The preliminary problems which have usually been paied little or no attention for analyzing investigated data are considered ; volume of samplers, diameter of sampling instruments, personal errors, temperature distribution in the drying oven and drying time of soil. The results obtained are summarized as follows :
1) Differences between volumes of each sampler are not recognized.
2) The sampling instrument because of its reduced edge diameter makes the volume of samples smaller than that of sampler itself(100cm3). Consequently, there is significant difference on the dry density of sample between the cases of using it and not.
3) Personal errors which is caused by sampling procedure are little.
4) In the non-blast oven, temperature distribution in it is very large, especially with moist samples. Therefore, it must be prevented to putt moist samples into the oven with somewhat dried samples.
5) In the blast oven, temperature differences at any points are at most 4°C and smaller than that of the non-blast oven. Still it is large enough to the indicated values of catalogue. Then the thermometer attached to the oven shows 5~6°C below minimum temperature of the thermoelectric couples setted in the oven.
6) The drying time is required at least 8 or 12 days in the case of volcanic ash soil or clayey soil. This is extremely long in comparison with popularly used time.
The factors concerning to the strength of the soil are very much, and among them water content in the soil mass is one of the most important factors. Increased water content in the soil mass causes partial or full rupture of the long si叩e and the high banking, and the landslide, which has been stabilized till then. This report is discribed with respect to matters as follows ;
1) Relationship between the strength of the soil and water content are studied experimentaly. Especially, a consideration of useful expression of the strength constant which suits to an analysis due to the finite element method has done.
2) A stress-strain analysis of a contact plane between the soil and another materials of construction.