It is important to evaluate characteristics of tensile strength of foundation and embankment material of fill-dam for the examination of the development conditions of crack which is one of the causes for hydraulic fracturing. Though it is possible to evaluate the tensile strength of hard rock by fixing both ends of the specimen with chucks and making it work directly, it is not possible to use the same method for soft material like cohesive soil. Hence direct tensile test was performed in this research to measure the tensile strength by changing the column type specimen for the compression test into an I-shaped specimen and using the devices that were experimentally-made for the test. Moreover, the stress generated in the specimen was calculated by the FEM analysis and the form of the specimen for the direct tensile test was suggested. It gave useful result for the direct tensile test, with the specimen being further thinned only in the center part of the I-shaped specimen.
One of the usual methods to prevent wind erosion is to sustain humidity of the soil surface by irrigating the soil. However, there have been no such specific methods defined in agricultural engineering. To define a concrete standard of preventing wind erosion, several irrigation methods, applying various irrigation intervals and water amounts, had been simulated by using a model to predict soil moisture dynamics under weather changes and irrigation events, from a case study of Oku-Nakayama upland in Iwate Prefecture. As a result of the simulation, it was found that applying usual intermittent irrigation, which requires shorten irrigation intervals, is not practical to prevent wind erosion due to the causes of frequent irrigation application and increased water requirement. On the other hand, timely irrigation to apply sufficient water when the soil fairly dehydrated contributes to effective prevention of wind erosion decreasing both irrigation intervals and water requirements. Although considering sprinkled water is susceptible to wind, this method was verified that the applying timely irrigation water is practicable to protect soil surface from wind, supposing enough irrigation facility capacity is substantially secured. Moreover, it was estimated additional capacity of irrigation facility for design adopted the function for preventing wind erosion under this method.
Frogs often drown in agricultural canals with deep concrete walls, which are installed commonly in paddy fields after land improvement projects in Japan, because they cannot escape after falling into the canal. Therefore, countermeasures that enable frogs to escape from canals are required in some rural areas. An experimental canal with partially sloped walls was used as an escape countermeasure to investigate the preferable angle of slope for the walls, water depth and flow velocity that enables Tokyo Daruma Pond Frogs (Rana porosa porosa), which have no adhesive discs, to easily escape. Walls with slopes of 30-45 degrees allowed 50-60% of frogs to escape from the experimental canals, frogs especially easily climbed the 30 degree sloped walls. When the water depth was 5 cm or flow velocity was greater than 20 cm/s, approximately 80% of the frogs moved downstream and reached the sloped walls because the frogs' toes did not reach the bottom of the canal. However, if the depth was 2 cm and the flow velocity was 5 cm/s, only 4% of the frogs climbed the sloped walls because they could move freely. The frogs appeared to not be good at long-distance swimming and could not remain a long-time under running water. Therefore, walls sloped less than 30 degrees and control of both water depth and flow velocity appears important for enabling frogs to easily escape from canals.
The surfaces of the servicing concrete structure for irrigation and drainage have the denuding aggregates. Various diagnoses can't be done properly by the test method for ultrasonic pulse velocity, because close adhesion between pulse terminal and aggregate denuded concrete surface is insufficient. In this research, the solution of this problem by coating method that mediated material is applied to the concrete was examined. As a result, the ultrarapid hardening cement and the epoxy clay were suitable as a mediated material, and the method to evaluate ultrasonic pulse velocity of the coated concrete by the mediated material were clarified. Moreover, the method to evaluate rebound number and impact points of the coated concrete by the mediated material was recommended.
This paper presents the experimental study on the agricultural use of sludge dredged from farm pond and its effects on plant growth. Komatsuna was used as the test plant and two types of soils, containing 10 and 30% of the dredged sludge mixing in decomposed granite, were prepared. The test results have revealed the relationship between the physicochemical characteristics of the sludge and the plant growth. The following findings have been clarified: 1) The soil with 10% of the sludge was suitable for the plant growth because the water retention adaptability was improved; 2) When the soil contained the excessive amount of the sludge, the plant growth was prevented due to the decreased drainage in the soil; 3) The soil containing dehydrated sludge grew the plant better than the soil containing the sludge without any treatment because of coagulant; 4) Inorganic component of dredged sludge had little influence on plant growth. Using composite soil with 10% of the sludge by soil dressing was beneficial, since it is important from the resources recycling point of view.
Characteristics of hydrological runoff in an artificial coniferous forest with delayed thinning were evaluated by comparing with hydrological data collected simultaneously in a reference watershed. In addition, the effect of thinning on the runoff was evaluated. An obvious increase in base flow was observed after thinning, and the main reason for this increase was thought to be the decrease in evapotranspiration by thinning. The increased base flow was observed for at least three years in the watershed with delayed thinning and for one year in the reference watershed. The runoffs on rainy days in the watershed with delayed thinning tend to be larger than those in the reference watershed in the cases of small or moderate runoffs. On the other hand for the drought-period runoffs, obvious difference is not found in the two watersheds with the effect of thinning being excluded.
From among the methods of computing one-dimensional unsteady open channel flow, space-time conservation method is picked out, which has flux limiter functions to prevent numerical oscillations and whose settings of various boundary conditions are easy to handle, that are decided by water control structures, discharge, water depth, etc. Then calculation methods in boundary sections which use the same algorithms as interior points are presented. As a consequence of improvement of algorithms in boundary sections at abrupt bed slope changing, the scheme becomes possible to compute equations without a numerical oscillation even in transition part from subcritical to supercritical flow or hydraulic jump. It is showed that the scheme that we propose is effective as a result of comparing numerical solution with theoretical solution for the analysis of reflection of bore and comparing numerical solution with steady water surface obtained by calculation of water surface profile for the analysis of flow in channel that has bed slope changing.
The water content and water potential of soil samples from paddy fields with varied cropping histories were measured under low water potential conditions. The relationships between the water content and the water potential were fitted to power equations. Analyses of the results for the fresh soils showed that the coefficient a (the water content at water potential of -1MPa) (CA) and the absolute value of the exponential index b (AB) of the fitted power equation was smaller in the soils under the cultivation of upland crops than the wetland rice. On the other hand, the difference in CA and AB for air-dried soil was not revealed between the soils under the upland crop cultivation and the soils under the wetland rice cultivation. The difference in CA for the fresh soil and for the air-dried soil and the difference in AB for the fresh soil and for air-dried soil were found to increase with continuous cropping of wetland rice, and decrease in response to continuous cropping of upland crops. These finding suggest these indices can presume cropping histories of rotational paddy fields.
Sloped farm field technology can provide rapid and effective surface drainage and surface irrigation for restored fields by sloping farm fields. However, there are concerns regarding the impact on farming due to cutting and banking during reclamation. There are also concerns about the growing burden on farmers who promote large-scale land use agriculture, considering that working hours are expected to increase due to reclamation involving soil conveyance. From the results of a survey on the influence exerted by cutting and banking depending on the soil physical properties, it has been found that the influence on three-phase distribution and soil hardness can be reduced by applying the surface soil of a certain thickness without creating any problems for farming. In addition, any subsidence by banking or reduction in level accuracy due to secular changes has not been found. By efficiently using a laser leveler, the number of working hours for the reclamation of a sloped farm field can be reduced to about that required for a conventional reclamation, and, as a result, cost reduction and labor-saving is achieved in sloped farm field technology.
Soil is known to exhibit hydrophobic properties after a forest fire. Experiments conducted by DeBano et al., (1976) showed that the organic compounds in the soil become volatized under high-temperatures, move downward along the soil temperature gradient, and form a hydrophobic layer deep within the soil profile. However, less is known about effects of oxygen atmosphere on morphological changes of organic matter in soil. In this study, we sought to clarify the increase in soil hydrophobicity as well as the changes in carbon and nitrogen content in response to heating of the ground surface in the field and both column and muffle furnace heating in the laboratory. In the muffle furnace burning, soil samples heated under oxygen-deprived conditions exhibited similar carbon and nitrogen dynamics and increased hydrophobicity with temperatures those observed in the field and column experiments. Soil samples under oxygen-deprived condition showed hydrophobicity and some carbon content by heating with 300°C and higher, while almost no carbon remained after heating with 400°C under oxygen available condition. Soil C/N ratio increased by heating with higher temperature under oxygen-deprived condition. Results suggested limited supply of oxygen might have an effect to produce soil hydrophobicity under soil surface burning.
To achieve the simultaneous measurements of sediment-surface-level hsed from the rod tip of probe set through water and sediment layers and electrical conductivity in water σw based on time domain reflectometry (TDR), a coupled-measurement model was tested for the both measurements in laboratory. In the model, the level hsed was estimated by partial-range propagation method (PPM) or whole-range propagation method (WPM). PPM is based on travel time tw of microwave step-pulse through only water layer, whereas WPM on travel time tt through water and sediment layers. By applying the estimated hsed and electrical conductivity σt around the rod, which can be measured by TDR probe, to the model, we estimated σw. Experimental results under conditions of σw= 0.005–0.103 S m-1 showed that the estimation errors of hsed and σw in PPM maintained low, while those in WPM increased with higher σw. As σt or the rod length increased, the electrical energy loss during propagating would expand. Therefore, the error of tt augmented with the loss, as well as low sensitivity of tt to the hsed-variation, could have induced the inaccuracy in WPM. Moreover, the maximum rod length Lmax, less than which we can measure hsed and σw under some σw-condition, was analyzed based on the energy loss theory. The result suggested that we can assume Lmax is approximately 4 m when measuring in typical river, in Japan, having σw= 0.013 S m-1.
Capillary barrier is the simple soil layer system which is composed of the fine soil (sand) layer underlain by the coarse soil (gravel) layer. The capillary barrier of soil was constructed in sand slope, and volumetric moisture contents in the soil were successfully measured together with precipitations for about four months. Soil moisture changes in the gravel layer were well compared those in the sand layer to confirm a practically excellent divergence of infiltration water along the tilted interface between the sand and gravel layers. The field measurement detected a possible percolation or breakthrough of water flow along the interface into the gravel layer. A divergence length of the capillary barrier where the percolation or breakthrough of water flow into the gravel layer occurred was estimated using soil properties determined by laboratory tests and structural configuration of the capillary barrier of soil. A fairly good correspondence of the divergence length between the observation and the estimation demonstrated a practical effectiveness of the equation previously published to calculate the divergence length. This should lead the capillary barrier of soil to an alternative and effective measure for soil slope stability because the divergence length determines the soil layer structure as well as the soil materials employed in the construction.
Based on previous research results concerning environmental conditions of fish habitats in valleys of the Kokaigawa river basin, we propose a fish habitat environment model incorporating a three-scale micro-to-macro approach. To verify the generality of this model, investigative surveys were conducted at nine valleys in the Kokaigawa, Okawa, and Sakuragawa river basins. The results are as follows: 1) On the macro scale, a relatively high number of fish species are found in valleys that have large basins, deep canals, or a high rate of rice paddy fields. In valleys where water networks and deep canals have been constructed, habitats of the Numamutsu and Tamoroko species can be found. Furthermore, the number of fish species and habitat distribution is determined by particular attributes of water areas. 2) On the meso scale, habitat distribution and density are directly affected by environmental gradients. For example, water temperature affects Hotokedojo habitatsand the cumulative height of dams affects Numamutsu habitats. 3) On the micro scale, the layout and structure of canals are factors that qualitatively affect habitat density. 4) Applying the habitat environment model, the findings suggest that the environmental conditions that affect habitat distribution have a stronger impact than those affecting habitat density.
In the Shimajiri District of Okinawa, a project is underway to reuse treated wastewater as irrigation water. However, chloride ion concentration in treated wastewater is high here due to the infiltration of saline groundwater from damaged sewage pipes that are laid below sea level. It is thought that lowering this concentration will require rehabilitation of sewage pipes to prevent infiltration of saline groundwater. To incorporate such rehabilitation into agricultural land improvement projects and other undertakings, it will be necessary to ascertain the total length of sections in which saline groundwater infiltrates sewage pipes. In this study, we first clarified the concentration and flow rate of chloride ion in wastewater through measurements taken at manholes and other locations at which the possibility of saline groundwater infiltration exists. We then identified the length of a saline groundwater infiltration section within a typical extent in which such infiltration occurs, and then estimated the entire length of the infiltration section based on ratios of infiltration amount. We further considered methods for estimating the lengths of saline groundwater infiltration sections that would be applicable for general use.