In the pipeline, the thrust force depending on the bending angle and internal pressure constantly acts on the bend. The passive earth pressure behind the bend is expected to resist the thrust force, but actually, the passive earth pressure decreases drastically when the liquefaction occurs. The seismic design method for the pipeline under the liquefaction is yet to be established. In this study, shaking experiments were carried out in order to discuss the dynamic behavior of flexibly jointed pipeline with a bend in the liquefied ground. As a result, it was clarified that the crushed stone foundation alone is insufficient countermeasure against liquefaction. In addition, it was confirmed that the chain structure pipeline is effective against the displacement of the bend.
In this paper, kinematic wave model was applied to simulation of rainfall-runoff processes. The kinematic wave model has been usually used for calculating overland flow from rainfall excess that is residual of total rainwater after subtracting infiltration and evapotranspiration. The developed model simulates overland and groundwater runoff from total rainfall considering infiltration. That is, the developed model simultaneously simulates overland and groundwater runoff and infiltration. The model was applied to simulation of 34 floods' discharge with peak specific discharge of 0.6 - 18 m3s-1km-2 in six watersheds of various sizes (10 m2 - 1,717 km2) with different land cover. The results show that the developed model well simulates flood discharge for all objective floods. Simulation accuracy of channel flow of the developed model is comparable to that of a model with diffusion channel flow model in large catchments, which suggest advantage of kinematic wave channel model to diffusion model in balance between accuracy and simplicity.
Detachment of joints is a common type of seismic damage on pipelines. Restraint joints, which have both flexibility and restraint force against detachment, are expected to be a new method to enhance the safety of pipeline against earthquakes. Prototypes of restraint joints for synthetic steel tube are made and applied to pull-out tests in order to verify their performance in flexibility and restraint force. It is confirmed that the restraint action successfully works in both straight and bent connections of the joints. A cumulative flexibility, which is the total flexibility of joints activated by restraint force, is proposed as a performance index for restraint joints considering both of flexibility and restraint force.
Determination of high salinity soil layers after leaching processes is required to safely resume farming in tsunami-affected regions. This study proposes a new method in which an electromagnetic induction sensor (EM38-MK2, Geonics) is used to determine the depth of the most saline layer. Based on a determination of horizontal spatial sensitivity of the EM38-MK2, we evaluate the applicability of the sensitivity function for four measurement modes, vertical and horizontal dipole modes with two coil separations. A field experiment compares EM38-MK2 measurements with a three-dimensional distribution of apparent electrical conductivity measured by time domain reflectometry (TDR). A positive linear correlation was obtained between the EM38-MK2 and TDR measurements. We found the sensitivity function to be applicable for the four measurement modes of the EM38-MK2. Comparison of EM38-MK2 data among the four different modes was able to identify the most saline layer from among five soil layers at depths of 0-20 cm, 20-50 cm, 50-75 cm, 75-150 cm, and 150+ cm. Our proposed method can provide useful information about underground salinity and will facilitate the resumption of farming in tsunami-damaged farmlands.
Recently, the evaluation of the failure potential of earth-filled dams has become important because of the increasing occurrence of storm rainfall. Although most instances of earth-filled dam failure are caused by overflow, in-depth knowledge of the mechanism of the erosion and failure process of embankments due to overflow is still lacking. This paper presents a numerical method for simulating an embankment erosion and failure process by the moving particle semi-implicit (MPS) method. To reasonably simulate the erosion and failure process of an embankment due to overflow, a simple erosion model whose parameters can be determined through erosion tests on embankment materials was newly incorporated into the original MPS method. An embankment erosion and failure process observed in a model test was simulated by the proposed MPS method to confirm its practicability. Although the simulation accuracy for the erosion rate is slightly low at the beginning of the erosion, the average simulated values of the erosion rate are almost the same as the experimental values. The proposed MPS method can be a useful tool in embankment design practices to simulate embankment erosion due to overflow and to discuss remedial measures against overflow.
This study aimed to clarify the relationship between the occurrence of rhizophore lesion and soil water transport properties using a numerical analysis in Chinese-yam upland fields in the Kamikita region of Aomori Prefecture in 2014. We investigated the impact of planting trenches formed using either chain-type or wheel-type trenchers on soil physical and chemical properties and moisture transport characteristics. The soil of a wheel-type trencher test plot at a depth of z > 70 cm was found to have low permeability; thus, the difference in the method of formation of the planting trench was revealed to have a significant effect on the water transport properties of soil at a depth of z > 70 cm. In response to the above, in the wheel-type trencher test plot during the heavy rain period in August 2014, the soil in the vicinity of tuber of the Chinese-yam was saturated. In addition, the results of numerical analyses revealed that, if the saturated condition persists for a long period, it poses a high risk of moisture damage to the Chinese-yam in the test plot for the wheel-type trencher. Thus, these results indicate a high probability that microbism and malformation around the tubers of Chinese-yams occur during this period.
Floods due to dam breaches have the greatest influential effect on hydraulic structures for irrigation and drainage, and estimating the costs of damage to these structures is important for risk assessment and management in agricultural land improvement projects. Existing methods for estimating damage costs require many types of asset data and usually a long time because of complications, and is not applicable for the practice in estimation of the damage costs. To overcome the problems, the authors have proposed a surrogate model called response surface (RS). This study aimed to verify the accuracy of the proposed RS by applying the surrogate model to risk evaluation of dam breaches due to rainstorms. We compared the damage costs of four earth dams calculated by using RS and existing methods, and found that the variances between the results of RS and existing methods was smaller than the unbiased variance of the RS based on 21 results of flow analysis. Therefore, the proposed method can easily estimate the risks of dam breaches due to rainstorms.
Iron is known to be significantly related with phosphorus runoff from watersheds, yet there is a lack of knowledge regarding this phenomenon from the viewpoint of the iron load. Therefore, we conducted a 17-month investigation on the behavior and annual mass balance of iron and phosphorus in a paddy field area where sediment of iron oxides accumulated. Most iron and phosphorus were present as particulate matter, with low concentrations of dissolved ions. Annual net-outflow loads of iron and phosphorus were 108.6 kg/ha (irrigation period: 37.3 kg/ha; non-irrigation period: 71.3 kg/ha) and 3.40 kg/ha (irrigation period: 1.49 kg/ha; non-irrigation period: 1.91 kg/ha), respectively. A possible reason that no phosphorus purification was observed at the study site despite the sufficient amount of iron, which has adsorption capacity for phosphorus, is sediment detachment and runoff due to water flow in the drainage canal. This suggests that management of phosphorus-rich sediment is an essential factor for controlling the outflow of phosphorus.
The objective of this study is to elucidate the effects of applying a wood bark-derived biochar to sand dune soil on water and nutrient retention properties in a field experiment. Biochar was applied into the soil at 0 (control), 20, and 40 t-DW ha-1. Applying biochar significantly enhanced the available water capacity of the soil. Compared with control, the available water capacity increased 20-30 % with 20 t-DW ha-1 and 50-60 % with 40 t-DW ha-1. In addition, applying biochar significantly enhanced the cation exchangeable capacity of the soil. Compared with control, the cation exchangeable capacity increased 2-4 % with 20 t-DW ha-1 and 8-9 % with 40 t-DW ha-1. Furthermore, the decrease in soil matric potential at the root zone of little turnips was suppressed by application of biochar with 40 t-DW ha-1. Our results clarify the positive effects of applying wood bark-derived biochar on water and nutrient retention properties of sand dune soil under field conditions.
In Chikugo River basin and its neighboring basin, the adequate distribution of irrigation water is a great issue especially during puddling paddy period, so that at first grasp of present water use is needed. Therefore, the aim of our research is understanding the actual water use by analyzing the satellite data (RADARSAT), the existing GIS data, and the water intake records. The satellite data (RADARSAT), which showed the surface of rice paddies, was used for deciding irrigation starting time. The GIS data, which is water distribution area, canal networks and farm layouts, was used for understanding water flow of distributed water. The water intake records, which is significant quantitative data, is used for analyzing the actual water use during puddling paddy period. As a result, from the RADARSAT analysis, puddling paddies were found in the downstream area in early June, and the area were found in the middle basin area one week later. From the water intake records analysis, the peak timing of intaking volume for downstream area was around 1 week earlier than that for middle basin area. Thus, the trend of puddling paddy area expansion corresponded to the trend of intake water increase, so it was found that irrigation water was supplied to downstream area 1 week earlier than to the middle basin area. Our results implied that the analysis of the satellite data, existing GIS data, and water intake records were effective methods for understanding the actual water use.