Railway embankment failure due to ballast layer breach caused by inundation flows     

Ryota Tsubaki  Yoshihisa Kawahara  Yasuhiro Ueda 《Natural Hazards》2017,87(2):717-738

A railway embankment constructed on a floodplain is at risk of damage due to flooding flows. The process and critical conditions that lead to railway embankment damage during flooding are not clearly understood, rendering risk estimations impossible and hindering the development of flood-resilient rail systems. For this work, we first reviewed records of railway damage in flood plains and flows through the ballast layer. The breaching process was selected as the focus of our study. We secondly specified the fundamental characteristics of flows through a ballast layer. The critical flow rate per unit width and the minimum upstream water depth required for initiating extensive ballast breaching were experimentally evaluated using a full-scale ballast layer with rails and sleepers constructed using materials originally utilized in actual railways. A two-dimensional flow model was then employed for estimating the flow through a ballast layer that was placed on an impermeable base embankment. A simple ballast breaching model was also employed in order to explore a higher flow rate condition that could not be represented in our experiment due to limited facilities. The breaching pattern represented by the simulation model corresponded to the breaching pattern observed in the experiment. In addition to the above, here, we also discuss the ballast breaching process based on qualitative field records and quantitative experimental results, as well as the ballast breaching process as represented by the simulation.  相似文献   

Estimation of particulate organic carbon flux in relation to photosynthetic production in a shallow coastal area in the Seto Inland Sea   总被引：3，自引：0，他引：3  

Yamaguchi H  Montani S  Tsutsumi H  Hamada Ki  Ueda N 《Marine pollution bulletin》2003,47(1-6):18-24

Sediment trap experiments were carried out three times from 1999 to 2000, in the western part of the Seto Inland Sea (Suo-Sound), Japan. We investigated both the particulate flux and the composition of chemical substances in the sediment trap samples. Based on the results, we discuss the origin of particulate organic carbon (POC) collected by the sediment traps in a coastal area. Moreover, we purposed to estimate the flux of the portion of the POC that is derived from phytoplankton photosynthesis. The fluxes of POC varied between 677 and 3424 mgC m(-2) d(-1). Significant positive correlations between POC and aluminum (Al) fluxes suggested that these components show almost the same behaviour. The mean value of the Al flux was about eight times higher than that of Al burial rates on the sediment surface. Therefore, it seems that the POC flux observed with the sediment traps was considerably overestimated. Moreover, judging from the fact that Al is a typical terriginous element, it seems that most of the POC collected in the sediment traps derived from the re-suspended surface sediment or sediment transported laterally from shallow flanks such as intertidal mudflats. The fluxes of chlorophyll a (Chl a) were independent of the POC fluxes, and a relatively consistent correlation was found between Chl a abundance in the water column and the Chl a flux. Moreover, surface sediment Chl a content was approximately 100 times lower than that of suspended matter. Therefore, resuspension and terriginous contributions to Chl a collected in sediment traps are likely to be negligible. The POC content in the trap samples varied between 22.4 and 70.7 mg g(-1) dry weight. The variations of POC contents were positively correlated with the Chl a contents: POC(mg g(-1))=76.5 x Chl a(mg g(-1)) + 26.0 (r=0.95, p<0.01, n=9). This result shows that POC contents strongly corresponded with phytoplankton and their debris. It was also considered that the fraction of POC derived from phytoplankton primary production could be estimated as Chl a content times a certain factor. In this study, we estimated the flux of the portion of the POC originating from phytoplankton production by multiplying the Chl a fluxes by 76.5 (the mean POC:Chl a ratio in the trap samples). These values varied between 308 and 758 mgC m(-2) d(-1), and accounted for 35.1+/-21.2% of total POC flux. Although the amount of POC that originates from phytoplankton photosynthesis was a small portion of total POC flux, it seems to be a large portion of potential primary production in the water column.  相似文献