PREVENTION OF SOIL COMPACTION ON HARD-PAN DUE TO CYCLIC WHEEL LOADS

农用机械轮式循环压实对农田土壤的不良影响已经显现出来，而农用机械的规模却在逐年增加。本文采用精确测量车轮行驶性能的土仓装置，对车轮行驶引起的土体压实现象进行了实验研究，并从理论上编制了弹塑性有限元程序。本文的主要研究结果如下：1)土粒通过车轮沿椭球轨迹运动。随着滑移的增加，轨迹相对于车轮向后定位。2)轨迹的大小随轮毂移动次数的增加而减小。随着滑移量的增加，其下降速度更为显著。3)近地表土壤压实显著。在60 mm深度前随深度成比例减小，然后迅速减小。此外，它随着车轮行驶的次数呈指数递减。4)随着滑移的增加，剪切应变的幅度增大，土体压实显著。也就是说，土体的压实受剪切变形引起的剪胀性的显著影响。5)刚性轮在砂土上行驶时，在滑移率为5-10%时，实现了最高的牵引效率和最小的土壤压实。6)结合下载面模型，编制了有限元程序。该程序对车轮下土体变形进行了定性预测。

The evil influence on soils for crop growing has been brought out by the cyclic compaction by farm wheels, whilst the sizes of farm machinery are increasing year and year. In this research the soil compaction phenomenon due to the wheel traveling is studied experimentally using the soil bin equipment for the precise measurement of wheel traveling performance and theoretically developing the elastoplastic finite element program. The main results obtained in this article are as follows :1) Soil particles traces an ellipsoidal locus by the passage of wheel. The locus locates backward relative to wheel as the slippage increases.2) The size of locus decreases with the number of wheel traveling. Its rate of decrease is more remarkable as the slippage increases.3) The compaction of soil is remarkable near the soil surface. It decreases proportionally to the depth until 60 mm depth and then decreases rapidly. Bedsides, it decreases exponentially with the number of wheel traveling.4) The amplitude of shear strain increases and thus soil compaction becomes remarkable with the slippage. In other words, the soil compaction is influenced remarkably by the dilatancy due to the shear deformation.5) The highest tractive efficiency and the smallest soil compaction is realized at the 5-10% slippage in the case of the rigid wheel traveling on sandy soil.6) The finite element program was developed incorporating the subloading surface model. The soil deformation beneath the wheel is predicted qualitatively by the program.