This experiment is investigate the relation between stability of soil aggregate and soil water content. A new soil conditiners (M) and usual soil conditioners (Krilium, Soilluck) were used, and the soil used was Kanto Loam.
An ability of these soil conditioners mearsured by means of Sediment Volume.
The sediment volume of the “M” soil conditioner was larger than that of other two soil conditioners.
Principally soil conditioners was added of solution at the rate of 0.1% and 0.4% by weight of 40g dry soil. then soil and soil conditioner was mixed.
The quantity of water to dessolve soil conditioner was about Plastic Limit of soil.
Water stable aggregate differece of each soil conditioner in the case of 0.1% and 0.4% tretment was shown, that is water stable aggregate in Krilium tretment was 60%-70% at 0.1% adding and more than 80% at 0.4% adding, that in “M” tretment was 50% and 60%-80%, and that in Soilluck tretment was 1/5-1/6 of former two soil conditioners.
The aggregate reformed was destroied at the water content less than 20% in 0.1% tretment and 28% water content in 0.4% tretment.
In the stability of aggregate, soil treted by the “M” soil conditioner was better than Krilium soil conditioner.

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Vegetable cover (rice plant) itself plays an important role of mulch by intercepting the solar energy to the soil surface to dampen soil temperature fluctuations and preventing evaporation from the free water surface of irrigation in paddy field. Mulch in itself is artificial, but the self-mulching action of rice plant arises inevitably in proportion to plant growth. So that the self-mulching action can not be removed even if it is unnecessary to the normal growth. Therefore the plant is compelled to grow under the environmental conditions that were characterized by the self-mulching action whether plant will need it or not.
The author examined the effects of the self-mulch on plant growth and its yield to clear up the facts that the plant height and the number of available tillers were characterized partially by the self-mulch and the development of root system was also characterized by this in part. After all, the yield of rice plant depends partially on the self-mulching action. So these results suggest that the utilization of the unavoidable self-mulching action must be taken into account positively in improving rice cultivation.

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The conditions for similar flows with a free surface are studied by means of themedium of flow net for the unsaturated flow, the characteristic of which is clarified theoretically.
The conclusions obtained are as follows.
1) The ratio of the height of static capillary rise should be controlled to be equal to the ratio ofgeometricallength.
2) The characteristic curves of k/k₀ and p/ρg/h_c should be equal in porous media of both model and prototype, where k and k₀: coefficients of unsaturated and saturated permeability, respectively, p: pressure, h_c: the height of static capillary rise.

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The pore pressure in embankments of fill dams under construction and after completion has a significant influence on the stability of embankments. The dissipation process of the pore pressure in complete earth embankments is approximately analyzed with Terzaghi's two-dimensional consolidation theory. But consolidation of fill dams under conbtruction can not be analyzed with Terzaghi's thory, because, in this case, consolidation takes place under the condition of moving boundary and increasing load. For this case, one may use Gibson's one-dimensional analytical method, but this method is only applicable approximately to consolidation of homogeneous earth dams.
In this pape, the authors showed the two-dimensional analysis of the pore pressure in embankments under construction taking the local variance of the nature of soil into consideration, and compared the method with Gibson's one-dimensional analytical method. From this result, the authors found that when the ratio of the height to the bottom width of an embankment was smaller than one, Gibson's equation was approximately applicable to the consolidation analysis of embankments under construction, because the error between the former and the latter was smaller than ten percents, but when the ratio of height to the bottom width was greater than one, the error becomes great, so it was necessary to analyze the pore pressure with two-dimensional method. And it was shown that the pore pressure dissipation occurd also during the construction piriod, although it had not been usually considered.

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The sand accumulation phenomena at the upper stream side of hydraulic structures cause many troubles, so it is a pressing need to foresee the feature of sand accumulation, and further to establish the suitable countermeasure to prevent sand accumulation.
The authors put a psammo-hydraulic interpretation on the fundamental problems in the case of applying a special sand elimination tube (a slit conduit or a vortex tube) to sand elimination of hydraulic structures.
At first, from the experiments on the flow in a slit conduit, the authors found out especially following facts.
(1) The flow velocity distribution characteristic in the tube is very different from that of the ordinary case.
(2) Froude number is the parameter that determines the state of the flow.
Next, from the experiments on the trapping efficiency of a vortex tube, the authors proposed some experimental equations, by connecting parameters based on the dimentional analysis, such as Ratio of depth to slit width h/b, Extracter ratio R_q= Qt/ Q, Sand water ratio R_SW= QS/ Q, Froude number Fr, Sorting index Sφ, Ratio of mean diameters to slit width dm/ b, and number of sand grains exposed per unit area N=Nd²₅₀, with the Trapping efficiency Qbt/ Qs.
In this case, the authors interpreted the grain size factor, such as Phi mean diameter Mφ(or mean diameter dm), Phi deviation measure (or degree of sorting) σφ, Phi skewness measure αφ, and Phi kurtosis measure βφ, in relation to the other parameters based on the results of experimental analysis or dimentional analysis.
Further, the authors proved that it is possible to eliminate sand almost perfectly, if a suitable form of vortex tube is designed, based on principal parameters which control the trapping efficiency.

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