A linearized differential equation for horizontal infiltration has been derived by the use of the approximate linear relationship between matric flux potential φ and Boltzmann variable η(=x/√t). It is solved analytically for the soil water diffusivity D=Di exp (βC), where Di and β are the constants, C is the normalized water content. Since the solution involves two parameters, simple methods are suggested for estimating them by means of “optimization” or “integral balance”. Sorptivity is also calculated by the solution. For general diffusivity functions, the linearization simplifies the procedure of the numerical solutions to a great extent. With some limitations, the results compare favorably with the accurate numerical solutions. Usually, the errors of the sorptivity values are within 0.1%.
Moreover, a quick and accurate method is proposed for estimating the constants, Di and β, of the exponential diffusivity using the values ∫¹₀ηdC and ∫¹₀η²dC obtained from the actual soil water distributions.

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In order to investigate the influence of adsorbed cations on the viscosity of soil of the mud or paste type, the following experiments were carried out and the results were analyzed. Kibushiclay containing non-swelling kaolinite as the main ingredient was used for these experiments. Soils haveing the viscosity of mud, sedimentation, liquid and plastic limits, etc. were adsorbed with Ca⁺⁺ions and Na⁺ions to the surface of the soil particles and showed the following results
1. The influence of cations adsorbed into the surface of the soil particles as regards consistency appeared large in the water suspension, but this influence became smaller when the water was decreased gradually and the liquid limit was approached.
2. The gel strength and yield value were larger for the mixed liquids of Ca-kaolin than for those of Na-kaolin. It can be assumed that this was caused by the fact that the flow state was influenced by the difference of dispersion and cohesion for the soil particles.
3. As is obvious from the yield value and gel strength, the solvent effect was the direct result of the addition of the ions, and was smaller for mixed liquids of non-swelling kaolinite than for those of swelling soil.
4. The concentration of the sedimentation part of the suspension corresponded to the inversion point of the apparent viscosity curves. Therefore, as was obvious from this result, the sedimentation of nonswelling clay also represented the transition points.

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Construction work on Kasaoka bay sea bottom polder was begun in 1966, reclaiming an area amounting to 1, 187 ha. This whole reclamation area is expected to be used as dry fields for farming, although traditionally polders have been utilized as paddy fields. Accordingly, harm due to salt to crops sensitive to salt has been a serious problem to overcome. Furthermore, Kasaoka bay polder has little rainfall and the climate is dry compared with other areas in Japan. Since the weather is urdesirable the possibility of damage due to salt is high.
As a result of the above problem, we made efforts to think up adequate salt exclusion countermeasures for normal crop growth. To succeed in this endeavor, we carried out a series of investigations and studies. In this report, we have examined the fundamental properties of muddy soil in polder and salt behavior, the relation between salt and crop growth, and several fundamental factors concerned with salt exclusion, and presented a fundamental mechanisim of salt exclusion in accordance with the information presented below.
The results obtained are summarized as follows:
1. We have classified and adjusted the influence of salt to crop growth as a result of the data we accumulated and clarified the points in question as regards the establishment of salt exclusion countermeasures.
2. For salt exclusion, it was found that the following countermeasures were very effective:(1) to give a strong contact action between the soil and the water ;(2) to hasten the drying of the soil.
3. The promotion of desalinization had a large influence upon the physical properties and its changes made more and more difficult the salt exclusion.
4. After careful examination of the above results, we had presented the fundamental idea of mechanism of salt exclusion shown in Fig. 8.

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This paper describes the influence of rain drops striking soil. The study of water erosion is constantly being carried out. However, concerning the influence of rain drops on the soil's surface, there is still not enough information. Basic research was carried to obtain data on this influence and to clarify the following:
1. To establish the measuring method to determine the impact of rain drops on soil.
2. To clarify the influence of rain drops striking the soil.
The results of the experiments were as follows.
1. It was clarified that a linear relationship existed between the maximum strain of the spring and the momentum of collision, and the degree of impact was able to be determined by measuring the elastic strain.
2. Using the sensor of the phosphor bronze-plate spring, it was pointed out that the linear relationship was able to be established between the maximum strain and the momentum of a steelball, bronzeball and nylonball, making the measurement accurate.
3. Due to the experiment using the water drops, it was affirmed that the aforesaid relation could be regarded as appropriate in that the slope of the straight line of the water drops was less than the slope in the case of the steelball and so on.
4. By comparing the results of the water drops with the results of the steelball and the like, it was confirmed that the impact of the water drops unquestionably had an influence due to the striking effect.

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Present paper evaluates quantitatively the structural development of the undisturbed clayish soils in connection with their shrinkage behavior.
Results obtained may be summarized as follows:
1) The shrinkage type of undisturbed soils was classified into four groups on the basis of the formal features of the shrinkage curve (Fig.1-6, Table 3).
2) The shrinkage types depended on the clay content and was related to the three soil phases (Fig. 9 and 10).
3) The soil volume change due to total shrinkage depended on the shrinkage type (Table 3), and it was related to the clay content and the degree of saturation (Fig. 11).
4) As a comparison of the shrinkage curve of undisturbed soils with that of remoulded soils, the slope of the normal shrinkage was larger in the remoulded soils than in the undisturbed soils, whereas the slope of residual shrinkage was nearly equal in both soils (Fig. 12 and 13).
5) In regard to the quantitative indx of the structural development of the undisturbed soils, the “Coefficient of structural development (C_sd) ” was defined. It is expressed by the ratio (e_f) _U to (e_f) _R, and (e_f) _U designates the final void ratio in the shrinkage curve of the undisturbed soils, and (e_f) _R is for the remoulded soils (Fig. 15 and Table 4).
6) On the basis of shrinkage behavior, the pore volume of the undisturbed soil was classified for the shrinking pore, structural pore and dead pore (Fig. 15). The structural pore volume increased in proportion to “Csd”(Fig. 16).
7) The saturated hydraulic conductivity and the water content under pF 3. 0 were closely related to “Csd”(Fig. 17, 19 and Table 5).
8) A certain correspondence between the kinds of morphological soil structure and “Csd” was recognized, that is, “Csd” increased in order of the massive structure, blocky structure and granular structure (Table 6).

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The Subsurface Irrigation based on the Different Negative Pressure (S. I. D. N. P.) between water fed by a porous pipe irrigation system and that (soil moisture) in the neighborhood of root zone in soil is characterized by the effect of self-controlled (mainly controlled by that water gradient) continuous irrigation.
In the conditions of popular cultivation modes in vinylhouse, various porous pipes were examined regarding the fundamental relationships between the above difference of water and the quantities of water supply, the distribution of water in soil, and daily variation of evaporation from the soil's surface. This system was analyzed theoretically by conformal mapping.These results are summarized as follows:
1) The suitable shape of porous pipe of S. I. D. N. P. for use in the above-mentioned conditions in order to maintain the effective low moisture tention zone is a porous ceramic pipe having length 10-20cm, outer radius of about 3cm, coefficient of water permeability above 10-4cm/sec with one of its ends being sealed.
2) Changing given water pressure in pipes controlled the quantity of the water supply very sensitively and varied the area of the wet soil surface above the porous pipes and the seepage zone in soil.
3) Daily variation and its peak time of water supply occurred almost simultaneous with those of evaporation from soil surface and so weather conditions affected its quantity which was supplied continuously day and night.
4) Theoretical analyses by conformal mapping are nearly simultaneous with the above experimental results. And so experiments of cultivation by S. I. N. D. P. are planned to be put into practical use.

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In the karstic mountains in Shikoku, Japan, a large-scale grassland was developed by bush clearing and burning. In such a grassland, the soil properties and hydrological systems should change due to development and subsequent grazing. In a series of previous papers, the soil properties of the grassland were discussed. Thus, in the present study, water balance and storm water runoff are investigated using the experimental catchment specially designed for this area.
The results are summarized as follows:
1) The amount of groundwater, which flows out of the catchment without draining into the stream, is as much as 20-25% of the total rainfall during the observation period, and it is an important component as regards water balance. The geological nature of the karstic formations are considered to be the cause of this groundwater flow.
2) Though the amount of direct runoff depends on various factors, such as total rainfall and soil moisture deficiency, the ratio of direct runoff to total rainfall ranges from 10 to 20% for mild storms to about 40% for heavy storms in this catchment.
3) The rainfall which does not contribute to direct runoff is held to change the soil moisture, percolates downward, or returns into the atmosphere by evapotranspiration. The change of the soil moisture was expressed in terms of evapotranspiration and the loss by percolation was related to the duration of direct runoff. Using these relationships, we were able to estimate the amount of direct runoff with accuarcy.

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For many reclamation dikes which are constructed on a soft soil deposit, the resistance to severe earthquake motion is a matter of great concern.
In dealing with this, it has become clear that surface waves have a great effect on dikes.
In this paper, the results of the measurment and analysis of surface waves involved in the microtremors, of IYA-reclamation dikes at CHUKAI Reclamation Project, are given. The obtained dispersion curves and incident angle of the wave, from the measurement, showed that, 2-types of surface waves, which are the Love and Rayleigh wave, travel along the dike's axis, from the west to the east.
The theoretical dispersion curves for the 2 models of the soil profiles were computed, one of which was based on the test boring sample and was 39m in thickness. The other model had a hypothetically stiff base layer and was 50m in thickness. In comparing the measured and theoretical dispersion curves, the measured results agree with the latter model of soil profile.
Therefore it was proposed that there should be a stiff base layer under the dike, about 50m in depth, even though its exsistence has not yet been verified. Several other properties of the surface wave on a dike were also mentioned.

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The concrete strength gains in a field structure is generally slower than that of the standard curing concrete specimens and so, at the same age, the former's strength is considerably lower than that of the latter. Nevertheless, the concrete strength of a field structure has to meet the specified concrete strength. This becomes a matter of great concern.
The main factors affecting the concrete strength are the quality of the materials, mixing proportions of the concrete, construction and testing method of the concrete and so on. Especially, the curing condition is a very important factor.
The strength gains in the field concrete structures are greatly affected by the temperature and humidity surrounding it. However, a very difference in the a verage temperature and humidity of a year exists regionally.
After taking this ditherence into consideration we repeatedly carried out experiments for three years to clarify the following two points;
(1) the relationship between the specified concrete strength and the strength of concrete cured in the field.
(2) the effect of the period for curing in the field on the 28 day-strength.
The bending strength, compressive strength and dynamic modulus of elasticity were measured at the age of 3, 7, 28 days, respectively.
The results obtained so far are summarized as follows.
1) The 28 day-strength of the concrete cured in the field was greatly affected by the maturity In an extreme case, it was about 60% less than that of the concrete specimens cured under standard conditions.
2) The concrete strength cured in the field for three or more days after placing and in water to the age of 28 days returned only to 90% of its specified concrete strength. Therefore, moist curing and keeping it warm for seven days at the very least are neccesary for the field concrete.
3) The concrete specimens placed in the winter season and cured under standard conditions showed higher strength than those in other seasons at the age of 28 days.

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