A large quantity of sand is needed as material for filtering and draining in earth dam. However, no natural sand exist except for sea sand which consists of dead coral polyp in the Okinawa area. So crushed sand of limestone is used for part of the public works projects. Both types of calcareous sand were dissolved in water dissolving CO₂, because it consists of CaCO₃.
The present paper reports on a solution of calcareous sand used as filtering and draining material. The solution of calcareous sand was investigated through gauging the sand mass and chemical analysis of Ca²⁺, and by dissolving in tap water.
The results are summarized as follows.
1) A calcareous sand solution is related to CO₂ regarding tap water, temperature, velocity of passing water and length of sample.
2) A solution rate by tap water with a 5. 9×10^-3cm/s passing velocity was about 15%/year in coral sand and 5-6%/year in limestone sand.
3) In carbonated water, containing CO₂ 100 times as much that in tap water, it took about 150 days in coral sand and 360 days in limestone sand to be completely dissolved.
Since both types sands are soluble in water, it is concluded that calcareous sand should not be used inside of earth dams.

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An attempt is made to study compaction mechanism by employing a static straincontrolled triaxial apparatus and using saturated Toyoura sand. Specifically, investigations are made into the effects of loading system, repeated number of loading-unloading (N), and magnitude of allowed radial strain (ε_rc) on consolidation and shear behaviors. For these investigations, repeated K₀-consolidation tests (zero radial strain) are performed. Besides, what are called in this paper “quasi-K₀ consolidation tests” with two types of ε_rc are also performed but only under normal consolidation (N=1). Results from these tests indicate that different loading systems follow quite different shapes of principal stress paths in repeated K₀-consolidation, and that N affects the magnitude of internal friction angle (φ'). On the other hand, magnitude of ε_rc also governs consolidation and shear behaviors.
With respect to the strain-controlled loading system, because unloading is controlled by reducing strain, K₀-unloading principal stress path tends to go down along the line of principal stress path of normal consolidation. In contrast, according to previous studies the stress-controlled loading system follows K₀-unloading principal stress path which tends to lie above the line of principal stress path of normal consolidation. Consequently, as compared with stress-controlled loading system, the strain-controlled one is subjected to higher stress deviator during K₀-unloading, thus more particle reorientation occurs followed by higher densification. Meanwhile, when subjected to repeated K₀-consolidation, φ' first decreases and afterwards increases with N. This result may be understood as the disturbance of the fabric formed at normal consolidation step by the initial unloading. Then the fabric is reconstituted into another new one, and becomes denser with N.
On the other hand, the K-value obtained from quasi-K₀ consolidation test fluctuates and is larger than the K-value from K₀-consolidation test. However, the K-values obtained from both tests tend to approach one another following consolidation. This result suggests that even when employing consolidation tests in which some radial strain occurs, as long as the consolidation continues, an accurate K-value can also be obtained. Moreover, in quasi-K₀ consolidation tests when magnitude of ε_rc increases, the dilatancy rate generated in shearing decreases, and thereby φ' drops. Consequently, it can be known that radial strain conditions in consolidation step considerably affects mechanical properties of soil.

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In a thin water layer on soil surface, a hemispherical cavity is formed under the water's surface at the same time of waterdrop impact. This cavity, after expanding in water for several ten milliseconds to reach maximum radius which depends on the kinetic energy of a waterdrop, begins to contract and dies away leaving the cylindrical water waves which propagate around the point of waterdrop impact. The movement and lift up of the soil particles on the soil surface is caused by the radial flow generated by the process of expansion and the contraction of cavity in water. In case that the surface water has a mean flow velocity, the suspended particles in the water are transported to downstream. Therefore, the slow flow which has a weak tractive force becomes the capacity of soil transportation.
According to a photographic analysis and a theoretical analysis of pressure changes using waterdrop impact, soil detachement undergoes three processes following by the behavior of underwater cavity in the following way; As a first step, soil is forced out by the application of hydraulic positive pressure. Next, soil particles are lifted up by the force of the hydraulic negative pressure as a result of cavity contraction, and the final process is when the soil particles, which were lifted up, are suspended in the water by the turbulent force caused by the cavity collapse.
In this paper, among these three processes, the first process was investigated. The model of detachment was made based on the idea that soil particles begin to detach if the pressure impulse exceeds limit value I₊₀, which depends on the physical properties of soil, and the total volume of the detached particles is proportional to the integrated value of difference between pressure impulse I₊and I₊₀ throughout the soil's surface. This model shows that the total volume of soil particles is related to the impact energy and the water depth.

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This paper presents the resluts of study on a fuzzy forecasting system for irrigation water.
Regarding irrigation water management of rice field, it has been previously clarified that the judgement of an administrator regarding determination of the amount of water supply is carried out, based on the mechanism of “If then algorithm” which consists of four elements, growing condition of rice: P, temperatature: T, weather condition: S and recorded water supply: Q.
On the other hand, when above-mentioned mechanism does not adjust, a past record in performance of water management, which has been learned as a precedent, by an administrator, is referred, to and the amount of water supply can be forecasted.
In this paper, in view of this fact, a new type of system forecasting the amount of irrigation water from formulation of fuzzy relation between Q and Y (past recorded water variation), under the influence of an environmental condition, P, T, and S, was studied.
To confirm that this system is available, verification was carried out by using irrigation water management record and then the system operation was clarified asing methodology.
As a result, the forecasted value showed a good correlation with the amount of irrigation water.

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Thermal convection due to differences in temperature in saturated porous media has been analyzed in general using the Boussinesq assumption and discussed in terms of the Rayleigh number or the aspect ratio. The results showed convection cell symmetry. However, a few works which had variable properties of density and dynamic viscosity with respect to temperature into consideration demonstrate that the shape of convection cells must be asymmetric. This paper deals with the characteristic properties of thermal convection using laboratory experiments in which tracer techniques were employed for the first time to obtain thermal convection trajectories. By number of experiments for the thermal convection performed, non-Boussinesq effect was also investigated.

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Natural convection due to the anomaly of density distribution of fluid and heat transfer due to heat conduction and the convection within saturated porous media were simultaneously analyzed using the finite element method for natural convection and characteristic finite element method coupled with a 2-dimensional spline interpolation for the heat transfer. Simulated results compared fairly well with the laboratory experiments although insulation of the experiments were not perfect. It was revealed through careful investigations of the simulated results that the phenomena of the thermal convection are affected by such factors as temperature-dependent dynamic viscosity and density of fluid within saturated porous media and hydrodynamic conductivity of the media and temperature gradient generated through vertical boundaries whereas thermal dispersion is almost negligible for the used data sets.

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The submerged iron contactor process as a simple and inexpensive phosphorus removal method suitable for small-scale domestic wastewater treatment plants including rural sewage treatment plants have been proposed.
In this process, iron contactors are submerged in disposal tanks usually used for secondary treatment of domestic sewage by means of the activated sludge process or biofilm method, and phosphate anions. in the sewage are chemically combined with iron cations produced through corrosion of the contactors. Then, the compound produced is precipitated and removed together with the biological excess sludge.
In this study, laboratory experiments were made on the treatment of artificial wastewater by using the aerating submerged iron contactor process, submerged iron contactor process and contact aeration. method in combination, and the following findings were obtained.
(1) Phosphorus could be continuously removed at a high and stable rate merely by periodically backwasing the iron contactors and removing any excess sludge. This is probably attributable to the fact that periodical back washing prevented the biofilm on the contactors from thickening to an excessive extent.
(2) The corrosion rate of the iron contactors and their phosphorus removal rate were hardly affected by the changes in the water temperature in the treatment tanks within the range of changes in water temperature which takes place in ordinary disposal plants.
(3) The corrosion rate of the iron contactors and their phosphorus removal rate were hardly affected by the changes in the flow velocity in the treatment tanks within the range of flow velocities which are observed in ordinary disposal plants.

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The submerged iron contactor process, which have been recently developed, is a new dephosphorization method suitable for small-scale domestic wastewater treatment plants such as rural sewage treatment plants.
In this study, we carried out laboratory experiments on the treatment of artificial wastewater by using the aerating submerged iron contactor process, submerged iron contactor process and contact aeration method in combination, and the following findings were obtained.
(1) The corrosion rate of the submerged iron contactors by sulfate-reducing-bacteria was affected by the changes in BOD loading on the contactors. This indicates that in determining the optimum total surface area of iron contactors to be submerged, consideration has to be given to BOD loading.
(2) Close interrelations were found between the T-P removal rate and molar ratio of iron cations dissolved from the iron contactors to T-P loading, and also between the molar ratio and T-P concentration of the treated wastewater. Judging from these interrelations, we concluded that the molar ratio has to be about 2 or more to obtain a phosphorus removal rate which is 90% or higher and that the molar ratio has to be about 1.5 or more to get a T-P concentration of treated wastewater which is 1 mg/l or less.
(3) More sludge was produced by this method than by the ordinary contact aeration method. However, the sludge produced by our method contained a lower percentage of water and was superior in dewaterability.
(4) The use of iron contactors had no significant unfavorable effect on the treatment of BOD, COD and SS or on nitrification. Neither did it cause any serious coloring of the wastewater. The alkalinity of the wastewater was increased by the treatment.

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Population movement of individuals occurs after determining the purposes and places of the movement. To grasp the relevancy of the purpose and places, an analysis of a population movement was examined using a log linear model in the case of Nagahama City, Shiga Prefecture.
As a result, the heterogeneity between out-migration and in-migration became clear. The relation between purpose and places of the movement is explained in terms of the probabilities by logit analysis.
Therefore, this paper complements the aggregation problem on the gravity model in our previous atricle and clarifies the bidirection between both models.
Using the results of the study, it will be possible to contribute to the measure toward activation. in Nagahama City by a definite examination of the present situation of its population movement.

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The influence, owing to the river bed inclination, which has both longitudinal and lateral direction on bed load motion, are considered in this paper. A sand particle on the slope is acted on by the tractive force induced by the flow and the additional tractive force caused by the steepest slope direction component of the gravity force. Due to this, the critical tractive force on the slope is effected by the additional tractive force. First, it is. clarified that the critical tractive force is provided with the inclination of the slope and flow direction by considering the properties of the forces. Second, the equations of equilibrium transport rate of bed load are derived using the relation of the forces. These equations have the same form as the equations of the K·T model derived for the description of non-equilibrium bed load in the previous reports. As a result of this reason, the equilibrium and non-equilibrium bed load motion can be described by using the local inclination of the slope consistently. Lastly, the numerical solutions obtained from these analyses for the critical tractive force and equilibrium transport rate of bed load are demonstrated assuming the river side slope as an example.

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It has generally been found that reclaimed farmland has distinct characteristics as watersheds because it is usually made up of regulated plots with discernibly uniform surfaces. To clarify the roughness coefficient in such farmland (which is an important factor in analyzing flood runoff) from a more physical viewpoint, experiments for runoff under a constant rainfall intensity were conducted. Here, a large lysimeter (2m×10m) was used as the minimum unit of an actual slope. The four experimental slope conditions were a bare surface, ridged surface with vinyl mulch, turf surface and weed surface.
First, the relationship between measured flow depth and discharge was examined. The flow was assumed to be uniform over each slope, accordingly Manning's law was applicable. Next, the recession coefficient determined by reference to a hydrograph was seen as increasing with an increase in the gradient and rainfall intensity. Lastly, the Manning roughness coefficient was estimated from the recession coefficient and analytical discharge calculated by the kinematic wave approach. The results obtained were as follows. Essentially, the roughness coefficient bore no relationship to the gradient and discharge but was related to the slope surface condition. The roughness coefficients for the ridged slope, bare slope, weed slope and turf slope were, in ascending order 0.04-0.06, 0.05-0.07, 0.1, 1s/m^1/3, respectively. The results, which are very interesting, indicate that the difference between the values for the ridged slope and for the bare slope was not as large as had been expected.

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This paper overviews the research field of the application of a Kalman filter to several structural and geotechnical engineering problems. First, the structure and algorithm of Kalman filtering are given. It is revealed that different formulations furnish three categories appeared in the applications of Kalman filtering to engineering problems, i. e., 1) identification, 2) estimation and 3) identification-estimation hybrid problems. We herein sketched a historical review of Kalman filtering applications in the field of structural and geotechnical engineering, respectively, and highlighted several new findings in those applications. Position of parameter identification scheme based on Kalman filtering among the vaious back analysis procedures is then discussed. It is pointed out that the specified formulation of Kalman filtering in conjunction with FEM for parameter identification in geotechnical field is identical to the Bayesian and the maximum likelihood approaches which utilize prior information in a probabilistic sense. Also, we briefly examined the current shortcomings to be overcome. Finally, future developments in this field are described from a practical viewpoint.

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