Civil Engineering Research Institute for Cold Region

Sediment entrainment thresholds in rivers have been widely studied, informing the prediction of bedload transport rates that underpin morphodynamic modelling. However, quantification of sediment entrainment in complex channels with varying degrees of bedrock exposure and sediment cover remains limited. Here, physical modelling was conducted to simulate a 1:10 scaled model of a bedrock reach from the River Garry in Scotland. Sediment entrainment thresholds were measured for isolated grains corresponding to selected percentiles of the bed grainsize distribution (D10, D50, D90) over a bedrock surface with five sediment cover percentages (0, 25, 50, 75, 100%). Bed roughness metrics (e.g. standard deviation of bed elevation) of each bed were calculated. Sediment entrainment was found to be modulated by the bed roughness, resulting from the bedrock topography and infilling of depressions with sediments. Particle tracking revealed the spatial transport of sediment grains, along with the influence of localised bed roughness features on sediment dynamics.

One method for effectively utilizing the unsuitable soil that is generated at construction sites is to improve it by solidification. This method is reliable, as it causes strength to develop over time. The shape of the embankment is toe of slope of the embankment is thinnest and thickest towards the top of slope, so the greatest load acts on the center of the embankment. For this reason, when an embankment is constructed on soft ground, the center of the embankment will settle the most and the bottom of the embankment will be subjected to tensile stress. Unsolidified soil will gradually follow the deformation of the ground even when subjected to tensile stress, but embankments made of solidified soil will not be able to withstand the tensile stress caused by settlement and will crack. If the embankment is a river levee, there is the risk of water leakage through these cracks. The plains of Hokkaido, Japan, are widely distributed with peaty soft ground. When river levees are constructed using solidified soil on such ground, similar issues can occur. Crushed solidified soil is a material created by crushing solidified improved materials after they have undergone a certain period of strength development. This material is compactable and exhibits only a small strength increase after compaction. Previous studies have investigated the geotechnical properties of crushed solidified soil. In this current study, to understand the strength characteristics of crushed solidified soil, a one-year investigation was conducted on compacted lab specimens and embankments constructed in the field using this material to examine the relationship between elapsed time and strength. The lab specimens were found to exhibit a certain increase in strength over time. It was confirmed that the embankment material had a low degree of solidification and that the material aggregated into small clumps of soil. These results show that embankments made of crushed solidified soil exhibit low strength development, making such soil a suitable material for constructing embankments on soft ground.

ABSTRACT This study presents a novel method for no-contact detection of water leakage in pressurized pipelines using digital image correlation (DIC). This method focuses on pipe deformation caused by water hammers including leakage information, which combines the idea of transient test-based techniques (TTBTs) and non-destructive testing (NDT). Water leakage induces the hydraulic energy loss in pipelines and the damping of both water hammers and strain energy stored in pipe. We focus on detecting the leak-derived damping of this strain energy using DIC. In experiment, we measured pipe deformation due to water hammers with water leakage using DIC for an in-service agricultural pipeline system. Experimental cases included the conditions of no leak, one leak at downstream and one leak at upstream. As a result, DIC can detect the hoop and axial strain changes due to the water pressure changes in the in-service pipeline. Based on these DIC strain changes, we determine the strain energy of this pipe. The further downstream a leak location is, the greater the damping of the strain energy is. This study provides the non-contact method for detecting water leakage in the pipeline system, which enables us remotely and safely to inspect in-service pipelines that are difficult to access.

For decades, leak detection methods utilizing pressure variations (transient test-based technique: TTBT) have been recognized as convenient and accurate for pipeline leak detection. However, their effectiveness in long-distance complex structured field pipelines has not been fully demonstrated, presenting significant challenges for practical implementation. This study, for the first time, tested the effectiveness of inverse transient analysis (ITA), a type of TTBT, on detecting a single-point leak in the Ogura irrigation pipeline system in Sado, Niigata, Japan. The system spans approximately 18 km and features several branches and diameter changes. We proposed a new ITA method using the transient model and the comprehensive learning particle swarm optimization (CLPSO) as the optimization technique. In the verification experiments, pressure variations were induced by closing the downstream valve under two different initial downstream flow rates (approximately 0.032 and 0.093 m3/s) in scenarios without a leak, with a leak near the downstream end of the main pipeline, and with a leak on the branch pipeline. The calibration of the transient model with the wave speed distribution as parameters was conducted prior to leak detection, demonstrating pre-estimation of this wave speed distribution is essential for accurate leak detection. The application of the proposed ITA for measured pressure variations resulted in averaged estimated leak location errors along the total length of the pipeline system with the standard deviations as follows: 0.217 ± 0.038% near the downstream end of the main pipeline for a 0.032 m3/s downstream flow, 0.978 ± 0.456% for a 0.093 m3/s flow, 1.843 ± 1.815% on the branch pipeline for a 0.032 m3/s flow, and 0.880 ± 0.560% for a 0.093 m3/s flow. In cases of the leak near the downstream end of the main pipeline, smaller steady flow rate resulted in smaller variability and higher accuracy in the estimated leak location. Conversely, for the leak in the branch pipeline, larger steady flow rate was better for the estimated leak position. This suggests that the optimal steady flow rate for accurate leak detection varies depending on the leak location. The leak sizes can be expressed as ratios of the estimated leakage discharges to the actual average irrigation water flow rate, resulting in values ranging from 4.86% to 8.58%. From these results, the proposed leak detection method is expected to contribute to reducing the effort and cost for irrigation engineers to narrow down potential leak areas in pipeline systems.

Abstract Recent climate change has resulted in severe and frequent natural disasters globally, prompting the need for adaptation to these events. As an adaptation measure, disaster prevention and mitigation using natural processes and mechanisms (or ‘green infrastructure’) have become widely recognized in many countries. Ecosystem‐based disaster risk reduction has been promoted in Japan since 2015. The ‘Tambo Dam’, a flood mitigation project using paddy fields in which the authors have participated, has the potential to become one of the most extensive forms of green infrastructure in Japan. This study outlines the runoff control mechanisms of Tambo Dams, demonstrates their effectiveness in reducing flood damage at the watershed scale, and discusses two key factors for successful sustainable efforts: the design of appropriate runoff control equipment and administrative schemes that support incentives for the efforts of farmers. The results indicated that Tambo Dam implementation represented a crucial strategy for managing agricultural resources. The functionality of paddy fields could be preserved by managing them as Tambo Dams. This approach not only contributes to flood control but also ensures a swift return to rice cultivation during emergencies. Moreover, establishing a system akin to the Tambo Dam initiative of Mitsuke City, supported by the ‘Direct Payment Scheme for Multifunctional Activities’ for maintenance and management, could ensure the feasibility of Tambo Dam implementation.

In this study, we propose a novel method for algal bed region segmentation using aerial images. Accurately determining the carbon dioxide absorption capacity of coastal algae requires measurements of algal bed regions. However, conventional manual measurement methods are resource-intensive and time-consuming, which hinders the advancement of the field. To solve these problems, we propose a novel method for automatic algal bed region segmentation using aerial images. In our method, we use an advanced semantic segmentation model, a ViT adapter, and adapt it to aerial images for algal bed region segmentation. Our method demonstrates high accuracy in identifying algal bed regions in an aerial image dataset collected from Hokkaido, Japan. The experimental results for five different ecological regions show that the mean intersection over union (mIoU) and mean F-score of our method in the validation set reach 0.787 and 0.870, the IoU and F-score for the background region are 0.957 and 0.978, and the IoU and F-score for the algal bed region are 0.616 and 0.762, respectively. In particular, the mean recognition area compared with the ground truth area annotated manually is 0.861. Our study contributes to the advancement of blue carbon assessment by introducing a novel semantic segmentation-based method for identifying algal bed regions using aerial images.

Abstract. Issuing appropriate evacuation information is a daunting task for municipalities during unprecedented heavy rainfalls. Due to their limited experience, they will encounter greater challenges in responding appropriately in future climate conditions, where the scale of floods will be greater. In this study, we proposed a method to make flood scenarios based on a climate projection database. We also developed an exercise method for municipalities to consider issuing evacuation information using the scenarios. Through a demonstration experiment in Hokkaido, Japan, we conducted a simulation exercise based on the method for a municipality. As a result, they considered specific response and provided valuable insights, thereby enhancing preparedness for potential future flood disaster.

This paper presents the field performance of vacuum consolidation method on peat ground and some technical learning from the field trial. Peat is well known to be a soft soil which has particular characteristics, including extremely high compressibility and greatly low undrained shear strength. In case of an embankment building over peat ground, sliding failure and large settlement often occur due to the particular characteristics. For actual construction sites on peat ground, therefore, some kinds of ground improvement methods are commonly used. One of the methods is the vacuum consolidation method which can load vacuum pressure with the soft ground by vacuum pumps and prefabricated vertical drains to accelerate the consolidation and increases the strength of soft ground. Peat ground distributed widely in Hokkaido, the northernmost land of Japan. A full-scale trial construction of vacuum consolidation was conducted in a highway project over peat deposit in Hokkaido of Japan to reveal its performance. Although the undrained shear strength of peat ground at the trial construction site was approximately 10 kN/m2 and extremely low, a 10.7 m high embankment was successfully built in only 45 days. This experimental fact implies that the vacuum consolidation method has extremely high effects in improving the stability of peat ground. Based on a result of the trial construction, it also revealed that the increase of undrained shear strength of the peat ground using vacuum consolidation and the suitable spacing of prefabricated vertical drains for peat ground.