Numerous problems in relation to the quantitative analysis of cohesive soil erosion by surface water flow still remain unsolved from a practical point of view since the resistance mechanism of the soil layer to the tractive force of surface water flow ha. s not yet been clarified. When the resistance of viscous soil such as farmland soil is supposed to be represented by the clay ratio (C_r*) and dry density (γd), the quantity of soil erosion (q_e) and dimensionless tractive force of a surface water flqw (τ₀/τ_c=u*²/u*c²) are able to be represented by the equation, q_e/u*d_k=a exp [αu*²/(γd/ρ) gd_k]. At the same time, when the depth (h) of surface water flow (q_w) was expressed by equation, h= (N. q_w/√sinθ) ^P, the hourly and widthwise quantity of soil erosion (q_e) by the surface water flow was able to be obtained by the following equation:
q=ad_k √Kb qw^P/2 exp [αKbqw^P/(γd/ρ) gd_k](provided that Kb=gN^P/(Sinθ) ^(P/2)-1)
Wherein a and α represent the coefficient and exponent, respectively, to be determined by the conditions of the native matter of soil and soil layer, p the constant (=3/5), d_k the average clod size of the surface soil layer, N the equivalent roughness of catchment area, ρ the water density, g the gravity acceleration and θ the gradient of the slope. An application of this equation was attempted using the N value adapted to the runoff analysis, to the sloped standard plot for soil erosion where the actual amount of surface water flow and loss of soil caused by natural rainfall had been measured. As a result, it produced a relatively close correlation between the value obtained by the calculation on the basis of the above equation and the quantity of soil loss by surface water flow actually measured at the time of the rainfall. This, therefore, indicated the possibility of estimating the loss of soil on sloped farmland, if the appropriate surface water flow on the slope of the farmland and the N value were able to be determined from the precipitation and runoff analysis.

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The soil in the fields situated in dunes has a poor water-retaining capacity, and the basic pattern of water utilization is clearly observed in such an area. By studying this pattern, it is assumed that data being of help for elucidating future problems concerning water usage may be obtained. From this standpoint, the actual circumstances of irrigation in dune fields were investigated, and the following findings were obtained.
1) There were three peaks in the monthly usage of water during the year. The first peak was during April to May, the growing period for watermelon and melon fruit, the second was in September when radishes and cabbage are sown and planted, and the third was during November to December when large amounts of water are required for harvesting radishes.
2) The amount of water used for each field tended to be greater than the planned value. This is because the dunes are not flooded even when the fields are excessively irrigated, and because the surface of the dune soil dries quickly. The irrigation intervals and rotation of watering blocks were not strictly kept. This tendency is due to the fact the time when water is needed is the same for the whole area, and that all the fields dry up at the same time after rain.
3) Fields are watered by rain mainly during summer to autumn. In the spring, the farmers grow crops in plastic tunnels to send crops to market earlier, which prevents rain from watering the crops. Since the amount of each rainfall from summer to autumn is large, the quantitative efficiency of rainfall during these seasons is small.
4) When plastic houses are used to grow crops in dune fields, the amount of water used in that area becomes larger because rain cannot water the soil in the houses, and the soil must be disinfected.
5) Much larger amounts of water are used for dunes than for loam or clay fields.
6) The water usage for irrigation of fields cannot be measured by the month because the time when irrigation is necessary in each field centers in ten or five-day units.

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In future, multipurpose fields hold great promise in farming. Multipurpose fields can be classified into two types for intensive use and for extensive use. There has been a lot of research on the intensive type, but very little on the extensive type. Accordingly, we have examined the behaviour of surface drainage using a new computer calculation method called the three-dimensional enclosure method.
The enclosure method has two calculation principles.
These are
1) Calculation of large areas is prior to that of small areas.
2) When water overflows, calculation of the overflow area is prior to that of streaming area.
By using these two principles, we can obtain an accurate and efficient computer simulation model. Provided with various inclinations and patterns of field topography, we made some calculations, and were able to grasp the effects of slopes and leveling.

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The quality of water taken from the southern basin of Lake Biwa has been observed at Keage Water Station, in Kyoto City on a monthly basis, for about 30 years. This paper describes the results of this statistical analysis regarding these time series from an eutrophicative viewpoint. The results are as follows.
Generally, the correlation structure of time series varies in accordance with the time scale. In the correlation analysis of the monthly data taken from that viewpoint, it is necessary to analyze them on an annual time scale, for example, by previous transformation into the annual mean series.
The synthetic estimate standard for the trophic state was derived by applying the Principal Compornent Analysis to the annual mean series. As a result of using this standard, the eutrophication of the southern basin was estimated to be progressing continuously in a large scope (Fig. 5).
Additionally, it was found that annual periodicitiy existed in the alrnost all the variations of water quality and the seasonal pattern was able to be classified into several types (Figs. 6 and 7).
In conclusion, the causalities among the indices at seasonal and annual time scale were able to be collected (Fig. 8).

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In order to investigate characteristics of salt concentration due to difference of soil texture, four kinds of specimen were prepared cylindrically with respect to the mixing ratio of Kibushi Clay and Toyoura Standard Sand. These specimens were saturated with NaCl solution and placed in a constant temperature and humidity chamber to concentrate salt. At each step of the drying stages, the specimen was divided into four parts of the sample at 50 mm height from the upper surface. Then, the soil solution contained in the divided sample was seperated by a centrifugal dehydrator at the primary wilting point of pF 3. 8. Characteristics of salt concentration were determined in relationship to concentrations and weights of NaCl in both the extracted solution and soil suspension.
The following results were obtained from the study;
1) Concentration of extracted solution was increased in the first upper layer and difference of increasing ratio of concentration was not recognized in all of soil texture conditions. Increased clay contents, decreased the maximum concentration of the extracted solution. Therefore, probability of damage to crops is estimated to be decreased. On the other hand, changes of concentration of extracted solution could not be recognized in the lower layers from the second layer.
2) Concentration of soil suspension was increased in the first upper layer and there was no evidence of these tendencies in the lower layers except homogeneous soil texture with Toyoura Standard Sand. Increasing pattern of concentration of soil suspension in the first upper layer was similar in all soil. conditions. But, since the concentration of the soil suspension was increased with increasing clay content, its tendency will be important in desalinization.
3) Weight of NaCl contained in extracted solution in the first upper layer resulted to increase with the increase of water evaporation ratio. And after reaching the maximum value, it showed to decrease giadually. However they decreased gradully in the lower layers. Weight of NaCl contained in soil suspension showed the exponential increase in the first upper layer and almostly constant in the lower layers. Depending on these results, characteristics of NaCl-transportation were recognized.

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In 1938 and 1942, S. B. Hendricks et al. and H. H. Macey reported that the absorbed water in the clay seem to be frozen structure. But their reports were not confirmed experimentally. The author experimentally calculated the second moments by using the N. M. R. spectra of the proton. On the other hand, the author described this process regarding the method for calculating theoretical second moments by the considering the lattice of the Kaolinite clay. By this method, the theoretical second moments could be calculated using drying Kaolinite clay. The theoretical values agreed well with the experimental results (Fig. 7), and it verified that the method was correct. Next, the theoretical second moments of S. B. Hendricks et al. and H. H. Macey's model were calculated in the random orientation of the clay particles. It was compared with the experimental results of the theoretical results.
The distance was 3.0 Å between absorbed water molecules and the neighboring molecules in S. B. Hendricks' model, with the theoretical results in good agreement with the experimental results (Fig. 9). However, H. H. Macey's model, the theoretical results were larger than the experimental results (Fig. 9), because the distance of 2.76 Å between absorbed water molecules and their neighboring molecules was relatively small.

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The purpose of this report is to examine the soil erosion during spring thawing in the areas where the ground is frozen in winter. Experiments for research were carried out of the freezing and thawing effects on the soil loss from sloped bare ground and the water-resistances of soil aggregate and soil mass. The information obtained is summarized as follows:
1) The surface runoff and soil loss from the bare slopes tend to decrease with year, which is partially attributed to the structural changes of the ground due to its freezing and thawing (Figs. 1 to 3).
2) The results of soil erosion experiments on soil specimens subjected to artificial freezing and thawing revealed that the amount of soil loss was far less for the pre-frozen sample than for the unfrozen sample (Fig. 5).
3) A comparison in terms of infiltration line of the unfrozen soil and the pre-frozen soil revealed that the infiltration intensity and linear gradient were grater for the pre-frozen soil than for the unfrozen soil, suggesting soil structural changes caused by freezing and thawing (Fig. 6).
4) The soil concentratio4 of surface runoff is tendentially smaller for the pre-frozen soil than for the unfrozen soil (Fig. 7).
5) The mean weight diameter of the soil aggregate, though changed by freezing and thawing, varies with different initial moisture content (Figs. 8 and 9).
6) The degree of influence of freezing and thawing on the water resistance of soil mass varies with the properties of soils, but is generally lowered by freezing and thawing. With organic soils, however, no such effects were observed (Table 5 and Fig. 13).
7) As for the organic soils with high stability, air-drying treatments contributed to the onset of the freezing and thawing effect, thus lowering its water resistance (Table 6 and Fig. 14).

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When we perform the stability analysis of the practical slope, we have to use the method of analysis which conforms to the condition of the slope. When we investigate the stability of the embankment on the inclined subsurface, we have to consider the condition of the boundary between the embankment and the natural ground.
In this study, the stability analysis of the above slope is performed using the method which was presented in the previous paper. That is; the boundary between the embankment and the natural ground is represented by the joint element.
As a result, the safty factor considering the condition of the boundary between the embankment and the natural ground can be shown in that way. And it is shown that the effects of the bench cut on the stability of the slope might be considered concretely.

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The purpose of this paper is to clarify dynamic properties and to define dynamic strength of soils subjected to initial shear stress for the accurate and rational earthquake resistant design of soil structures with slope. A series of dynamic triaxial tests of an actual earth-fill dam material was conducted applying static shear stress prior to the application of dynamic stress.
From the experimental results, the following can be stated: the major effect of initial shear stress is to increase axial strain significantly and to restrain the development of pore pressure; dynamic behavior can be divided into two groups according to the degree of stress reversal (for stress reversal, axial strain increases with number of cycles N; for no stress reversal, it approaches a constant value as N increases).
Furthermore, a new criterion of dynamic failure is proposed, which is based on strain rate: if strain rate increases and reaches a constant value, a soil element begins to fail. When applying this criterion to actual practice, we can not only get the accurate and rational earthquake resistant design but also prediction of dynamic failure of slopes, by the observation of strain rate or acceleration of soil elements.

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The purpose of this investigation is to determine quantitatively shear modulus G and damping ratio D which are needed for the dynamic response analysis of soil structures with a slope. A series of dynamic triaxial tests were conducted using actual earth fill dam materials: the first material is the random zone material, which is mainly located in the upper and lower slopes of the dam subjected to initial shear stress; and the other material is the core zone material, which is located the central part subjected to isotropic stress. Thus, in these tests, initial shear stress was applied to the random specimens prior to the dynamic stress application.
First, the following previous experimental results were confirmed from these test results of the random specimens subjected to initial shear stress, of which intensities were determined by static mobilized stress ratio MSR (MSR= 0.0, 0.1, 0.3 and 0.5):(1) The major effect of initial shear stress on the dynamic behavior of soils is the significant increase of plastic axial strain ;(2) Initial shear stress has a considerable influence on D but little on G.
Then, we obtained the following, conclusions as the result of considering the quantitative determination of G and D: Both shear modulus G and damping ratio D of the random material subjected to initial shear stress and the core material subjected to isotropic static stress could be determined by the following equations, which have been obtained by an investigation previously carried out by the authors.
For shear modulus
G, G/G₀= [G/G₀] p'=1·(p') ^m (γ_a)
For damping ratio D,
D= (a+b·G/G₀)
In this investigation, quantitative functionG₀, [G/G₀] p'=1-γ_arelation m' (γ_a)-γ_arelation (for shear modulus G), parameter ‘a’ which decreases with the number of N cycles and parameter ‘b’ which is constant for the same material (for damping ratio D) are given.

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