In this paper, an effective method for river-mouth improvement is proposed on the basis of the results of the experiments described below. Regarding the improving method, a local scouring phenomenon, which occurs due to the series pile system was set up near a sand bar on the river-mouth, is applied. The series pile system is composed of several piles arranged in a zigzag pattern with proper separations. The local scouring scale in a wave-current coexistent system like a river-mouth is larger than that in non-coexistent system, because the bottom of river and sea is scoured by the interference of the waves and current. The improvement method made use of this phenomenon very positively.
In this experiment, several scouring phenomena in the post-breaking wave region in the wave-current coexistent system were investigated. The phenomena were affected by the influence of the waves and current on the scouring scale in the case of the single pile system the scouring scale in the case of series pile system, the optimum separation of the each pile in the series pile system and the location set up the series pile system for restraint of the sand bar formation near the river-mouth.
Taking the above experimental results into consideration, it was confirmed that the series pile system has both effect ; restraint of the river-mouth closing on the ordinary discharge or droughty one of the river and acceleration of the sand bar traction and the lower level maintenance of the river bed regarding flood discharge.

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In an open channel a translatory wave accompanied with a mass transfer is formed when a steady flow is turned into another steady flow by changing stream discharge at the upper end. This wave is called the “Cenveyance Wave” here.
In this study, transitional process of conveyance wave, whose Froude number is relatively small and on which rolling waves are not caused, is analyzed numerically. The Froude number is below about 1.5, when the Manning formula is used in friction term.
The results are:
(1) Positive conveyance waves, which are formed when the discharge is increased, are all transformed into uniformly progressive wave at the last stage.
With these numerical results, the conclu.sions of previous report are verified.
Negative conveyance waves, on the contrary, continue to be transformed and never become uniformly progressive waves.
(2) Characteristic features of conveyance waves are explained schematically throught all stages, that is, from the first stage to the last stage. Furthermore, no singularities are caused and found.
(3) Bore height, upper-end depth and wavelength turmed out to be apPropriate indexes for understanding the transitional process of the conveyance wave.
Effects of Fr₀ and a for these indexes are examined by theoretical partial analysis, and their characteristic time-dependent features are explained to some extent.(Fr₀: Froude number of initial uniform flow.α: change rate of discharge)

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In the previous paper the conveyance waves with a small Froude numbe were analyzed mainly by numerical simulation. Here, several problems shown in the previous paper are further analyzed theoretically.
Those problems are causal relations between Fr₀, α and characteristic features of time-dependent changes of the following values:(1) bore height, upper-end depth, etc. in a rapidly varied phenomenon, and (2) wavelenght in a gradually varied phenomenon.
The results of this study on those problems are as follows.
(1) As for the former relationship, a method to gain an approximate integral surface was discovered.
In this method, the dependent variables, namely, depth, velocity and bore celerity are expanded in Maclaurin series. Those variables are substituted in the Saint-Venant equations, initial condition and boundary conditions. Coefficients of the series are determined one by one from the terms of lower order.
(2) As for the latter relationship, the Saint-Venant equations, in which nonlinearity cannot be ignored, are approximated by the Burgers equation based on some assumptions. This equation is applied to the Riemann problem and is solved using the Cole-Hopf transformation.
Those solutions obtained in this study coincide well with results obtained from numerical simulations of the previous paper, except for some cases in which α is extremely large and nonlinearity is domir ant.(Fro: Froude number of initial uniform flow, α: change rate of discharge)

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The change in volume and moisture content of soils in the field of centrifugal force, where soils are subject to actions of dehydration and loading at the same time, are discussed compared with the change obtained by two methods: airdrying (or “non-loading method”) and standard consolida tion test, for five kinds of clayey soils with different conditions of their geneses, and for the parts of soil sample far from free-water table in the centrifugal tube.
The relationship between volume and moisture content of soils was classified into three types (I, II, and III). The types I, III, and II show no volume change (ΔV=0) with change in moisture content, the same quantity in change of volume as that of moisture content (ΔV=ΔV), and intermediate in behavior between I and III (ΔV<ΔVw), respectively.
Type II or III appeared in the moisture range from saturation to about pF 4. 2 for the five claye clayey samples made of disturbed soils in the field of centrifugal force. However, type I appeared in a range of low centrifugal force, where the soils was high in moisture content, for compacted soils still having well developed structure. The relationship between volume and moisture content changed in strength of the actions and rigidity in soil matrix and fabric of the sample.
The relationship between volume and moisture content was dependent on the distance from boundary (reference surface) for the sample with 5 cm length in centrifugal tube. The upper parts of sample in the tube, which were nearer to center of rotation, had the type II. That type were similar to that by non-loading method (suction and pressure plate methods, etc.). The lower parts of sample had the type III. That type were similar to that by consolidation test for the saturated sample.
The two types of the relation correspond to two fundamental mechanisms, which determines state in volume and moisture content in case of soils subject to actions of dehydration and/or loading. Rigidity of soil structure and formation of meniscus respond to the actions, which corresponds to type I. Access of soil particles to each other responds to the actions, which corresponds to type III. Type II is the mixture of two mechanisms.
It is pointed out that states in volume and moisture content of soil resulted from behavoir of soilbased on the two mechanisms. The responding mechanisms are so as simultaneously to adjust a mechanical balance in soil system and a potential balance of soil water under the actions of dehydration and loading. This way of thinking can give the state a comprehensive explanation.

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Effects of soil compression by centrifuging method on water retention characteristics are discussed on the base of characteristics by “non-loading method” for water retention measurement (suction, pressure plate and pressure membrane methods) for soils with three types. The types I, III, and II show no volume change (ΔV=0) with change in moisture content, the same quantity in change of volume as that of moisture content (ΔV=ΔV_W), and intermediate in behavior between I and III (ΔV<ΔV_W), respectively.
(1) Two methods of centrifuging and non-loading gave almost same pF-moisture content curve for type I sample. There was, however difference in the curves between two methods in the range of 10-30% moisture content. The difference is ascribed to redistribution of moisture after centrifugation for the sample with great moisture gradient.
(2) Moisture content measured by centrifuging method was smaller than that by non-loading method at a same pF value for type III sample except for uppermost part of sample in centrifugal tube. Such difference in moisture content was nearly equal to that in volume measured by two methods at the same pF. The plots (pF, moisture content) by the centrifuging method had a tendency to lie on the curve by the other method in the uppermost part far from free-water table, where the compression force due to centrifuging is smaller than that of other parts.
(3) Between the two methods, difference in measured moisture content was resemble to difference in measured volume in pF range below about 3 for type II. The former difference was larger than the latter in pF range above about 3. The plots (pF-moisture content) obtained by the two methods were close to each other at pF below 2 and about 4. That is related to small compression at low pF and to moisture retention at high pF.
It is referred that effect of compression on pF-moisture content curve measured by centreifuging method gave smaller moisture content than the curve for such soils as II and III types which were liable to change in volume with drying and pressure. The degree of effect is dependent on the work by which moisture is squeezed from the soils under centrifugal force. Hence, the effect of squeeze caused by load due to centrifugal force is important. The effect should be taken into consideration of the relationship between pF and moisture content measured by centrifuging method. The prevailing method for water retention measurement by centrifuging can be used in the case of type I corresponding sandy soil.

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In this paper the Hvorslev failure riterion is extended based on the adhesion theory of friction and the results obtained by studies in micro-rheology. Then the applicability of the extended Hvorslev failure criterion is investigated based on the data of constant-volume direct shear tests for remolded clays. The results obtained are summarized as follows.
Relations between water content, w_f, at failure and effective cohesion, c_e, and between effective angle of internal friction, φ_e, and effective normal stress, σ_f', at failure in soil varied due to the difference in the initial soil condition (liquidity index, I_L) before consolidation. However unique. w_f-c_e, φ_e-σ_f' relations existed in the soils which had the same initial condition before the consolidation.
The Hvorslev failure criterion is applicable to soils in which relation between shear strength, τ_f and σ_f' in normal consolidation process is linear. The extended Hvorslev failure criterion, which is proposed in this paper, should be applied to soils in which this relation is nonlinear.

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Apparent thermal diffusivity measurements of two frozen soils, Toyoura sand and Kanagawa sandy loam, have been made during the melting process at temperatures between-30 and 0°C using the least squares method based on a finite difference scheme. Both measured values showed a similar trend of increasing the apparent thermal diffusivity as the water and ice content increased. This increase is associated with the increase in the thermal conductivity based on the mechanical arrangement of soil components. The apparent thermal diffusivities decreased as the temperature was increased and became zero near 0°C. The apparent thermal diffusivity of sandy loam began to decrease at lower temperatures than that of sand. This result can be explained in terms of the temperature dependence of the unfrozen water content. It is concluded from these results that the apparent thermal diffusivity of frozen soil can be expressed by the ratio of an apparent thermal conductivity to an apparent heat capacity related to the temperature dependence of the unfrozen water content.

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In this paper, the soil materials which have been made by mixing volcanic ash soil with organic matter (Kuroboku) and purmice flow deposit (Shirasu) are investigated, for the purpose of increasing the undrained strength of Kuroboku soil.
The mixed soil has strength characteristics similar to Kuroboku soil when the mixing ratio is below about 50 percent; while when it is above 80 percent, the mixed soil comes to have those similar to Shirasu soil. The intermediate characteristics are shown in the range from 50 to 80 percent.
The secant modulus shows a certain degree of scattering, which is bounded by the predicted limits in the mixing ratio; that is, this modulus changes along lower bound when the ratio is below 50 percent, and is far from it in case the ratio is greater than that. Therefore, some improvements in the strength can be expected at about 60 percent.

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A sloping reclaimed field of decomposed granite soil was used to analyze the actual condition of soil erosion from the view point ridge and catch canal, taking soil conservation into consideration.
Based on experimental results, the following conclusions were drawn.
1) An arrangement of ridge and catch canal was determined by the behavior of surface drainage and work.
2) In general, soil loss from field flows mainly from the catch canal.
3) Gully erosion in the catch canal was considered to increase gradually, in proportion to the control area and the slope.
4) When the arragement of ridge and catch canal was changed, the volume of soil loss from the whole field also changed.

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In recent development of mass concrete structures, the problem of cracking associated with thermal expansion has been a matter of great concern, especially in those structures requiring high watertightness. This paper focuses on the effects of placement conditions of mass concrete structures, such as the proper season for placement, height of lift, interval of placement and curing time, on the development of cracks due to thermal expansion. Numerical and parametric studies were carried out using FEM, on the basis of an experimental planning method, to examine quantitative relationships between them. Concluding remarks drawn from the present study are summarized as follows.
(1) The height of lift is to be the most influential factor on the temperature increase in concrete. The variance analysis on the temperature increase showed that the height of lift and the interval of placement were of 1% significance and the curing time of 5% significance in the variation. The contribution ratio to the temperature increase was extremely large for the height of lift as compared to other factors, showing 94-95%.
(2) The height of lift also showed a large influence on the development of thermal stresses in concrete. According to the variance analysis on the maximum tensile stress, all factors exhibited 1% significance in variance. The contribution ratio to the maximum tensile stress were 84-87% for the height of lift, 7-10% for the interval of placement, and 3% for the curing time, indicating a predominantly large contribution of the lift height.
(3) The maximum tensile stress in the surface part of concrete showed a considerable decrease due to the decrease in the lift height, its decreasing rate being almost exponential.
(4) Evaluation of thermal-crack index also revealed a large influence of the lift height on craking potential. This again confirmed the need for special consideration regarding the height of lift in the design and construction of mass concrete structures.
Practical measures to control thermal cracking have already been discussed and taken into account in the actual construction procedures, though they are from qualitative points of view as a result on experience. Numerical experiments performed here, on the other hand, made it feasible to conduct quantitative evaluation of the influence of placement conditions on thermal stresses and cracking potential.

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The drip irrigation method is slow and frequent application of irrigation water through an emitter and the efficiency of this method is usually very high when viewed from the point of saving water.
This paper provides examples on designing a drip irrigation system, and points out the problems needing clarification to develop better designs.
They are as follows.
(1) The main object of designing drip irrigation is the uniform application of water. As one of the advantages of drip irrigation method is effective use of water resources, the utilization of wastewater will commonly occurred. From the view point of uniform application of water, the problem of an emitter clogging must be investigated.
(2) It is necessaty to investigate the method of uniform application of water along the lateral line. Most drip irrigation laterals are designed by a single pipe size. For example, by utilization of different size pipes, the pressure variation along the lateral direction will be reduced.
(3) The method of design using the design chart is very easy and convenient. But nowadays, the utilization of computers is very common place, so, we must examine the use of computers for more precise calculation of the drip irrigation design.

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