Pressure Produced when Fluid is Introduced under Pressure into a Soil-Bed Layer (III)

Draft reduction of sub-Boiler by injecting fluid to break down soil

Abstract

In the previous report, the breakdown of soil when fluid was introduced under pressure into the soil-bed layer in a acryl resin soil-bin, was investigated. It became clear from this experiment that the soil could be broken down easily with a small energy by water jets. This paper reports that a test sub-soiler which injects water from the top in order to break down the soil in front of the sub-soiler, was designed as an application of the results of the previous experiment. The following points were examined; to what degree the draft of this sub-soiler was reduced and to what degree the traction horsepower was reduced. The results of this experiment were as follows;
1. When air or water was caused to flow under pressure into the soil-bed layer (clayey loam with about 15% in moisture ratio) in the soil-bin under fixed conditions of the test sub-soiler, the breakdown of soil as shown in Photo 1 was observed. In this case, the energy with which water broke down the soil was about 1/180 times smaller than that of air.
2. When the energy of the static pressure was compared with that of the kinematic pressure in the total energy required to break down the soil, the former was more than 10 times larger than the latter in either case of the water or air flow. It became clear from this result that the soil was broken down almost by the energy of static pressure (eq. (6), (7)).
3. The type of the sub-soiler in which the nozzle port was directed toward the travel-direction (Photo 3), was of no practical use because the nozzle port become clogged with soil. Therefore, a kind of protector added to the nozzle port was necessary to prevent soil from clogging the nozzle port.
4. The type of sub-soiler in which the kinematic energy of the water jet ejected from the nozzle port was made larger by narrowing the nozzle port to 3.2φ was effective for the breakdown of soil above ground but was quite ineffective below the surface. The pressure produced at the nozzle port of this type was very high and a larger horsepower was required to caused the water to spurt.
5. As for a sub-soiler with more than two nozzle ports (Photo 4), only one of the nozzles around which the resistance of the soil was lowest operated well and the remaining nozzles were all clogged with soil and rendered useless. Consequently, when the sub-soiler had more than one nozzle port, the same number of water pipes with that of the nozzle port were required.
6. Under a constant flow rate of water, in proportion to the traction velocity of the sub-soiler that increased, the draft by injecting water decreased and the produced pressure at the nozzle port fluctuated heavily. This demonstrated that the water worked effectively and broke down the soil when the traction velocity of the sub-soiler was high (Fig. 6, Fig. 9).
7. In this experiment, the draft was reduced to less than half when water of more than about 500cm³/s was injected.
8. When the flow rate of injected water was small and the traction velocity of the sub-soiler was slow, the water hardly broke down the soil but flowed along the surface of the sub-soiler. In such case when the lubricating effect of the sub-soiler by water was seen, the reduction of the traction draft was hardly observed. (Fig. g)
9. The traction horsepower could be reduced because the draft was reduced by flowing water. But another energy was required in order to make the water spurt. The total amount of reduced energy resulted from the balance between the horsepower reduced and the horsepower newly required for the above, was greater in proportion to the traction velocity of the sub-soiler. This reduced horsepower was about 0.33 PS when the traction velocity was 13.6cm/s. Since the traction horsepower of the sub-soiler was 1.09 PS when it was drawn at same velocity without water flow, horsepower amounting to about 30% could be reduced (Fig. 10).
The auther wishes to express his gratitude to the Hokkaido Univer