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

随着农业机械的不断大型化，农用车轮的循环压实对土壤的不良影响日益显现。本研究利用土槽装置精确量测车轮行走特性，并从理论上发展弹塑性有限元程序，以实验研究车轮行走所造成的土壤压实现象。主要结果如下：1）土壤颗粒在车轮作用下沿椭球轨迹运动。随着滑移率的增加，轨迹相对于车轮向后移动。2）轨迹的大小随着车轮走行次数的增加而减小。随着滑移量的增加，其减小速度更显著。3）土的压实度在靠近土表面的地方比较显著。它与深度成比例地减小，直到60 mm深度，然后迅速减小。侧移时，剪应变幅值随轮数的增加呈指数规律减小; 4）滑移时，剪应变幅值增大，土体压实显著。换句话说，土壤压实显着的影响，由于剪切变形的粘性。5）最高的牵引效率和最小的土壤压实实现在桑迪土壤上行驶的情况下，在刚性轮5-10%的滑移。6）有限元程序开发结合子加载面模型。该程序对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.