The authors evaluated the soil erodibility of 31 types of soil based on the measured soil loss from the first stage of rainfall and thin film flow, and, on the slope gentleness, presented decision criteria of soil erodibility for all soils. The soil erodibility was clarified by using the new terms: “clay ratio”, “increment of soil loss” and “ratio of erosion hazard”.
The major results are summarized below.
1. The prediction equation for soil loss for all soils is:
e_Dv=b₀+b₁x₁+b₂x₁₂+b₃x₁₇
where e_DV, is the soil loss (mm³/cc), x₁ is the “clay ratio”, x₁₂ is the coefficient of aggregation, x₁₇ is the natural logarithms of the infiltration ratio, and b₀=5, b₁=16, b₂-0.02 and b₃=-0.03.
2. It was found that the “clay ratio” was the most important parameter for use in initial erosion by rainfall and thin film flow. The “clay ratio” alone explained 84 percent of the variation in soil loss.
3. Soil erodibility can be evaluated from the “clay ratio” and “increment of soil loss”. The “increment of soil loss” can be determined by the “ratio of erosion hazard”.
4. The prediction equation in the “ratio of erosion hazard” for all soils is:
e_H=C₀+C₁X₂+C₂X₁₆+C₃X₂₆+C₄X₂₇
where e_H is the “ratio of erosion hazard”, X₂ is the percent of clay, x16 is the infiltration ratio, x26 is the real-specific gravity, .r27 is the natural logarithms of the liquid limit, and c₀=1.20, c₁=-0.01, c₂=0.26, c₃=-0.10 and c₄=-0.06.

View full abstract

The amount of rainfall and eroded soil were measured under natural rainfall for two bare sloping fields of kuroboku soil with (a) 2m in width, 20 m in slope length, 5°45' in slope gradient, and (b) 2m in width, 10m in slope length, 10°07' in slope gradient.
Applying these data to Universal Soil Loss Equation (1), the following results were obtained.
1. Field (a):
(i) annual rainfall factor R_y (=E·I₆₀) =271m² t/ha/hr, annual amount of soil loss E_ry=7.49t/ha and factor K·SL=0.0276 hr/m² for 27 measurements (July 1976-June 1977).
(ii) R_y (=E.I₆₀) =477m² t/ha/hr, E_ry= 11.2t/ha and K·SL=0. 0236 hr/m² for 21 measurements (July 1977-June 1978).
(iii) R_y (
E·I₆₀) =592m² t/ha/hr, E_ry= 23.0 t/ha, and K·SL=0.0398 hr/m² for 29 measurements (July 1978-June 1979).
2. Field (b):
(i) annual rainfall factor R_y (=E.I₆₀) =313m² t/ha/hr, annual amount of soil loss E_ry=20. it/ha and factor K·SL=0.0642 hr/m² for 19 measurements (July 1977-June 1978).
(ii) R_y (=E.I₆₀) =622 m² t/ha/hr, E_ry=56.2 t/ha and K·SL=0.0904 hr/m² for 30 measurements (July-1978-June 1979).
3. If we express steepness and length of slope factor SL by Equation (3) and define that 20m-5°45'slope field is standard, SL was described as follows,
SL=√L (-0.772s+29.6s²)
Using this equation, the estimation equation of annual amount of eroded soil E_ry at the same soil fi eld were obtained,
E_ry=0.0321·R_y√L (-0.772s+29.6s²)
where, 0.0321 is an average value in 20m-5°45' slope field for 2 years (July 1977-June 1979).
4. E_ry on bare sloping field of 20m in length and 10° in slope inclination were obtained as follows,
E_ry=0.112 R_y
5. When we estimate the amount of eroded soil for every continuous rainfall somewhat roughly, follwing functions of El or I on E_r may be used.
At 20m sloping field:
At 10m sloping field:
E_r=0.00439 R₆₀^1.45 (r=0.869)
E_r=0.00274 R₃₀^1.45 (r=0.891)
E_r=0.000319 I₆₀^2.45 (r=0.814)
E_r=0.000212 I₃₀^2.50 (r=0.844)
E_r=0.0125 R₆₀^1.45 (r=0.894)
E_r=0.00833 R₃₀^1.42 (r=0.909)
E_r=0.00127 I_602.25 (r=0.798)
E_r=0.000628 I₃₀^2.17 (r=0.797)
6. As a result of the existence of volcanic ash soil like Kuroboku soil which contained a large amount of humus, gully erosion rarely occured, but sheet erosion, for which the surface of the soil is stripped off in thin layers, did occur.

View full abstract

The results obtained from the basic soil desalinization and area reclamation test are very important, but direct application of results, even though it has a high degree of accuracy, should not be applied directly to a large scale soil desalinization and leaching program. Consequently, until now all the empirical and model founded equations could not be directly applied without parameter modifications with consideration given to the wide range of environmental conditions.
Therefore, for parameter modification, as well as for the success of practical application, field experiments have been strongly recommended. Research treatment in the field is quite technical, needing a lot of manpower as well as time and expense. Due to these factors, the minimization of the effects of external factors regarding the results obtained is a very important aim of the field research.
When a large amount of data has to be treated, there are three alternative methods which can be employed: the analytical, graphical, or statistical method. Among these the last method is more accurate. What makes this method valuable is that it keeps the openions of the researchers separate from the results obtained.
The statistical method in our study was applied by means of the dependent, independent T-test, as well as by the variance analysis using the F-test and followed by the T-test.
The summary of the results are as follows.
(1) The student's T-test for both cases of dependent and independent is not the proper way for obtaining results for chemical changes in the soil and for a disalinization survey, because it will act on the mean depth-values of the data obtained, and will not clarify the effect of depth sampling as well as their interactions.
(2) Analysis of the variances by means of the F-test followed by the T-test gives us the ability to accurately judge the chemical changes in the soil during soil desalinization and its related results can be finalized by means of:
(a) The identification of the differences in the data taken before and after leaching with respect to soil depth;
(b) Interaction effect of time on sampling (leaching process) and sampling depths in the soil profile;
(c) High degree of accuracy regarding the significance of the changes of measured factors, before and after leaching, as well as the depth effect on soil sampling.
(3) To a certain degree, EC_e (mmhos/cm), and soil pH showed significant and highly significant differences between the sampling depths. And overall, the effect of the leaching process on soil salinity and alkalinity changes have been found significant and highly significant.

View full abstract

In the runoff analysis, it has been recognized that a precise estimation of effective rainfall leads to a more accurate runoff analysis.
Up until now, many methods for estimating effective rainfall have been proposed, however, none of them were evaluated as being adequate. A method utilizing the relation between cumulative rainfall and cumulative water losses is generally used as the most rational method.
However, even this method has a crucial drawback in that the relation between cumulative rainfall and cumulative water losses is not always identified as a single-valued function because of the influences caused by the soil moisture condition in the catchment, differences in rainfall patterns and so on.
In this paper, the function, L_d=(S_max-q_b/K) ·(1-e-a^p) is proposed, in which cumulative water losses (Ld) is related by cumulative rainfall (P) and discharge at the beginning of the storm (qb), to deal with the above problem (S_max, K and α are the constants inherent in the catchments).
Applying this method to the hydrological data of the Geum River basin, Korea (Area=7, 179km²) and the Kamigamo experimental catchment in Kyoto, Japan (4. 39 ha), the adaptability of this method is higher than that of the previous method which is in ordinary use (Figs. 11, 12, 13 and 14).
That is to say, the deviation of data is diminished and the relative error decreases from 16% to 7% in the Geum River basin and from 23% to 16% in the Kamigamo experimental catchment (Tables 3 and 4).

View full abstract

In this paper, we proposed three methods of diagnosing a drainage system using anonuniform flow model and examined the fitness of these methods by applying them to a field basin.
At first, the runoff phenomena in the drainage channel system were simplified into a nonuniform flow model. Secondly, the computed values of this model were arranged according to the following three methods proposed in this paper, by which the weak points of the drainage system were clarified.
(1) The method of evaluating “Field drainage capacity”.
(2) The method of diagnosing the factors which restrict field drainage using “The drainage dischargewater level relationship”.
(3) The method of evaluating “The conveyance of each section in the drainage channel system”.
The above methods were applied to the drainage channel system in the Chayago district. As a result, its drainage condition could be evaluated exactly and the causes of poor drainage were grasped precisely.

View full abstract

As an erosion and sediment control method during and after reclamation work for sloping land, the authors proposed a graded temporary levee method to help with sediment control across a field slope in an effort to try to reduce the soil loss from field lots.
In this paper, the actual conditions causing sedimentation along the graded temporary levee were studied based on the results of a field test which was carried out in various sets of field slope degrees and levee gradients.
The results obtained were as follows.
1) The upper limit of the temporary levee gradient causing sedimentation was from 4 to 5 degrees, according to field slope of from 6 to 10 degrees (Fig. 4).
2) Along the high gradient temporary levee under the upper limit, sedimentation seldom progressed very effectively, but the temporary effect of sedimentation was expected in heavy storms soon after the construction of temporary levees (Figs. 5 and 6).
3) Temporary levee gradient causing effective sedimentation was under about 3.5 degrees for thefi eld slope under 10 degrees (Fig. 7), and effective sedimentation was caused in orthogonal sediment fans against temporary levees.
4) Along the low gradient temporary levee under about 1 degree, surface drainage was restricted because of irregular sedimentation, and as a result, levee failure occurred along the lower side of the temporary levee.
5) Grain size distribution of the sediment tended to be finer as the temporary levee gradient was increased over 2 degrees (Table 1).
6) Sedimentation phenomena along the graded temporary levee seemed to be complexly affected by the sediment transport characteristics of the various size grains and the shear stress which changed every moment and varied with location.
7) The most suitable gradient to help effective sedimentation and adequate drainage seemed to be from 2 to 3 degrees, with a field slope of 6 to 10 degrees.

View full abstract

This paper describes the properties which concern thermal cracking in ondinary portland cement concrete.
For protection against thermal cracks within a mass concrete structure, we must be able to know how to analyze thermal stresses and know the properties to use in the analysis.
Therefore, the typical properties in ordinary portland cement concrete widely used in civil engineering structures are examined.
The results are as follows.
1) Slowly loaded tensile strength is the function of age and can define fracture i. e. cracking.
2) Tensile strain capacity is not the function of age, but is scattered in 50-300×10^-6.
3) Tensile stress relaxation coefficients calculated from tensile creep data are greater than the experimental results.
These experimental stress relaxation, coefficients in tension differ from those in compression.
Therefore, we have to use the experimental tensile stress relaxation coefficients in thermal stress analysis.
In addition, we must apply the results in air curing at the surface parts of the structures.
Finally, a simple method of the thermal stress analysis is suggested.
The experimental data previously mentioned is used in this method.
The method also can be applied to the drying-shrinkage stress analysis.

View full abstract

This paper discusses the characteristics of seepage flow under a weir with a cutoff wall. Especially, the effect of a cutoff wall with weep-holes for the uplift pressure acting on the underside of an apron is discussed.
An analytical method has been developed by using the conformal mapping technique. The numerical calculation is carried out and the results obtained are compared with those obtained by the finite element method. The boundary condition used for analysis using the conformal mapping technique is an infinite permeable layer. The weep-hole widths used for this calculation, which is substituted for the two-dimensional analysis, are 0.0006m, etc.
Restilts obtained show that the longer the width of the apron, the more the effect of the weep-holes for total uplift pressure decreases and the deeper the depth of the cutoff wall, the more the effect of the weep-holes for total uplift pressure increases. Total uplift pressure obtained by the finite element method about a finite permeable layer gives a larger value than results obtained by the conformal mapping technique.

View full abstract