Studies on the Mole-Piercers (I)

Analytical Experiments of the Mole-Piercers with Various Wedge-shaped Heads and Square Sections

Abstract

The power requirements, the amount of soil surface rise and soil breaking characteristics were determined in a wide variety of shapes, working depths, travel speeds and soils with models of sharped head type.
The composition of resistance forces were explained by analytical experiments such as the wedge-shaped head which was constructed with only upward or downward oblique plane or both planes. The results were as follows:
(1) The horizontal force reduced slightly and downward force increased with the height of blade in the case of only upward oblique plane. In the case of only downward oblique plane, however, the horizontal and upward forces increased considerablely, and this tendency increased with a decrease in the oblique angle, and hence, it is presumed that the more oblique angle reduce, the larger will be the influence due to the increase of mole-piercer diameter.
(2) In the case of symmetrical wedge with the same height of blade and the same section, the upward force and the tendency of refloating of blade increased with a decrease in the wedge angle, but horizontal force which was concerned directly to tractive resistance was not almost reduced.
(3) The power requirements due to the shank were very large, and all horizontal forces increased with working depth; on the other hand, the vertical forces showed a large variation, the upward force increased with an increase from negative value to 0°, and decreased with an increase from 0°to about 30°in the shank angle, and it changed to downward force at near 30°, and increased greatly with an increase in the positive shank angle.
(4) In the event of only upward oblique plane or synmetrical wedge, the amount of soil surface rise increased with the height of blade and the wedge angle, and the amount was numerous at deep and reduced at shallow; in the case of only downward oblique plane, it increased especially at deep with a decrease in the height of blade at the same downward oblique angle, and with an increase in downward oblique angle at the same height of blade.
(5) The center of resistance was situated on near the sharped head. The both forces increased slightly with travel speed; the conditions of soil breaking and the amount of rise were not almost changed by the change of travel speed or kind of soil.