心土破砕機の利用拡張に関する研究 (第7報)

昭和35年3月に実施した根釧試験地における土壌の凍結状況調査結果

抄録

The present study wass designed to make clear the difference in the freezing condition between panbroken and untreated soils. The investigation which is a continuation of the previous report (Journal of the Society of Agr. Machinery, Japan. Vol. 22, No. 3, 1960) was carried out at “Bekkai village” in Hokkaido in 1960.
The results of the investigation were as follows;
Several types of soil freezing could be found, according to the soil and climatic conditions.
1. Results of the investigation at “Harauchi” plot;
For the untreated soil, the ice layer formed by compact accumulation of thin ice plate could be found under the upper layer with 4-8cm. depth which consisted of only frozen soil without distinct ice crystal.
For the treated soil, on the other hand, the ice layer under the upper layer consisted of the alternate layers of thin ice plate and frozen soil. The density of this layer of the treated soil was lower than that of the untreated soil.
These facts showed that there was the difference in permeability of rain-water before beginning of severe cold weather between treated and untreated soils.
2. Results of the investigation at “Momono” plot;
There is no snow-accumulation by strong wind at this plot. For the untreated soil, the frozen soil of 9cm. thick existing under the upper layer of 17cm. was mixed compactly with lots of ice blocks of 1 or 2mm. diameter.
For the treated soil, however, the ice blocks could be found in 1/3 of the upper part of the frozen soil of 8cm thick.
Under-layer of these ice block layers also consisted of frozen soil. Although the ice plate of 1 or 2mm. thickness accumulated compactly in this under-layer with 6cm. depth for the untreated soil, the hole which was made by the chisel of pan-breaker could be found in the under-layer for the treated soil.
Thus, the effect of pan-breaking appeared evidently in this case, too.
3. Results of the investigation at “Kudo” plot;
This plot is a lowland between hills. There were two cases, A and B at this plot.
A). The frozen soil with ice crystal in the subsoil was 13cm. thick (from 6cm. to 19cm. from surface) for the untreated soil, and it was 25cm. (from 5cm. to 30cm. from surface) for the treated soil. However, the density of the frozen soil of the treated soil was lower than that of the untreated soil.
B). For the treated soil, the compact alternate of ice plate and frozen soil could be found.
For the untreated soil, ice plate and ice block accumulated mutually. The density and thickness of the frozen layer of the untreated soil were higher than those of the treated soil.
4. Hardness of the frozen soil;
The upper part of the frozen layer was as hard as concrete, and a pick was leaped up. However the hardness decreased gradually in accordance with depth increases.