(1) The tests were carried out to clarify the influences of field conditions to the drawbar pull and trafficabilities on soft reclaimed field in a region of Lake-Biwako in Shiga prefecture on July 1965. Three crawler tractors equipped with 300, 400 and 500mm width of track shoes respectively, a four wheel tractor and a Japanese small power tiller with rubber track shoes were used.
(2) The test field was so soft that Soil Values Meter TN-4 had no penetrating resistance within the depth of 20cm. As the results of measuring the shearing stress of soil by TN-4, angle of internal friction was 15°-25° and cohesion c was 0.08-0.12kg/cm
2 for undisturbed soils, but as to the disturbed soils passed over by wheels of tractors, was almost zero.
(3) The mean value of coefficient of traction of crawler tractors was 0.585 at 100 percent slippage and within the trafficable limits, it was 0.52 at 20 percent slippage. Running resistances of them were nearly proportional to their sinkage, that is, 500kg at 6cm sinkage, 1200kg at 15cm and at 17cm sinkage they could not move. The rate of running resistances to weights of tractors when they lost its running abilities was found to be 0.65.
(4) On turning, the sinkage of the inner track shoe was 1.3-1.4 times deeper than that of the outer one, but there were little differences of sinkage by the length of turning radius.
(5) A single moldboard 40cm plow was used to the plowing test in the mean depth of 22.4cm and the speed of 0.55m/s. when both track shoes were on the unplowed land, 3 percent slippage was found, but when the right ran in a furrow, there arose a difference of slippage between the right track shoe (19 percent) and the left (2 percent).
(6) The critical soil hardness at which each tractor could run was measured by TN-4. As for the tractor equipped with 300mm width of track shoes, it was 6-7kg in the penetrating resistance (with the own weight of TN-4), with 400mm width 4.5-6kg and with 500mm width 3.5-4.5kg. These values coincide well to the estimated one from V. C. I.. Tractors could not run under the conditions of above 20 percent slippage or 0.52 coefficient of traction when loaded. Furthermore, they could not move forward at all in the time of transportation with a mounted plow. The sinkage of the semi-crawler tractor with half-track shoes—specially that of the front wheel was deeper than the estimated sinkage from V. C. I.. Then, it is necessary to take larger value from V. C. I. in case of prediction of the trafficabilities of semi-crawler tractors.
(7) The estimated driving power from the contact area of track shoe, weight of tractor, field conditions etc., nearly coincide to the actually measured one. The drawbar pulls obtained in the plowing tests were only 1/6-1/8 times of those in the simple drawbar pull tests, and above that drawbar pull, the tractors could not move.
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