Numerical simulation of mitigation for liquefaction-induced soil deformations in a sandy ground improved by cement grouting

This paper presents a numerical study of mitigation for liquefaction during earthquake loading. Analyses are carried out using an effective stress based, fully coupled, hybrid, finite element-finite differences approach. The sandy soil behavior is described by means of a cyclic elastoplastic constitutive model, which was developed within the framework of a nonlinear kinematic hardening rule. In theory, the philosophies of mitigation for liquefaction can be summarized as two main concepts, i.e. prevention of excess pore water pressure generation and reduction of liquefaction-induced deformations. This paper is primarily concerned with the latter approach to liquefaction mitigation. Firstly, the numerical method and the analytical procedure are briefly outlined. Subsequently, a case-history study, which includes a liquefaction mitigation technique of cement grouting for ground improvement of a sluice gate, is conducted to illustrate the effectiveness of liquefaction countermeasures. Special emphasis is given to the computed results of excess pore water pressures, displacements, and accelerations during the seismic excitation. Generally, the distinctive patterns of seismic response are accurately reproduced by the numerical simulation. The proposed numerical method is thus considered to capture the fundamental aspects of the problems investigated, and yields results for design purposes. From the results in the case, excess pore water pressures eventually reach fully liquefied state under the input earthquake loading and this cannot be prevented. However, liquefaction-induced lateral spreading of the foundation soils can be effectively reduced by the liquefaction mitigation techniques. An erratum to this article can be found at     

A meta-modeling approach for spatio-temporal uncertainty and sensitivity analysis: an application for a cellular automata-based Urban growth and land-use change model

The paper presents a computationally efficient meta-modeling approach to spatially explicit uncertainty and sensitivity analysis in a cellular automata (CA) urban growth and land-use simulation model. The uncertainty and sensitivity of the model parameters are approximated using a meta-modeling method called polynomial chaos expansion (PCE). The parameter uncertainty and sensitivity measures obtained with PCE are compared with traditional Monte Carlo simulation results. The meta-modeling approach was found to reduce the number of model simulations necessary to arrive at stable sensitivity estimates. The quality of the results is comparable to the full-order modeling approach, which is computationally costly. The study shows that the meta-modeling approach can significantly reduce the computational effort of carrying out spatially explicit uncertainty and sensitivity analysis in the application of spatio-temporal models.     

Next steps in geoengineering scenario research: limited deployment scenarios and beyond

Climate engineering has received increasing attention, but its discussion has remained on the sidelines of mainstream climate policy. The policy relevance of this previously exotic option is poised to rise because of the gap between the temperature goals of the Paris Agreement and slow global mitigation efforts. It is therefore crucial to understand the risks and benefits of the proposed schemes, and the social implications of policy choices. Assessment of the risks and benefits of solar geoengineering strongly depends on scenarios, but previous scenarios have not reflected the full range of social choices. In light of concerns over risks, a newer set of scenarios is desirable, which represents both uncertainties and social choices more fully. Borrowing and extending lessons from recent literature on the new community climate scenario process, we envision a possible scenario-building process that combines interdisciplinary scholarship with the involvement of stakeholders and citizens. The resultant scenarios would better characterize uncertainties of, and policy choices for, solar geoengineering, and foster critical appraisal of its risks and benefits. Such societal choices might include not only total ban and large-scale deployment, but also limited deployment, which has received less attention in the scenario literature. The interaction between scenario and governance research would be able to highlight the central issues at stake, including ethical, social, and political dimensions.

Key policy insights

• A more comprehensive assessment of solar geoengineering is necessary to evaluate its risks and benefits, necessitating new scenario research

• It is crucial to reflect the full span of policy choices and uncertainties with interdisciplinary collaboration in such scenarios

• Such societal choices might include not only total ban and large-scale deployment, but also limited deployment, which has received less attention in the scenario literature

• Participatory scenario research would enable incorporating the concerns and opinions of stakeholders and citizens in scenario creation

     

Uneven Distribution of Pseudotormentus De Wever et Caridroit (Radiolaria, Protozoa): Provincialism of a Permian Planktonic Microorganism

The Permian planktonic distribution is not well known, in contrast to other fossil distributions of nekton and benthos. Radiolaria are representative microfossils of plankton in the Permian palaeocean. This study compares both correlated radiolarian occurrences (Pseudotormentus De Wever et Caridroit and Quadriremis Nazarov et Ormiston) in literature data from the Pacific Rim and quantitative data from the Liuhuang and Gujingling sections in South China. Pseudotormentus distributions are concentrated in the Panthalassa, whereas Quadriremis occurrences are distributed over both the Panthalassa and the Palaeotethys. The uneven distribution of Pseudotormentus seems to have been controlled by a difference in the oceanic basins, indicating the presence of faunal differences in Permian planktonic microorganisms between the Panthalassa and the Palaeotethys. In other words, this study infers the provincialism of Permian planktonic microorganisms. The uneven distribution is explainable by a hypothesis that Pseudotormentus was strongly affected by a Panthalassan equatorial current.     

Study of the structure of silica film by infrared spectroscopy and electron diffraction analyses

Amorphous silicon oxide films have been studied on the basis of electron diffraction (ED) analyses and infrared (IR) spectroscopy in order to elucidate the relationship between the structures. After the heat treatment of the film in air at 300 and 500°C, the ED pattern showed halo rings, and the IR spectra clearly changed. Intensity analysis of the ED pattern provided evidence for the structural change of the amorphous film. It was concluded that the spectral changes in the ranges of 9.2–10.2, 12.5–13.5 and 19.5–22.5 μm were the result of phase transitions of the microcrystallites of α-cristobalite to β-cristobalite, and α- or β-quartz. Astrophysical implications have been discussed.     

Vesicle layering in solidified intrusive magma bodies: a newly recognized type of igneous structure

 We report a novel type of layering structure in igneous rocks. The layering structure in the Ogi picrite sill in Sado Island, Japan, is spatially periodic, and appears to be caused by the variation in vesicle volume fraction. The gas phase forming the vesicles apparently exsolved from the interstitial melt at the final stage of solidification of the magma body. We call this type of layering caused by periodic vesiculation in the solidifying magma body "vesicle layering." The presence of vesicle layering in other basic igneous bodies (pillow lava at Ogi and dolerite sill at Atsumi, Japan) implies that it may be a fairly common igneous feature. The width of individual layers slightly, but regularly, increases with distance from the upper contact. The layering plane is perpendicular to the long axes of columnar joints, regardless of gravitational direction, suggesting that the formation of vesicles is mainly controlled by the temperature distribution in the cooling magma body. We propose a model of formation of vesicle layering which is basically the same as that for Liesegang rings. The interplay between the diffusion of heat and magmatic volatiles in melt, and the sudden vesiculation upon supersaturation, both play important roles. Received: 15 February 1996 / Accepted: 24 June 1996     

Distribution and sources of organic matter in surficial sediments on the shelf and slope off Tokachi, western North Pacific, inferred from C and N stable isotopes and C / N ratios

Organic carbon (C) and total nitrogen (N) contents and corresponding isotope ratios were determined in surficial sediment (0–3 cm) at 94 stations ranging from 21 to 1995 m water depth off Tokachi, Hokkaido, Japan, to elucidate the distribution and source of sedimentary organic matter. Suspended particulate organic matter (POM) in the seawater and suspended POM and sediment in the Tokachi River were also examined. δ¹³C, δ¹⁵N and C / N ratios of the samples in the Tokachi River suggest that the spring snowmelt is an important process for the transport of terrestrial organic matter to the coastal waters. δ¹³C values of suspended POM in the surface seawater were higher in May and November than in August, while δ¹⁵N values of the POM were higher in May and August than in November. These changes are attributed to seasonal changes in phytoplankton growth rate and nitrate availability. δ¹³C and δ¹⁵N values in the sediments off Tokachi were lowest near the Tokachi River mouth, and increased offshore to constant values that persisted from 134 to 1995 m water depth. The spatial variation in C / N ratios in the sediment mirrored those of δ¹³C and δ¹⁵N. Comparison of δ¹³C, δ¹⁵N and C / N ratios in the sediments off Tokachi with those in the Tokachi River and seawater indicates that about half of the organic matter in the sediment was of terrestrial origin near the Tokachi River mouth, and the sedimentary organic matter from 134 to 1995 m water depth was of marine origin. The organic C content in the sediment was high near the Tokachi River mouth, and also around 1000 m water depth. The C content was significantly correlated with silt plus clay content, with different regression lines for those stations shallower and deeper than 134 m, owing to several stations of higher C content with the elevated C / N ratio on the inner shelf. These results suggest that transport and deposition of organic-rich fine sediment particles by hydrodynamic processes were major factors controlling C content off Tokachi. In addition, the supply of a fraction of terrestrial organic matter with high C / N probably also affected C content on the inner shelf.     

Responses of diatoms to iron-enrichment (SEEDS) in the western subarctic Pacific, temporal and spatial comparisons

Phytoplankton species composition was analyzed inside and outside of the iron-enriched patch during the SEEDS experiment. Before the iron-enrichment, the phytoplankton community consisted of similar proportions of pico-, nano- and micro-sized phytoplankton, and the micro-phytoplankton was dominated by the pennate diatom Pseudo-nitzschia turgidula. Although all the diatoms, except the nano-sized Fragilariopsis sp., increased during the two weeks of the observation period, the flora in the patch dramatically changed with the increase of phytoplankton biomass to a centric diatom-dominated community. Neritic diatoms, especially Chaetoceros debilis, showed higher growth rates than other diatoms, without any delay in the initiation of growth after the enrichment, and accounted for 90% of the micro-phytoplankton after day 9. In contrast, the oceanic diatoms showed distinct delays in the initiation of growth. We conclude that the responses of the diatoms to the manipulation of iron concentration were different by species, and the fast and intensive response of the phytoplankton to iron-enrichment resulted from the presence of a small amount of neritic diatoms at the study site. The important factors that determine the dominant species in the bloom are the potential growth rates under an iron-replete condition and the growth lag. Abundant species in the patch are widely distributed in the North Pacific and their relative contributions in the Oyashio area and at Stn KNOT are high from spring to summer. However, a characteristic difference of species composition between the SEEDS bloom and natural blooms was the lack of Thalassiosira and Coscinodiscus species in the patch, which usually account for a major part of the phytoplankton community under blooming conditions in the western North Pacific.     

钢材在海水—海气变换界面区的腐蚀行为

于1993年9月通过对241A，24KU，SS41三个不同钢种极化曲线的测定，对镜层本身的氧化还原电流的测定及X线分析，研究在海水一海气交换界面区锈层在腐蚀中所起的作用。结果表明，海一气交换界面区的钢由于锈层本身的氧化还原反应，其阴极电流均较裸钢为大，这说明锈层的还原反应起着重要作用．根据锈层本身的还原时间和还原电位，可以在某种程度上评价钢材本身耐腐蚀性能的好坏。