Authors

Abstract

The rheological behavior of paddy soil plays a critical role in determining traction resistance, trafficability, and the operational performance of agricultural machinery. This study quantified the effects of moisture content on the steady-state and dynamic rheological properties of remolded paddy soil using a rotational rheometer. Soil samples were prepared at four moisture contents (23%, 26%, 29%, and 32%) and tested under steady shear and oscillatory loading conditions. Steady shear tests (0.1-100 s-1) revealed pronounced shear-thinning behavior, which was well described by a power-law model (n < 1). Within this shear rate range, the apparent viscosity decreased from 11.57-1600 Pa·s at 23% moisture content to 1.343-238.7 Pa·s at 32%. Amplitude sweep tests indicated a transition from solid-like to liquid-like behavior, with the yield strain increasing approximately linearly with moisture content, while the yield modulus decreased. The loss factor increased with strain following a power-law relationship, and the fitted exponent decreased from 0.449 to 0.336 as moisture content increased. Frequency sweep tests identified a crossover frequency of approximately 40 Hz, at which the dominant response shifted from viscous- to elastic-dominated behavior under the test conditions. These results provide quantitative parameters and critical thresholds for understanding the structural stability of paddy soil under cyclic loading, and offer guidance for the optimization of running gear design and anti-slip/anti-sinkage strategies in paddy-field machinery.

Abstract in Chinese

水田土壤的流变行为直接影响农业机械的耕作阻力、行走通过性及作业质量。为探究含水率对水田土壤流变力学特性的影响规律，本研究采用旋转流变仪，对不同含水率（23%、26%、29%、32）的重塑水田土壤进行了稳态流变和动态流变试验。结果表明：1）水田土壤表现出显著的剪切稀化特性，符合幂律模型（n<1），为典型假塑性流体。2）水田土壤存在临界屈服应变点，且临界屈服应变随含水率增加呈线性增加趋势，说明随含水率增加固-液转化过程越慢，损耗因子随剪切应变增加呈幂函数式上升，明确了土壤结构失稳的临界条件。3）随着频率逐渐升高，存在临界频率使得土壤的主导力学行为会发生从类流体到类固体转变。研究构建了以含水率为变量的水田土壤流变状态演化关系，定量和定性地表征了水田土壤的流变特性，可为水田作业机械行走机构优化设计提供理论依据和数据支撑，对机械防滑防陷研究具有指导性意义。