Rain infiltration into the ground is basic phenomena related to plant growth, ground stability, groundwater recharging, etc. The infiltration phenomena, though, have been studied mainly from the viewpoint of ponded infiltration on which the phenomena of rain infiltration are not well explained. It may have been considered that varying rain intensity is averaged by the ground surface, and only the total amount of rain has an influence on infiltration.
However, such ground hazards as landslides or slope failures which are caused by rain often occur when the rain intensity increases after a long duration of weak rain, or several hours after rain. These observations indicate that the behavior of soil water in the ground should be related to the varying rain intensity on the ground.
The present study is focussed on dynamic behavior of the soil water content change responding to varying rain intensity. Considering the phenomena of rain infiltration from the viewpoint of the dynamic system, the phenomena are characterized by:(1) Infiltration is performed under an unsaturated condition.(2) Ponding does not always exist on the ground surface through which rainwater should infiltrate.(3) Rain water is supplied to the surface of the ground not as a succession of water, but as raindrops from a microscopic viewpoint, and as a varying rain intensity with intermissions from the macroscopic viewpoint.(4) It is considered that the soil water content changes responding to the varying patterns of rain intensity.
To investigate the phenomenon of rain infiltration, a series of experiments were planned and conducted under the conditions of different soils, different pattern of rain intensity, and different ground depths. A new measuring method of soil water content was developed theoretically by use of the apparent electrical specific resistance of soil to follow the varying rain intensity with enough speed, and realized in these experiments.
The results of the experiment under the step-type (continuous) intensity are shown and discussed. Selected phenomena of the results are as follows: (1) Velocity of movement of the wetting front is higher under a heavy rain intensity than under weak rain intensity. (2) The wetting front moves downward at a constant velosity under the constant rain intensity. (3) Soil water content above the wetting front reaches its constant value under the constant rain intensity, and equilibrium infiltration is established. To explain the phenomena of rain infiltration, “Open Unsaturated Capillary Perocolation” model is proposed.

View full abstract

The progressive failure and scale effect of trap-door problems were investigated by measuring the load-displacement relationships and observing shear band developments. Trap-door tests were performed in passive and active mode using two kinds of apparatuses. The trap-door width of the smaller apparatus was 5 cm and the larger one was 10 cm. The load of the smaller apparatus was measured using circular soil stress measurement cells and the larger measured using 11 separate rectangular cells embedded in the face of the trap-door. The shear band developments were observed using thin horizontal colored sand layers placed in the sand bodies. The progressive shear band development was recognized both in the passive and active mode but the scale effect was only recognized in the passive mode. The progressive failure in the passive mode tests was also indentified by the load-displacement relationships obtained by 11 separate rectangular stress measurement cells.

View full abstract

The finite element method is applied to the solution of a transient problem in a closed pipeline system. For primary investigations, however, considerations are restricted to the problem of a single pipeline system although the method, inherently versatile, is well suited for problems involving complex interconnected networks. Based on the non-simplified equations with lesser important terms, two different explicit finite element models, aided by the Kawachi scheme and the two-step Lax-Wendroff scheme for time marching, are built, including the selective consistency (or lumping) technique in the approximation of the time derivatives. Both frictionless and frictional waterhammer problems in the infinitely stiff pipe are practically solved by operating the two models developed, to examine their validities and compare their basic features. Accuracy of the solutions obtained is then estimated referring to the well-defined exact and non-interpolated characteristics solutions. It is demonstrated through those numerical experiments that in both models numerical dissipation as well as computational stability depend importantly upon the degree of consistency in time advance, and that especially the model combined with the Kawachi scheme has an advantage of being stable for time increment exceeding that allowable in the commonly used explicit schemes.

View full abstract

For two different finite element models previously developed for pipeline transient analysis, i.e., the first and second order models incorporating the Kawachi scheme and the two-step Lax-Wendroff scheme respectively, stability and accuracy analyses are performed to theoretically investigate how the consistency parameter as well as the common computational key factors affect the computational stability and the numerical dissipation and dispersion and to discuss the relative advantages of both schemes. The analyses demonstrate that in any case the Kawachi scheme, with the stability criterion: Courant number ≤2 in an extreme case, provides higher stability limit than the Lax-Wendroff scheme, and that both schemes with non-zero consistency parameter are dissipative attenuating useless high frequency wave components and then selective dissipativeness can be better achieved by the Lax-Wendroff scheme with a high level Courant number. In consequence, both models are qualified as of better suitability for an analysis of shock or steep-fronted wave like a waterhammer. Additionally, it is suggested that without any extra procedures, the Kawachi scheme can efficiently solve the variable wavespeed problems of air-water mixture when taking the benefit of being stable for a wider range of wavespeed variations.

View full abstract

Using mixed soil with clay and tuff, the influence of the percolation of water for the consolidation of compacted soil and the properties of consolidation during the increase or decrease of water pressure at the base of specimen u_b are tested in a laboratory. The coefficient of permeability k obtained from the permeability test is compared with those obtained from the consolidation test. The following results are obtained from these experiments:
(1) In wet side of optimum moisture content, the percolation of water has a small influence for pore pressure coefficient B and B is mainly changed due to a variation in the moisture content.
(2) The change in pore pressure and displacement when u_b is increased or decreased instantaneously is able to be approximated with a one-dimensional consolidation equation, but that during the increase i_n is delayed more than that during the decrease.
(3) The coefficient of permeability k due to the permeability test is equal to or slightly greater than k by the consolidation test and consolidation during the decrease in u_b. The coefficient of permeability k by consolidation during the increase in u_b is about one-fifth. of k by the other methods.
(4) The pore air has an influence for the properties of consolidation and permeability of compacted soil even though pore pressure is greater than zero.
(5) Coefficient of consolidation c_υ for the calculation of pore pressure during the change in the reservior water level is obtained from m_υ during the unloading of the consolidation pressure and k from the consolidation test as c, is equal to k/γ_ωm_ν.

View full abstract

In previous papers, writers discussed the windproof characteristics of model greenhouse using a wind tunnel. However, the wind in a wind tunnel differs from natural wind because of its unique characteristics. So, in this paper, a small-scale, gabled greenhouse covered with plastic film is set up on the ground and the vibrations of the vinyl, covering and frames at the time it is subjected to a natural wind are measured. Wind fluctuations are measured at the same time. The mean wind speeds measured were between 8-11 m/s. Time series data obtained were processed by a personal computer and the power spectral densities and coherencies were subsequently calculated. The following results were obtained.
The vinyl covering vibrated with the 1 st natural frequency of the greenhouse for all of the wind intensities. Correlation between wind fluctuation and vibration of the vinyl covering was stronger on the leeward side than on the windward side as it seems the vortices generate in the wake. During free vibration, the frame members vibrated with the 1 st natural frequency and its harmonic frequencies; however, at vinyl covering, they vibrated over.a wide range near the natural frequency in natural wind.

View full abstract

Vinyl covering greenhouses are very lightweight structures and is often pulled out due to the wind. Therefore, improvement in the windproof capability of greenhouses is an important problem. Particularly, uplift capacity of the pile foundations is one of most important subjects regarding the windproofing of greenhouses.
Normally, footing foundations are not used due to economic and construction considerations with cylindrical concrete piles generally being used. Therefore, two types of cylindrical concrete model piles with shear keys on the surfaces have been proposed for the purpose of increasing ultimate uplift capacity. The shape of a shear key is semi-spherical and its diameter is 15 mm.
Pile diameter is 7.5cm and L/D are 2.6-5.3.
Pull-out tests were carried out using sand have two densities loose and dense. Uplift capacities of piles with shear key are compared with uplift capacity of piles with no keys.
Results obtained are as follows: The rate of increase in ultimate uplift capacity become larger due to the increase in the pile length of the embeddment. In the case of loose sand, an increase in ultimate uplift capacity is slightly smaller for both piles, but in the case of dense sand, an increase of about 30-50% in ultimate uplift capacity in the case of a pile with a key. The pile movement at the time in which the pile is pulled out occurs in proportion to the pile length of embeddment in both piles.

View full abstract

In this study, the relation between soil moisture and the influence of harrowing is examined in connection with the dynamic properties of soil to clarify the suitable soil moisture of rotary tillage in rice fields.
The results obtained are as follows
In the succeeding soil of puddled wetland rice, the rotary tillage in the soil moisture of the range of pF 2.0 had a high rate of soil pulverization with low resistance. In the succeeding soil of barley, the tillage in the soil moisture extent of about pF 2.6 had a high rate of soil pulverization with low resistance.
In the succeeding soil of the paddy rice, the cone index increased as the soil dried, the tillage in the range of the cone index 6.0 kgf/cm² had a high rate of soil pulverization with low resistance. However, in the succeeding soil of barley, the cone index showed no change with drying, and the tillage in the same cone index showed a remarkable difference in the rate of soil pulverization and resistance.

View full abstract

Water qualities and loadings have been intensively monitored at the drainage canal in a paddy field area during storm-periods. Among 5 storm runoffs, the No.3 runoff was in the fertilizer application period.
Characteristics of concentrations behaviors and loading outflows are as follows:
1) The concentrations of T-N (except the No.3), T-P, T-COD and SS increased with the increasing discharge. However, the nitrogen concentrations in the No.3 runoff decreased, the initial concentrations being much higher than those of the other runoff events.
2) Linear relationships on logarithmic paper were found between specific cumulative loadings of T-N (except the No.3), T-P, and T-COD and specific cumulative discharge. The point of T-N for the No.3 appeared above its regression line, as a result of the outflow of dissolved fertilizer applied a few days earlier.
3) The tendency was found that the runoff loading of the paddy field area are less than those of the river basins, i. e. agricultural basins and urbanized basins.

View full abstract

The effects on micrometeorology of sparse vegetation with sprinkling at high summer temperatures are discussed on the basis of a field experiment and, a physical model. In this paper, the heat balance model is constructed and simulated. This model estimates the heat balance structure and the surface temperature in the sprinkling field from the micrometeorological data in the control field.
The main results obtained are as follows:
1) In regard to the heat balance structure during sprinkling, the following features are found. Under the dry condition, the Bowen ratio decreases as the wind speed increases, and it has negative values except for the case of a very low wind speed. Normally, the sensible heat flux flow from the atmosphere to the ground, and it increases as the wind speed increases. Under the wet condition, the Bowen ratio has positive values, and it increases or reaches a constant as the wind speed increases. Usually, the sensible heat flow from the ground to the atmosphere regardless of the wind speed, and it increases as the wind speed increases.
2) In regard to the surface temperature of the vegetation during sprinkling, the following features are found. In the case of low wind speed, the surface temperature decrease rapidly as the wind speed increases. Under the dry condition, optimum wind speed, which causes the minimum surface temperature, exists. Under the wet condition, the surface temperature decreases as the wind speed increases. The surface temperature is always higher than the air temperature regardless of the wind speed.

View full abstract

The long and short terms runoff model (LST-II) is applied to the Yoshii River basin of 1, 717km². On the basis of theoretical discussion on peak flood discharge, lag time is introduced into the model in order to overcome the constraint that calculated peak discharge is not greater than rainfall intensity at the peak discharge. A set of 14 unknown parameters in the model is obtained considering the lag time by the SP method, which is one of the mathematical optimization techniques. The calculated hydrographs are shown to agree well with the observed hydrographs for both flood and long-term runoff.
For real-time forecasting of flood runoff, we propose a simple, practical technique in which storage depth of the upper zone in the top tank of the model is updated directly from observed discharge using the relationship between the storage and discharge for the upper zone. It is demonstrated that the proposed technique performs as well as the extended Kalman filter.

View full abstract

Until now, the movement of a drainage front in vertical drainage from initially saturated conditions for glass beads and sand was studied. In these types of drainage, the capillary drainage forces which are the water pressure head of drainage front are not only constant but also are variable regarding boundary conditions and Darcy style equation on the drainage can be applied.
In this paper, two kinds of Kanto loam, that is, volcanic ash soil (plow layer and subsoil) and sandy loam (plow layer) are investigated. The phenomenon of drainage in packed Kanto loam and sandy loam which we discussed in this paper is the same as that which can be observed at packed glass beads and sand. Experimental data on the drainage in three kinds of soil indicated reasonably good agreement to the theory.

View full abstract

A simple expression for the non-equilibrium transport rate of bed load was derived from consideration about the “relaxation process” which occurs on transient process of sand movement on movable bed. In this derivation of the equations for the expression, examinations of the following effects were involved also; propagation of disturbance on the river bed and saltation motion of sand particles.
And one-and two-dimensional calculation methods were deduced for estimating the river bottom transformation processes. Both methods based on flow analysis for non-uniform or unsteady flow and the present non-equilibrium transport rate of bed load formula. Two cases of the bottom transformation processes were calculated by these methods; recovery from a local scouring profile to flat bed by supercritical flow and the formation of alternative bars in the.experimental channel.
The bottom profiles and bottom transformations processes obtained by these methods showed close agreement with those observed in movable bed experiments. That is, the model proposed in this paper is capable of describing the aspects of non-equilibrium sand movement on movable bed.

View full abstract

This report analyzes water surface disturbance like an oblique shock wave and a bottom transformation induced by pile-like construction on a steady supercritical flow. In the flow analysis, the two-dimensional shallow water flow theory was used, and the reflection of an oblique shock wave at the channel side wall and the distribution of velocity under the shock wave field were calculated using the ADI numerical calculation method. The water surface profiles and distributions of velocity of the oblique shock wave coincided fairly well with those observed in the fixed bed experiments.
The local scouring phenomenon at the front of the pile and non-equilibrium behavior of the sand movement were considered in the analysis of the bottom transformation. A bed load formula to describe the local scour was derived based on a reasonable estimation of the horseshoe vortex intensity and power model of bed load formula. Also, equations derived in our previous report were used to calculate non-equilibrium transport rate of bed load. The bottom transformations generated on alternative bars by the piles were calculated by use of the river bed analysis model incorporated the bed load formulae of the local scour and non-equilibrium of sand movement. The local scouring profile and the bottom transformation obtained by these analytical methods agreed well with those observed in the movable bed experiments.

View full abstract