Three experiments with different saturated conditions 'were carried out in order to examine the retentivities and permeabilities of unsaturated fine and coarse sands which are affected by pore air behaviors. First experiment (Exp. I) was done in the two iron boxes filled respectively with the unsaturated fine and coarse sands in a large rainfall simulator of the National Research Center for Disaster Prevention. An iron column packed with the unsaturated fine sand was used for second experiment (Exp. II). In these experiments, volumetric water contents were measured by a neutron moisture meter, and a tensiometer was used for measuring pressure heads. In third experiment (Exp. III), a small PVC column packed with the fine sand under a perfectly saturated condition was used. In this experiment, sampling and oven-drying methods for measuring volumetric water contents were employed, and pressure heads were obtained from the elevation with respect to a standard datum at which stands in a riser after draining for three weeks.
Experimental results were shown as follows: 1) hysteresis effects are exhibited in soil water characteristic curve for fine and coarse sands, the relationship between hydraulic conductivity and pressure head for fine sand, and the hydraulic conductivity versus volumetric water content relation for fine sand; 2) an upper boundary of capillary fringe corresponds to the pressure head value at the disappeared point of the hysteresis effect in soil water characteristic curve; 3) there occurs a pseudo-saturated part due to entrapped air behaviors in soil water characteristic curve during desorption and then an air entry value depends on its development; and 4) the hydraulic conductivity of coarse sand increases extremely in low water content but that of fine sand increases gradually as the water content increases.

View full abstract

A new technique is developed to detect the flow rate of underground water. Theoretically, it is based upon some temporal variations of existing stream potential associated with movement of saline solution injected into underground water. In several landslide regions in Japan, experimental measurements are carried out for the variations of streaming potential with the lead electrodes which are arranged in various geometries on the ground surface, after injection of saline solution into shallow underground water.
It is shown that the flow rates detected by the present“ Streaming Potential Technique” are in good agreement with those by the conventional tracer technique. The streaming potential technique gains an advantage over the tracer technique in getting possible instantaneous values. Moreover, it is expected to estimate the mass flux of underground water from the variances of streaming potential.

View full abstract

Recently, attention has come to be paid to groundwater contamination caused by human activity. To cope with the problem, we must obtain the more detailed informations about groundwater-bearing condition and its flow system taking long strides from the conventional way of thinking.
The distinguished mark of this study is the application of the sedimentary facies analysis to specify the groundwater system of the study area.
Analysis shows that there are three facies to devide the groundwater and the characteristics of the groundwater flow is limited by the sedimentary facies and structure. On the basis of the facies analysis, the tracing of groundwater is carried out at the several plots using electric conductivity method. As a result, it is clarified that the velocity and direction of groundwater vary with the season, topographic locality and sedimentary horizon of groundwater.

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract