis both corresponded well with in-situ measurements. We have confirmed that MYM can estimate the actual behavior of discontinuous rocks with adequate accuracy for practical application. © 2012 Elsevier Ltd.

Iwata N.,Chuden Engineering Consultants Co. | Sasaki T.,Suncoh Consultants Co. | Yoshinaka R.,Saitama University
Harmonising Rock Engineering and the Environment - Proceedings of the 12th ISRM International Congress on Rock Mechanics | Year: 2012

The authors are analyzed two practical examples of large scale vertical excavations 20-30m in depth and two earthquake response analyses of the discontinuous rock slope and rock foundation of large building, and are presented the applicability of MultipleYield Model (MYM). MYM is a kind of finite element method constituted the mechanical properties of intact rock and discontinuity systems in rock mass, and can be analyzed the non-linearity of deformation under loading and unloading stress paths considering the confining pressures of rock joints. For analyzing, the geometrical models of rock mass were determined from site investigations and the physical parameters were determined by laboratory test and also considering scale effect. The results of MYM analysis were well corresponded to the measurement and it is confirmed that MYM is effective for static and dynamic response on jointed rock masses. © 2012 Taylor & Francis Group, London.

Iwata N.,Chuden Engineering Consultants Co. | Yoshinaka R.,Saitama University | Sasaki T.,Suncoh Consultants Co.
International Journal of Rock Mechanics and Mining Sciences | Year: 2013

The stability, deformation behavior, permeability and other properties of discontinuous rocks are greatly influenced by the geometrical distribution of discontinuities in rock mass, and extremely important infrastructures such as nuclear power plants, large-scale underground excavations, long-span bridges, etc. built on or in discontinuous rock mass are also influenced by these same effects. However, a seismic analytical method such as for earthquake response, to correctly evaluate discontinuous conditions of rock mass has not been developed. This paper describes a new seismic response analytical method using the multiple yield model as a kind of FEM. The applicability of this method was verified by making comparisons between the seismographic records obtained with several underground deaths at The 2005 offshore Miyagi Prefecture Earthquake (MW=7.2) and The 2011 offshore the Pacific coast of Tohoku Earthquake (MW=9.0), both of which seismic motions were obtained at the same large and very important nuclear power plant, and the results of the response analyses using the seismic motions recorded at the deepest earth level of seismographs. The geological condition of the foundation ground is one of strongly folded hard sedimentary rocks. From this study, we have confirmed that the multiple yield model is an effective method for seismic response analysis. © 2013 Elsevier Ltd.

Iwata N.,Chuden Engineering Consultants Co. | Sasaki T.,Suncoh Consultants Co. | Sasaki K.,Suncoh Consultants Co. | Yoshinaka R.,Saitama University
Rock Mechanics in Civil and Environmental Engineering - Proceedings of the European Rock Mechanics Symposium, EUROCK 2010 | Year: 2010

This paper describes the validity of the MultipleYield Model to the earthquake response analysis of the discontinuous rock by two examples of the actual collapsed rock slope caused during the Mid Niigata Prefecture Earthquake in 2004 (M 6.8) and the large scale and/or very important facility like as a nuclear power station on rock. Results show that geometrical and mechanical conditions of joints have strong influence on the seismic response. © 2010 Taylor & Francis Group.

Sasaki T.,Suncoh Consultants Co. | Hagiwara I.,Suncoh Consultants Co. | Ohnishi Y.,Kyoto University | Koyama T.,Kyoto University | Miki S.,KisoJiban Consultants Co.
47th US Rock Mechanics / Geomechanics Symposium 2013 | Year: 2013

The authors analyse rock fall problems using three dimensional Discontinuous Deformation Analysis (3D-DDA) developed by Shi (2001). The shapes of the mountains or valleys are very complex and require much computation time for integrations; up to 80 to 90 per cent of the total calculation time in the three dimensional analyses. The ratios between the base blocks of the modelled mountain and the rock fall blocks are extremely large and cause numerical instability in the linear algebraic equations losing effective digits in the space domain. The authors have improved the fixed block option for rock fall problems based on three-dimensional DDA. The fixed block option assumes a rigid body for a block and we calculate the rock fall models using the fixed block option for the base blocks of the modelled mountain and assume an elastic body for the falling blocks. Since, introducing these assumptions, the integration of the complex shapes of the base blocks of the mountain can be avoided for each time step. Hence, the calculation time is ten times faster than when using the original algorithm and realizes good numerical stability. Copyright 2013 ARMA, American Rock Mechanics Association.

Miki S.,Kiso Jiban Consultants Co. | Sasaki T.,Suncoh Consultants Co. | Koyama T.,Kyoto University | Nishiyama S.,Kyoto University | Ohnishi Y.O.,Kyoto University
International Journal of Computational Methods | Year: 2010

Discontinuous Deformation Analysis (DDA) and Numerical Manifold Method (NMM) have been widely used for the analyses of discontinuous rock masses. Recently, these discontinuum-based numerical methods have been applied to the simulations for slope failure due to earthquakes, where one of the key issues is the estimation of traveling velocities and distances for the collapsed rock blocks. For the dynamic response analysis of rock slopes, it is necessary to consider the local variation of seismic forces, especially when the slope size is large and/or the slope geometry becomes complicated. In DDA, there is difficulty to consider the local displacements and stress condition of the single block for the basement because of mathematical principle (in DDA, the displacement function is defined at the gravity center of the blocks and the strain in the block is uniform). On the other hand, NMM can simulate both continuous and discontinuous deformation of the block systems. However, the rigid body rotation of blocks cannot be treated properly because NMM does not deal with the rigid body rotation in explicit form. According to the above-mentioned features and drawbacks, it is reasonable to combine DDA and NMM from practical point of view. In this paper, the formulation for the coupled NMM and DDA (NMM-DDA) was presented. For the formulation, NMM and DDA can be easily combined by choosing displacements of the DDA blocks and NMM cover nodes as unknowns, because the processes to establish the equilibrium equations (minimizing total potential energy) and kinematics for block system are same between DDA and NMM. In this paper, some applications of the NMM-DDA to both dynamic and static problems were also presented and the validity and applicability of newly developed DDA-MM were discussed. © 2010 World Scientific Publishing Company.

Takagishi M.,Japan Research Institute of Innovative Technology for the Earth | Hashimoto T.,Japan Research Institute of Innovative Technology for the Earth | Horikawa S.,Suncoh Consultants Co. | Kusunose K.,Japan National Institute of Advanced Industrial Science and Technology | And 2 more authors.
Energy Procedia | Year: 2014

This paper describes passive seismic monitoring at the large-scale CO2 injection site, Cranfield oilfield, Mississippi, U.S.A. We constructed a horizontal near-surface monitoring network and have been monitoring for more than two years to elucidate relationship between large-volume CO2 injection and occurrences of induced seismicities. We have detected no microseismic events that occurred in and around the Cranfield site for now. The detected signals were all identified as cultural noises, natural noises due to weather changes, and distant earthquakes. We also estimated minimum detectable magnitudes of the monitoring network by theoretical calculations and confirmed that the system could enough ability to detect microseismic events. © 2014 The Authors. Published by Elsevier Ltd.

Nakata N.,Colorado School of Mines | Snieder R.,Colorado School of Mines | Kuroda S.,Japan National Institute of Rural Engineering of Japan | Ito S.,Suncoh Consultants Co. | And 2 more authors.
Bulletin of the Seismological Society of America | Year: 2013

For health monitoring of a building, we need to separate the response of the building to an earthquake from the imprint of soil-structure coupling and from wave propagation below the base of the building. Seismic interferometry based on deconvolution, where we deconvolve the wave fields recorded at different floors, is a technique to extract this building response and thus estimate velocity of the wave that propagates inside the building. Deconvolution interferometry also allows us to estimate the damping factor of the building. Compared with other interferometry techniques, such as cross-correlation and cross-coherence interferometry, deconvolution interferometry is the most suitable technique to monitor a building using earthquake records. For deconvolution interferometry, we deconvolve the wave fields recorded at all levels with the waves recorded at a target receiver inside the building. This receiver behaves as a virtual source, and we retrieve the response of a cut-off building, a short building that is cut off at the virtual source. Because the cut-off building is independent from the structure below the virtual source, the technique might be useful for estimating local structure and local damage. We apply deconvolution interferometry to 17 earthquakes recorded during two weeks at a building in Fukushima, Japan, and estimate time-lapse changes in velocity and normal-mode frequency. As shown in a previous study, the change in velocity correlates with the change in normal-mode frequency. We compute the velocities from both traveling waves and the fundamental mode using coda-wave interferometry. These velocities have a negative correlation with the maximum acceleration of the observed earthquake records.

Sasaki T.,Suncoh Consultants Co. | Hagiwara I.,Suncoh Consultants Co. | Sasaki K.,Suncoh Consultants Co. | Yoshinaka R.,Saitama University | And 3 more authors.
International Journal of Computational Methods | Year: 2011

In this paper, the stability including stress distribution of two ancient masonry structures, the pyramid of the Pharaoh Khufu, Egypt and the Pont of Gard, were analyzed using discontinuous deformation analysis (DDA) and numerical manifold method (NMM). For the simulation using NMM, the newly developed four-node isoparametric element was used. The stress distributions/concentration were calculated and compared between the two methods. The calculated results show qualitative agreement with observations. DDA and NMM are applicable to simulate the physical phenomena of masonry structures. © 2011 World Scientific Publishing Company.

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