In this paper the author investigates the effects on the ground level in the low land peat soils, which are generally in the Tohoku District in Japan, by variations in the ground water level. In the experiment, two procedures are used. One is a laboratory test on the settling and deformation by water level control and load test. The other is a field test with the settling and observation of the ground water table.
The results obtained are summarized as follows:
1) The settling phenomenon consists of two parts: shrinkage and consolidation by lost of buoyant force.
2) The settling curves decrease very steeply at first. However, after a certain amount of time the curves begin to decrease slowly. The reason why these phenomena occur is discussed detail.
3) It is found that sharing parts of consolidation in the total settling are rather small, after the calculating results of consolidation settling.
4) In the field test, the top layer is sensitive to variations in the water level, while the sublayer does not show.
5) The total settling of the peat soil layer can be analyzed assuming four layers: the first layer above the water table, the second layer affected by variations in the water level, the third layer affected by consolidation below the water table, and fourth layer not affected by consolidation below the water table.

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Unsaturated water movement and volumetric expansion in clay can be analyzed according to the mathematical theory applying Darcy's law to both water and soil particles. This paper examines this problem by determining water diffusivity-water content and solid diffusivity-solid content relationships from infiltration experiments with the unsaturated bentonite. Both diffusivities exponentially increase during water movement in a liquid, when the water and solid content increase, respectively. However, they show a constant 0.55cm²/day for water diffusivity and 0.23cm²/day for solid diffusivity, during water movement in a vapor, that is, in the range of volumetric water content 0.05 to 0.45cm³/cm³.
When both diffusion equations of volumetric water and solid content are solved regarding infiltration in an unsaturated bentonite by the use of these diffusivities, the calculated water and solid profiles agree quite well with the measured data. The changes of cumulative infiltration and volumetric expansion with time computing from the surface flux of water and soil particles, also, appear to be agreed excellently with the measured data.

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Differences in soil strength and pore configuration between natural-structure soil and compacted-structure soil with volcanic ash soil and brown forest soil were compared, and their effects on the elongation of grass roots were examined.
In natural-structure and compacted-structure soils, it was found that even though the bulk density was equal, their soil strength and pore configuration were different. Soil strength of natural-structure soil was greater than that of compacted-structure soil because the structure of the former soil was stable. On the other hand, compacted-structure soil had continuous pores. Root growth in these soils with a different structure was not controlled by the soil core containing continuous pores, even if soil strength were great; and it was hindered in soil with discontinuous pores. And, the quantity of the coarse pores of the compacted-structure soil was increased when the grass was grown. From these results, it was surmised that root elongation was influenced by pore formation rather than by bulk density and the quantity of pores in the culture beds. In natural-structure soil, the formation of soil pores influences root elongation directly, and in disturbed and compacted soil, roots alter their pore formation.

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Erosion of Kuroboku soil by a thin film flow is a complex process. Soil erosion is comprised of four component processes. It is important to analyze separately each component process of the erosion by water. The major objective of the research reported in this paper was to study basic relationships between soil erosion from a thin film flow and the most important factors affecting it and to develop a soil loss prediction equation.
The following results were obtained:
1. The soil loss was linearly related to the sand content.
2. The dimensionless form on the rates of erosion of Kuroboku soil by a thin film flow was proposed.
3. It was found that the boundary shear stress, velocity of flow, average diameter of soil and water depth were the most important parameters to be used in soil erosion by a thin film flow. The prediction equation developed from the regression of data was:
qB=e^5.407τ₀^2.848v^1.803d_m^0.580/h^0.817
The multiple-correlation coefficient for the above equation was O.964.
4. The boundary shear stress alone explained 76 percent of the variations regarding soil loss.
5. Velocity of flow can be predicted in terms of runoff rate excess, slope length and slope steepness.

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The soil behavior of grazing grassland was investigated from 1973 to 1980 in Shikoku Karst mountain area. The grazing grassland was developed using an unplowed method in August, 1973. In this paper, annual changes in soil dry density in situ (ρd: Mg/m³) are discussed as the typical property representing the soil behavior. The results obtained are summarized as follows.
1) ρd increased during the grazing season. A positive correlation is recognized between the amount of the increase and the population of grazing stock in case of surface soil. In the beginning of the grazing period (1974, 1975), the cattle hoofs seem to remarkably influence the surface soil causing an increase in its dry density.
2) On account of the freezing and thawing action, the soil became loose and a decrease in ρd occurred in spring. The amount of this decrease is nearly directly proportional to the freezing index. And it shows an annual reduction with an accumulation of the compaction effect as a result of the cattle hoofs. In the first winter season just after the development into grassland, grasses such as mischanthustype with a height of about 1 meter had been removed and the sowed grasses grew insufficiently. Because of such a change in the ground surfacecondition covered uithgrasses, it seem to reeluce the dry dencity remarkably.
3) It was thus found that the ρd of the grazing grassland changed cyclically. It seems to be due to grazing (increase) and the freezing and thawing action (decrease). And it was found that the compaction effect by the cattle hoofs accumulated in the soil and brought about a slight increase in the soil dry density on the surface soil, annually.

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A theoretical analysis of the orientation of water molecules absorbed in clay was discussed in the fourth report. In this report, the orientation of the molecular absorbed water layer in Allophane clay was discussed. The results have been summarized as follows.
1. The second moments were experimentally calculated using the N. M. R. spectra of protons in one molecular absorbed water layer and two or more absorbed water layers in Allophane clay were not continued between pF 6. 34 and pF 6.50. From the view point of their discontinuity, the proton in the Allophane clay's absorbed water layer can be roughly classfied into one molecular absorbed water layer and two or molecular absorbed water layers (Figs. 1, 2).
2. The distance of 2.23 Å and 2.35 Å between the Allophane clay's structure hydroxyles (OH) and their neighbouring structure hydroxyles (OH) by two experimental methods were obtained. Their results were in good agreement, but their results were smaller than the distance of 2.94 Å between the structural hydroxyle (OH) and their neighbouring structural hydroxyle (OH) in Kaollinite clay.
3. The author obtained the common orientation of water molecules absorbed in Allophane clay (Fig. 3).

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In this paper, the actual amount of irrigated water in dry fields, especially its level in quantity, its annual variation patterns.
Irrigation, and its inherent problems etc, were discussed multilaterally, concerning the C area in the district of cultivated vegetables (greenhouses and fields coexistently mixed) and the A district of cultivated fruit (oranges).
For the actual amount of irrigated water in dry fields, the importance of introducing the conception of average within some term were proposed throughout this paper, with consideration given to some special short maximum term.
It was demonstrated that the quantitative level in field irrigation is unexpectedly low regarding an average value within some term range, about 1.0 mm/day is regarded as the criterion for the upper maximum value for dry field irrigation; and moreover, about 2.0 mm/day is the standard in only the greenhouses set up in the area, which is considered the maximum for various dry field irrigation.
It is expected that new methods of planning and designing regarding dry field irrigation systems should be developed, considering the term of the dry field irrigation water amount.

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Entrainment accompanying the internal fall depends on the energy loss and entrainment ratio (entrainment from the lower layer over the upper layer).
When there is no stratification in ambient fluid, energy loss is a function of internal fall height. The results show that the entrainment is a function of 3 rd order of the fall height.
In case of the stratified ambient fluid, the energy loss can be neglected, and the relationship between entrainment and fall height is experimentally obtained.

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In a series of studies, the seepage failure problem of a pice-wise homogeneous sand column caused by a vertically ascending seepage flow has been considered. In the preceding papers, the author studied the seepage failure problem in the one-, two-and three-layer cases. In this paper, based on the previous studyn, the seegage failure problem in a multi-layer case is considered.
As mentioned in the 6 th paper, the “critical state chart for seepage failure of a sand column” indicates almost all the information about seepage failure of the sand column. It is also very useful in considering the safety fatocr for seegage failure of the sand column, and in designing a loaded filter which is placed on the top of the sand column to avoid seepage failure. Thus it is considered that the critical state chart is the condensed chart which represents the analytical results of a sand column obtained from the treatment of the seepage failure problem of the sand column on the basis of internal effective stress.
As mentioned in the 7 th papern, the author's approach to the seepage failure problem (i. e., an approach based on the internal effective stress) has more advantages than the Kahn's approach (i. e., an approach based on the “critical equilibrium of forces”). On the other hand the author's approach is more troublesome as alyers of a sand column increase in number than the Kahn's approach. Combined with Kahn's approach, therefore, the author's apprnach may become very useful, in spite of the increased number of layers of a sand column.
In the present study, combining the author's approach with the Kahn's approach, and based on the concept of a “minimum criterion”, a new simple method of obtaining the “critical state chart for seepage failure of a multi-layered sand column” is shown.
Using the critical state chart for seepage failure of a multi-layered sand column, the pressure exerted on the “Yokushi Ban” which is placed on the top of the sand column, and the effective stress diagram within the sand column with the “Yokushi-Ban” after a critical time can be calculated.
Thus the critical state chart for seepage failure of a multi-layered sand column can be obtained very easily through the use of the method developed by the author, and can be widely utilized:
(i) to consider a seepage failure problem in the case of a multi-layered sand column from the standpoint of internal effective stress,
(ii) to judge the safety factor for seepage failure of a multi-layered sand column,
(iii) to design a loaded filter to prevent the seepage failure of a multi-layered sand column, and
(iv) to consider a seepage problem of a multi-layered sand column with the “Yokushi-Ban”.

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