In this paper, the alternative formulation proposed by the authors is applied to one-dimensional elasto-plastic problems including softening. The formulation results in a variational problem at loading, unloading, and reloading stages, and analytical solutions are obtained for all these stages. An elastoplastic zone cannot be determined in the variational problem, and a condition that determines its size at the onset of plastic deformation is proposed. Discussions are made on the analytical solutions obtained according to the alternative formulation to develop more stable numerical analysis of elastoplastically softening problems.

 There have been many studies on countermeasures for train-induced ground vibration. However, many of the countermeasures are not clear about the mechanisms and reduction values of the vibration. Therefore, in general, we choose the countermeasures based on previous cases or empirical judgments. In this paper, using a numerical simulation consisting of a running train, tracks, supporting structures, and the ground, we investigated a method for extracting primary factors of the train-induced ground vibration and a method for suggesting countermeasures based on the primary factors. The results showed that it is possible to extract the primary factors, which increased the train-induced ground vibration, by evaluating the characteristics of vibration source, vibration characteristics of viaducts, and propagation characteristics of the ground. This study presents a flowchart showing how the primary factors are linked to the countermeasures.

 This paper develops a thin shell theory consistent with continuum mechanics as an extension of a thin curved beam theory that has been developed by the authors. A curvilinear coordinate system is defined for the thin shell and the asymptotic expansion with respect to the ratio of thickness to curvature radius is used to compute covariant derivative. Governing equations and boundary conditions are derived from a functional of linear elasticity using suitably approximated displacement and stress functions. Cross-sectional force equilibrium is discussed for the comparison of the developed theory with ordinary shell theories.

 Continuous monitoring using fixed-point cameras is effective for the early detection and understanding of scum behavior in urban tidal rivers. Scum-detection techniques using U-Net have been developed in previous studies. However, a lot of effort and time required to create the label images necessary for training makes it difficult to apply the method to multiple locations. In this study, we developed a new learning method using dummy images and evaluated its effectiveness by comparing it with conventional methods based on the following evaluation indicators: precision, recall, F-value, and mIoU (mean value of intersection over union). Our results showed success using our method in detecting scum with higher accuracy than conventional methods, while substantially reducing the effort required to create labels, which is a bottleneck in conventional training models. Our method makes it possible to understand a wide range of spatiotemporal behavior of scum. Additionally, by applying this method to suspended solids other than scum, it can be used as a general purpose technique for the continuous monitoring of river debris.

 In recent years, rainfall intensity in Japan has shown an upward trend, and sediment inflow disasters caused by mountain streams are increasing in number. As there are a significantly large number of mountain streams along railway lines, considerable time and effort are spent on local surveys for identifying dangerous mountain streams. Additionally, as there are a variety of diverse factors such as terrain and different geological features that collectively determine the hazard posed by mountain streams, risk-level assessments are not consistent among technicians. Above all, the risk-level assessment of upstream areas located in positions widely separated from the railway tracks and dispersed over a wide area require a huge amount of time and effort, and there may be a large disparity among the assessments made by engineers. Therefore, in this paper, we describe a simple method of evaluating the risk level of mountain streams in upstream areas using uniform criteria, without requiring local surveys. In concrete terms, we developed a scoring sheet that could assess the risk level mainly using quantitative data from a digital evaluation model (DEM). Through numerous comparisons, it was shown that the evaluation obtained using the DEM-scoring table was almost the same as the evaluation provided by local surveys.

 Meteotsunamis by atmospheric pressure disturbances following the 2022 Tonga volcanic eruption were investigated based on theoretical analysis and observation. The atmospheric pressure with an amplitude of approximately 2 hPa and sea surface elevations greater than 1 m were observed around Japan. For a uniformly sloping bottom, analytical solutions of sea level change due to atmospheric pressure disturbance were derived. They include the forced wave and two free-wave components propagating in opposite directions, which are described in terms of the Hankel functions of the first and second kinds of order zero. The approximated solution for the forced wave was obtained by neglecting the terms of order of the bottom slopes, which was similar to Proudman’s forcing-wave component. The envelope functions of tsunami waves were estimated by using the Hilbert transform of tsunami waveforms and the arrival times of amplified waves and their average propagation speeds were also estimated. As a result, the average propagation speeds were about 170–220 m/s, which approximately coincides with the speed of the gravity waves in the Pacific Ocean. The amplitudes of amplified waves, energies, and energy fluxes of sea level fluctuations showed that they mostly increased with the great-circle distance from Tonga to the stations, which implied that energy was transported from the air to tsunamis. Lamb wave, acoustic wave, and atmospheric gravity wave components were decomposed by using the time series model with the trend, autoregressive, and noise components. The atmospheric gravity waves were extracted from the autoregressive component, and their celerity was estimated to be about 200 m/s at 15:00 (UTC). Tsunami waves in the ocean were found to be amplified up to several tens of times due to the Proudman resonance with the atmospheric gravity waves when the resonance time becomes 1–2 h.

 The one-dimensional (1D) flood flow calculation method coupled with existing runoff models has a limitation in the accuracy of water-level prediction, because of its disability to take the effect of the river vegetation resistance into account. This study proposed a method to improve the accuracy of water-level calculation during floods using the 1D flood flow calculation method in the Rainfall-Runoff-Inundation (RRI) model. We derived the surface flux vector using the two-dimensional (2D) diffusion wave approximation from the shallow water flow equation. From 2D flood-flow analysis results, it is clarified that the roughness coefficient considering vegetation can be expressed as a function of water depth. The modified RRI model is confirmed to reproduce well the water-level hydrograph during a big flood event in the Nuta River basin.

 The step height of stair-type seawalls is typically set between 0.2 to 0.3 m. These short-rise stair-type seawalls have a gradual slope that creates aesthetic problems, such as an increase in the construction area, as well as functional problems, such as an increase in the wave run-up. To solve these problems, this study recommends that the step height be increased to 1.0 - 1.4 m. Numerical calculations using CADMAS-SURF clearly identify the characteristics of the dimensionless run-up height and wave reflection coefficient for varying cases with step heights between 0.2 m and 1.4 m. The validity of the numerical simulations is compared to experimental results on smooth slopes by Savage and Greslou-Mahe. The dimensionless run-up height and wave reflection coefficient are unified by the surf similarity parameter. It is demonstrated that increasing the step height generally reduces these parameters and that there is an increase in reflection coefficient for the gradual slope conditions. These parameters are also associated with wave-breaking morphology, step steepness, and the reflection from the step surface.

 Kinematic and angular conditions have been predominantly used as the occurrence conditions in the study of a breaking wave. The author defined new occurrence conditions for a breaking wave based on mechanical conditions by achieving a balance between the centrifugal and gravitational forces acting on water particles at the wave crest. Furthermore, it has been demonstrated that, for a breaking wave, the new occurrence conditions are equivalent to the universal constant. Based on these new occurrence conditions, the breaker index of deep-sea waves was derived. In addition, the author derived the breaker indices for long waves and any water depth using the universal constant for a breaking wave.

 In the inspection of existing bridges, measurement of natural frequency by vibration test is relatively safe and easy. The natural frequency can also be obtained from numerical analysis. In this study, we numerically investigated influence of partial decay of timber members, such as arches and joints between columns and girders, on the natural frequency of deck-type timber arch bridges. Concretely, we estimated sensitivity of the decay parts using the regression plots between natural frequency and magnification to the original Young’s modulus of the decay parts. The results showed that the decay at the part of the vibration antinode was highly sensitive, while the vibration node was low-sensitive. Lastly, we tried to estimate the actual state of decay of the target bridge adjusting parameters, such as Young’s modulus and specific weight, so that the natural frequency could fit the measured value.

 Rural water supply facilities (RWSFs) serve approximately 20 million people in Kenya, which accounts for 40% of the population. Many RWSFs are managed by the community under a community-based management system. The low functionality of RWSFs because of mismanagement of the community is often argued. However, the low capacity of community management is not necessarily attributed to the low functionality. Based on the current status of RWSFs, which were constructed with the support of the Japan Official Development Assistant, we found that only two out of 18 nonfunctional facilities were due to the issue of community management. Furthermore, a total of 24 out of 62 hand pumps were upgraded to motorized schemes, thanks to the efforts of local county governments. Through literature review and detailed study of existing RWSFs, we suggest five factors for sustainability: i) salinity of groundwater, ii) practice of fee collection and type of facility, iii) external support, iv) adoption of operation and maintenance system according to socioeconomic condition, and v) improving the capacity of community organizations and ensuring transparency on revenue. In addition to the five factors, we presented specific features with respect to the five factors in the context of Kenya. The motorized schemes of the target facilities indicate a higher functionality than that of hand pumps. This is because the motorized scheme, especially the piped schemes, has the potential for the practice of fee collection thanks to its contribution to better accessibility, resulting in better sustainability. Given the poverty and nature of RWSFs, achieving full cost recovery of RWSFs is challenging. However, we strongly suggest that the water fee of RWSFs must cover daily operational costs, and the cost of major repair as much as possible.