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.

 In bridge pier foundation construction, rapid construction may be necessary in narrow areas, mainly in urban locations. In the previous paper, the authors proposed a new structure to construct bridge pier foundation rapidly in narrow areas by changing the hoop of reinforced concrete foundation to the steel segment. The behavior under the low axial force condition was then evaluated. In this study, the analytical model construction and evaluation are carried out referring to the results of the reversed cyclic loading test using scale test specimens of the proposed mixed structural foundation. Then, it was confirmed that the mixed structural foundation in the high axial force condition has the same structural performance as that of the general reinforced concrete foundation. In addition, the behavior of steel segments consisting of multiple bodies when the lateral restraint effect are exerted was clarified for the construction of a practical design formula in the future.

 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.

 Confluence improvement projects in sewage systems have seen some progress, but the management accuracy of the quantitative control facility, which is the basis of sewer management has remained low. Moreover, there are still issues in environmental load reduction and effective heavy rain measure in the pipeline system through utilization of stock, which may become problems in the future in terms of maintenance management and project operation. This study is based on the hydraulic engineering theory and hydraulic experiment verification that enables diversion control with high accuracy, and the previous studies designed to extend the information from sewer standard books and related cases into practical use. It presents a method for planning a rational sewer pipeline system considering the environment and safety in an urban area, including the pollution load in a public water area and heavy rain measure in a residential area that still experiences issues even after the confluence improvement project. Promoting the efficiency of the sewer project requires reliable sewage flow rate management and the effective utilization of stock in the pipeline system. The pipeline system utilizing the sewage flow rate control technique in this study is seen to contribute to the effective achievement of the project objective through quantitative evaluation and cost reduction.

 The wave overtopping characteristics at an upright seawall installed on a horizontal base interacting with regular waves was clarified by numerical calculations using CADMAS-SURF and large-scale hydraulic experiments. To determine the wave overtopping rate for a seawall on a uniform slope, Kikkawa et al. introduced a formula for a steady flow over a weir to calculate the overtopping rate for a seawall on a horizontal base and gave a formula for calculating the overtopping rate per wave. Goda developed a diagram for calculating the expected overtopping rate for a seawall in the case of irregular waves. To understand wave action on seawalls during severe ocean conditions, it is often required to estimate the maximum overtopping rate per wave. Mainly, numerical calculations show that the dimensionless overtopping rate can be systematically explained by the relative crest level of the seawall, and reflection and wave overtopping of a wave are explained as co-occurrence phenomena.

 Our study aims to build a deep learning model that can predict even flood events caused by unprecedented rainfall events to improve the accuracy of water-level predictions at a regulation pond in a drainage pumping station. To improve the accuracy of the deep learning model, a physical model created a large amount of pseudo-flood data using virtual rainfall of 100, 300, and 500 mm for 72 h. The pretrained model of these flood data was applied to the observed data using transfer learning. After extracting only the flood events from the observed data, the deep learning model predicted the largest flood event (TOP 1). The pretrained model with 300 mm/72 h produced more accurate results than those of the model without transfer learning. We performed another prediction using the same pretrained model for the observed data, including dailydrainage operations. The results showed that the prediction accuracy was similar to that of the non-transfer-learning model as well as a good reproduction of the peak water level for TOP 1.

 Recently, it has been suggested that saturated lateral flow on a local scale, such as hillslope hydrodynamics, affects the terrestrial water heat balance, including evapotranspiration and soil moisture, and that the affected areas are not uncommon globally. However, no study expresses the contrast of hydrological quantities on the hillslope at a fine resolution on the global scale with reasonable computational cost. Here, we implemented a subgrid saturated lateral flow scheme in the integrated land simulator (ILS), and carried out a global simulation for 163 years. Then, we expressed the hill–valley moisture contrast by diagnostically downscaling the simulation results using subgrid topography information. The results suggested that by considering the saturated lateral flow, the soil moisture and the evaporation tend to decrease in a wide range of the global average, and the runoff amount increases in the area where the evaporation decreases, especially in the alpine area. We re-evaluated the land surface water balance from the viewpoint of water redistribution by the hillslope dynamics, and experimentally explained the possibility of the existence of vegetation in the valley in the arid area. In addition, we compared the downscaled result with high-resolution soil moisture satellite observation data (SMAP) and expanded the possibility of verification of a global land model by high-resolution satellite data. Although it is necessary to improve the method of applying land cover in the subgrid and climate forcing dataset, it was suggested that the hill–valley moisture contrast can be represented in the global land model with the saturated lateral flow.

 Drone technology is expected to play an important role in various fields, including topographic survey, wave and current monitoring, lifesaving, etc. in the ocean. In the present paper, we propose a new method for bathymetry, with the combination of an unmanned aerial vehicle (UAV) and an unmanned surface vehicle (USV). First, the motion of the USV is evaluated using images obtained by the UAV. Second, the pixel shift values of the seabed are calculated through underwater images by the USV. Finally, based on these results, the water depth is acquired by applying triangulation. The experimental results obtained using a wave basin have shown the maximum estimation error of 1.1cm, indicating the effectiveness of the proposed method.

 We attempted to improve the accuracy of dam inflow prediction using deep learning by augmenting the training data and validated the applicability of the proposed method to multiple basins in Japan. The proposed data augmentation method assumes a steady-state condition of constant rainfall and uses a virtual rainfall-runoff dataset that is based on the theory of hydrology as the augmentation data such that the total rainfall and dam inflow into the watershed are equal (runoff coefficient = 1.0). The applicability of the data augmentation method to recent large-scale floods was validated in case studies for four dam basins: the Terauchi, Miyagase, Nomura, and Kanayama dams. The prediction accuracy of the data augmentation method was confirmed for each dam. However, when the test flood was much larger than the training floods, the prediction improvement was limited.

 To understand the influence of shallow-rooted trees on channel morphology and river planforms, we conducted hydraulic experiments using bentgrass as a substitute for shallow-rooted trees, such as willow trees, that commonly flourish along the banks of gravel-bed rivers. The experiment demonstrated a meandering flow progression that maintained a channel planform with curved bank lines. Vegetation did not significantly inhibit bank erosion near the apex points in the meandering channel, where the bed near the riverbank was relatively deep. Conversely, vegetation inhibited bank erosion downstream of the meandering channel, where the bed near the riverbank was shallow. The results suggest that the inhibitory effect of vegetation on bank erosion varies depending on the riverbank height and channel depth, thereby influencing the channel morphology and river planform characteristics.

 The overtopping rates and reflection coefficients of regular waves for a block mound seawall and a terrace-type seawall were studied through the use of large-scale hydraulic experiments and numerical simulations using CADMAS-SURF. Then, the results were compared with those for a vertical seawall. For the overtopping rates of irregular waves, the characteristic hydraulic phenomena were masked by data averaging because the wave conditions and the overtopping rates were generally averaged. Even if a wave-by-wave analysis is applied for irregular waves, the information gained using regular waves is required as a basis for the interpretation to understand the overtopping phenomena of individual waves. In this study, the effects of relative seawall height, wave period, incident wave height, and water depth in front of the seawall on the overtopping rate were analyzed in detail. Then, the overtopping characteristics of waves for block mound and terrace-type seawalls were explained through comparison with the overtopping rate for a vertical seawall. The results showed that the dimensionless overtopping rates for both block mound and terracetype seawalls were almost the same as that for a vertical seawall.

 Severe damage from river flooding carrying driftwood has become a critical problem. We have developed a code for 3-D simulations of water flows carrying a lot of driftwood by using the cumulant lattice Boltzmann method (LBM) coupled with the discrete element method (DEM). Adaptive mesh refinement (AMR) makes it possible to apply the code to large areas with a high-resolution mesh, and a GPU implementation greatly accelerates the computation. A small-scale water-tank experiment with a driftwood model showed that the computational results were in good agreement with the experiment results. For an actual river-flooding disaster that occurred on the Omoto River in Iwate Prefecture, Japan, we conducted two large-scale computations of large areas with a total of 1000 pieces of driftwood and a maximum resolution of 7.8125 [cm]. The simulation results identified three driftwood accumulation processes: trapping in narrow channels, hitting building corners, and stagnation in front of buildings.

 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.

 The concentration of sulfide contained in the bottom sediment is a crucial indicator of environmental pollution in enclosed coastal seas. Acid-volatile sulfide (AVS) is widely used as an index of sulfide concentration in Japan. However, AVS contains a large amount of sparingly soluble bound sulfides that have little effect on living organisms. Therefore, its accuracy as an environmental index for evaluating the effect on living organisms is considered low. However, there are few measurement examples of dissolved sulfide (hereafter abbreviated as DS) because it is difficult to collect and analyze many samples in a short time. We devised a method to easily collect pore water from sediments and analyze the DS contained in pore water. The accuracy of this analysis method was examined and it was confirmed that sufficiently practical measured values could be obtained. By comparing DS with conventional AVS at the survey site of Hakata Wan enclosed coastal sea using this method, it was found that the DS concentration is a highly independent index different from AVS and is an effective index for evaluating environmental pollution.

 Tunnels in weak rock may be subjected to plastic ground pressure not only during tunnel excavation but also after completion, resulting in deformations such as side wall displacement. At this time, although the rock bolts are installed and the axial load is sometimes measured, there has not been sufficient discussion on how to evaluate the axial load measurement results of the rock bolts after tunnel completion. Therefore, the authors investigated the axial load distribution of rock bolts by numerical analysis, targeting rock bolts used as reinforcement work for tunnels that are subjected to plastic ground pressure after completion. Through this investigation, the authors present four distinct scenarios: ineffective rock bolts, insufficient length, yielding, and decoupling. They also provide examples of axial load distribution. Furthermore, the measured data of rock bolt axial load in actual tunnels were evaluated, confirming the usefulness of the insights obtained in this study for the assessment of axial load measurement results.

 Recently, foreign tourists traveling to Japan are pursuing self-likeness, self-worth, and diversified travel experiences as tourism needs have become increasingly personalized for visitors. In this study, we used the Latent Dirichlet Allocation model and Word2vec model of natural language processing to analyze the web travel notes posted on the Chinese visitor website Mafengwo written by Chinese tourists who visited Japan. Using the analytical results, we identified the tourism themes and the visit patterns of the Chinese tourists travelling to Japan and how they have changed. Furthermore, we also identified impressive and attractive local and regional tourism resources in some regions in Japan. Based on the analytical results, the policy to promote inbound tourism industry in local regions was also discussed.

 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.

 Animal waste contains some antibiotics administered to livestock. Therefore, when they are applied to agricultural land as compost, the antibiotics are released into the soil environment. This study investigated sulfamethazine (SMZ) sorption and degradation in three types of soil and their behavioral mechanisms. Furthermore, a tracer experiment using SMZ labeled ¹⁴C was conducted to obtain the percentage of degradation products of SMZ in gray lowland soil. SMZ was degraded with contact time in andosol and gray lowland soil, whereas little degradation and sorption were observed in brown forest soil. SMZ degradation was suggested to be a primal process in soil attributed to the activity of soil microorganisms. Moreover, the soil sorbed some SMZ degradation products, and the others rapidly degraded to CO₂.