The aim of this study is to evaluate quantitatively the influence of characteristics of rock, depth of ponding and filling rate on hydraulic fracturing of rock foundation and is to propose the criterion for hydraulic fracturing in rock foundations of embankment dams. The hydro-mechanical coupled finite deformation analysis using Cam-clay model was applied as the evaluation method. In this paper, three kinds of laboratory hydraulic fracturing test for rock and clayey soil materials were simulated to approve the validity of this method before proposal of the criterion. As the result, by using the tensile strength of material and the yield surface of Cam-clay model as failure criterion, it can be seen that failure initiation from borehole surface or notch/slit edge and the injection pressure at hydraulic fracturing could be evaluated. The method to determine the Cam-clay parameters for rock, particularly compression and swelling index and yield stress, were considered.

View full abstract

In this paper, the influenceofthe depth of ponding and the filling rate on hydraulic fracturingofrock foundation is evaluated quantitatively by considering the characteristics of rocks, and the criterion for hydraulic fracturing in rock foundations of embankment dams is proposed. For that purpose, the finite deformation analysis, of which the validity was approved in the companion paper, was used and the failure propagation due to pressure of ponding from the edge of a single fracture was simulated by considering the measured material properties of 297 kindsof rock. As the result, the criterion for hydraulic fracturing was proposed as a chart with non-dimensional parameters, i.e. the ratio between water pressure at hydraulic fracturing and the overburden pressure (γ_wh_c/σ₀), the ratio between filling rate and hydraulic conductivity (v_a/k) and the critical state parameter (M). The effectiveness of the criterion was checked by application to the failure of Teton dam. To make the criterion with applicability for general situation, the extension of criterion to general rock mass was examined by using the mechanical properties deduced from the rock classification.

View full abstract

In Public Communication, the planner must give information to residents for clearing their misunderstandings that distort their valuation of the project. For that purpose, I built the parametric model that specifies these misunderstandings in Awase reclamation project in Okinawa. In the project which will lead to destruction ofthe environment, the residents who highly concern the environmental issue may have the different structure of valuation from that of the residents who do not. If so, the population must be segmented. In this paper, I investigated this by using bootstrap Chow test and concluded that the structures of the project valuation between these 2 groups were significantly different although each parameter estimate was not seriously different.

View full abstract

We surveyed the current situation that irrigation water users associations face in the Kanto region and classified their drought susceptibilities by means of a questionnaire-based survey. The following facts were obtained: 1) 80% of the water users associations see the puddling and transplanting period as being the most critical period; 2) pipeline systems tend to mitigate the disparity in water availability between upstream and downstream users; 3) the water users associations take care to be impartial over the whole beneficiary area when responding to drought conditions; 4) drought impact can be shown as a power function of the irrigation water deficit rate, and the exponent of the function can take a value of less than unity depending on the associations' situation; 5) the drought susceptibility of water users associations is not constant over the irrigation season and varies according to the cropping stages; and 6) the drought susceptibility of Tochigi and Gunma Prefectures, located at the upstream sections of the Tone river basin is relatively low, but that of Saitama and Chiba Prefectures, located on the south side of the Tone river, is high.

View full abstract

Water plays a prominent role in rice production. The continuous presence of water on rice fields also generates water percolation and groundwater recharge, which are often beneficial for other water uses. The experiment was conducted during summer 2002 in two locations, one with subsurface drainage and the other without subsurface drainage. This field experiment evaluated the suitability of irrigation water level for two new and short rice crop varieties under different subsurface drainage conditions. Results indicated that the water losses due to percolation might be quite high in irrigated rice cultivation in Egypt. The reduction of amounts of applied water was more pronounced in experimental fields without subsurface drainage status as compared with subsurface drainage status. The mean values of applied water increased with increasing irrigation water level under both drainage conditions. With regard to the water use efficiency (WUE), treatments without subsurface drainage status achieved higher values. Regarding to irrigation water levels, controlled water level at zero cm achieved the highest values of WUE for both drainage conditions with and without subsurface drainage. The data clearly showed that treatments without subsurface drainage status gave higher grain yield. Rice grain yield increased in the two selected varieties with increasing controlled water depth. The subsurface drainage status improved soil salinity characteristics by reducing SAR_{1: 5}, EC_{1: 5}, and total anions and cations in all the analyzed soil layers. Rice cropping and water management with deeper ponding depth led to improved soil salinity characteristics.

View full abstract

Surfactants are used in detergents, shampoos, chemical fertilizers, agricultural chemicals etc., and much amount has been discharged to the environment. Their adverse effects on the soil environment are suspected. In this study, sodium dodecyl sulfate (SDS) solutions of different concentrations were infiltrated with capillary rise into dry material columns in order to investigate the influence of the anionic surfactant concentration on water infiltration. The capillary rise equation was proposed and the influence of SDS was explained by using this equation. For hydrophilic inorganic materials, glass beads and sand, infiltration rate decreased as the SDS concentration increased due to the decrease of the surface tension of the solution. For hydrophobic organic materials, polyethylene particles and peat, infiltration rate increased with the SDS concentration mainly because of the decrease of the contact angle. For leaf mold, infiltration rate decreased as the SDS concentration increased probably due to the development of swelling.

View full abstract

A notion that larger-scale irrigation development is more advantageous from the structural perspective is commonly accepted on the basis of experiences in practical works, however it has not been fully analyzed yet. This paper aims to identify factors affecting the “economies of scale” of irrigation development projects from structural aspects utilizing examples of projects planned by Japanese ODA.
Three factors affecting the economies of scale of irrigation development projects are identified as the one related to; 1) water resource development potential, 2) designing of irrigation facilities, 3) construction works. This paper showed that economies of scale can be applied to each factor. In addition, when the project sites do not have difference in natural conditions, the principle of the economies of scale can be valid among different irrigation schemes of different scale.

View full abstract

Effect of floc density on the size distribution of soil sample determined by sedimentation is analyzed by comparing the result of conventional method and that based on the newly proposed method. In the proposed method, the relation between the settling velocity and the diameter of a soil floc determined by the experiment is incorporated into the analysis of pipet method. Experiment was conducted using Kunigami maaji soil picked at the field of sugar cane in Okinawa island. Tow types of soil sample treated with 0.1M CaCl₂ solution and 0.1g/l (HPO₃) ₆ solution were prepared. The power law relation between the floc density and the floc diameter was confirmed from the measurement of the settling velocity against floc diameter. No significant difference in the relation between V_f and D_f was found even if the sample was treated in different manner. In the analysis of size distribution, the proposed method was found to give a successful result for the sample treated with CaCl₂ solution. However, result in dispersed sample didn't agree with result of microphotograph in a range below 10μm. This inconsistency was interpreted as unique colloidal characteristics of the soil sample.

View full abstract

Evaluation of soil properties from laboratory test results usually faces serious problems due to limited data available and often large scatter caused by sample disturbance. So, the in-situ testing methods are desired to establish the method to predict directly soil properties. The electronic cone penetration tests are the most widely used in-situ test for foundation design, liquefaction analysis and determining stratification with excellent potential.
This paper discusses the electronic cone penetration test results, which were carried out at six sites of Ariake clay to predict the wet density ρ_t as a physical property and undrained shear strength s_u as a mechanical property. A semiempirical equation was derived to predict the wet density of clay. Electronic cone factor N_kt was derived as a function of roughness of cone surface and sensitivity ratio s_t. N_kt value of 11 was proposed to predict the values of S_u for highly sensitive clays.

View full abstract

It is important to estimate the distribution of permeability for the environmental impact assessment of construction of agricultural facilities. The budget for the in-situ investigation is, however, going to decrease because of governmental cost-cutting. In this case, if the other properties are used for the estimation of permeability, the cost for the in-situ permeability test will be controlled. In this study, to raise the accuracy of the estimation result by the indicator simulation, the method to clarify the difference of cumulative probability distribution in each class of the soft data is introduced. To validate the proposed method, the hypothetical field having a given distribution of permeability and the other data is firstly examined, and the proposed method is proved to be effective. Then, actual data obtained at a field are applied for the proposed method. It is found that the accuracy is improved by using the multiple properties giving the good estimation by themselves.

View full abstract

Under recent severe agricultural situations, land improvement districts (LIDs), which maintain and operate irrigation and drainage facilities, need to strengthen their management structure by a merger of LIDs. The purpose of this paper was to analyze effects of the merger of LIDs by the financial analysis and questionnaire data from the Teshiogawa LID in Hokkaido. The results indicate that economic merits in the merger of LIDs were realized i) by reduction of management costs after restructuring of directors and representatives, ii) by building a group of technocrats for operation and maintenance after integration of bureaus, and iii) by reduction in the non-monetary burden of members through a decline in the frequency of their obligation to serve in the managerial posts in turn. The primary factors causing above merits are changes in O & M activities, treatment of differences in financial affairs between old LIDs, and transmission capacity of information between LID and members.

View full abstract

Divided channel method is practical method to analyze the flows on the compound or locally vegetated channel. In the flow resistance prediction on non-uniform flow, lateral flow effect at the boundaries of divided channel should be considered as same as apparent shear stress. In this study, new semi two-dimensional calculation method was proposed by using continuity and momentum equations which included lateral flow term, and verified with non-uniform flow experimental data. As the result, proposed model performed good agreement with observed data, and momentum transfer by lateral flow was significantly important compared with apparent shear stress on the nonuniform flow region.

View full abstract

This case study in Ehime Prefecture aims to clarify the basic conditions and characteristics of high abandoned paddy ratio area under the Rice Production Adjustment System (Seisan-Chosei of Rice). The data of whole paddy fields under its system are analyzed by a unit of municipalities to classify them into 5 types from a view of paddy usage and management. The basic conditions and characteristics of the types with a high abandoned paddy ratio area are followed;
1. “Urbanizing Area” and “Mountainous Area” classified by the way of “Classification Agricultural Area”
2. With the 20-50% paddy area in the whole cultivated area
3. With 15-50a of paddy area per a farm household
In these type, a lack of labor and less favored foundation are also causes of paddy abandonment. It is also pointed that the present system of the Rice Production Adjustment System (Seisan-Chosei of Rice) has causeda division or set-a-side of whole lot of paddy field, resulting in dilapidation of paddy field.

View full abstract

The influence of differences in release operations on flood mitigation function of an agricultural dam during a flood is simulated by means of runoff analysis and one-dimensional unsteady flow analysis in a case study of the Anou Dam. The results quantitatively showed that the differences in peak inflow discharge and peak release discharge decreased, and the flood damage in a downstream area increased with exclusion of artificial release operation during flooding. These results indicate that deterioration of maintenance and management system of the agricultural dam with spillway gates lead to failure of its flood mitigation function.

View full abstract