The liquefaction of backfill materials induced by earthquake shaking may cause the movement of pipe bend resulting in joint separation. Thus, in order to prevent the movement of pipe bend buried in the site where only backfill material is liquefied, we propose a thrust restraint using soil-cement produced by grouting or mixing cement with sand as a backfill material. Dynamic centrifuge tests were conducted to validate the restrain method. The test results indicate the followings: (1) When only the backfill material is liquefied, the pipe moves mainly within the range of the backfill material and the original ground is barely deformed; and (2) placing the soil-cement as the backfill material around the sides of the pipe along the direction of thrust force can significantly reduce the pipe movement during an earthquake. Even if the excess pore water pressure generated in the sand―which is the backfill material―is transmitted to the soil-cement, which can resist the thrust due to its adhesive force.

Tsugaru area in Aomori prefecture is located in a cold snowy region and is known as a major apple producing area. The purpose of this study is to understand the mass and energy transport phenomena in apple orchard soil in gravelly brown forest soil by applying the field monitoring system (FMS). The author observed the characteristics of year-round changes in soil moisture, electrical conductivity and soil temperature from 2016 to 2020. Focusing on the characteristics of soil moisture, it was found that the apple orchard soil was in the process of drying during the 4-years observation period because of the cumulative total soil moisture change (ΣΔTSM) tended to increase. Regarding the characteristics of electrical conductivity (EC), a steeply and apparently increase in the soil solution EC with time was observed during the period when the matric potential was below -4,000 cmH₂O (corresponding to pF 3.6), which is the measurement limit (θ < 0.1 cm³/cm³). In addition, it was showed that the effect of fertilization in early spring was difficult to appear to the soil solution EC. Regarding the characteristics of the soil temperature, the fluctuation was small compared to the change in the soil temperature during the non-snowy period due to a heat insulating effect of snow during the snow cover period. It was found that the soil temperature at a depth of 10 to 100 cm decreased within a short period at the end of the snowmelt period, and the decrease in soil temperature became more remarkable in the deeper part due to percolate the snowmelt water.

The purpose of this study is to understand the behavior of macronutrients such as nitrogen, potassium and magnesium in apple orchards with gravelly brown forest soil in snowy and cold region. During from 2016 to 2020, including the period of snow cover and melting, which is the dormant period of apple trees, soil pore water was collected by porous cup and syringe from a depth of 10 to 70 cm in the apple orchard ones to three times per a month. pH, EC and the concentration of ion species of the sampled pore water overtime were measured. In May-September 2019, when the amount of precipitation was less than usual year, soil drying was remarkable, and reflecting the suppression (antagonistic effect) of magnesium uptake accompanying the promotion of potassium uptake in roots of apple tree, and the potassium-concentration of soil pore water was low. Therefore, the condition showing low concentration of potassium and high concentration of magnesium continued. The NO₃-N concentration in the soil pore water during the snowmelt period was higher than the after leaching by rainfall during the growing period. In addition, significant leaching of NO₃-N was observed due to the infiltration of snowmelt water at the end of the snowmelt period. However, it was revealed that the roots of apple tree are in a nutrient condition that enable to sufficiently uptake the NO₃-N remaining in the soil pore water after the dormancy breaking of apple tree. It was suggested that by continuing to understand the characteristics of year-round changes in soil pore water quality, it is possible to estimate the mode of nutrient uptake from apple tree roots.

The flood analysis method and its conditions were verified by comparing inundation depth data obtained from flood traces. The flood traces were left behind by the small earthen dam breach induced by heavy rain. Previously, a simplified flood analysis method was applied but it did not predict the local deep-inundated area which was identified from flood trace analysis. Adjustments to analysis conditions such as inflow hydrograph or roughness coefficient had little effect on simulated inundation depth and did not improve reproducibility. We then incorporated precipitation effect and wall structure to the flood analysis model. After making these improvements, the difference between simulated and actual inundation depth was <7 cm at all the observed flood trace points. These results indicate that considering the effect of rainwater outflow and / or barrier structures are important to reliable flood mapping of small earthen dam.

To establish a method of testing the abrasion resistance of cementitious repair materials in situ, we developed a portable sandblasting system and performed an accelerated abrasion test for mortar using this system to examine the appropriate test conditions in terms of the injection pressure and distance from the blast gun to the specimen (hereafter referred to as pressure and distance, respectively). Silica sand, with an average particle diameter of 0.5 mm, was the abrasive. The test results indicate that ‘0.20 MPa and 50 mm’ and ‘0.15 MPa and 25 mm’ were suitable combinations of pressure and distance, respectively, for evaluating the abrasion resistance within 2 mm from the surface. In addition, the two combinations yielded acceleration ratios of 630 and 510, respectively, in the water jet with sand for 10 h. It was confirmed that a depth gauge can measure the abrasion depth with the same accuracy as that of a laser.

Improving field drainage ability of converted paddy fields are required, but an evaluation method of the ability is not established. In this article, the evaluation method of the field drainage ability based on monitored soil water content (volumetric water content) was developed. The soil water content monitoring was carried out at 14 fields in Tatsuno city Hyogo prefecture (6 fields during soybean cultivation and 8 fields in wheat cultivation). In this method, t₁₀₀ (h) which is time required to decrease in soil water content equivalent to increase in one by rainfall event, was calculated by analyzing decline rate of soil water content following the rainfall event with an approximated exponential formula. The results of the t₁₀₀-evaluation and perspective evaluations by one who knows the properties of the fields in Tatsuno city were agreed well. It was confirmed that the proposed method in this article can evaluate the field drainage ability well.

Expansive additives that is used to reduce the cracking of concrete are admixtures, and develops chemical prestress under restraint conditions. Although adequate strength development by the use of expansive admixtures is an extremely important issue for the safety of the structure, the relationship between the restraining force during curing and the strength of the expansive concrete has not been sufficiently investigated. In this study, mortar specimens containing the expansive admixture are used, and the effect of changes in restraint conditions during curing period on strength development were evaluated from bending and compression test results. As a result, it was found that the appropriate confining pressure in the initial stage of curing did not reduce the strength due to drying. In addition, no difference in strength was confirmed due to the difference in the magnitude of the confining pressure applied during curing.

We applied the installation of a "corridor blockade fence" based on the analysis of agglomeration and connectivity of wild boar habitat to the site and verified its damage countermeasure effect. As a result, abandoned cultivated land may improve the agglomeration of habitats even if the area is small, but if a "corridor blockade fence" is installed in the part where the largest cluster of habitat can be effectively divided, habitat connectivity can be reduced. In addition, as a result of verifying the effects of "corridor blockade fence" by wild boar haunting frequency surveys using sensor cameras, captured wild boar population surveys, questionnaires and interview surveys, the synergistic effect of the "corridor blockade fence" and capture has significantly reduced the damage and infestation frequency of wild boars. It was also confirmed that even if the number of captured individuals are decreasing, the effect of suppressing the damage and infestation frequency throughout the site is continuously.

As for the flow passing through gates, it is becoming more and more necessary to evaluate not only the discharge but also the upstream depth in order to plan for flood management of the area upstream of the gates because of the extraordinary heavy rain fall in these years. The present study aims to formulate the mutual-dependence relation between the upstream depth and discharge of the flow under sluice gates in free flow condition employing momentum theorem. As the results, unique relationship was obtained between the upstream depth normalized by gate opening, h₀/a, and the normalized critical depth of open channel flow, h_c/a. The relationship proved to be expressed by a quadratic equation between these two dimensionless parameters from which expressions of the upstream depth and discharge of the flow in question were obtained. The obtained expressions showed both good agreement with the previous experiments and consistency with the previous discharge formulas.

This study proposed a new index, the canal detour degree index, to provide information for the functional evaluation of irrigation canals that support agricultural areas of hilly and mountainous areas. First, the proposed index was tested on a virtual geometric irrigation canal, which confirmed that the index varies with the detour degree and the number of detours. Next, the index was applied to 189 real-life irrigation canals in Japan and its relationship with the topography such as valleys and ridges was examined. The results confirmed that this index appropriately quantifies the influence of topography such as valleys and ridges in irrigation canals length. However, the relationship among the index, the canal length, and the intake elevation was unclear.

Agricultural pipelines generally have a curved pipe placed at the bending point to protect force due to internal pressure of a thrust block. On the other hand, a construction method in which the straight pipe is bent little by little and no thrust block method is effective. However, when a thrust block is used, a structural weakness appears when it is laid on soften ground or in the event of a large-scale earthquake, causing damage such as remove the joint. Therefore, polyethylene pipes, which can completely fused joint of pipes, have highly earthquake resistance and can be expected to be applied when they are constructed with pretty curved pipelines. However, polyethylene pipes have only a standard with an inside diameter of 300 mm or less about agricultural pipeline, there are few practical experiences. In order to confirm the safety when applying a medium diameter polyethylene pipes, a full-scale experiment was conducted. As a result, it was found that the thrust force generated in the integrated polyethylene pipe was widely dispersed in the curved pipe and was received in the entire pipe.

Shear bond strength between inorganic repair material and concrete with different conditions of calcium leaching and surface roughness were evaluated. It was confirmed that shear bond strength increased with an increase in roughness of concrete surface and that shear bond strength decreased due to calcium leaching from concrete surface. The decrease in shear bond strength due to calcium leaching was significant when concrete had smooth surface, resulting in quite small shear bond strength in this condition. However, such decrease is unlikely to occur in actual concrete structures used for water supply because flowing water causes not only calcium leaching but also selective abrasion of mortar on concrete. In contrast to concrete with smooth surface, in cases where concrete had rough surface so that aggregate was exposed, although shear bond strength decreased due to calcium leaching, it showed relatively high value.

This paper describes that a comparison between actual evapotranspiration (ETa) estimated by inverse analysis, recently proposed method by authors, versus the penman evaporation (Ep) and the complementary relationship evapotranspiration (Eac) using four sites climate data during about ten years. After confirming the reasonability of the daily ETa and Ep relationship, the monthly changes of the ETa/Ep estimated, resulting in the ratio is 0.7~0.9 during from April to October. And the monthly changes of the ratio exhibit almost the same through the sites. After confirming the relationship of daily and monthly change for ETa and Eac using energy load coefficient 1.26, the relationship presents that the yearly change of the Eac and ETa is almost coincided each other. Subsequently, we conducted the optimum determination of the coefficient by comparing the sum of daily ETa and Eac data, resulting in the coefficients 1.23~1.37. Then, the coefficients apply the four sites, resulting in the ETa and Eac very well coincided. From the above analysis we concluded that complementary relationship Eac is strongly supported by the inverse analysis ETa. On the contrary, the inverse analysis is supported by the complementary relationship, if apply Eac>0 constrain for complementary relationship.

We investigated the impact of paddy field water management practices on the reproduction of the endangered Tokyo Daruma Pond Frog, Pelophylax porosus porosus, in the paddy waters of the plain-field region. The relationship between young frog and tadpole emergence and paddy field water management practices was investigated in field block units (2017, 2018) and in every paddy field (2019). Field block unit surveys showed that the population density of young frogs was lower when the midseason drainage period was longer and was higher when the midseason drainage period was shorter, in 2017 and 2018. In the paddy field survey, young frogs and tadpoles were not found in paddy fields where midseason drainage occurred, but were observed at several peaks in the paddy fields where midseason drainage did not occur, in 2019. This case study has demonstrated that midseason drainage negatively affected the reproduction of this species. Further analysis is required to determine the relationship between the emergence of young frogs and tadpoles and the water management practices of paddy fields.

Although geosynthetic clay liners (GCLs) have been increasingly used in recent years for retrofitting small earth dams because of the shortage of core materials, design methods for small earth dams using GCLs have not yet been established. A challenge is that a method for drawing the phreatic line downstream of GCLs has not been developed yet, and calculations for the downstream embankment stability cannot be performed adequately. In this study, a parallelogram including a GCL was proposed as a virtual sloping core to apply the proven method for conventional sloping cores to the GCL. In addition, a method of determining the hydraulic conductivity of a virtual sloping core, including multiple soil materials, that is, an embankment material and a GCL, was proposed. It was verified through FEM of seepage flow that the phreatic line set using the proposed method was reasonable.

The damage of embackment in irrigation reservoirs is observed due to debris flow casued by heavy rain. In this study, model experiment is performed under various conditions from the Sabo-related plan to verify the load acting on the embankment of an irrigation reservoir. In the model experiment, the fluid force in the Manual of technical standards for the Sabo master plan is examined for an irrigation reservoir. The results show that the maximum load was due to the flow of the following sediment after the deposit of a part of the flow sediment. The ratio of the sediment load between the sediment load and the total load was larger because the inflow velocity was low. The calculation result of fluid force in the Manual of technical standards for the Sabo master plan is close to the differential value between the maximum load and sediment load.

Sheet pile construction has often been adopted for installations of pipelines in cases such as limited worksites or high ground water level. However, the sheet-pile extraction is likely to cause significant damage to buried flexible pipe. In the Japanese current design standard for irrigation pipeline, the influence of the sheet-pile extraction is empirically considered only by reducing the coefficient of subgrade reaction e´₀. Thus, the difference in construction conditions is not accurately reflected in the design. In this study, the model tests on the sheet-pile extraction were conducted under the difference conditions of breadth of sheet-pile, using the flexible pipe in which the 20 biaxial load cells were installed circumferentially. As a result, the significant decrease in the earth pressure acting on the pipe and most of the pipe deformation occurred before the lower end of sheet-pile was extracted to the top of pipe. In addition, the wider the breadth between sheet-piles in this study was, the smaller the pipe deflection was, because the reduction of horizontal earth pressure was suppressed and vertical one was decreased.

In irrigation facilities in the Tohoku region where concrete made with limestone (hereinafter referred to as LS) coarse aggregate is used, crater-like depressions have formed as a result of selective leaching of the coarse aggregate underwater. This study sought to clarify the mechanism of this phenomenon through field surveys, aggregate tests, and replication tests of coarse aggregate leaching using concrete specimen under various flow velocity conditions. In field surveys, leaching was confirmed in a precast concrete water channel made with coarse LS aggregate, a cast-in-place concrete water channel, and the spillway of a concrete dam. Abrasion test showed that coarse LS aggregate meets the JIS standard but is inferior to andesite coarse aggregate. Leaching replication test using coarse LS aggregate showed that the leaching depth of coarse aggregate is directly proportional to the number of days elapsed and more evident in areas with greater flow velocity; in addition, leaching depth of LS coarse aggregate was predicted as 0.5 mm/year at a flow velocity of 0.5 m/s.

Integrated flood control in the entire basin has been focused as a flood control. The flood mitigating function of rice paddy fields is expected to reduce direct runoff during rainfall events, and the installation of discharge control plate in a paddy-plot drainage tank has been attracting attention to enhance this function. In this study, we quantified the peak runoff mitigation effect of the installation of discharge control plates at paddy plots in the Yamato Plain, Nara Prefecture. As a result, the peak runoff mitigation effect was 30% and 21% for the non-irrigation and irrigation periods, respectively, when the 10-year return period rainfall was input to the runoff model. The sensitivity analysis of the model parameters related to the plot characteristics showed that the peak runoff mitigation effect by the discharge control depended on the ponding water depth at a plot at the beginning of rainfall, the factors that determine the amount of water flowing out over the weir board at the outlet of a plot, the infiltration rate of a plot, and the height of the top of the weir board. The peak discharge was stably reduced, indicating the effectiveness of the discharge control plate in the peak runoff mitigation.

We estimated the necessary irrigation quantity of water of the turf field by the simulation using a tank model to evaluate the influence that climate change gave to irrigation. The simulation intended for the past 41 years from 1979 through 2019. As a result, the necessary irrigation quantity of water was a tendency to meaningful increase, and the irrigation quantity of water was found to have risen 15% in 41 years. We performed a multiple regression analysis to assume necessary irrigation quantity of water as the objective variable, while the explanatory variable was meteorological conditions. Using a multiple regression type, we evaluated the influence that each meteorological elements gave for increase of the necessary irrigation quantity of water. As for the ratio of the increased factor of the necessary irrigation quantity of water, two of the temperature and the maximum consecutive dry weather days accounted for 81.1% of factors. In addition, the planning irrigation quantity of water was decided using past data, but it was shown that there is the possibility that the irrigation security degree decreases because necessary irrigation quantity of water increases as the progress of years.

In Japan, direct irrigation in agricultural facilities using treated rural sewage without dilution requires validation of sewage treatment processes and impact evaluation of soil by treated sewage irrigation. In this study, we evaluated water quality fluctuation in treated rural sewage, and examined additional water treatment processes for pathogen reduction using faecal coliform number as a human health risk indicator. We also cultivated tomato in an agricultural greenhouse and tested soil columns using treated rural sewage. The results suggest that for raw crops, additional treatment is desirable before irrigation with treated rural sewage, such as chlorine efficiency enhancement, UV treatment, or membrane treatment. Moreover, although the impact of the application of treated water on the soil environment could not be confirmed in the short-term cultivation of tomato in the greenhouse, the soil column test results suggest that salt accumulation in soil and changes in soil organic matter composition need to be considered when treated rural sewage is used for a long term.

The effect of the improvement of stabilized soil using lime and cement, and the collapse situation and the changes in unconfined compression strength after slaking history were experimentally investigated. In the case of a humid curing condition only, the cement-stabilized soil had a higher unconfined compression strength than that of the lime-stabilized soil, and the cement improvement was so effective in satisfying the type 4 construction generated soil standard. On the other hand, the hardening rate of the stabilized soil was faster in the lime-stabilized soil than that of the cement-stabilized soil. Next, the lime-stabilized soil had higher slaking resistance than that of the cement-stabilized soil, when the water content and the additive amount of stabilizer were in the same condition. In addition, from the results of the unconfined compression test for the specimen with the slaking history, it was clarified that moderate drying results in the increased strength of the stabilized soil, but a clear relationship was not particularly recognized between the strength and the slaking resistance.

To contribute to the formulation of a paddy irrigation plan that matches the actual farming conditions, the irrigation starting date and the planted rice type (use, cultivar) for each rice field were captured in the district, where rice cultivars were diversified, and introduction of rice for new demand was progressing, using multi-temporal Sentinel-2 satellite data and paddy cultivation ledger data. Subsequently, the relationship between irrigation starting date and planted rice types was analyzed based on the irrigation blocks. As a result, it was identified that the area ratio values of the rice fields, where irrigation had started before April 10th, differed greatly between irrigation blocks. One of the factors of the difference was the difference in area ratio of the rice fields planted with 'Akitakomachi' (very early maturing cultivar) between the irrigation blocks. Furthermore, it was identified that the soil puddling period for each cultivation category (early, medium-term, and late cultivations) should not be set uniformly within the target district, but rather for each irrigation block when calculating the required amount of irrigation water.

In this study, based on the soil constants obtained from the soil test results, the settlement of the Hachirogata clay ground were predicted by considering the consolidation theory and secondary consolidation behavior for the pipeline buried structure ground model. The coefficient of volume compressibility, the coefficient of consolidation, and the coefficient of permeability in the normally consolidated region were in the range of 10^-4 to 10^-2 m²/kN, 5 to 400 cm²/d and 10^-9 to 10^-7 cm/s, respectively and the coefficient of secondary consolidation increased as the stress condition approached the normally consolidated region, showed a maximum value of about 0.15, and tended to decrease with the subsequent increase of the pressure. It was found that the degree of consolidation at the start of secondary consolidation is in the range of 60 to 85%, and is particularly concentrated in 60 to 70%. As a result of predicting the settlement of the irrigation structure in consideration of the secondary consolidation, it was suggested that the differential settlement and reverse gradient between the main irrigation channel may occur based on the adopted calculation conditions.

In the joint repair work of irrigation channels, the joint filling method using sealants is often adopted for ease of construction and economic efficiency. However, some sealants used with the joint filling method generate deformations such as cracking and peeling within a few years following construction. In addition, their water stoppage often deteriorates. In this study, a test was conducted to confirm the water resistance and tensile properties of waterway sealants that have been submerged in water for a longer period as compared with those under the conventional test method. Results showed that the modified silicone-based sealant exhibited high water absorption and volume change rates as well as inferior water resistance. In addition, of the sealants examined in this test, the one-component modified silicone-based sealant and polyurethane-based sealant had changed tensile properties over a short period. They also exhibited greatly reduced adhesiveness when immersed in water for a long period.

A prototype of a radio-controlled mowing machine is developed for aquatic plants in irrigation canals by combining commercially available equipment and parts. An engine-driven brush cutter having an attachment with two disc-shaped cutting blades is utilized as the cutting device of the mowing machine. The hull of the mowing machine is a frame made of floats and aluminum pipes. The mowing machine could move forward / backward and turn right / left by the two outer wheels attached to the left and right sides of the hull. The wheels are driven by gear motors and independently operated by radio control. The purchase cost of the primary equipment and materials for the mowing machine was less than 180,000 yen. The total weight of the mowing machine was about 20 kg. The mowing machine went straight at about 0.36 m/s by rotating the two wheels forward and turn with a radius of about 0.74 m and an angular velocity of about 0.28 rad/s by reversing the two wheels in a still water state. The mowing machine could mow a plant community consisting mainly of Elodea nuttallii in an irrigation channel by radio control.