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Oji S.,Chuo Kaihatsu Corporation | Sawada S.,Kyoto University | Goto H.,Kyoto University
Bulletin of the Seismological Society of America | Year: 2017

Characterized Green’s function method (CGFM), a new approach for estimating the response spectra of earthquake ground motion, has been proposed by Oji et al. (2012). The CGFM is based on the concept that the spatial average of estimated results is equal to a conventional attenuation model. The site-specific deviations can be modeled by the source rupture effects, such as directivity pulses and radiation patterns, which are represented by the frequency-dependent factors obtained from a superposition of simple characterized waveforms obeying the omegasquare model. In this article, we expand the CGFM to include nonlinear site response at a specific site. This response is calculated using the estimated time history of ground motion on the engineering basement from the response spectrum and the simulated phase waveform obtained by the original CGFM. The proposed CGFM is verified by comparing the estimated results with the records from the 1995 Kobe and the 2007 Chuetsu-Oki earthquakes, Japan. © 2017, Seismological Society of America. All rights reserved.

Lin W.,University of Tokyo | Mao W.,Chuo Kaihatsu Corporation | Koseki J.,University of Tokyo
Springer Series in Geomechanics and Geoengineering | Year: 2017

Current experimental techniques used to understand the shear banding process in sands provide little insight into the internal micro-structure evolution. To this end, Acoustic Emission (AE), as a non-destructive testing technique, was proposed in this paper with great interest in characterizing the internal micro-structure response leading to the evolution of shear bands formed in laboratory triaxial compression. Silica sand was used to conduct consolidated-drained triaxial compression tests at a constant axial strain rate under an effective confining pressure of 100 kPa. AE events were collected and analyzed. Insights regarding relations of the deviatoric stress, source rates and dissipated energy rates of AE events with the increasing global axial strain are offered. The result indicated that with the increase of relative densities, the evolution envelope of AE source rates transits from a steep shape to a flat shape, and total amount of AE source events decreases gradually. According to the evolution of AE energy rate, shear banding process can be divided into four stages in terms of O-A, A-B, B-C and C-D, corresponding to the strain hardening regime, incipient strain softening regime, highest rate of strain softening regime and residual stress regime. From which point A could be considered as an omen of the initiation of strain localization, point B as the initiation of visible shear band and point C as the completion of shear banding. AE technologies can be provided as an alternative means to clarify and indicate the initiation and evolution of shear banding in sand. © Springer International Publishing AG 2017.

Che A.,Shanghai JiaoTong University | Wang H.,Shanghai JiaoTong University | Feng S.,Shanghai JiaoTong University | Siguyama T.,Chuo Kaihatsu Corporation
Journal of Applied Geophysics | Year: 2014

An identification analysis method of the rock mass characteristics is proposed using microtremor measurements in the boring hole. The method is based on the assumption that the epicenter of incident waves of each observation point in the same boring hole almost agrees. And the calculations are deconvoluted by the multiple reflection theory. The procedure applicable to the identification of the average elastic characteristics of in situ rock masses is presented. It is based on the minimization of an error function representing the difference between microtremor measurements performed on the rock mass and the corresponding data obtained by a numerical analysis subjected to known external actions. The method requires the formulation of the elasticity inverse problem and is based on the least square minimization procedure. As an example the approach has been applied to the identification of the dynamic properties and the predominant characteristics of the rock mass underlying a deep excavated quarry in west of Shanghai city. The inverted rock mass characteristics are compared with the PS logs at the sites and show consistency, confirming that the proposed inversion is promising. © 2014 Elsevier B.V.

Miyazaki K.,Japan National Institute of Advanced Industrial Science and Technology | Tenma N.,Japan National Institute of Advanced Industrial Science and Technology | Endo Y.,Chuo Kaihatsu Corporation | Yamaguchi T.,Toho University
ISRM International Symposium - 8th Asian Rock Mechanics Symposium, ARMS 2014 | Year: 2014

Geomechanical behaviors of methane-hydrate-bearing sub-seabed layers have not been sufficiently clarified, although they are essential to ensure sustainable exploration of methane hydrate in marine sediments. In particular, the viscoelastic properties of methane-hydrate-bearing layers are thought to have great significance in the long-term prediction of the geomechanical behaviors. It has been clarified that methane-hydrate-bearing sand has significantly strong time dependence for a geomaterial. Thus a constitutive equation used for the long-term prediction of the geomechanical behaviors is required to consider the viscoelasticity (time dependence) of methane-hydrate-bearing sand. To date, however, there has not been any viscoelastic constitutive equation modeled based on experimental results. This study aims to discuss the viscoelastic properties of methane-hydrate-bearing sand specimens obtained from drained triaxial compression tests and propose a viscoelastic constitutive equation. The results of three types of triaxial compression tests, e.g., constant-strain-rate test, constant-stress-rate test and creep test, on artificial methane-hydrate-bearing sand specimens are reviewed, mainly focusing on the viscoelastic behaviors. Then, a nonlinear viscoelastic constitutive equation is proposed for methane-hydrate-bearing sand, considering the strain-rate and stress-rate dependences of mechanical properties and creep behaviors. The model prediction fits well with the test results of stress-strain relationships in constant-strain-rate and constant-stress-rate tests before the peak failure point and primary creep behavior. © 2014 by Japanese Committee for Rock Mechanics.

Fujita K.,Tohoku University | Fujita K.,Chuo Kaihatsu Corporation | Asami R.,University of Ryukyus | Takayanagi H.,Tohoku University | Iryu Y.,Tohoku University
Island Arc | Year: 2015

In order to investigate biota and sedimentary facies, and to delineate processes of carbonate sedimentation in seagrass beds, we conducted sedimentological investigations along three onshore-offshore transects at two sites (Nagura and Yoshihara) on Ishigaki-jima, Ryukyu Islands. Along the transects, the seagrass beds extended seaward 20-40m from shore, and their widths parallel to the shore ranged from 60 to >110m. The seagrass was dominated by Thalassia hemprichii, Cymodocea rotundata and subordinate C.serrulata. Seasonal changes in seagrass coverage were evident, with mean coverage relatively higher in summer and fall (July and October) than in winter and spring (January and April). The surface sediment throughout the seagrass beds was dominated by medium to very coarse sand-sized bioclasts displaying grainstone/packstone fabrics. Bioclasts were dominated by corals and coralline algae, with lesser benthic foraminifers, mollusks, echinoids, and Halimeda. The grainstone/packstone was underlain by gravelly sediment with coral clasts, showing a rudstone fabric, at the Nagura Site. The lower part of the core sediment was blackened, indicating a reducing environment. Two dates of corals collected at the Nagura and Yoshihara sites (24.5cm and 16.5cm below the sea bottom) were 2781-2306 and 4374-3805 cal BP (2σ age range), respectively, suggesting extremely low sedimentation rates (<0.1mm/year). Sediment influx was higher during July-January than during January-July. The relatively large influx during summer and fall is caused by massive sediment transport during typhoons and storms. The total sediment influx (i.e., suspension-load sediment transportation) is 74-96kg CaCO3/m2/year at the Nagura Site and 21-57kg CaCO3/m2/year at the Yoshihara Site. Sediment influx was significantly greater in the seagrass beds than in surrounding areas, providing supporting evidence for an sediment trapping function of seagrass beds. Our data indicate that seagrass beds in the Ryukyu Islands are characterized by high sediment fluxes and extremely low sedimentation rates. © 2015 Wiley Publishing Asia Pty Ltd.

Uchimura T.,University of Tokyo | Towhata I.,University of Tokyo | Anh T.T.L.,University of Tokyo | Fukuda J.,University of Tokyo | And 10 more authors.
Landslides | Year: 2010

A low-cost and simple monitoring method for early warning of landslides is proposed. To detect abnormal deformation of a slope, this method employs a tilt sensor in place of an extensometer on the slope surface. In order to examine the relevance of measuring rotation angle on a slope surface by tilt sensor, model tests were conducted, and rotation on the slope surface was observed together with slide displacement along the surface. The rotation data responded 30 min before failure in a model test, which could be useful as a signal for early warning. However, the behavior of rotation before failure varies from case to case, and thus, criteria to issue warning should be defined more carefully. For a model slope made of uniform loose sand, measurement of slide displacement along the slope surface is sensitive to failure at the toe, while the measurement of rotation on the slope surface is useful to detect the development of progressive failure upward along the slope. Wireless sensor units with microelectromechanical systems (MEMS) tilt sensor and volumetric water content sensor were also examined on a real slope in Kobe City, and a long-term monitoring was attempted. A simple but possible way to define the criteria of judgment to issue warning can be proposed based on combination of data obtained by the tilt sensors and volumetric water content sensors. © 2009 Springer-Verlag.

Wu J.,Chongqing Three Gorges University | Feng S.-K.,Chuo Kaihatsu Corporation | Li H.-J.,China Three Gorges University
Yantu Lixue/Rock and Soil Mechanics | Year: 2011

Collecting the digital images of geological drilling holes and interpreting the underground geological structure is a new method of geological prospecting. The interpretation of structural planes on drilling holes images is usually done by hand; and results of interpretation may be quite different for different people. Automatic identification system of structural plane (AISSP) can process the digital images of drilling holes to get structural plane parameters automatically. First of all, the images conversion from RGB color space to HSV color space should be done to highlight the structural plane region. Secondly, the S component images are filtered and enhanced for the next processing step. After the image segmentation, the binary image edge will be extracted and thinned by image morphology method; and edges of the structural plane are effectively extracted. Finally, structure plane altitude and thickness parameters are obtained by the Hough transform of sine curve and identified edge points. As example, a real digital drilling hole picture is analyzed by AISSP and the space parameters of the 4 structural planes appearing in the picture are calculated. Compared with the results interpreted by people, the results from AISSP are more precise and unique.

Lin W.,Chuo Kaihatsu Corporation | Ichiro S.,Chuo Kaihatsu Corporation | Shunsaku N.,Chuo Kaihatsu Corporation | Taro U.,University of Tokyo
15th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering, ARC 2015: New Innovations and Sustainability | Year: 2015

Monitoring and early warning is one of the most effective methods toward reduction of accident induced by landslide and slope failure during rainfall. The traditional methods such as extensometers and borehole inclinometers are common monitoring ways, but the traditional equipment is expensive and not easy to install in field site. The authors have developed a tilt sensor unit and proposed an early warning system as one of more feasible countermeasures to avoid slope failure accident. The warning system including developed tilt sensor unit, has been deployed in several actual slopes for validation and verification of field performance in Japan.

Uchimura T.,University of Tokyo | Lin W.,Chuo Kaihatsu Corporation
15th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering, ARC 2015: New Innovations and Sustainability | Year: 2015

Moisture content is the most important factor affecting the stability of slopes against heavy rainfall events. In most of risk management methods for slope disasters, the rainfall intensity is used as the dominant index to evaluate the probability of failure events in an area. However, each slope should have individual hydraulic characteristics, and its probability of failure should be different from other slopes even under the same rainfall conditions. Some slope may contain a lot of water quickly after starting of rainfall, while some slope may show quick drainage after it stopped to rain. Such individual properties of each slope can be evaluated by observing the time histories of moisture contents in the slope ground together with rainfall records. In this paper, an attempt to establish a mathematical model on drainage process in a slope ground is reported. There is a simple relationship between the current moisture contents and the drainage rate of moisture, although this relation is affected by the adjacent rainfall intensity. The drainage properties of a slope can be evaluated by watching the behaviors of moisture contents at rainfall events with relatively low intensity. And the model parameters obtained by such weak rainfall events can be used to estimate the drainage rate after heavy rainfall events with some correction of the parameters, by using real time monitoring system.

Towhata I.,Asia of ISSMGE 4 38 2 | Uchimura T.,University of Tokyo | Seko I.,Chuo Kaihatsu Corporation | Wang L.,Chuo Kaihatsu Corporation
IOP Conference Series: Earth and Environmental Science | Year: 2015

The present paper addresses the newly developed early warning technology that can help mitigate the slope failure disasters during heavy rains. Many studies have been carried out in the recent times on early warning that is based on rainfall records. Although those rainfall criteria of slope failure tells the probability of disaster on a regional scale, it is difficult for them to judge the risk of particular slopes. This is because the rainfall intensity is spatially too variable to forecast and the early warning based on rainfall alone cannot take into account the effects of local geology, hydrology and topography that vary spatially as well. In this regard, the authors developed an alternative technology in which the slope displacement/deformation is monitored and early warning is issued when a new criterion is satisfied. The new MEMS-based sensor monitors the tilting angle of an instrument that is embedded at a very shallow depth and the record of the tilting angle corresponds to the lateral displacement at the slope surface. Thus, the rate of tilting angle that exceeds a new criterion value implies an imminent slope failure. This technology has been validated against several events of slope failures as well as against a field rainfall test. Those validations have made it possible to determine the criterion value of the rate of tilting angle to be 0.1 degree/hour. The advantage of the MEMS tilting sensor lies in its low cost. Hence, it is possible to install many low-cost sensors over a suspected slope in which the precise range of what is going to fall down during the next rainfall is unknown. In addition to the past validations, this paper also introduces a recent application to a failed slope in the Izu Oshima Island where a heavy rainfall-induced slope failure occurred in October, 2013. © Published under licence by IOP Publishing Ltd.

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