Many of the paddy fields in Japan, constituting about 20% the total paddy field area, have recently been converted temporarily to dry farming without major change in the geophysical features of the land or irrigation equipment.
The reason for this is to cut down on the over-production of rice. These paddy fields are referred to as “multipurpose paddy fields” in this paper. They require many miles of additional pipe drains.
Since the publication of the first Standard Design Book of Irrigation and Drainage Engineering, Division of Planning of Pipe Drain in 1955 and its revision in 1977, the development of pipe materials, machines and research on planning and practice have been continuosly carried out.
The authors studied on-farm water management and on the basis of the results obtained, propose a method for the design of pipe drain systems in multipurpose paddy fields.
The following results were obtained;
(1) By equation L=2H√k/D, determination is made of pipe drain spacing (L), where D is the requirement for pipe drains, k, hydraulic conductivity, and H, the depth of the permeable layer (surface cultivated soil layer).
(2) Using equation 1/L²=1/a²+1/b², the spacing of pipe and mole drains for a combined drain system is determined, where a and b are the spacings of pipe and mole drains respectively.
(3) k in this equation must use the modified k_s determined by α(k=αk_s) where α is the modification coefficient and k_s, the hydraulic conductivity observed in a field.
(4) On-farm water management and integrated drainage systems are discussed.

View full abstract

Our previous paper presented three equations, L=2H√k/D…(1) 1/L²=1/a²+1/b²…(2) k=α·k_s…(3) where L is the spacing of pipe drains, H, depth of the permeable layer, k, hydraulic conductivity, D, requirement for a pipe drain, a and b, spacings of pipe and mole drains for a combined drain system, k_s, hydraulic conductivity observed in fields, and α, the modification coefficient.
On the basis of hypothetical considerations, the authors believe the hydraulic conductivity k in the equation (1) to be very different from k_s, observed in fields. The reason for this is that aggregates, cracks and fractures influence soil structure and effect on hydraulic conductivity. Even the hydraulic conductivity of fractured or blocky structured clayey soil is often much higher than that of sandy soil. Unfortunately, it is very difficult to determine directly the actual k for an entire field, such as by the auger hole method.
The present paper presents a method for determing the actual hydraulic conductivity k for an entire field using the hydrograph of a pipe drain discharge observed in a field already installed with pipe drains on the basis of k_s measured in a field and equation (3). The procedure for obtaining pipe discharge and the estimation of α is presented.

View full abstract

In previous two papers, the theory for the design of pipe drains for multipurpose paddy fields was presented using the following three equations, L=2H√k…(1)
1/L²=1/a²+1/b²…(2) k=α·k_s…(3) The procedure for determing each factor in a field using the hydrograph of a pipe drain discharge was also discussed.
The authors investigated a number of hydrographs and field measurement data for pipe drains installed in fields and estimated k and α. The following results were obtained.
(1) Modification coefficient α values were approximately 50-100 for k_s=10^-4 cm/s, 100-500 for k_s=10^-5 and 500-4000 for k_s=10^-6 respectively.
(2) Use of the modification coefficient α is one possible means for representing soil structure.
(3) Pipe and mole drains for a combined drain system designed on the basis of equation (2) were found to greatly improve field drainage espcially for difficult soil. The discharge of mole drains was 70-90% that of the total drain discharge.
(4) On the basis of the above findings, a standard design for pipe drains and pipe and mole drains foa a combined system was made for actual use in fields.
(5) The table for design of pipe drainage was provided for practical use, regarding to spacing, hydraulic conductiuity, depth of permeable layer and requirement for a pipe drain using the modification coefficient (α)

View full abstract

Energy budgest of rice planted paddy fields are discussed, and a new water temperature estimation method is proposed to avoid cold weather damage to rice. Energy budgets and water budgets data were collected from the experimental paddy fields during the summer of 1984 in Fukagawa, Hokkaido. They show that the heat transfer coefficient is small at night, and big and fluctuating greatly during the daytime. Although it has been often treated as a wind function, its relation to time is clear than to wind. The new temperature estimation method, using the heat transfer coefficient as the time function, is in good agreement with the observed values. This method is applied to other paddy fields about 8 km from the experimental fields. The results show that this method also gives good estimates here, and prove its availability.

View full abstract

A laboratory study was carried out to make a comparison of single-, double-and dual-gamma ray measurements of soil and water. The beam was produced by placing a 45-mCi source of ¹³⁷Cs behind a 100-mCi source of ²⁴¹Am and was collimated through a narrow slit. The equipment was designed to move vertically and horizontally, stop at any distance within an accuracy of ±0.1 mm, measure the counts of gamma rays and calculate the average intensity automatically. A scintillation probe was connected in parallel to receive both pulses in a band of 572-818 keV (for ¹³⁷Cs, a 662-keV peak) and pulses in a band of 30-86 keV (for ²⁴¹Am, a 60-keV peak).
The differences_ofAmass absorption coefficients of soils obtained through the single beam method and the dual beam method were mainly attributable to correction of the ²⁴¹Am background intensity in the dual beam method, which was caused by ¹³⁷Cs in the low energy band. The thicknesses of materials were well predicted with the single beam method and the double beam method but poorly predicted with the dual beam method. The bulk density of a volcanic ash soil column was estimated excellently with the double gamma beam method but the water content was slightly underestimated. Using the method of Gardner et al. theoretical variances of bulk density or water content could be estimated as functions of the thicknesses.

View full abstract

It is well known that anisotropy of undrained shear strength exists in many alluvial clay deposits. The strength anisotropy of Ariake marine clay deposits was investigated by direct shear tests and the results obtained are summarized as follows.
(1) Anisotropy of undrained shear strength (S_u) exists in all layers of Ariake marine clay deposits except for the surface layer at a depth of 0-2 m. If α is the angle between the shear plane and the horizontal plane, the S_u of Ariake marine clay deposits indicates a maximum value at α=45°-60° in active shear and a minimum value at α=30°-45° in passive shear. If specimens are sheared in a Y-direction perpendicular to the X-Z plane on which a vertical section of clay layers is defined, S_u is nearly equal to those horizontal shear value regardless of the value of α.
(2) The difference between shear stress-displacement curves and normal stress-displacement curves in constant-volume direct shear tests between active and passive shear is large. This indicates that the dilatancy is different in active and passive shear.
(3) It is reported that remarkable strength anisotropy exists in clays which have a low plastic index(I_p). In Ariake marine clay deposits, however, there is no correlation between the magnitude of strength anisotropy and I_p, and remarkable strength anisotropy exists within the range of I_p=30-80.
(4) For practical purposes, the trend of strength anisotropy of Ariake marine clay deposits is well explained by eq.(4) and eq.(5) which are derived from the equation proposed by Casagrande and Carillo. For Ariake marine clay deposits, the ranges of parameters a and b in eq.(5) are a=-0.15-0.45 and b=0.05-0.35.

View full abstract

A centrifuge is a quick means for obtaining the relation between soil wetness (W) and suction (h), and is widely used for this purpose in Japan.
This method encounters problems such as the existance of suction profiles in soil samples, movement of water in continuous system following centrifuging and the influence of soil compaction due to soil weight in the centrifugal force field. In this paper an examination is made of the influence these problems have on the W-h relation measured, and the most ideal method for using a centrifuge is proposed.
The average wetness (W) of a soil sample measured can be regarded as an approximation of the proper functional wetness corresponding to average suction (h) determined as follows.
_??_
where, r₀, r₁, r₂ are the distance from the axis of rotation to the boundary h=0, and the lower and upper plains of the sample, respectively. d₀ is sample radius and ω and g are the angular velocity and acceleration of gravity, respectively.
If the function W (h) is linear, W is always equal to W (h), but generaly, non-linearity of W (h) results in a difference between W and W (h). However, such a difference is lessened by placing the soil sample on a ceramic plate, since the suction range in soil becomes narrow and W (h) can be approximated linearly within such a range.
Two experiments were carried out on three types of soil using a centrifuge; one with a ceramic plate and the other without a plate. The results were compared with data obtained by the other methods using a suction plate, pressure plate, and a vapor pressure method. The data obtained using the ceramic plate agreed with those from other method.
Moisture flow from a ceramic to soil sample following centrifuging could be estimated by an additional check of centrifuging ceramic alone, and soil moisture content which were in equilibrium could be accurately determined.

View full abstract

When the effect of seepage control and the safety of banking structure (for example, embankment dams, river embankments) and natural foundations are examined, the seepage analysis is very important. Most natural foundations consist of several layers which have mutually different physical properties and it must be considered that many banking structures consist of several layer in the light of constructional properties, too.
For free surface seepage, most of the previous finite element procedures involve modifications of the finite element mesh below the free surface with successive iterations. But, it is difficult to analyze free surface seepage through the layered porous media by these procedures because of the modification of the finite element mesh.
There are some finite element procedures based on the invariant finite element mesh concept which were investigated by Desai, Bathe & Khoshgoftaar and Neumann. However, under the present condition the.procedure investigated by Neuman (N procedure) is impractical because it has physical constants which are difficult to determine without knowing the unsaturated seepage.
In this paper, the suitability of the finite element procedures investigated by Bathe and Koshgoftaar, and Desai (B-K homogeneous procedure, and D procedure) only for analyzing the free surface seepage through homogeneous porous media were studied for analyzing the free surface seepage through layered porous media along with their respective characteristics.
It was concluded that the two approximate finite element procedures are proper for analyzing free surface seepage through layered porous media.
Following are the characteristics of the two procedures:
1. The free surface locations by B-K procedure are affected locally by the finite element mesh.
2. The free surface location by D procedure is affected wholly by the finite element mesh.
3. Sometimes, because of the characteristics 1. and 2. above, the free surfaces located by the two procedures have hardly any difference. Since both the procedures utilize almost the same input data, the same model should be analyzed to check the free surface location by cne procedure with the other.
4. The discharge by B-K procedure has generally bigger reliability than the one by D procedure.
5. With B-K procedure, approximate discharge is calculated fairly easily because only small computation error arises even if free-surface is not taken into consideration.

View full abstract

Remote sensing analysis of Landsat MSS data has been studied for more than ten years with good results being obtained in some fields. However, it is still insufficient for really practical purposes, for example, in the case of land use classification. That is mainly because of the existence of mixed pixels in the images of Landsat MSS data. The problem of mixed pixels is very difficult but important.
So a new method for geometric corrections over a small area of Landsat MSS image has been proposed in this paper.
The original image data of Landsat MSS of the Kanto plains was analyzed in this paper. This MSS data was very precisely corrected with the new geometric corrections method developed in this paper. Then, the relation between the MSS values of the mixed pixels and mixture rates of land covers in those mixed pixels were statistically examined by sampling mixed pixels in which mixture rates of land cover were various.
The results are as follows:
a) The new method of geometric corrections is proposed and its efficiency is certified.
b) The mixing method seems to hold in the case of the pixels in which two land covers are mixed, paddy field and asphalt pavement.
As a result of this, a more precise analysis of remote sensing will be possible.

View full abstract

In this study, the ultimate strength theories of reinforced concrete section are investigated probabilistically.
Ultimate bending moment depending upon the popular Hognestade and Whitney theory, and also the Elastic theory which is basic for the working stress design are probabilistically examined. The equations for calculating an ultimate bending moment are based on some assumptions and contain adjusting coefficiens. These assumptions and t coefficients are considered to provide safety margin against variations of the moment. For quantitative evaluation of this safety margin an unexcess probability is applied, which expresses the probability of ultimate bending moment not exceeding its deterministic one with each theory.
Some of the conclusions derived are as follows;
(1) For tensile failure, the safety margin of each theory is unvaried for different design condition and there is no wide difference between the degree of safety margin of each theory.
(2) However, for compressive failure, the safety margin shows different characteristic for each design condition and its degree varies from one to the other.
(3) With elastic theory, as compared with the other theories, under any design condition the results are always on the safe side.

View full abstract