A cyclic elastoplastic constitutive model and effect of non-associativity on the response of liquefiable sandy soils     

Fusao Oka  Sayuri Kimoto 《Acta Geotechnica》2018,13(6):1283-1297

A large number of constitutive models for geomaterials, such as soils and rocks, have been proposed over the last three decades. Those models have been implemented into computer codes and have been successfully used to solve practical engineering problems particularly under monotonic loading conditions. Compared with the models for monotonic loadings, more improvements for cyclic models are necessary in order to obtain more accurate predictions for the dynamic behavior of geomaterials, e.g., the behavior during earthquakes. A cyclic elastoplastic model has been developed in this study for sandy soils; it is based on the kinematical hardening rule with a yield function that includes the changes in the stress ratio and the mean effective stress considering the degradation of the yield surface. From a simulation with the present model, it has been found that strong non-associativity leads to a large decrease in the mean effective stress during cyclic deformations under undrained conditions, while the model with the associated flow rule does not. This result is quite important because the mean effective stress becomes almost zero at the state of full liquefaction. Compared with the experimental results, the model can accurately reproduce the cyclic behavior of soil.  相似文献   

Crystal chemistry and oxidation state of Fe-rich prehnite from a hydrothermally altered dolerite     

Nagashima  Mariko  Iwasa  Kiyoka  Akasaka  Masahide 《Mineralogy and Petrology》2018,112(2):173-184

Mineralogy and Petrology - Fe-rich prehnite, Ca2(Al,Fe)(AlSi3)O10(OH)2, in a hydrothermally altered dolerite sill from Mitsu, Shimane Peninsula, Japan, was studied using 57Fe Mössbauer...  相似文献   

Temperature Profiles Within and Above an Urban Canopy     

M.?KandaEmail author  R.?Moriwaki  Y.?Kimoto 《Boundary-Layer Meteorology》2005,115(3):499-506

The seasonal trend of vertical temperature profiles within and above an urban canopy has been investigated. We measured air temperatures and wind velocities along a 29-m tower in a residential area of Tokyo, Japan continually for 14 months. The height of the daily maximum temperature Z_Tmax varied with the season; Z_Tmax was at the roof level in winter but near the ground in summer. The seasonal change of Z_Tmax is likely due to the change of height at which solar energy is absorbed. At the time of the maximum temperature, the atmosphere above the canopy is always unstable whereas the air within the canopy is unstable in summer but stable in winter.  相似文献   

A large-scale excavation in soft Holocene deposit and its elasto-viscoplastic analysis     

Fusao Oka  Naoki Takada  Kazuyuki Shimono  Yosuke Higo  Sayuri Kimoto 《Acta Geotechnica》2016,11(3):625-642

In the present study, the large-scale excavation in the construction is numerically back-analyzed using a soil–water-coupled finite element method with an elasto-viscoplastic model which considers the strain-induced degradation. The measurements of the deformation have been performed during the construction of a new railway station in Osaka, Japan, in which a large and deep excavation has been successfully carried out using a special deep mixing type of soil improvement method with earth retaining walls through the thick Holocene Osaka Umeda clay deposit. A comparison between the numerical results and the measurements of the excavation at Osaka shows that the simulation method can reproduce the overall deformation of the soft ground and the earth retaining walls including the time-dependent behaviour during the excavation and a deep mixing soil improvement method as an additional technique for stability are effective.  相似文献   

CoPIVEP: a theory-based analysis of coupled processes and interannual variability in the Equatorial Pacific in four coupled GCMs     

M. Pontaud  J.-P. Céron  M. Kimoto  F. Pluviaud  L. Terray  A. Vintzileos 《Climate Dynamics》2000,16(12):917-933

 The interannual variability over the tropical Pacific and a possible link with the mean state or the seasonal cycle is examined in four coupled ocean-atmosphere general circulation models (GCM). Each model is composed of a high-resolution ocean GCM of either the tropical Pacific or near-global oceans coupled to a moderate-resolution atmospheric GCM, without using flux correction. The oceanic subsurface is considered to describe the mean state or the seasonal cycle through the analytical formulations of some potential coupled processes. These coupled processes characterise the zonal gradient of sea surface temperature (hereafter SST), the oceanic vertical gradient of temperature and the equatorial upwelling. The simulated SST patterns of the mean state and the interannual signals are generally too narrow. The grid of the oceanic model could control the structure of the SST interannual signals while the behaviour of the atmospheric model could be important in the link between the oceanic surface and the subsurface. The first SST EOFs are different between the coupled models, however, the second SST EOFs are quite similar and could correspond to the return to the normal state while that of the observations (COADS) could favour the initial anomaly. All the models seem to simulate a similar equatorial wave-like dynamics to return to the normal state. The more the basic state is unstable from the coupled processes point of view, the more the interannual signal are high. It seems that the basic state could control the intensity of the interannual variability. Two models, which have a significant seasonal variation of the interannual variance, also have a significant seasonal variation of the instability with a few months lag. The potential seasonal phase locking of the interannual fluctuations need to be examined in more models to confirm its existence in current tropical GCMs. Received: 30 July 1999 / Accepted: 25 April 2000  相似文献   

Large deformation and failure analysis of river embankments subjected to seismic loading     

Shahbodagh  B.  Sadeghi  H.  Kimoto  S.  Oka  F. 《Acta Geotechnica》2020,15(6):1381-1408

Acta Geotechnica - A numerical model based on the theory of mixtures is proposed for the nonlinear large deformation and failure analysis of river embankments subjected to large earthquakes. The...  相似文献   

Steric sea level changes estimated from historical ocean subsurface temperature and salinity analyses   总被引：13，自引：0，他引：13  

Masayoshi Ishii  Masahide Kimoto  Kenji Sakamoto  Sin-Iti Iwasaki 《Journal of Oceanography》2006,62(2):155-170

An historical objective analysis of subsurface temperature and salinity was carried out on a monthly basis from 1945 to 2003 using the latest observational databases and a sea surface temperature analysis. In addition, steric sea level changes were mainly examined using outputs of the objective analyses. The objective analysis is a revised version of Ishii et al. and is available at 16 levels in the upper 700 m depth. Artificial errors in the previous analysis during the 1990s have been worked out in the present analysis. The steric sea level computed from the temperature analysis has been verified with tide gauge observations and TOPEX/Poseidon sea surface height data. A correction for crustal movement is applied for tide gauge data along the Japanese coast. The new analysis is suitable for the discussion of global warming. Validation against the tide gauge reveals that the amplitude of thermosteric sea level becomes larger and the agreement improves in comparison with the previous analysis. A substantial part of local sea level rise along the Japanese coast appears to be explained by the thermosteric effect. The thermal expansion averaged in all longitudes from 60°S to 60°N explains at most half of recent sea level rise detected by satellite observation during the last decade. Considerable uncertainties remain in steric sea level, particularly over the southern oceans. Temperature changes within MLD make no effective contribution to steric sea level changes along the Antarctic Circumpolar Current. According to statistics using only reliable profiles of the temperature and salinity analyses, salinity variations are intrinsically important to steric sea level changes in high latitudes and in the Atlantic Ocean. Although data sparseness is severe even in the latest decade, linear trends of global mean thermosteric and halosteric sea level for 1955 to 2003 are estimated to be 0.31 ± 0.07 mm/yr and 0.04 ± 0.01 mm/yr, respectively. These estimates are comparable to those of the former studies.  相似文献   

Development of a thin diatom layer observed in a stratified embayment in Japan     

Goh Onitsuka  Yutaka Yoshikawa  Tomoyuki Shikata  Kei Yufu  Kazuo Abe  Takahisa Tokunaga  Katsunori Kimoto  Takeshi Matsuno 《Journal of Oceanography》2018,74(4):351-365

The temporal evolution of a thin phytoplankton layer was observed by field measurements using a research vessel and mooring instruments in the Yatsushiro Sea, a semi-enclosed narrow embayment in Japan, in early August 2013. The subsurface chlorophyll maximum developed into a thin layer within 2 days just below the pycnocline at around 10-m depth, where turbulent mixing (the dissipation rate of turbulent kinetic energy) was weak (low). The layer persisted for 1.5 to 2 days and declined after irradiance drastically decreased at the sea surface. At the peak period, the layer thickness, which is defined as the full-width at half-maximum of the peak in chlorophyll a concentration, ranged from 0.6 to 1.4 m, and the maximum concentration reached 42.3 mg m^?3. The horizontal extent of the layer was approximately 10 km along the longitudinal axis of the bay. The phytoplankton population characterized by the layer was dominated by a chain-forming centric diatom, Chaetoceros spp. The formation mechanisms of the thin diatom layer were investigated using the observed data and a vertical one-dimensional model that includes physical and biological processes. The results suggest that the development of the thin layer was caused by in situ growth and aggregation due to nutrient-dependent sinking of the species under weak turbulence. The study highlights that continuous multidisciplinary observations and understanding species-specific physiological responses to environmental variations are necessary to elucidate drastically fluctuating phytoplankton dynamics in a coastal water.  相似文献   

Perceived ambiguity about earthquake and house destruction risks     

Toshio Fujimi  Masahide Watanabe  Ryuji Kakimoto  Hirokazu Tatano 《Natural Hazards》2016,80(2):1243-1256

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POC fluxes estimated from 234Th in late spring–early summer in the western subarctic North Pacific     

Hajime Kawakami  Makio C. Honda  Kazuhiko Matsumoto  Masahide Wakita  Minoru Kitamura  Tetsuichi Fujiki  Shuichi Watanabe 《Journal of Oceanography》2015,71(3):311-324

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