Transactions of The Japanese Society of Irrigation, Drainage and Rural Engineering
Online ISSN : 1884-7242
Print ISSN : 1882-2789
ISSN-L : 1882-2789
Volume 85 , Issue 2
Showing 1-23 articles out of 23 articles from the selected issue
Research Papers
  • Motohei KANAYAMA, Motoi KUDO, Mei FUJII
    2017 Volume 85 Issue 2 Pages I_137-I_143
    Published: 2017
    Released: July 12, 2017
    JOURNALS FREE ACCESS
    There is a growing concern socially for the recycling of waste materials. In the geotechnical engineering community ground improvement by reusing wastes is expected to be developed. In the present study, laboratory tests have been conducted to examine the cementation of soil due to precipitates of calcium phosphate compounds by using waste oyster shell and phosphoric acid. Variations of Ca2+, PO43-, pH and EC in the solution were measured for the column test. It was found that the calcium phosphate compound was precipitated by reaction between the oyster shell powder and the phosphoric acid solution. According to the results of unconfined compression test and image observation, it was recognized that the strength of the sample was increased with an increase of curing day and the precipitated compounds were contributed to the increment in strength of the specimen. It was found that the strength of the specimen with the oyster mass mixing ratio not less than 1 and at the curing period of 10 days was above the target strength of 100 kN/m2.
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  • Akiko HIGASHIGUCHI, Satoshi HOSHINO, Shizuka HASHIMOTO, Kenichirou ONI ...
    2017 Volume 85 Issue 2 Pages I_145-I_157
    Published: 2017
    Released: August 08, 2017
    JOURNALS FREE ACCESS
    This study aimed to identify determinants of resident's behavioral intention about the collective implementation of countermeasures by residents of rural communities against agricultural damage by wildlife. Employing the collective protection motivation model as an analytical framework, this study analyzed how collective behavioral intention is formed and how its process is vary by gender. Using structural equation modeling, our analysis identified that, in the case of the fence to prevent agricultural damage by wildlife, male's major determinants of collective behavioral intention were the following three cognitions: threat cognition, efficacy cognition, and responsibility cognition. For females, the thread cognition was the strong determinant in particular. In the case of chasing off monkeys, male's major determinants were same as those for the fence, whereas female's major determinants were threat cognition, ability to act cognition, practician ratio cognition. Also, the threat from deer to community and individuals, and the threat from monkey to community showed minor influence on the formation of behavior intention compared with the wild bore's threat to community and individuals, and with the monkey's threat to individuals. Our results suggests that the government should organize information sessions suitable for each of male and female to raise awareness.
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  • Susumu MIYAZU, Natsuki YOSHIKAWA, Satoshi ABE
    2017 Volume 85 Issue 2 Pages I_159-I_167
    Published: 2017
    Released: August 08, 2017
    JOURNALS FREE ACCESS
    To investigate the proper design of runoff control device adopted in Mitsuke city, Japan, where paddy field dam has been promoted, this study firstly, classified the existing runoff control devices into “function-integrated” and “function-independent” type to compare their advantages and disadvantages; secondly, introduced the basic design concept of a new runoff control device suitable for the conventional cylindrical drainage outlet; and finally, evaluated flood mitigation effect of the newly developed device. The following superiorities of the function-independent device in which the function of runoff control and water management are mutually independent became clear; (1) a sustainable runoff control performance under heavy rainfall events, (2) minimal disruption to the farmers' daily water management practices under small rainfall events, and (3) stable runoff control function due to little influence of paddy field water level changes. In response to these superiorities, authors fundamentally reexamined the structure of the runoff control device already adopted in Mitsuke city, and developed a new function-independent device suitable for the cylindrical drainage outlet. As a result of the evaluation by computer calculation, it became clear that the new device presented a better performance in functionality and sustainability than the conventional one.
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  • Nao ISHIKAWA, Keiko CHIBA, Ayumi ITO, Teruyuki UMITA
    2017 Volume 85 Issue 2 Pages I_169-I_175
    Published: 2017
    Released: September 05, 2017
    JOURNALS FREE ACCESS
    A serious disease caused by exposure to arsenic via drinking water from wells has been observed in wide areas of Asia. We investigated the suitability of the agro-byproducts, rice husk ash and bone ash of livestock, as low cost As adsorbent for use in water purification in developing countries. The result showed that bone ash had higher adsorption capacity than rice husk ash, and concentrations of elements such as Cd and Mn dissolved from the bone ash were within the concentration criteria for drinking water. In addition, since the amount of adsorbed As from As(III) solution was higher than that from As(V) solution, we thought that As(III) oxidizing treatment was not necessary for As adsorption by the bone ash. We also found that As concentration was lower than 50 μg/L in the liquid phase, which is the standard value for drinking water in Bangladesh, when 0.5 mg/L As(III) solution was treated with bone ash at solid-liquid ratio higher than 0.075 (3 g : 40 mL).
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  • Satoshi SAKATA, Koji NOSAKA, Tadashi TANAKA, Kunio TATEISHI, Hitoshi K ...
    2017 Volume 85 Issue 2 Pages I_177-I_183
    Published: 2017
    Released: September 05, 2017
    JOURNALS FREE ACCESS
    Promoting labor saving for water management during rice cultivation by utilizing information and communication technology (ICT) is stated as one of the government policies, including “Basic plan for food, agriculture and rural areas”. Studies have not been sufficiently conducted to develop a device to attain the water management system utilizing ICT, and verify the effects on the contribution of this device to labor-saving. In this study, a water management using auto-irrigating devices operating with personal digital assistance, was compared with the conventional water management by using simplified GPS trackers fitted on farmer's cars. In the case of using auto-irrigating devices, the operating time per device and area were reducing by 27% and 41%, respectively. In the case of conducting the water management in an intensified area, the reduction of operating time of valve manipulation can be thought to have a profound effect because the percentage of the operating time of valve manipulation is approximately half of the total whole water management time, including the transfer.
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  • Masahiro HYODO, Masayuki ISHII, Hidehiko OGATA, Keiji KISHIMOTO, Tetsu ...
    2017 Volume 85 Issue 2 Pages I_185-I_190
    Published: 2017
    Released: September 05, 2017
    JOURNALS FREE ACCESS
    The authors have proposed the Internal Loading Method as a new strength evaluation method for buried pipes. This method is applied to RC pipes in previous studies and its effectiveness has been confirmed. However, these studies used test pipes with grooves to simulate cracks. In this research, damaged RC pipes are prepared by applying various loads with a compression-testing machine, and their stiffness is measured by the Internal Loading Method. In addition, the stiffness of RC pipes by different manufacturers was also examined. As a result, the Internal Loading Method was able to detect the trend of the relationship between the deformation and load on RC pipe. Furthermore, cross-sectional stiffness of joined pipes and a non-joined pipe was almost the same. The constraint of the connecting part on the pipe does not affect the stiffness with deformation of 70 micrometers. Finally, it was found that the relationship between the load and deformation differed by the manufactures of RC pipes.
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  • Yuki KUGISAKI, Kunio WATANABE
    2017 Volume 85 Issue 2 Pages I_191-I_198
    Published: 2017
    Released: October 04, 2017
    JOURNALS FREE ACCESS
    Exposure of a ground surface to subzero temperatures leads to the formation of a frozen soil layer. Understanding the soil water redistribution associated with thawing of the frozen soil layer is important when considering soil water and nutrient management of farmland. In this study, we performed a one-directional soil column freezing and thawing experiment using unsaturated Andisol, monitored the soil temperature and water profiles in the column, and attempted to simulate the results by using an existing numerical soil freezing model. At the onset of thawing, surface meltwater flowed into and refroze in the middle part of the frozen soil layer. During the thawing, water continued to flow from the unfrozen soil to the frozen soil layer when the soil temperature was lower than -1 °C. When the temperature of the frozen soil layer stagnated at near 0 °C, meltwater infiltrated through the frozen layer, which still contained a certain amount of ice. Two major issues were found for application of the existing soil freezing model to the soil thawing process: (1) modeling the retardation of soil water freezing near 0 °C and (2) improving the hydraulic conductivity model for frozen soil based on the unfrozen water content.
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  • Yoichi HAYASHIDA, Susumu MASUKAWA, Hidekazu TAGASHIRA
    2017 Volume 85 Issue 2 Pages I_199-I_207
    Published: 2017
    Released: October 04, 2017
    JOURNALS FREE ACCESS
    Influences of regions of modeled area and material property of dam's rock foundation on seismic behavior of dam body are investigated by the numerical experiment. From the experimental results, it is clarified that acceleration amplitude ratio, Fourier spectrum ratio and 1st predominant frequency of dam body mainly depend on the material property of dam's rock foundation. And modeled area of rock foundation does not remarkably effect on them. These phenomena can be caused by deformation modes of dam body based on the interaction between dam body and rock foundation. Deformation modes of dam body mainly depends on material property of dam's rock foundation. And regions of modeled area hardly effect to deformation modes of dam body.
    Seismic characteristics of dam's rock foundation are effected by the predominant frequency of dam body. So, it is important to decide the modeled area of dam's rock foundation in seismic response analysis that predominant frequencies of dam body are not close to that of its rock foundation.
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  • Susumu HANAYAMA, Yuri KANAYA, Takeyuki ANNAKA
    2017 Volume 85 Issue 2 Pages I_209-I_214
    Published: 2017
    Released: October 14, 2017
    JOURNALS FREE ACCESS
    Phosphate accumulated in paddy soils is released from the soils to flooded water when pH of the flooded water is much increased by photosynthesis of periphyton on the soil surface. The growth of periphyton depends on nitrogen in the soils. We investigated the effect of nitrogen form in a paddy soil on change in pH of flooded water caused by photosynthesis of periphyton at 15℃. In this experiment, we applied 0g/m2, 5g/m2 and 10g/m2 of nitrogen as potassium nitrate and the same amount of nitrogen as urea to each soil. As the result, the pH of the flooded water on the soil to which nitrogen was not applied increased from 5.4 to 7.1. The increase in the pH of the flooded water on those soils in which 5g/m2 and 10g/m2 of nitrogen as urea were applied was almost identical to the increase in pH of the flooded water on the soil to which nitrogen was not applied. However, the pH of the flooded water on those soils in which 5g/m2 and 10g/m2 of nitrogen as potassium nitrate were applied increased from 5.1 to 8.1 and 9.7, respectively. This suggests that when periphyton uses nitrate nitrogen in the soil, photosynthesis is more activated, increasing pH of the flooded water.
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  • Yuki HASEGAWA, Keita KOJIMA, Shushi SATO, Isamu NATSUKA
    Type: Research Papers
    2017 Volume 85 Issue 2 Pages I_215-I_220
    Published: 2017
    Released: November 08, 2017
    JOURNALS FREE ACCESS
    In this research, applicability of sandblast method for evaluation on abrasion resistance of inorganic material was examined. Influence on the difference of abrasive particle size to test result and decrement of abrasion performance with time increment were examined as estimation of fundamental performance of sandblast. Additionally, surface condition, mass decrement and abrasion depth of mortar specimen was evaluated. As a result, it was confirmed that mass decrement of specimen increased with increment of abrasive size. On the other hand, decrement of abrasion performance with time increment was not confirmed. It was clarified that variation of test result increased with increment of test time, and test result was stable at 10 and 30 seconds of test time. Moreover, the abrasion depth of sandblast method at 30 seconds of test time was equivalent with that of abrasion tester using water jet with sand method at 10 hours.
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  • Akira ENDO, Daiyu ITO, Koh KATO, Chihiro KATO, Choichi SASAKI
    Type: Research Papers
    2017 Volume 85 Issue 2 Pages I_221-I_231
    Published: 2017
    Released: November 08, 2017
    JOURNALS FREE ACCESS
    The authors estimated spatiotemporal dynamics of inorganic nitrogen concentration of pore water in Apple orchard of Gray lowland soil in Tsugaru region, Aomori prefecture by numerical analysis with FEM solver, taking snow cover and snowmelt into account. Under non-consideration condition of snow cover and snowmelt, it was indicated that the traveling velocity (Δzt) of the NO3-N concentration peak reached to a depth of 100 cm (Δzt = 20-26 cm/month) in about 4 months from late November to the early March of the following year. On the other hand, considering snow cover and snowmelt, it was indicated that the high concentration of NO3-N reached to the depth of 100 cm (Δzt = 100-130 cm/month) in just one month from early March to early April. Consequently, from the perspective of promoting environmental conservation and reducing the environmental load, the importance of soil moisture transfer during winter season was quantified by numerical analysis. Thus, it was necessary to discuss the behavior of NO3-N in soil pore water and the nitrogen budget, taking into consideration the snowmelt water from the soil surface in early spring.
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  • Yoshitaka OTSUKA, Kazuko ENDO, Yoji KUNIMITSU
    Type: Research Papers
    2017 Volume 85 Issue 2 Pages I_233-I_243
    Published: 2017
    Released: November 21, 2017
    JOURNALS FREE ACCESS
    This study investigated the psychological processes for office workers in a land improvement district for technology acceptance using a qualitative research method with trial experiments of the GIS software “VIMS” developed by the Institute for Rural Engineering, NARO. As a result of the analysis using the modified-grounded theory approach, following five categories for acceptance of technology were generated from the statements of office workers in the land improvement district obtained by a semi-structured interview: <internal factors of the land improvement district>, <background of the land improvement district>, <technological factors>, <external factors from the developers> and <trust>. As the hypothesis of the psychological processes in technology acceptance, we concluded that <technological factors> were the primary elements for accepting the technology and <external factors from the developers> and <internal factors of the land improvement district> indirectly influenced this acceptance. In addition, <background of the land improvement district> was a key factor for <internal factors of the land improvement district>. Therefore, to promote technology acceptance, it is important to build <trust> with office workers in the land improvement district and understand their background.
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  • Ryohei YAMASHITA, Shinsaku NAKAJIMA
    Type: Research Papers
    2017 Volume 85 Issue 2 Pages I_245-I_251
    Published: 2017
    Released: December 06, 2017
    JOURNALS FREE ACCESS
    The complexity of having an optimal route for traveling across a farmland may increase depending upon the expansion of farm management area. Such a problem is called the traveling salesman problem and should be considered when farmers propose management plans. Therefore, we analyzed increases in the total travel distance and time taken for observing the paddy fields under a simulated situation of farming area expansion.
    The results of this study revealed that the increase pattern of the total travel distance diminished gradually compared with the additional number of paddy fields by renting them randomly, and that the total travel time showed a different increase pattern to the total travel distance. In particular, the total travel time corresponded approximately to the increase pattern of additional number of paddy fields under the setting of this simulation analysis. Thus, our basic simulation provided some useful information about the situation, necessary for the development of future scale expansion.
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  • Kazuhiro NISHIDA, Marie MITSUYASU, Shuichiro YOSHIDA, Sho SHIOZAWA
    2017 Volume 85 Issue 2 Pages I_253-I_263
    Published: 2017
    Released: December 19, 2017
    JOURNALS FREE ACCESS
    To obtain relationships between water depth, and water and soil temperature in a paddy field during rice ripening period, changes in water depth, water and soil temperatures were measured in conventional paddy fields at Ishikawa prefecture, Japan, in 2012 and 2013. A multiple regression analysis was applied to the measured data, and empirical equations were developed for the maximum and minimum water temperature during rice ripening period as a function of water depth, atmosphere conditions, initial water temperature, and days after heading date of rice. Predictions of the equations were in good agreement with the observed temperatures; root mean square errors (RMSE) for minimum and maximum water temperature were 0.49 and 0.81 °C, respectively. Then, relationships between water depth, and water temperature and day water temperature difference were obtained; decrease in 1 cm average water depth decreases maximum water temperature of 0.01±0.10 °C and minimum water temperature of 0.18±0.05 °C, and increases daily water temperature difference of 0.16±0.12 °C. Finally a prediction formula on daily soil temperature difference was developed from an analysis using heat conduction equation of soil and the obtained relationship between water depth and day water temperature difference.
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Technical Papers
  • Kenichi YATAYA, Mattashi IZUMI, Nobuyuki AZUMA, Atsushi MARUI
    2017 Volume 85 Issue 2 Pages II_53-II_59
    Published: 2017
    Released: July 12, 2017
    JOURNALS FREE ACCESS
    To understand the swimming ability of demersal fish for the design of a fishway, swimming experiments involving small Goby (Gymnogobius urotaenia sp.) during their upstream river migration period were conducted. The experiments were conducted using high velocity flows to prevent the Gobies from using the suction cups on their ventral fins. Our observations were as follows: 1) the body length of the Gobies was approximately 3-4 cm, and their average swimming speed was found to range from 70 cm·s-1 to 171 cm·s-1; 2) a swimming-curve formula defining the relationship between the swimming speed and swimming time was obtained; 3) at flow velocities of 83 cm·s-1 or less, 67% or more of the Gobies moved at least 50 cm; and 4) according to the swimming ability index, the swimming ability of Gobies exceeded that of the Ice Goby, Loach, and Medaka for the same body length.
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  • Yuki KADOWAKI, Yuka KUBOTA, Shigeki SANUKI, Kazuyoshi NAKATA
    2017 Volume 85 Issue 2 Pages II_61-II_70
    Published: 2017
    Released: August 08, 2017
    JOURNALS FREE ACCESS
    Freshwater fishes inhabiting agricultural channels change their distribution area according to the life history stages, and the fish habitat can change among seasons (i.e., reproductive season, growing season and wintering season, etc.). Thus, to evaluate the effectivity of the restoration methods for fish, we have to understand the seasonal difference of habitat preference by fish and then reflect the knowledge to restoration methods in agricultural channel improvements. In this study, we conducted fish samplings in restoration areas, as well as non-restoration areas, of an agricultural channel, to clarify the difference of habitat preference by fish between the active and wintering seasons. The results of multiple regression analysis indicate that important environmental factors for fish habitats are different between the active and wintering seasons and that the factors are the water depth diversity, average water velocity and minimum water velocity in the active season and are the maximum water depth, average water velocity and rate of vegetation in the wintering season. These results indicate that fish inhabitation areas in the agricultural channel are different between the active and wintering seasons. To create restoration areas for fish habitats in agricultural channel improvements, we need to consider the difference of the habitat preference by fish between the active and wintering seasons.
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  • Manabu SEGAWA, Toshisuke MARUYAMA, Keiji TAKASE
    2017 Volume 85 Issue 2 Pages II_71-II_81
    Published: 2017
    Released: September 05, 2017
    JOURNALS FREE ACCESS
    This research undertook flood discharge analysis from urbanization using the unit flood discharge concept. The test site was selected at the Kurabe River basin, which is 17.5 km2 in area having a very steep landscape. Twenty-one rainfall events at 10-minute intervals were selected, and five urbanized years (1976, 1987, 1991, 1997 and 2009) were tested. It is estimated that the flood discharge increase to approximately twice during period from 1976 to 2009 (35 years), in which residential areas increased from 23% to 48%. Furthermore, we investigated the flood discharge changes due to urbanization from various aspects. For example, the flood discharge changes in the hydrograph, the effect of a small reservoir aiming to cut down the peak discharge, and the relationship between the unit discharge and, block and whole basin discharge, and the relationship between the discharges of our method and of estimated by a ‘Rational Formula’. Finally, the validity of our method was confirmed at the test site in the observed discharge.
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  • Yukio OKUDA, Haruyuki FUJIMAKI, Yoshinobu KITAMURA, Iwao KITAGAWA
    2017 Volume 85 Issue 2 Pages II_83-II_90
    Published: 2017
    Released: September 05, 2017
    JOURNALS FREE ACCESS
    Secondary salinization of irrigated lands in Uzbekistan has been caused by excessive irrigation and rising groundwater level due to drainage system malfunction. Measures, such as maintenance of drainage system or leaching, had been conducted, but there are still fields where salinity levels remain high. The use of a shallow sub-surface drainage system has been proposed to ensure complete removal of percolation water after leaching, but it is considered as an expensive option. Therefore, the possibility of introducing a drain drilling machine (Cut-drain) which has been developed recently in Japan was investigated. Employing Cut-drain has presented some problems; it rises up to the soil surface and causes the occurrence of preferential flow under dry soil conditions. In this study, we examined the soil moisture conditions suitable for the construction of Cut-drain and the effectiveness of a method for mitigating preferential flow. The results showed that there was a border soil moisture condition needed in the construction of Cut-drain. More than 9-11% moisture was required in the first soil layer (from the surface to 20 cm below it) and 12-15%, in the second layer (from 20 to 40 cm). Furthermore, it was found that the preferential flow could be mitigated by irrigating the furrows before the construction.
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  • Shinichi TAKESHITA, Haruka OYAMA, Natsuho ATAGO
    2017 Volume 85 Issue 2 Pages II_91-II_96
    Published: 2017
    Released: October 04, 2017
    JOURNALS FREE ACCESS
    A simple pyranometer can be a useful instrument in science education. Its measurement principle is based on the correlation between the amount of solar radiation absorbed and the subsequent increase in water temperature within the device over a short period of time. In this study, the accuracy of the measurement hourly-accumulated solar radiation was assessed over a five month period. All the data was collected between May and September 2015 at Miyazaki University, Japan. Thus, the relationship between the hourly-accumulated solar radiation and water temperature of the simple pyranometer was derived and approximating expressions were formulated. Satisfactory accuracy was obtained using these expressions when the water temperature was normalized. This normalization was divided into two processes, namely, upward and downward, when the ascending vertical angle of the equipment surface was set to 45° given its operation at northern latitude of 31.8°. Moreover, the accuracy got higher by considering heat exchange between open air and the equipment. Under fine weather, the simple pyranometer can measure the hourly-accumulated solar radiation at error of 0.26 MJm-2h-1 and measure the changes in the solar radiation over time.
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  • So FUJIYAMA, Yuki ITO, Kouichi NAGANO, Hiroyuki TARUYA, Toru NAKADA, Y ...
    Type: Technical Papers
    2017 Volume 85 Issue 2 Pages II_97-II_102
    Published: 2017
    Released: November 21, 2017
    JOURNALS FREE ACCESS
    Some devices such as laser displacement sensors and digital still cameras have been used for measuring Manning's roughness coefficient in concrete open channels. Owing to their high accuracy in estimating roughness coefficients, these devices require skills and vast experience. Moreover, they cannot be used for channel surfaces under submergence conditions. Therefore, in this study, we propose a new method that uses manufactured plates to estimate Manning's roughness coefficient and examine the effectiveness of the method. The roughness of the plates is characterized by the different aggregate exposure conditions on the surface. We chose four plates, with variable exposure conditions, and applied them in the estimation of Manning's roughness coefficient in the existing concrete open channel used for irrigation. The results showed that the difference between the coefficients estimated by the plates and the laser distance meter was 0.001. Therefore, we conclude that the developed plates allow to estimate Manning's roughness coefficient without great effort even when the concrete surface is under water.
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  • Shigeru NAGAI, Tsutomu TANAKA
    Type: Technical Papers
    2017 Volume 85 Issue 2 Pages II_103-II_111
    Published: 2017
    Released: November 21, 2017
    JOURNALS FREE ACCESS
    In the excavation of soil within a cofferdam, upward seepage flow occurs and the seepage failure of soil becomes a problem. In this study, to examine the appropriateness of several design-manuals' (or standards') calculation methods, safety factors based on these methods were considered. The effects of upstream residual soils on stability against seepage failure, which are usually neglected, were discussed under various flow conditions: two-dimensional (2D), two-dimensional concentrated within double sheet piles (2DC), three-dimensional (3D), and axisymmetric (AXS) seepage flows. The following results were obtained: (1) With respect to the safety factors against seepage failure, the real factor of safety Fs (True) can be expressed as the product of the safety factor included in calculation Fs (Formula), safety factor in design Fs (Design), and safety factor given by upstream residual soil Fs (Upstream residual soil), i.e., Fs (True) = Fs (Formula) × Fs (Design) × Fs (Upstream residual soil). (2) The design-manuals' calculation methods provide an accurate estimation of the critical hydraulic head difference Hc in many cases, but give excessively small or large estimations in some cases. (3) The effects in the case of upstream residual soil on Hc values are as follows in descending order: 2D, 2DC, 3D, and AXS. The effect of 3D is almost the same as AXS.
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  • Yoshiaki SUNAGA, Hiroyuki MATSUI, Kazutoshi OSAWA
    Type: Technical Papers
    2017 Volume 85 Issue 2 Pages II_113-II_119
    Published: 2017
    Released: December 06, 2017
    JOURNALS FREE ACCESS
    We investigated the temporal change in particle size distributions of suspended solids (SS) in the irrigation water and the drainage water at paddy fields located in Utsunomiya. We clarified the followings. First, the particle size distributions of SS in the drainage water tended to be coarse as the time proceeded from the paddling and transplanting period, while the particle size distributions of SS in the irrigation water tended not to change. Second, large amounts of fine fraction were discharged from paddy fields when turbid water containing a high concentration of SS was discharged during the paddling and transplanting period. Third, fine fraction tended to become suspended in paddy fields and be discharged from paddy fields under no rain condition. Finally, an proper turbidity - SS concentration calibration line is desired for the paddling and transplanting period and the other period, since particle size distributions of SS in these periods are different.
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