Relationships between Shapes of Ground Contact Surface and Sinkage Behaviors of Japanese Combine Harvesters

Abstract

Farm lands generally consist of two layers, i. e., a hardpan and a soft tilth on it. Noting this feature of farm lands, we carried out sinkage tests of various rectangular loading plates with sizes and shapes of ground contact surfaces of rubber crawlers in Japanese combine harvesters, in a shallow soil bin (12.5cm depth) corresponding to tilth in paddy fields. From these tests, for the size and the shape of ground contact surfaces of rubber crawlers of Japanese combine harvesters it could be concluded that under the same contact pressure i) the wider the loading plate with a same length and ii) the stockier the loading plate with a same area, the smaller the sinkage is.
These trends are entirely inverse to those observed in homogeneous semi-infinite grounds. Some mechanical reasons for the opposite trends are described by resolving the sinkage resistance into the compression resistance of soils under the loading plate and the shear resistance of soils arround the plate, and especially it is indicated that the compression resistance has a large effect on a sinkage in the soils on a hardpan.